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Hey guys. Posted a few times asking questions about cams. since i had lifter tick with stock torque down nuts. little history 1967 GTO correct 400 with 670 heads. 3 speed dearborn with 3:55 gears. Ok I So finally got around to cracking it open. under the valley pan looked good. Wanted your opinion on the pistons. stock? What can the look of the pistons and valves tell you? Timing chain looks loose to me but its been a long time since I have ventured this far. And now the cam. so i measured every one with a caliper and the measurements tell the story. one lobe was nearly rounded (see pic). Can any of these pics tell you what size cam i have? So I need to order my cam,lifters, rockers, springs and new push rods still. looking to just go stock. I have already purchased a double roller chain,oil pump,fuel pump,gasket set,water pump and may be forgetting something. Before its all said and done I am sure I will have more questions. Yours are welcome as well. Ill post pics as well.
 

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Discussion Starter #2
Hey guys. Posted a few times asking questions about cams. since i had lifter tick with stock torque down nuts. little history 1967 GTO correct 400 with 670 heads. 3 speed dearborn with 3:55 gears. Ok I So finally got around to cracking it open. under the valley pan looked good. Wanted your opinion on the pistons. stock? What can the look of the pistons and valves tell you? Timing chain looks loose to me but its been a long time since I have ventured this far. And now the cam. so i measured every one with a caliper and the measurements tell the story. one lobe was nearly rounded (see pic). Can any of these pics tell you what size cam i have? So I need to order my cam,lifters, rockers, springs and new push rods still. looking to just go stock. I have already purchased a double roller chain,oil pump,fuel pump,gasket set,water pump and may be forgetting something. Before its all said and done I am sure I will have more questions. Yours are welcome as well. Ill post pics as well.
was'nt sure how to add more pics. but here they are.
 

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Somebody has been in the engine before "No Retorque" head gaskets. So I would want to know why it was torn down/rebuilt and/or what was done to the engine. Might have been some previous problems someone tried to do a quick fix on and unload the car.

If factory cam, you may find a small letter code stamped on the front snout that may ID the cam.

Time for the machine shop. All the metal from the worn lobes went somewhere and suspect you have some in your bearings. I would want to have the block cleaned/boiled out to get any metal out from all the oil passages. I would also install threaded plugs in the oil galley passages at the front of the block. Install new cam bearings. Install all new freeze plugs.

Chain is definitely shot. A good double roller set-up is the best. Would not simply re-assemble the short block without checking the bore for wear. Cast rods would be checked for roundness and resized with ARP rod bolts as a minimum BUT........I would go with forged I-Beam replacements which are a little more, but insurance. Probably will need to rebalance it all if you go new rods and/or new pistons. New pistons could lower your compression so you could run pump gas, or you could keep your 10.5 compression and use the racing gas/additives.

Check crank as it may be scored up from metal particles and need to be ground down to clean it up.

Many cam choices. Depends on many factor. If you keep everything factory to include the compression, the "068" is a hard cam to beat for all around performance - you may need matching springs.

You will want to freshen up the heads or at least have them checked for excessive play at the valve stem/guide - which leads to oil burning. Check heads for any warping.
 

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Discussion Starter #4
Somebody has been in the engine before "No Retorque" head gaskets. So I would want to know why it was torn down/rebuilt and/or what was done to the engine. Might have been some previous problems someone tried to do a quick fix on and unload the car.

If factory cam, you may find a small letter code stamped on the front snout that may ID the cam.

Time for the machine shop. All the metal from the worn lobes went somewhere and suspect you have some in your bearings. I would want to have the block cleaned/boiled out to get any metal out from all the oil passages. I would also install threaded plugs in the oil galley passages at the front of the block. Install new cam bearings. Install all new freeze plugs.

Chain is definitely shot. A good double roller set-up is the best. Would not simply re-assemble the short block without checking the bore for wear. Cast rods would be checked for roundness and resized with ARP rod bolts as a minimum BUT........I would go with forged I-Beam replacements which are a little more, but insurance. Probably will need to rebalance it all if you go new rods and/or new pistons. New pistons could lower your compression so you could run pump gas, or you could keep your 10.5 compression and use the racing gas/additive
Check crank as it may be scored up from metal particles and need to be ground down to clean it up.

Many cam choices. Depends on many factor. If you keep everything factory to include the compression, the "068" is a hard cam to beat for all around performance - you may need matching springs.

You will want to freshen up the heads or at least have them checked for excessive play at the valve stem/guide - which leads to oil burning. Check heads for any warping.
PontiacJim thanks for your response. So if I was to go the lower compression route and change pistons. what affordable pistons and rod kit would you suggest? Would I have to change heads or could I freshen up my existing heads? My existing cam has the #'s 524009 which I looked up seems close to stock. Correct me if I am wrong. I am not well versed in cams so if I did the piston change would I be able to use a 068 cam and change springs. All I see at this point are $$$$$$. And I would hate to spend that kind of money and have a failed cam break in and start all over again. You may get the feeling I have been down this road before. Had someone rebuild a mustang and Z28 engine the z did not go so well. So I may have to go roller cam and avoid all this even tho its a street driven car. Look forward to any advise. Thanks
 

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Piston selection should be made after you know what the cc's are of your combustion chamber. This is best done after the heads have been assembled as milling the heads can change the cc's, the valve type and/or valve job can change the cc's, and cc's can also be changed should you have any chamber work.

