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post #1 of 17 (permalink) Old 07-14-2018, 05:29 PM Thread Starter
 
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Need help figuring what piston I need. (wallace calculator)

So I am having trouble figuring out how to use the comp calculator. could use some help. I have a 67 gto original 400 has not been decked before and will be getting its 1st bore at 0.30. current 670 heads are 75cc.. if you need more info let me know. I did not know what the gasket bore is off hand. The machinist took the liberty of ordering some flat top pistons he mentioned in a prior conversation once I gave him the go ahead to do the bore.He believes it may have to be decked also removing #s off my block.The pistons below is what butler recommended with the info I gave them. And the book pic is what the machinist ordered. what do you guys think? he is aware of the 40-45 quench. by the way 068 cam.
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post #2 of 17 (permalink) Old 07-14-2018, 06:19 PM
 
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So I am having trouble figuring out how to use the comp calculator. could use some help. I have a 67 gto original 400 has not been decked before and will be getting its 1st bore at 0.30. current 670 heads are 75cc.. if you need more info let me know. I did not know what the gasket bore is off hand. The machinist took the liberty of ordering some flat top pistons he mentioned in a prior conversation once I gave him the go ahead to do the bore.He believes it may have to be decked also removing #s off my block.The pistons below is what butler recommended with the info I gave them. And the book pic is what the machinist ordered. what do you guys think? he is aware of the 40-45 quench. by the way 068 cam.
Looks like the same type pistons - the "D" dish with 17 cc's. KB346 pistons, not the flat top at the top of the page - its for the 151 4-cyl engine.

Plugging in the numbers at the Wallace site, I come up with 9.17 compression and plugged in 4.30" for the head gasket. I also used the .041" head gasket thickness and 000 on the deck clearance as this would be the same as .041" quench distance. If you went for a .045" quench distance, compression on the calculator is then 9.09.

He may or may not measure for the .040" - .045" quench, but he also might. This is something you need to ask. Simply tell him you rather not cut the deck if possible and use the thinner Cometic head gaskets (which are as thin as .027" and also come in other thicknesses) if this would work instead. They can also be closer to the actual overbore of the cylinder which will add cc's compared to a larger bore size like the Felpro. Cometic gaskets are $100 each, but probably the best. So it may be cheaper to mill the deck and go with Felpro gaskets that come in the engine gasket rebuild kit. Again, this is something to discuss with your builder and voice your concerns and then listen to what he says - he may have a preference or none at all.

Here is what I have saved on head gaskets gathered from the web:

Fel-Pro introduced PN-8518 for the Pontiac V-8 during the 1970s. Containing a bore diameter of 4.3 inches and a preflattened thickness of .041 inch, it’s a stock-replacement design that’s compatible with most Pontiac blocks. an affordable choice for any stock rebuild, and even performance applications with a compression ratio up to 10.5:1, or slightly more.

A second Pontiac offering appeared in the Fel-Pro catalog during the early 1980s. PN-1016 is specially designed for high-performance applications with high compression and/or combustion pressure. Constructed of a Teflon-coated solid-steel core, it features stainlesssteel combustion armor and a wire ring combustion seal for maximum combustion containment. It contains a chamfered bore diameter or 4.3 inches and pre-compressed thickness of .039 inch. it’s a good choice for naturally aspirated engines with a maximum compression ratio of 12:1 and/ or mildly boosted applications.

Cometic is the only company that presently produces MLS cylinder head gaskets for the Pontiac V-8. Bore diameters range from 3.75 to more than 4.4 inches and standard compressed thickness measures .040 inch. Any other bore diameter and thickness from about .020 to .120 inch is available on a customorder basis. Suitable for stock rebuilds and max-performance applications.

Each .010-inch difference of head gasket thickness alters the static compression ratio by about .15:1.
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post #3 of 17 (permalink) Old 07-14-2018, 07:29 PM
 
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I would not use those "Hypercast" pistons under any circumstances. If they are used, you must have a really big top ring gap. There have been lots of wiped out engines because of using those pistons & a gap that was too small.

