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350 Cylinder compression

20K views 91 replies 6 participants last post by  KowalskiCW 
#1 ·
So I did a little research on here to see what a normal cylinder compression is and seems 150 is key. I checked my compression this weekend while the engine was cold one spark plug at a time. I got 100-110 no higher no lower. I've been noticing quite a bit of smoke at start up lately that eventually goes away, so that's what prompted the check. Also the fact that I have a open diff and can't do a one wheel burnout to save my life haha. 115k on the original motor.
Now I read that you are supposed to do this test with the engine warm, all plugs out and carb open. Did I really get that far off of a reading or is this still indication of a worn out engine? I don't seem to be going thru oil but I've only had it for the summer and haven't had to add oil yet on the initial oil change I did.
I just can't believe a 350 with a cam and 4 barrel carb can't burn one wheel...not even a brake stand!
Thoughts?
 
#2 ·
I just did more searching and realized I did the compression test all wrong. I'll warm the engine, take out all the plugs(hopefuly not burn myself!) and hold the carb open and try again. I'll report back.
Still don't know why this car can't do a damn burnout! 265hp 335ft lbs should be able to....I digress.
 
#3 ·
That's why most people don't like the 350. And most have low compression.

But, a 350 can be built to make some decent power. The strongest 350's were the '68 & '69 350HO engines. They had over 10:1 compression. And the '69 model even had #48 big valve heads. I had one of these, with a bigger cam, that made 434hp on the dyno. It ran mid 12's in a '69 Tempest. :smile3:

And, about the burnout: you probably have some highway gears, like maybe 2.56, 2.73, or 3.08. You'd probably need a 455 to burn rubber with those high speed gears. For any kind of good acceleration, with a low compression 350, you'd need 3.55 gears. 3.73 would be better.

Or, you can go with a stall converter that will flash to around 2800rpm when you nail it. That might break the right rear loose. :grin2:
 
#4 ·
I to have a 69 custom s with bone stock 350 motor all original with little over 111,000 on the clock. I have no problem getting a burnout when brake torqueing but not much off the line without brakes held down. Im not sure what gears I have since I just bought it couple months ago but it really gets up and goes for a stock motor. I am gonna install a shift kit next week if my buddies tranny shop can fit me in. This winter I am pulling the motor to replace the rear main seal which is leaking bad and wanting to install a ram air cam like in the 69 350 ho possibly and ram air manifolds. Not sure if Im gonna go with the # 48 heads. Currently have #47 stock heads. Havnt had much time on researching that. Its no matching motor so want to keep the drivetrain in it though a 400 would be nice!
 
#5 ·
My advice would be to avoid the Ram Air cam and go with something like the Lunati Voodoo line. These cams were designed by Harold Brookshire (of Lunati Ultradyne, and Bullet Cams fame). He designed the Voodoo's with closing ramps like GM used, better for your valves and valve seats. In contrast Comp's XE's tend to bounce off the valve seats as they close too fast. Jim Hand, very well known Pontiac performance man for decades (and still racing) uses a Ram Air cam in his 455 LeMans and still does things to bolster low end torque for his big 455 since the Ram Air cam is sadly lacking in low end torque. (From Pontiac Jim---- Building a Strong Street Machine ? Part 5: Pontiac Camshafts | Dallas Area Pontiac Association )

To get more low end torque with a cam change try one of these two Voodoo's. Besides torque to fry your tire, they also increase cylinder pressure in low compression engines for more power. Just be careful to evaluate for detonation.
Voodoo Hydraulic Flat Tappet Cam - Pontiac V8 256/262 - Lunati Power
Voodoo Hydraulic Flat Tappet Cam - Pontiac V8 262/268 - Lunati Power

BigD's advice was very good, do consider it. If you do some mods to increase torque, you might look into the stronger 8.5" GM rear end with the gears recommended.

Rather than swapping engines, here is an article to give you an idea how strong a Pontiac 350 can become.