If you are not at a high elevation, ie Denver, you want to shoot for around 9.0 with iron heads so you can run pump gas. You can probably go a tad bit higher based on cam selection and "quench," but it seems no higher than 9.5 compression. Quench article here: What Is The Ideal Quench Height? - Hot Rod Network

You would want to try to achieve around a .045" quench - the distance from the top of the piston to the flat surface found on the head that surrounds the chamber. This forces the air/fuel mixture into the chamber and can eliminate detonation.

The typical Pontiac piston top is about .015" - .020" down in the cylinder bore and trying to get a good quench area can be done a number of ways. Some will mill the block surface to achieve a "zero deck" clearance where the piston top is even with the piston. There is plenty of material at the top of the block to do this, but you might change other geometry angles, ie the head's intake surface, which may need to be milled a matching amount. The valley pan may need some trimming to fit/seat squarely. You also want to ensure that none of your head bolts bottom out and crack the block - so depending on head gasket thickness used, they should be checked/mic'd. I have used the ARP head studs and mistakenly ordered the RA IV studs which have a couple longer studs than the standard 400 head and inserted an extra washer under the head to get the length correct - might not be the correct or advised way to do things, but it worked with no issues.

Another way is to have your machinist measure the distance from the crank's rod throw to the top of the block's deck surface and calculate where the piston pin needs to be located, using your connecting rod of choice, to get the top of the piston even with the block's deck. This is something done if ordering a set of custom pistons-to-order.

Both of the above methods make it easier when ordering head gaskets as having a "zero deck", you simply order a head gasket having a .045" crush. (Some will say .040" works as well, but I use .045" based on what my machinist recommends to take into consideration the heat of expansion, future wear, and even stretch at higher RPM's. If you use nitrous on the engine, he recommends more and says some of his nitrous engines go .060" or more if a really big shot.)

The third option, which I went with on my 455 I am building was to use a thinner head gasket along with the pistons being down in the cylinder .020". I purchased a set of Cometic brand head gaskets ( which run about $100 each, but are some of the best) having a thickness of .027" So, the .020 "down in the hole" plus the .027 gasket equals a quench distance of .047" which is right about where I want it. I also plan on about a 100-125 HP shot of nitrous.

So why is this important? The cc's of your head, the cc's of the area above the piston to the block deck, and the cc's of the head gasket you select will all add up to a total number of cc's. With this information in hand, you can then use one of the online compression calculators to determine how many cc's you will need to incorporate through either a dished piston or the valve notches found in the piston tops to achieve your 9.0 +/- compression ratio.

Additionally, depending on cam lift/duration and cam advance/retard, you want to make sure the valve notches in the piston tops will give you the needed clearances so the valves don't kiss the piston tops.

Cam selection is one of many opinions and I have mine. These are by no means absolutes. The cams with the 110-112 Lobe Separation Angle (LSA) work better in a street engine with less than 9.0 compressions as they build additional cylinder pressure. The cams with 113-115 LSA (like stock cams) work better in a street engine with over 9.5 compression as they can lower cylinder pressure at lower RPM's which get picked back up at the higher RPM's. So for me, the compromise for a street engine having 9.0-9.5 compression is 112 LSA. This is what I selected for my 455 build.

Other important factors are Intake Closing point, duration, lift, and valve overlap. For lift, stock heads don't flow much past .450" lift and is why Pontiac cams increase duration versus lift, EXCEPT for the better breathing RA/SD Heads.

So, would the "068" cam work with lower compression- yes. Might there be a better choice - probably. LOL You don't want to go much over 280 degrees duration for the street, and less can sometimes be even better depending on trans/torque converter stall & rear end gearing. Build a Pontiac for Torque over HP. Perhaps the "068" ground on a 112 LSA might be a good cam with 9.0 compression.

I did a comparison, perhaps not 100% accurate by any means, but still a good comparison, using the 1977 Trans-Am Cam specs in both the 400 & 455 engine. This cam is not what I would consider very radical, but a good street cam. I used an engine Dyno program giving each engine a streetable 9.25 compression. Then I changed the rate of valve lift which mirrors the assorted Pontiac factory cams while still using the 1977 cam duration and LSA. Each engine can be compared at a base line of 2,000 RPM's and then for a maximum HP & TQ at their best RPM. You will see that the HP increases quite a bit from the base line to the maximum/best HP number, but the TQ not so much because the torque remains strong and somewhat flat throughout the entire range - which is what you want as TQ is what moves the car and smokes the tires. The .469" of lift would be about max for stock heads. See attachment.

Roller cams certainly have their advantages, probably more over a flat tappet cam. The down side is of course cost. I am also one who would strongly recommend using the lifter valley brace when using a roller cam - and I would not do without it if I used a roller. As far as bad cams, I think there are many factors that go into those stories & experiences of them going flat. I read that many issues stemmed from the Chinese lifters that were being introduced into the country in high numbers and cheap cost - they were junk. That has since change. How bad can a flat tappet cam/lifters be when you have a supplier who sells both roller and flat tappet cams guarantee them not to go bad or they will replace them? Our cams are guaranteed not to go flat!