Some guys use the cheaper SP L2262F forged pistons & have a dish machined into 'em. But if your budget will stand it, I'd recommend Auto Tec custom pistons. They can position the pins so that you can get zero deck height, without cutting extra material off the block.

Other advantages are lighter weight & floating pins. Only negative I can think of is price. Will probably cost between $500 & $600.
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post #4 of 17 (permalink) Old 07-14-2018, 09:36 PM Thread Starter
 
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So Forgot to mention I am looking to run on pump gas 91-93 octane here. I would like to get the most compression that is safe. What do you guys think that would be? And is that possible w/o decking the block dont want to run no race gas no additives. It will be a cruiser and just get on it now and then. No track. I have only put 3000 miles in 10 yrs. May be less now that I got a travel trailer. BigD you still down on those pistons with that info?

Last edited by RMTZ67; 07-14-2018 at 09:37 PM. Reason: misspelling
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post #5 of 17 (permalink) Old 07-14-2018, 10:08 PM
 
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bigD: "I would not use those "Hypercast" pistons under any circumstances. If they are used, you must have a really big top ring gap. There have been lots of wiped out engines because of using those pistons & a gap that was too small."

PJ: Hold on, don't throw the baby out with the bath water. You might not use them, but Butler did not have a problem recommending them and I'm sure they use them or they would not have recommended them.

You are correct with regards to the ring gaps BUT, most piston manufacturers recommended ring gaps with their pistons based on piston material & use. Even the ring gaps used on the "better" forged pistons vary based on things like power adders. My machinist told me that some of these engines he builds for big shots of nitrous look like oil burners when running because the ring gaps have to be so wide. Once they hit the nitrous, the heat takes over and expands the pistons and closes the gaps to where they need to be - if not, they would but and break rings & pistons.

The manufacturer of my forged pistons has a recommended gap when using nitrous. Why? Same as the hypereutectic pistons, heat. Nitrous generates more heat and if the rings gap is not spaced wider, they too will butt and bust the ring land or piston top off. So I don't think it fair, or justified, to slam the hypereutectic pistons and get RMTZ67 all concerned when the piston is actually not the problem, but rather the heat of expansion. Ring gaps need to be set according to the piston manufacturer and not by the factory service manual unless you are using a like material piston.

This is from another forum and describes the problem to a "T":

"I've beat the snout outta hypereutectic pistons- massive nitrous hits, vicious over-revving, and now 2 supercharged engines.

99% of the complaints about hypereutectic pistons "shattering", in my opinion, come from improper setup/machining. Hypereutectis want tolerances that are very different from either a forged or a standard cast piston. Recommended ring gaps are usually much wider on a hypereutectic because the material and the design of the piston throws a LOT of heat at the rings. If you don't follow recommendations you'll butt the ring ends together (especially if you encounter detonation), instantly "shattering" the piston. Usually involving ripping the ringland above the top ring off the piston, and instantly destroying the engine.

Also, Hypereutectis want a bore-to-piston clearance much tighter than a typical forged piston- much more like a regular cast piston. In the range of .0015-.0020 for a N/A application, .0020-.0025 for a nitroused or blower application. Anything wider and you're just beating up the piston by letting it rock in it's bore too much.

I am currently using KB Hypereutectic pistons in my 383 blower motor. Top ring gap is a MASSIVE .032". Almost TWICE what a typical cast or forged piston would require. And exactly what KB recommends for my application. Works fantastic. I have personally, in the past, made the mistake of gapping too tight thinking I knew better than the manufacturer (did them at .025). I was wrong. First time I hit detonation I butted the ring ends and ripped the top ringlands off the pistons, destroying the engine.

Now that I've got the gaps set right I have encountered similar situations with detonation but the pistons held up just fine this time. Do it EXACTLY like they tell you to and you can push Hypereutectics a LONG LONG way. They aren't made of glass. They're tough little suckers.