Small-Bore Pontiac Performance Engine Build - Revenge Of The 350 - Hot Rod Network

Hope this is of some help!:smile3:
 
#6 ·
Put a set of 3.90's or 4.33's out back and you should be able to fry tires. No top end however, and your engine won't like highway driving. The 2 series gears or the 3 series ratio's under 3.55's will need some good torque/horsepower to spin tires with an automatic. With a 3/4-speed manual trans you can do it because you can rev the engine, dump the clutch, shock the tires, and spin em'. Unless you want to put your automatic in neutral, rev it way up, and drop it into drive, you may not spin your tires. But this is not my recommendation and you might just drop the tranny.

The 350CI in my book seems to be under rated because everything centers around the more available 400CI and its stroker abilities. I had a '67 Firebird with 350CI 3-speed manual trans that had no problem laying down long strips of rubber with its one-legger rear end and the old 14" 78 series tires. I had an aftermarket tach in it and I'd spin it 6,000 RPM's with no problems.

I'd like to build a hi-revving Pontiac 350CI just to try it, 6800-7200 RPM's, 475HP/410 ft lbs. Not sure how I would go with trans/rear gears.

My basic build (which could change with better research) off the top of my head would be:

350 block .030" over
Forged pistons 10:1 ratio

4-bolt splayed main caps fitted

forged crank with BB 2.20 rod journals

80 PSI oil pump and big pan

BB 6.7 forged H-beam rods to give a rod/stroke ratio of 1.79 for high revs.

350 CI 1.94/1.66 Iron heads:
1.stock intake port flow @ 190-210 just cleaned up, no port larger RA IV gasket matching, just stock gasket matching to equalize.
2. fitted w/screw-in BB 7/16" studs & Pontiac guide plates. Pushrod holes elongated for large lift cam.
3. 2.02" valves on the intake. I think I would leave the 1.66" exhaust to keep exhaust gas velocity up.
4. bronze valve guides & teflon seals
5. 3-angle valve job and some port blending and "boat-tail" the intake guides in the bowl.
6. matching valve springs/retainers
7. 1.5 ratio roller rockers to take advantage of the slower opening rate vs 1.65's for a little more improved bottom end performance.

Solid Cam, 112 LSA, 109 ICL, 295 duration -.500" Int, 300 duration -.520" exhaust. Intake closes at 76 ABDC.

Torker single plane intake
780 CFM Holly

1 5/8" headers, duel 2.50" pipes with X-over, low restriction mufflers.

Electronic Dist. & MSD

:thumbsup:
 
#7 ·
Im gonna check my gears but pretty sure they are stock highway gears. I will prob take the advise and run 3:55 gears so it will still turn good rpms at highway speeds. Looking into the cams suggested. Dont want to spend money doing head work when Im pretty happy with the weekend cruiser just looking for a few extra horses etc. I have a edelbrock performer intake with new edelbrock 650 avs that we just tuned but still gotta tweek the vacum secondaries. Slight hesitation when kicked in. Just installed new 2 1/2 pypes exhaust but havnt installed the tailpipes as of yet. Did make a difference from the 2 1/4 exhaust and sounds great with the new pypes headpipes and streetpro mufflers. I have read many threads from aly and bear in regards to the 455 swap and would like to do that in the future and still keep the no matching 350 but that is down the road ideas.
 
#8 · (Edited)
I'd think twice about putting a Voodoo cam your stock, and possibly tired 350.

Those cams are designed to increase cylinder pressure. Your stock engine may not react well to that extra pressure.

Since you have mentioned the possibility of a big engine later on. I think it might be a good idea to not spend any more than you have to on the 350. Buy only parts you can later use on the bigger engine.

But, if you really wanna make some power with your 350 block, you can build a stroker, similar to the 383, in the posted link. The guy who built that engine and sold those parts is no longer in business. However, Butler sells both the 4" stroker assembly, and a 4.25" assembly. The 4.25 assembly will put your 350 over 400 cubes, and make lots of low end torque, which should make plenty of tire smoke.

http://butlerperformance.com/c-1234...es-stroker-kits-350-blocks-383-413-cu-in.html

But, the reason that very few build a 350, is that you can build a 400 block stroker cheaper, and get a lot more torque & power.