First is improper break-in, from not using a good cam/lifter lube that sticks to the parts rather than a slimy liquid that runs off. (I would venture to guess that some people have put the lighter cam lubes on and then let the engine sit for a while. By the time they were ready to fire up the engine, the lube had all but dripped/seeped off.) Installing the cam/lifters and a good break-in lube should be done when you are just about ready to fire up the engine - its in the car and you are buttoning it all up.


Using improper break-in oil. A good specific break-in oil with the correct amount of Zinc in it should be used. You can also add a Zinc additive to other oils that may not have the needed amount, but I think the best way to go would be to use the correct formulated oil right from the start. Using an oil that is too thick - which can affect the flow/bleed rate of the lifters which can mean not enough oil supply at the most critical time in breaking in the cam/lifters. I plan on using the Brad Penn break-in oil, but the Joe Gibbs break-in oil also gets good reviews. I will then follow up with the oil with the formulated Zinc additive before going to the store bought oil and adding a container of Zinc additive like Rislone puts out.

Priming the engine just before starting. Again, don't prime the engine and let it sit for a week or more. It would also be a good thing to rotate the engine by hand to ensure all air pockets are worked out and oil gets to all places it needs to go. My machinist uses an oiling pressure system that he taps into the oil pressure fitting and pressurizes the oil into the engine.

Several lifter suppliers now offer their lifters with a small hole lasered into the base that lets a small amount of oil to seep out onto the cam lobe thus lubricating the cam/lifter. Rhodes Lifters have a tiny channel that runs along the side to do this, and there is even a tool that will scour the lifter bore and allow oil to flow down the channel much like the tiny channel found on the outside of the Rhodes lifter bodies. I would go with the Rhodes before scouring my lifter bore with a channel.

Many install BIG lift cams that require heavy pressure valve springs - typically a dual spring set-up. The added pressures, along with many who then add the higher 1.65 lift rocker arms, puts excessive pressures on the cam lobes/lifter bases and can cause them to wear prematurely if there is any starvation of break-in lube or oil. It is suggested to run just the outside spring for cam break-in and then add the inner spring once this is accomplished. It is the spring rates that really determine this. I am using double valve springs and my machinist said I don't have to pull the inner springs to break in my cam. I think my lift is .490" on the cam I am using.

Varying the engine speeds when breaking in a cam is important. Have seen a few YouTube videos claiming first time fire up and they let the engine idle or rev the crap out of it. My machinist uses an engine break-in stand and says he likes to vary the engine speed and get the engine up to temperature and then shut it down to allow it to cool. He repeats this a couple times. It works for him and he would not be doing it if it caused problems.

You also want to have the timing adjusted as soon as you get it fired. I have never experienced a cam failure, but that was when oil had all the ingredients to protect them from wear.

So roller or flat tappet is a choice and I'd go with whatever you feel most confident with. For me, its about cost and the roller set-up is more than I care to spend for a street engine. If I were to go all out with aluminum heads, BIG HP & TQ, then I'd step up to the plate and go roller.

For rods, you have choices here too. I like light rods - less rotating mass. I think the forged I-beam rods might be lighter than the H-beam's. They are just like stock rods except forged. The H-beams are for higher HP engines and strokers. For a street engine and cost effectiveness, I'd go with the forged I-beam rods.

Piston choice, once you know how many CC's you need out of them, can be almost any manufacturer. Forged are the best, but most expensive. I went with the ICON FHR pistons on my 455 build as they were forged and meet my goal of 9.0 compression. Hypereutectic piston can be a reasonable cost. I used these in my brother's built up Mopar 360CI street engine. These are better than cast, but not as good as forged - kinda in between in my opinion. Some love them, other hate them. Lastly are cast pistons. Fine for a stock rebuild and will hold up if kept under 6,000 RPM's.

With new pistons/rods, you will have to have the engine balanced.

:thumbsup:
 

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Check out Wallace Racing Website Cam Specs @ Wallace Racing - Pontiac Factory Cam Specs
1964 GTO or 421 C 273 113 .407" .447" 54 289 113 .407" .447" 524009
The "009" cam first showed up in 1963 on the 320HP 421CI engines. It was used again in 1964 on the 421 engines and the '64 389CI GTO engine. It is the same cam used from 1965-1976 and better known as the "067"/letter code "P" cam. Typically used in automatics while the hotter "068"/ letter code "S" HO cam was typically used in manual transmission cars.
 