I am NOT recommending that you throw hypereutectic pistons into your next boosted/nitroused motor. Forged pistons will still take more punishment, in my opinion. But ANY piston will eventually fail if you run it in detonation. Some just take longer to fail than others."

Followed by: "I agree with everything that you said, but remember that you're running KB hyper... pistons, which are much better then most."

PJ: Forged have their place, cast has their place, and hypereutectic has its place. Each choice requires that the manufacturers specs be followed by the machinist and/or the engine assembler/builder. Used the hypereutectic in my brother's engine and still going strong. I would not have a problem using them in one of my engines as a replacement for cast pistons and if costs were a factor. I don't think I would use them with nitrous either. But otherwise, I would not have a problem. As stated above, detonation will kill them or any piston if not checked. With the lower 9.0 compression, I don't think detonation should be a problem unless the wrong cam is selected that builds more cylinder pressure & thus more dynamic compression that could lead to detonation.
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post #6 of 17 (permalink) Old 07-15-2018, 09:51 AM
 
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To each, his own.

My opinion is: Why take a chance, when there are plenty of stronger, lighter forged pistons available ?

Only reason I can think of is if using them will save you hundreds of dollars, and you're on a very tight budget.

We all have our opinions. This is mine, about hypercast pistons.

http://www.pontiaczone.com/forum/sho...20&postcount=6
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post #7 of 17 (permalink) Old 07-15-2018, 02:06 PM
 
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To each, his own.

My opinion is: Why take a chance, when there are plenty of stronger, lighter forged pistons available ?

Only reason I can think of is if using them will save you hundreds of dollars, and you're on a very tight budget.

We all have our opinions. This is mine, about hypercast pistons.

PONTIAC ZONE TECH FORUMS - View Single Post - What pistons to buy??

Agreed, we all have our opinions - and diverse opinions can only help some in asking more questions, doing more research, or making better informed choices. You would not run with the hyper's whereas I would and I would not run a roller cam without the lifter brace whereas you would.

The post you linked to was put up in 2005. It is now 13 years later. Improvements, or even better awareness, of setting up these pistons can only have evolved since 2005.

From what I gathered, since these pistons are a casting, many were setting ring tolerances according to what they were familiar with and would have used for the factory or replacement cast piston - not the hypereutectic pistons. They are of a different composition just as forged pistons can be made of different materials & mixtures of alloys and ring placement was made higher putting them into more heat.

In my opinion, they have features that are better than cast WHEN used in a stock or mild performance engine not using nitrous or supercharging.

Hypereutectic pistons are simply a stronger type of alloy with a higher silicon content. Silicon doesn't expand so you can run tighter clearances with these pistons than with others, which helps seal-in the combustion pressure, plus the alloy used in these types of pistons is better than what other cast pistons have so they are stronger than any typical cast piston, but they are still cast pistons, which have limitations to what kinds of stresses and such they can be put through.

KB Pistons can be installed tighter than other performance pistons. A close fitting piston rocks less, supports the rings better, and seals the engine for maximum power.

The Keith Black pistons unique thermal conductivity, ring location and varied end use requires special attention be paid to top ring end gap. KB pistons make more HP by reflecting heat energy back into the combustion process and, as a result, the top ring runs hotter and requires additional end clearance. Increasing ring end gap does not affect performance or oil control because normal end gaps are realized at operating temperatures. Failure to provide sufficient top ring end gap will cause a portion of the top ring land to break as the ring ends butt and lock tight in the cylinder. The broken piece may cause further piston or engine damage.

Hypereutectic piston engines will require 2-4 degrees less total ignition timing. One key to top performance is to have all cylinders igniting and producing a like flame travel that produces the same timing numbers. Equal air flow, fuel mix, quench, chamber temperature, swirl, and compression at each cylinder work to this end.