"... edelbrock 650 avs that we just tuned but still gotta tweek the vacum secondaries. Slight hesitation when kicked in..."

That might be one reason you can't spin a tire. I recommend a GOOD Q-jet. The 325hp 350HO engines had a 750 Q-jet. With a Q-jet you don't have to worry about having too much cfm. They provide the engine what it needs. Even some of the little 301 engines came with a Q-jet, as did some of the OHC inline six engines. When they are built and tuned right, a good Q-jet is hard to beat.IMO
 
#9 ·
#10 ·
So yea I know there is more to the 1 wheel fail than I shared. The PO put a high rpm cam in and never matched a torque converter to it. Still has stock converter and 3.08s I believe. I have a 2000rpm B&M torque master sitting in a box and a shift kit on order. I hope to install a new rear-end with 3.31 or 3.55s in it at some point with posi but that's a later date thing. I need to change out the cam for a more normal operating range cam but this will all take time.
It also has a crap Edelbrock carb and none matching intake. I want to go back to a Q-jet from this guy SMI CarburetorSMI- Sean Murphy Induction
My buddy used his and can't say enough good things about them.
Right now I just want the compression test done right and the torque converter and shift kit installed.
The shop by me wants $700 to install the torque converter alone. Does that seem like a lot? I wish I had a way to get the tranny out in my garage but I don't at this time or I'd do it myself.
 
#11 ·
Redman how did the install of those Pypes go? I've been looking at those too. I have some rusted ass stockish dual exhaust on mine that has holes all over. That system is cheap on the price spectrum but reviews have been good so far. Any droning?
 
#12 ·
I have only intstalled the head pipes and muffllers but so far very happy besides the pass pipe is to close to the tranny pan but gonna take it to a shop to have it bent abit. I didnt purchase the kit because at the time of purchase they had the x pipe on sale as well as the head pipes thru summitt and thought I would piece it together in time. My old exhaust was just pieced together like you wouldnt believe and kept falling off. Anyway after it was all said and done the price came out the same except I couldnt find anyone who carried just the pypes tailpipes so ordered flowmaster tailpipes instead thru summitt. Should be here any minute. Drone is not bad at all considering there is no tailpipes or turn downs. Mufllers are clamped with band clamps right off the headpipes and sit just under the front buckets for now. Sounds much better than the flowmasters 44s I had on there with less drone. Im also gonna order the repop 69 exhaust tips from pypes because they come in the 2 1/2 in. not like the originals that are 2 1/4. My only problem I see is mounting the muffler hangers. Having trouble finding a good pic of how they bolt up. I bought exact repo hangers from summitt as well made by pypes. I will update once everything is in place.
 
#13 ·
"...The shop by me wants $700 to install the torque converter alone. Does that seem like a lot?..."

That's OUTRAGEOUS ! :surprise:

Try to find some local drag racers. There are usually some of them that do mechanic work on the side, to make extra racing $$. I'd say that job shouldn't cost more than $200 max. Hey, back in the day, I'da been glad to do it for $100. But, I reckin everything was cheaper then.


"... I have a 2000rpm B&M torque master..."

I'm sorry to tell you, but that converter is not worth using. A stock converter will stall nearly that much. You want gain a thing. I once bought a B&M Holeshot converter. I couldn't tell that it stalled any higher than the stock converter. :(

In order to see a real difference behind a weak 350, you'll need at least a tight 10" converter, which will actually flash stall to at least 2500-2600. An engine with more torque will make a converter stall higher. So, with your 350 you may need a converter which is advertised to stall at least 2800.

There are a lot of cheap converters, in this range, on Ebay.

GM TH350 TH400 10" Torque Converter 2700 3000 Stall RPM Jegs 60401 | eBay

TH350 TH400 10" Performance Race Torque Converter 2600 2800 Stall | eBay

http://www.ebay.com/itm/2700-3000-S...ash=item58a3fdfa45:g:T9wAAOSwAvJXBoyb&vxp=mtr

Allstar Performance 2700 3000 RPM 10 in TH350 400 Torque Converter P N 26900 | eBay
 
#14 ·
Damn serious? I called B&M and asked them and described my set up to them. Although without knowing the exact cam they couldnt for sure say but they said 2k would be a safe bet. Weird...I don't know if I can return it to Autozone or not but I guess I'll try. I'll look into the higher stall.