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Discussion Starter #8
Hey guys So i spent a little time in the garage this weekend and measured the cc volume in both the heads and piston/bore at tdc. The heads measured 75cc and the piston/bore at 15cc. I measured my deck height with a straight edge and filler gauges and caliper and it sits around 0.27 down in the bore. For money sake I will build it back stock. I t seems my cam is (C ) #524009 which seems like a close to stock cam. PontiacJim you were correct about the shavings going some where. seems my crank and bearings have some minor scratches but oddly enough the cam and cam bearings were not affected. So does anyone have any idea what my compression could possibly be? when I check my compression #'s they were roughly in the 155-160 numbers across the board. is it possible to get anywhere close to be able to use pump gas w/o new pistons rods balance and the like? my plan was stock cam but if a 068 with new springs will work maybe I would go that route. would I be able to use stock pushrods with that set up? pontiacjim mentioned a 068 cam was used on (manual) cars which is what I have. I will also install Doug thorley ceramic 3 tube headers (Pray for me) and 2.5" exhaust. I will install studs for the headers while the engine is out. Can you purchase those anywhere?
 

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Use your numbers in the Wallace calculator. Compression Ratio Calculator - Wallace Racing

An option might be to open up the chambers a little by "unshrouding" the valves. Ferrea has "dished" valves which may give up a cc or two. I would contact any of the big name Pontiac builders like Butler, KRE, or SD and see what they might recommend to lower the compression but retain the stock short block and 670 heads.
 

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Discussion Starter #10
Well guys I am taking this engine build slowly refreshing my memory and building my knowledge. Gonna take my heads in to refresh them only I hope. Engine had been rebuilt in its past w/ almost no ridge at the top of the cylinder bores. Car ran good no smoke but the cam lobes wore down (lifter tick) on stock torque rockers. Since I have owned it I have used vavoline vr 1 racing oil which I believe has 12-1300 parts zinc. so not sure why. . Anyway heres my latest find.(PIC) Somewhat expected. bearings did there job and limited the crank to minor scratches which will head to the machine shop soon.
 

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Discussion Starter #11
torque down or adjustable lifters

The "009" cam first showed up in 1963 on the 320HP 421CI engines. It was used again in 1964 on the 421 engines and the '64 389CI GTO engine. It is the same cam used from 1965-1976 and better known as the "067"/letter code "P" cam. Typically used in automatics while the hotter "068"/ letter code "S" HO cam was typically used in manual transmission cars.
Pontiacjim I have a question. So i have decided to go the stock route on my 400 with a 068 cam. Now is it best/ok to use the torque method or get 7/16 studs and polly locks? Torque seems like the easy way out but maybe not the best? I got the correct pontiac lifters stock push rods new valve springs with 95-105 lbs closed spring pressure and the open spring pressure is below 300 lbs. Thanks for your opinion. Also the addition of the 068 and 3 tube header/2.5 exhaust I will need a good tuning on my quadrajet. Any one on the forum do this? and will my stock point distributor need any updating? Thanks again.
 

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Discussion Starter #12
Sent my block in for cleaning and honing, heads for a refresh w/ new springs guides and seals. and crank needed a minor grind to clean it up. ordered a 068 cam lifters,oil pump ,water pump fuel pump, 3 tube ceramic coated headers, 2.5 exhaust w/ magnaflow mufflers. plus some cosmetic goodies. may break out the wallet for 4 wheel disk brakes while the motors out since there is a good portion of lines vacuum assist stuff in the engine bay. Also you may see pics of me on skid row after all this. But ill have my GTO. Stay tuned for updates.
 

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Discussion Starter #13 (Edited)
UPDATE: So heard from the machine shop and my 400 will need its first bore. they will do either 0.20 or 0.30 over. so guess what that means? New pistons and probably rods and balance.$$$$$$$ On the positive side it will end up running on pump gas just fine. Does anyone have a reasonable priced piston and rod combo you can recommend? skid row here I come.
 

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Pontiacjim I have a question. So i have decided to go the stock route on my 400 with a 068 cam. Now is it best/ok to use the torque method or get 7/16 studs and polly locks? Torque seems like the easy way out but maybe not the best? I got the correct pontiac lifters stock push rods new valve springs with 95-105 lbs closed spring pressure and the open spring pressure is below 300 lbs. Thanks for your opinion. Also the addition of the 068 and 3 tube header/2.5 exhaust I will need a good tuning on my quadrajet. Any one on the forum do this? and will my stock point distributor need any updating? Thanks again.
Personally, I prefer the 7/16" ARP BB rocker arm studs because you are getting rid of the bottle neck 7/16" base with the 3/8" threaded top - thus the term "bottle neck." The poly locks have to be used with the 7/16" studs to lock the rocker arms down. I also feel it much easier to adjust your valves to the "zero lash" setting while engine is warm and running and be done with it. With the bottle neck studs and torque down method, you can't really take advantage of the "zero lash" setting. However, the Bobcat Kit used to tune-up and increase performance on the Pontiac engines included a set of stock looking rocker arm nuts with the nylock tops so you could "zero lash" your lifters and they would not back off. I would think these would have needed a little attention to checking them every so often so they did not loosen up, but no doubt they worked.

Not sure if the stock push rod purchase at this time was the way to go. If your machine shop mills the heads, make sure it is a clean-up cut and minimal just to square things up. If he makes a larger cut for some reason, then you might need to go with a different length push rod. So keep this in mind.

Make sure you reassemble your heads using the metal oil shields that go over the valve springs. Some leave these out, but they are needed to aid in controlling oil consumption and keeping oil off the valve stem.
 