HYper's had some set-backs when they first hit the market and from what I have read all over the net is it came from improper ring gaps and taking into account that they were said to be stronger than cast and guys running power adders which further aggravated the ring gap problem - suffice to say that the pistons were not the true problem, but the expansion found in the rings at the higher temps due to the higher location of the top ring land which required wider ring gaps. Once the hyper's, like any engine product, gets tarnished or is given a bad review, the stigma of a bad product seems to hang over them like a cloud even though it is a good product when used as intended and manufacturer specs are adhered to. Finding blogs, threads, & forums that are current and not 15 years old seem to put hypereutectic pistons in a more favorable light.
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Hypercast pistons

Quote:
Originally Posted by bigD View Post
I would not use those "Hypercast" pistons under any circumstances. If they are used, you must have a really big top ring gap. There have been lots of wiped out engines because of using those pistons & a gap that was too small.

Some guys use the cheaper SP L2262F forged pistons & have a dish machined into 'em. But if your budget will stand it, I'd recommend Auto Tec custom pistons. They can position the pins so that you can get zero deck height, without cutting extra material off the block.

Other advantages are lighter weight & floating pins. Only negative I can think of is price. Will probably cost between $500 & $600.
Quote:
Originally Posted by RMTZ67 View Post
So I am having trouble figuring out how to use the comp calculator. could use some help. I have a 67 gto original 400 has not been decked before and will be getting its 1st bore at 0.30. current 670 heads are 75cc.. if you need more info let me know. I did not know what the gasket bore is off hand. The machinist took the liberty of ordering some flat top pistons he mentioned in a prior conversation once I gave him the go ahead to do the bore.He believes it may have to be decked also removing #s off my block.The pistons below is what butler recommended with the info I gave them. And the book pic is what the machinist ordered. what do you guys think? he is aware of the 40-45 quench. by the way 068 cam.
Quote:
Originally Posted by PontiacJim View Post
Agreed, we all have our opinions - and diverse opinions can only help some in asking more questions, doing more research, or making better informed choices. You would not run with the hyper's whereas I would and I would not run a roller cam without the lifter brace whereas you would.

The post you linked to was put up in 2005. It is now 13 years later. Improvements, or even better awareness, of setting up these pistons can only have evolved since 2005.

From what I gathered, since these pistons are a casting, many were setting ring tolerances according to what they were familiar with and would have used for the factory or replacement cast piston - not the hypereutectic pistons. They are of a different composition just as forged pistons can be made of different materials & mixtures of alloys and ring placement was made higher putting them into more heat.

In my opinion, they have features that are better than cast WHEN used in a stock or mild performance engine not using nitrous or supercharging.

Hypereutectic pistons are simply a stronger type of alloy with a higher silicon content. Silicon doesn't expand so you can run tighter clearances with these pistons than with others, which helps seal-in the combustion pressure, plus the alloy used in these types of pistons is better than what other cast pistons have so they are stronger than any typical cast piston, but they are still cast pistons, which have limitations to what kinds of stresses and such they can be put through.

KB Pistons can be installed tighter than other performance pistons. A close fitting piston rocks less, supports the rings better, and seals the engine for maximum power.

The Keith Black pistons unique thermal conductivity, ring location and varied end use requires special attention be paid to top ring end gap. KB pistons make more HP by reflecting heat energy back into the combustion process and, as a result, the top ring runs hotter and requires additional end clearance. Increasing ring end gap does not affect performance or oil control because normal end gaps are realized at operating temperatures. Failure to provide sufficient top ring end gap will cause a portion of the top ring land to break as the ring ends butt and lock tight in the cylinder. The broken piece may cause further piston or engine damage.

Hypereutectic piston engines will require 2-4 degrees less total ignition timing. One key to top performance is to have all cylinders igniting and producing a like flame travel that produces the same timing numbers. Equal air flow, fuel mix, quench, chamber temperature, swirl, and compression at each cylinder work to this end.