I'll definitely ask around for the install because I thought that seemed insane. I'm new to this city so I don't know enough car people yet like I did in the last place I lived but I'll ask around! Thanks

As for the piecing together the Pypes stuff I hope it all works out and glad to hear the drone isnt bad an its all gone together pretty well. I'll have to put that on my list....my ever growing list haha
 
#15 ·
"I've been noticing quite a bit of smoke at start up lately that eventually goes away, so that's what prompted the check."

Might just be you need new valve seals. They are rubber O-rings and dry-out or rot away and this allows a little oil to seep down the valve stem, past the valve guides, & into the cylinder, typically after you turn the car off and it sets. On start-up, you get the oil smoke because the oil has entered the cylinders and then clears up after a little driving.

New ones can be installed easy enough and may help your condition.
 
#16 ·
So the other complaint about my car is the extremely firm brake pedal feel. Also some pulsing so I brought it in to get the rotors resurfaced and they did some checking and told me my cam is pulling such high vacuum that there is none going to the brake booster. I knew that cam was a piece of crap for this car. So now I have to replace that if I want any sort of pedal feel.

Also good to know about the valve seals. Guess a new cam/lifters and valve seals hell maybe even a full valve job is in order. Like I've said in other posts I don't think its got hardened seats as I've had some pinging issues only to be solved with 93 octane gas and some octane booster. Timing is at 30 deg and runs great til putting load on.
 
#18 ·
I think you mean the cam is pulling NO vacuum. If it were pulling high vacuum, you'd have no problems.

Changing the cam will help your vacuum. It may not help your detonation, but might if you select the right cam. Compression is what causes the detonation (which dictates what grade of gas you will need to run on). Changing the cam may not solve this. It is possible to use a slightly thicker head gasket to lower compression, but you need to know what the cc's are of your head. A thicker head gasket may open up the "quench area" above the piston and create another opportunity for detonation/pre-ignition to come back and bite you.


Redoing the heads may cause problems. Now you have a tight sealing head, it may overtax the rings and you'll have blow-by.

Personally, if you are going to rebuild the heads, install new cam/lifters, possibly a new timing chain/gears, (you'll want to replace the harmonic balancer if it is stiff factory) and gaskets, why not just pull the engine and rebuild it right and be done with it?

Otherwise, to just do it cheap until you can afford a rebuild or upgrade to a 400CI, just install a better cam/lifters, new valve seals with heads on the car, and leave it at that. :thumbsup:
 
#17 ·
Gee, Kowalski, aren't cars fun???? Have you been able to get any warm engine compression readings yet? Although the readings may be lower than actuality because of the cam holding the valves open longer. Valve guide seals can be done without pulling heads using an air compressor fitting in the spark plug hole to keep the valves closed. If you do have a valve job done, remember Pontiac used 30 degree valve seats rather than 45 degree like Chevy. Find a GOOD machinist who knows this stuff.

Also, hardened valve seats do not affect pinging, detonation does-----fuel/air mixture igniting too soon because of wrong ignition timing, carbon buildup igniting the fuel/air pre-maturely, hot spots on the piston or combustion chamber, etc. etc.

Keep asking things, there are many good and knowledgeable people here willing to help.
 
#19 ·
These cars are fun! Just wish I had the budget to do what I want RIGHT NOW! Haha don't we all.

So I got the my car back from the shop and they tagged me with new lower ball joints, repacked wheel bearings, new brake pads and resurfaced drums and rotors and now my brake pedal feel is perfect! So that's taken care of haha.

As for the cam/lifters/valve job its all "plans" only if my compression checks out. Either way it's a high mileage original never taken apart lower half with 116k on it. I have been checking around like crazy in MN for a used 400 or 455 and cannot find anything. So far the wife is starting to put the brakes on my car spending as I've only had it since May haha. I still plan on checking the compression but might not get to it til next week as I'm heading on a fishing trip this weekend.