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UPDATE: So heard from the machine shop and my 400 will need its first bore. they will do either 0.20 or 0.30 over. so guess what that means? New pistons and probably rods and balance.$$$$$$$ On the positive side it will end up running on pump gas just fine. Does anyone have a reasonable priced piston and rod combo you can recommend? skid row here I come.

At this point, go with forged rods. You don't need the H-beams unless you simply want them. Running a basically stock engine, the forged I-beam rods are superior to the stock rods and better priced than the H-beams. If you were going a rotating assembly, then the "kit" typically includes the H-beams along with forged pistons. Forged I-beam rods here - https://butlerperformance.com/i-24453555-rpm-5140-forged-i-beam-rod-6-625-2-250-pontiac-rj.html These are added insurance and will take more RPM's than your engine will probably ever see. Note that these are press-fit wrist pins like stock which are fine.

Pistons are an open subject. If you go .020" over, it may mean custom sized forged pistons. .020" also means your next overbore could be .030", so you kinda get another boring out of the engine IF you freshen it up earlier than most do and there is no deep scouring of the cylinder walls. Otherwise, you might have to skip .030" and go .040" on the next (if ever) rebuild.

Going .030" over will generally open you up to more choices as this is a "standard" size overbore.

Piston selection is also based on your compression choice. For pump gas & iron heads, typically 9.0-9.3 is about it. Quench area is important to aid in controlling detonation. You want to shoot for .040 - .045" depending on piston material - forged pistons expand more than cast or hypereutectic pistons. So you want to measure and know what your actual head cc's are, not what the websites says they are. You also need to know what the volume is above the piston when in the bore (or down in the bore). Typically Pontiac pistons can be anywhere from .010" - .020" down in the bore. This number can be calculated into cc's to go along with your head cc's. The head gasket choice/thickness & bore adds a few more cc's. These numbers all totalled into a final cc number will then determine what kind of piston crown you will need to give you a compression near 9.0 to 1. It may be deeper 4 valve reliefs or even a dished piston. So the piston crown volume/cc's will affect your piston selection.

Forged pistons are best and can take more punishment from detonation. They are also typically heavier and more expen$ive. You can reduce piston weight by selecting a lighter piston pin, but this may be an extra cost option rather than included with the piston. I like lighter pistons/pins, but you are going to pay for it.

Cast pistons are actually OK. The factory cast pistons were good up to 6,000 RPM's. So if you kept your RPM's below this, and 5,800 RPM's was about the limit of the cam anyway, you were good. Ran those crappy 8-valve relief cast pistons in my last 400CI build. Actually ran well and I would spin the engine up to 5,700 RPM's where the cam/power dropped off like a stone.

Next up are the hypereutectic pistons. Used these in my brother's built up 360 Mopar after doing some research. Cheaper than forged and stronger than cast - reasonably priced. Engine is kept under 6,000 RPM's. They expand less when hot so you can run a tad bit tighter clearances (forged pistons need more clearance to account for their expansion). I figure this might also help with wear because they expand and contract less. Personally, I would not have a problem running them on a stock type engine build or one slightly warmed over.

On my 455 .060" over build, I went with the Icon FHR series pistons. I plan on a little nitrous, so forged is the way to go with any power adder. I also run my cars hard, so again, forged is best here. The Icon FHR has assorted crowns that allow you to select one that may work with your engine to get you near the 9 to 1 compression range. I did not "zero deck" my block which some do and my pistons are .020" down in the bore. So I chose a Cometic head gasket at .027" thickness to give me a .047" quench distance (.020" + .027" = .047" total quench). Keep in mind that using the thinner head gasket gets me my desired quench numbers, but it also drops my head closer to the piston just as it would if I had milled the head .012" if the typical head gasket (Felpro) crush is .039". So in my case, and because I know the heads have had a clean-up pass on the milling machine, I will use a push rod checking tool to verify the correct push rod length for my engine. I will also check my valve-to-piston clearance as well. So keep this in mind should you use the thinner head gasket to reduce the quench area.

Now this is not an absolute thing, but the better quench measurement is an added preventative that may prevent detonation when maximizing your timing advance. Not saying a wider quench will not work, but it may require the timing to be adjusted less aggressively to counter any detonation - something we used to do anyway when you heard the engine "pinging" under load on those hot summer days. So something to discuss with your machinist.

So get the needed cc numbers and then do some research and reading in selecting the piston for your application. Your shop should help you on all this. :thumbsup:
 

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Discussion Starter #16
piton and rod selection

At this point, go with forged rods. You don't need the H-beams unless you simply want them. Running a basically stock engine, the forged I-beam rods are superior to the stock rods and better priced than the H-beams. If you were going a rotating assembly, then the "kit" typically includes the H-beams along with forged pistons. Forged I-beam rods here - https://butlerperformance.com/i-24453555-rpm-5140-forged-i-beam-rod-6-625-2-250-pontiac-rj.html These are added insurance and will take more RPM's than your engine will probably ever see. Note that these are press-fit wrist pins like stock which are fine.

Pistons are an open subject. If you go .020" over, it may mean custom sized forged pistons. .020" also means your next overbore could be .030", so you kinda get another boring out of the engine IF you freshen it up earlier than most do and there is no deep scouring of the cylinder walls. Otherwise, you might have to skip .030" and go .040" on the next (if ever) rebuild.