HYper's had some set-backs when they first hit the market and from what I have read all over the net is it came from improper ring gaps and taking into account that they were said to be stronger than cast and guys running power adders which further aggravated the ring gap problem - suffice to say that the pistons were not the true problem, but the expansion found in the rings at the higher temps due to the higher location of the top ring land which required wider ring gaps. Once the hyper's, like any engine product, gets tarnished or is given a bad review, the stigma of a bad product seems to hang over them like a cloud even though it is a good product when used as intended and manufacturer specs are adhered to. Finding blogs, threads, & forums that are current and not 15 years old seem to put hypereutectic pistons in a more favorable light.
Well thanks BigD and pontiacJim for your input. Varying opinions is expected in most any question brought to the table. That being said everyone should do there research and take in to account others opinions. When I started out this venture I was expecting to replace a cam and has grown to a entirely different scope. So to say it was unexpected would not be the truth. But its been a long time since I have been this deep into a engine so trying to refresh myself and learn a few things along the way.This forum is indeed a life saver. So thanks to all those who help the least of us out. If the plan was to completely go thru this engine I would have saved up a fortune. But since this build was unexpected I have to make due. Hyper pistons, use my current rods with arp bolts.Refresh my 067 heads. Well you get the picture. Like you said PontiacJim Butler recommending them is saying something. I doubt they would sell them if they did'nt have there place. The machine shop and owner that recommended the pistons has been in business here for over 40 years. "BUT" they need to know your needs and wants for your engine. With what I will use my car for I could probably use coffee cans for pistons lol. Car shows and the occasional sunday cruise. Dont get me wrong I like spinning those wheels like everyone else but only on occasion. So thanks for your input guys. And I am sure this will not be the last question I ask. RMTZ67
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post #9 of 17 (permalink) Old 07-16-2018, 08:12 AM
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You're taking the right approach by taking your time and doing the research. Like every other topic on the internet you'll find opinions and ideas all over the map. It's a great source of information but one must dig deeper into all of it and consider background and the logic behind what people have to say in order to arrive at the real truth. Personal experience and even personal biases do play a part. I ran a solid roller on the street and on some long distances for more than 5 years with no lifter bore brace and it wasn't an issue. However the cam profile was not super aggressive and didn't need monster springs to keep it under control. It was a rocker arm failure that sidelined it, and to be truthful that was partially my fault for failing to recognize some warning signs. I'm going with a more aggressive cam this time that yields more lift and about 20 degrees more duration even after 'dropping back' to 1.5 rockers - and using a lifter bore brace. I'm also using stainless steel full roller rockers in place of aluminum ones. I went through one of those long "multiple opinion" challenges with regard to the lifters and oiling not too far back. I'm using Crower "HIPPO" (high pressure pin oiling option) lifters and during mockup realized that they would not be getting oil whenever they were at zero lift on the cam base circle. The question was, "will that be an issue"? Opinions were everywhere, even from different people I talked to at Crower over a period of several weeks. Ultimately I opted to provide full time oiling, and my first 'solution' of modifying the lifters themselves left me with a brand new set of $800 lifters that I had essentially ruined. (My solution 'worked' at zero lift, but also caused oil leakage at max lift - doh!). I have a second set of new lifters and a solution now that will work as intended, but it was scary because it involved modifying the lifter bores in my original to the car numbers matching and therefore irreplaceable at any price block. Gulp. I used a small rotary tool to cut some grooves at the bottom of the lifter bore oil feed holes to extend them 'downward' so that they now feed oil to the lifter oil bands at zero lift, but also don't leak pressure 'anywhere'. I had to really think about that one long and hard before I picked up that tool, let me tell you!
Anyway, you're doing the right thing. Take your time and understand not only what you're doing but why you're doing it, and everything that can logically result from the choices you make. It all eventually makes sense.

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post #10 of 17 (permalink) Old 07-17-2018, 06:10 PM
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The thing that concerns me the most is that the machinist said that decking will remove the numbers on the block. Only Chevrolets have that issue, due to engine number and VIN number location on the pad on top of the deck. Pontiacs have the number on the front of the block, below the passenger cylinder head, next to the timing cover. In an area that would never get machined or milled in any way. In my experience, Chevy-savvy machinists are NOT then ones to use when doing a Pontiac Strato-Streak V8!! YMMV.........but you've been warned.
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