I'll keep you posted.

Good to know about the 30deg valves. I also thought hardened seats helped with unleaded fuel usage. Oh well I'd have it done no matter what if the time comes. As far as I know the timing is perfect according to that shop which I am slowly beginning to wonder if I can trust as you guys feed me different info than their "resident classic car guy" who's been working on my car.
 
#20 ·
Im glad to hear you got the brakes fixed. Was it the same shop that wanted to rape you on the torque converter swap? I didnt get my exhaust on as of yet. Hurt my back before I got started. Going to the shop next week after I get my pypes gto exhaust tips delivered. Im still on the cuff in regards to the gas tank but the one on ebay from tomsclassics is looking better for the price and comes with sending unit. Seem to have good feedback but if anyone else has good or bad expieriences with them im all ears.
 
#21 ·
It is indeed the same shop. They are just stupid convienent(close to my house and have a free shuttle service) I'm searching and asking around.
Sorry about the back but I'm hoping you can share a sound clip or something when your exhaust is done.
I'm having trouble with my fuel gauge too haha just another thing. Mine reads over full til I get down around a 1/4 tank then it reads around 1/2 a tank. The tank appears to be aftermarket new but I guess that doesn't mean the sending unit is. It worked fine the first few months but recently stopped reading correctly. Just another thing to check into.
 
#22 ·
Not an expert on the fuel gauge but from what I have read here on the forums if its reads empty all the time its a ground if full its the wiring and or gauge.Sounds to me like the fuel sending unit needs to be replaced but mabe someone with more knowledge can chime in. Im replacing both sending unit and tank soon but gonna check all the wires and connections plus the gauge once tank is dropped. Im lucky and happen to have a very good friend who is a master union electrician that is gonna help me diagnose my problems once I drop the tank and new one aririves. Nothing worse than not knowing how much gas you have or if you fill it past half its leaks all over.
 
#23 ·
Got the complete exhaust installed today and I am very happy with the performance of the 2 1/2 in exhaust. I can finally get the rear tire to burn off the line without brake torquieng and I am running 278 stock gears. No drone with the pypes street pro mufflers and x pipe but way to quiet for what I like but seems the back pressure is much better now. I will prob leave it alone for now but might ck into the more aggressive mufflers down the line. The shop charged me 100.00 and that included bending the down pipe away from the tranny. Sounds good to my friends but not as aggressive I would like but very nice system for the no matching 350 which Im keeping by the way. Rear main seal leak turned out to be loose pan bolts. Car really screams down the road for a 350 and I have had some performance cars including 400 gtos.
 
#24 ·
Man good to know. I will save my pennies! My gas tank thing is not consistent. I ran it to almost empty and the needle worked normally. Now I filled it and it actually isn't past full like it usually is. Maybe I hit a bump hard enough to have it correct itself haha. We'll see how it goes before I have to store it for winter. Stupid MN weather.
 
#25 ·
So with my tired 350 I decided to just keep the motor, but rebuild it. Nothing too crazy but want opinions. Working with a budget as is everyone what do you guys think of this package of stuff? Also anyone have a thought on how much an engine shop would charge to tear down and build up the motor using parts I'd supply? Rough estimate? I'll be pulling it, stripping the paint off/painting and reinstalling with a buddy.
Engine kit
https://www.summitracing.com/parts/fem-mkp621d-311
Cam kit
https://www.summitracing.com/parts/cca-k51-232-3
Rocker/pushrod
https://www.summitracing.com/parts/cca-rpm1451-16
Of course I'd change to threaded studs during the rebuild if feasible as well.
Top this off with the Pypes X-system and some headers.
 
#26 · (Edited)
I wouldn't buy a kit. I'd buy individual parts. You don't know what your overbore will be, or your bearing undersizes. The best cast pistons are probably the SP 357P. The cheapest forged pistons are from Auto/Tec, for around $500 shipped.