Going .030" over will generally open you up to more choices as this is a "standard" size overbore.

Piston selection is also based on your compression choice. For pump gas & iron heads, typically 9.0-9.3 is about it. Quench area is important to aid in controlling detonation. You want to shoot for .040 - .045" depending on piston material - forged pistons expand more than cast or hypereutectic pistons. So you want to measure and know what your actual head cc's are, not what the websites says they are. You also need to know what the volume is above the piston when in the bore (or down in the bore). Typically Pontiac pistons can be anywhere from .010" - .020" down in the bore. This number can be calculated into cc's to go along with your head cc's. The head gasket choice/thickness & bore adds a few more cc's. These numbers all totalled into a final cc number will then determine what kind of piston crown you will need to give you a compression near 9.0 to 1. It may be deeper 4 valve reliefs or even a dished piston. So the piston crown volume/cc's will affect your piston selection.

Forged pistons are best and can take more punishment from detonation. They are also typically heavier and more expen$ive. You can reduce piston weight by selecting a lighter piston pin, but this may be an extra cost option rather than included with the piston. I like lighter pistons/pins, but you are going to pay for it.

Cast pistons are actually OK. The factory cast pistons were good up to 6,000 RPM's. So if you kept your RPM's below this, and 5,800 RPM's was about the limit of the cam anyway, you were good. Ran those crappy 8-valve relief cast pistons in my last 400CI build. Actually ran well and I would spin the engine up to 5,700 RPM's where the cam/power dropped off like a stone.

Next up are the hypereutectic pistons. Used these in my brother's built up 360 Mopar after doing some research. Cheaper than forged and stronger than cast - reasonably priced. Engine is kept under 6,000 RPM's. They expand less when hot so you can run a tad bit tighter clearances (forged pistons need more clearance to account for their expansion). I figure this might also help with wear because they expand and contract less. Personally, I would not have a problem running them on a stock type engine build or one slightly warmed over.

On my 455 .060" over build, I went with the Icon FHR series pistons. I plan on a little nitrous, so forged is the way to go with any power adder. I also run my cars hard, so again, forged is best here. The Icon FHR has assorted crowns that allow you to select one that may work with your engine to get you near the 9 to 1 compression range. I did not "zero deck" my block which some do and my pistons are .020" down in the bore. So I chose a Cometic head gasket at .027" thickness to give me a .047" quench distance (.020" + .027" = .047" total quench). Keep in mind that using the thinner head gasket gets me my desired quench numbers, but it also drops my head closer to the piston just as it would if I had milled the head .012" if the typical head gasket (Felpro) crush is .039". So in my case, and because I know the heads have had a clean-up pass on the milling machine, I will use a push rod checking tool to verify the correct push rod length for my engine. I will also check my valve-to-piston clearance as well. So keep this in mind should you use the thinner head gasket to reduce the quench area.

Now this is not an absolute thing, but the better quench measurement is an added preventative that may prevent detonation when maximizing your timing advance. Not saying a wider quench will not work, but it may require the timing to be adjusted less aggressively to counter any detonation - something we used to do anyway when you heard the engine "pinging" under load on those hot summer days. So something to discuss with your machinist.

So get the needed cc numbers and then do some research and reading in selecting the piston for your application. Your shop should help you on all this. :thumbsup:
Pontiacjim thanks for your help. So I contacted butler with this info and there recommendations were similar or same as yours 1967 gto 400 stock engine will be getting its first bore @ 0.30 over 068 cam,stock 75 cc heads ( measured) 3 speed manual,355 rear gears 5000 altitude and 91-93 fuel. I am not well versed in posting links so the butler recommendation will be on the next post. I am familiar with stock builds without a bore being necessary,rings bearings,cam oil pump etc. But pistons rods and quench is new to me. I have learned a lot since joining this forum. So my questions are as follows. Do you think there recommendation is a go? my engine had a stock cam 067 and the machine shop is just freshening up my heads. no mill. My stock engine had 15cc @ tdc on the pistons. Am I supposed to buy the they pistons recommended then install to determine my quench once piston to deck are cc'd? I will be putting the engine back together. The machine shop is going to supply the rings and bearings.
 

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Hmmm. Not sure what you mean in that you had 15cc's on top of piston @ TDC. Assume you did a volume measurement which would inlclude the valve reliefs plus the area above the piston to top of block deck?

What is needed to determine quench is the drop from the top of the block deck to the top of your piston @ TDC. A digital micrometer can give you this, which should measure between .010" and .020". This is what is needed, but, different manufacturers can have slightly different piston pin heights and it is the piston pin height ( measured from the center of your piston pin hole to the top of the piston) that can change the piston height down in the bore.

You could measure your drop from top of block to top of piston, then when you pull a piston, have your machinist measure the pin height which will give you a number you can use in selecting your new pistons OR use the difference for calculating how far down in the bore your new pistons will be - if any difference at all.

As I said earlier, this number, top of the piston to block deck is used in determining your quench distance. If you look at your head, you will see the obvious chamber area. Then you will see the flat area on each side of the chamber. The flat area of the head will meet the top of the piston @ TDC. No combustion should take place here as it all takes place in the combustion chamber. To ensure that all of the air/fuel mix is squeezed into the combustion chamber, the distance between the top of the piston and the flat area of the head is called the quench area. That little space between the 2 is where you want to have a .040"-.045" distance which compresses to force the air/fuel mixture out and into the combustion chamber. If there is a much larger space, it is possible for the air/fuel mix within that area to ignite and can be a cause of detonation as the air/fuel mixture does not burn efficiently.

Again, as noted, to get the best quench measurement of .040" - .045" (depending on piston material/expansion), you need to know how far down in the hole the piston top is @ TDC AND the compressed thickness of your head gasket.

If the piston were .010" down in the hole and you selected a Cometic head gasket of .027" thick, your quench distance would be .037" which could be too tight and you may have a piston hit the head. On the other hand, if the piston was .010" down in the hole and you selected a Felpro .041" thick head gasket, your quench distance would be .051" which is a little more than the ideal of .040" - .045".

In both instance above, your piston being down in the hole .010" is a fixed number, you really can't change it (unless you were to deck the block .010" to get a "zero deck" height.) But without altering the block, the piston would be .010" down from the deck. So to achieve the desired quench, you select a head gasket that would give you .040" - .045". So you would want a head gasket that compresses to .030" - .035" (.010" + .030" = .040" OR .010" + .035" = .045")

Now, you say you have 15 cc's above the piston @ TDC. How far down in the hole is it? If it was .020" and then you selected a replacement piston that is now .010" down in the hole, your cc's will change. The change in cc's could affect your final compression ratio by increasing it UNLESS you compensate with more cc's in the piston dome through the use of 4 valve reliefs or even dished pistons.

My opinion here, but if you shoot for 9 to 1 compression or a little more, then slight changes won't have any big effect on final compression because you are building in a little buffer to cover any slight changes in calculations - your total cc numbers.

I use the Wallace compression calculator Compression Ratio Calculator - Wallace Racing to get a pretty close number for compression. You can play around with the numbers so it is helpful in selecting a piston top configuration having "X" amount of cc's built into it. Most all pistons will give you the number of cc's the valve reliefs take up or any dished area will use - so you will see numbers like 6 cc's, 11 cc's, 14 cc's or 18 cc's.

On the calculator, you want the deck height & gasket thickness to fall between the quench distance of .040" - .045" when they are added up together - and this is why you need to know how far down in the hole the piston top is (deck height). Head cc's you know as 75 cc's. So you will play around with the piston cc's to arrive at a compression ratio of between 9.0 and up to 9.5 max with the iron heads and 93 octane. The "068" cam may bleed off some compression at the very lowest of RPM's due to its overlap thus making compression pressure a little lower at these lower RPM's which of course will pick right back up once your RPM's get into higher numbers.

Butler knows their stuff, as do several other Pontiac engine builders. I have emailed them myself and gotten good responses. So I would trust their input. Now you can ask them about the quench distance just to confirm what I have thrown at you. They may have another opinion - I certainly am no expert and don't know everything, and each engine build is unique. :thumbsup:
 

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Discussion Starter #19
Quench

Hmmm. Not sure what you mean in that you had 15cc's on top of piston @ TDC. Assume you did a volume measurement which would inlclude the valve reliefs plus the area above the piston to top of block deck?

What is needed to determine quench is the drop from the top of the block deck to the top of your piston @ TDC. A digital micrometer can give you this, which should measure between .010" and .020". This is what is needed, but, different manufacturers can have slightly different piston pin heights and it is the piston pin height ( measured from the center of your piston pin hole to the top of the piston) that can change the piston height down in the bore.

You could measure your drop from top of block to top of piston, then when you pull a piston, have your machinist measure the pin height which will give you a number you can use in selecting your new pistons OR use the difference for calculating how far down in the bore your new pistons will be - if any difference at all.

As I said earlier, this number, top of the piston to block deck is used in determining your quench distance. If you look at your head, you will see the obvious chamber area. Then you will see the flat area on each side of the chamber. The flat area of the head will meet the top of the piston @ TDC. No combustion should take place here as it all takes place in the combustion chamber. To ensure that all of the air/fuel mix is squeezed into the combustion chamber, the distance between the top of the piston and the flat area of the head is called the quench area. That little space between the 2 is where you want to have a .040"-.045" distance which compresses to force the air/fuel mixture out and into the combustion chamber. If there is a much larger space, it is possible for the air/fuel mix within that area to ignite and can be a cause of detonation as the air/fuel mixture does not burn efficiently.

Again, as noted, to get the best quench measurement of .040" - .045" (depending on piston material/expansion), you need to know how far down in the hole the piston top is @ TDC AND the compressed thickness of your head gasket.

If the piston were .010" down in the hole and you selected a Cometic head gasket of .027" thick, your quench distance would be .037" which could be too tight and you may have a piston hit the head. On the other hand, if the piston was .010" down in the hole and you selected a Felpro .041" thick head gasket, your quench distance would be .051" which is a little more than the ideal of .040" - .045".