If your overbore is .030 here are some pistons & moly rings.

http://www.ebay.com/itm/Sealed-Powe...ash=item2364e3a18b:g:cioAAOSwv9hW5~rn&vxp=mtr

https://www.summitracing.com/parts/slp-357p30/overview/make/pontiac

https://www.summitracing.com/parts/pcr-40076cp-030/overview/

https://www.summitracing.com/parts/slp-e-245k30/overview/

And there are much better cams. That one is a single pattern, with a 110 LSA. On a fresh rebuild, the small 256 Voodoo that was mentioned earlier, might be a good choice. OR, to save a few bucks, you could go with the Summit K2800 cam & lifter kit.

http://www.lunatipower.com/Product.aspx?id=1774

http://www.jegs.com/i/Crower/258/66...3Q0XZ8a7NUNyFhaD_U4xHOs7i-NITnmmWbRoCJ_jw_wcB

https://www.summitracing.com/parts/sum-k2800

The Melling M45DS oil pump is sorta std equipment for most street Pontiac engine builds. That's what I used in all my Pontiac engine builds.

https://www.amazon.com/Melling-M54DS-Replacement-Oil-Pump/dp/B000C4PO6E

I don't think there are any 350 Pontiac head gaskets made now except for the high priced brand. Most guys just use the Fe-Pro gaskets which were made for 400 & 455 engines. The bore size is 4.3", which is much larger than the 350 bore size. This will reduce compression. You can go with thinner Cometic gaskets, to increase compression. If your deck height is zero, you can go with .040 thickness. If it's .005 you can go with .036 thickness, if .010 go with the .030 thickness, & if over .010, go with .027 thickness. This will help keep the quench distance close to the recommended .040 number. These gaskets can be made for blocks with or without the chamfers at the top of the cylinders. It is said that the deck needs to be a certain smoothness, for these gaskets to seal correctly. So, you need to make sure your machine shop can produce this type deck surface.

http://www.jegs.com/i/Cometic-Gaskets/245/C5710-040/10002/-1

http://www.jegs.com/i/Cometic-Gaskets/245/C5710-036/10002/-1

http://www.jegs.com/i/Cometic-Gaskets/245/C5710-030/10002/-1

http://www.jegs.com/i/Cometic-Gaskets/245/C5710-027/10002/-1

If you plan to use a Voodoo or similar cam, I'd have screw-in studs installed in the heads. If your budget can stand it, I'd also go with new stainless valves. There are 2 ways to do the screw-in studs. I think the most popular way is to use the ARP studs which have a 7/16 top, but 1/2" base threads. With these, you simply pull the old studs and tap the holes for the new studs. If the holes are not deep enuff, some will have to be ground off the bottom of the ARP studs, since the base thread portion is longer than stock studs. The other way is to pull the studs and have 7/16 heli-coils installed. Then you can use the BBC type studs, which have 7/16 base threads. BUT, since it will probably cost $200 or more to do the screw-in stud thing, I'd recommend buying some good 6x-4 or 5c-4, or the late '73 & '74 #46 heads. All these heads have screw-in studs and factory hardened valve seats.

http://www.jegs.com/i/ARP/070/290-7201/10002/-1

https://www.amazon.com/ARP-290-7201-Rocker-Arm-Stud/dp/B001T6CRDC

http://butlerperformance.com/i-24452864-arp-7-16-x-1-2-rocker-stud-kit-arp-290-7201.html



"...anyone have a thought on how much an engine shop would charge to tear down and build up the motor using parts I'd supply? Rough estimate?..."

That price can vary WIDELY. Some prices are reasonable--MANY are not. AND, here is the best advice: don't have it built by a shop that has very little experience building Pontiac engines. A Chevy shop can REALLY mess up a good Pontiac engine. :(

But, if I had to make an estimate, I'd place it at $1000-$1500 just for machine work & labor.
 
#27 ·
Thanks BigD for the info. I'll research those parts and start compiling my laundry list. I don't want an insane rebuild($ or HP) but I do want more power and reliability so if some parts are better than others and cost a little more I'll do it.
I also need to start looking for Pontiac builders. I've met a couple GTO drivers around the area so I'll start with them.
 
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