In both instance above, your piston being down in the hole .010" is a fixed number, you really can't change it (unless you were to deck the block .010" to get a "zero deck" height.) But without altering the block, the piston would be .010" down from the deck. So to achieve the desired quench, you select a head gasket that would give you .040" - .045". So you would want a head gasket that compresses to .030" - .035" (.010" + .030" = .040" OR .010" + .035" = .045")

Now, you say you have 15 cc's above the piston @ TDC. How far down in the hole is it? If it was .020" and then you selected a replacement piston that is now .010" down in the hole, your cc's will change. The change in cc's could affect your final compression ratio by increasing it UNLESS you compensate with more cc's in the piston dome through the use of 4 valve reliefs or even dished pistons.

My opinion here, but if you shoot for 9 to 1 compression or a little more, then slight changes won't have any big effect on final compression because you are building in a little buffer to cover any slight changes in calculations - your total cc numbers.

I use the Wallace compression calculator Compression Ratio Calculator - Wallace Racing to get a pretty close number for compression. You can play around with the numbers so it is helpful in selecting a piston top configuration having "X" amount of cc's built into it. Most all pistons will give you the number of cc's the valve reliefs take up or any dished area will use - so you will see numbers like 6 cc's, 11 cc's, 14 cc's or 18 cc's.

On the calculator, you want the deck height & gasket thickness to fall between the quench distance of .040" - .045" when they are added up together - and this is why you need to know how far down in the hole the piston top is (deck height). Head cc's you know as 75 cc's. So you will play around with the piston cc's to arrive at a compression ratio of between 9.0 and up to 9.5 max with the iron heads and 93 octane. The "068" cam may bleed off some compression at the very lowest of RPM's due to its overlap thus making compression pressure a little lower at these lower RPM's which of course will pick right back up once your RPM's get into higher numbers.

Butler knows their stuff, as do several other Pontiac engine builders. I have emailed them myself and gotten good responses. So I would trust their input. Now you can ask them about the quench distance just to confirm what I have thrown at you. They may have another opinion - I certainly am no expert and don't know everything, and each engine build is unique. :thumbsup:
PontiacJim I was just reading thru some of my prior posts after the machinist calculated my compression ratio with everything mocked up. This is a little confusing to me but here goes. He tells My heads are at 69 cc after milling. Says the piston is .35 down in the hole. using the pistons below. and figuring the felpro stock gasket(.42?) If I do no decking I will have 9.1 compression. since the piston is so far down in the hole how does that affect my quench. and what is the best way to proceed? I called to talk to the owner but he starts early and had already left. this is all thats left to decide on. I'll have to give him a call tomorrow so that gives me some time to gather some info and opinions before I talk to him. Thanks RMTZ67
 

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OK, piston is in the hole .035", not .35" - otherwise the Wallace calculator puts you at below a 6-to-1 compression. LOL So I too come up with 9.1 compression using the Felpro .041 gasket @ 4.2" bore size.

.035" down in the hole plus .041" gasket gives you a quench of .076" - a bit too much in my opinion.. And from everything I read, anything over .050" - .060" is really too much and can lead to poor burning of the air/fuel mixture and possibly detonation problems.

Let's shoot for .045" for the Quench area. .076" (what you have) - .045" (what you prefer) = .031" (what you need to remove).

I would use the .027" Cometic head gaskets (another $100 each). That gives you your present .035" down in the hole + .027" = .062" for your Quench area - still a bit too much, but better than .076".

So how do you get to the .045" Quench? If you can get a .062" Quench (from above) by using the Cometic head gaskets, take that number .062" - .045" (the desired Quench) leaving you with a difference of .017" which is the amount you would need to deck the block. .035" down in the hole + .027" Cometic gasket = .062" MINUS the .017" milled from the deck = .045".

.017" is next to nothing with regards to milling. Milling .017" from the block deck would then have your pistons .018" down in the hole (.035" - .017" = .018" down in the hole).

.018" (pistons down in the hole) + .027" (Cometic head gasket) = .045" Quench area - just what you want to shoot for.

Now this will change your compression a bit. Wallace Calculator says the new compression will be 9.76-to-1. Getting a little too high. But, with a good Quench and a long duration (larger overlap cam), you might get way with 9.76 on 93 octane.

Now you have to figure a course of action to get the compression down.

A. - assemble the engine as is with the larger Quench - not recommended.

B. - get an additional 6 cc's from somewhere to drop compression to 9.25
1. - open up the head chamber a few more cc's
2. - mill a little more away on the raised area on the dish where the valve reliefs are
3. - combination of both

My guess would be that the pistons would be the easiest place to remove/mill the needed 6 cc's versus opening up the head chamber. My guess would be less labor in milling the pistons once the milling machine was set-up - it would be repeated on each piston so it would be consistent.

As you can see, no simple solution, and it will add more $ to the build. Would I do it? Yes. I would not want to take a chance of building an engine and then have detonation problems or have to retard my timing back and kill power.

Again, take all this as my opinion and suggestions - and I hope I got it all right. LOL You want to talk to your machinist and run this by him to see how he feels about it as he is the guy building your engine. He may be onboard and agree 100% or tweak a few things to get to where you want to be. :thumbsup:
 
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