350 Cylinder compression - Pontiac GTO Forum
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post #1 of 92 (permalink) Old 09-19-2016, 01:00 PM Thread Starter
 
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350 Cylinder compression

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?

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post #2 of 92 (permalink) Old 09-19-2016, 01:37 PM Thread Starter
 
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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.

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post #3 of 92 (permalink) Old 09-19-2016, 02:53 PM
 
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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.

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.
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post #4 of 92 (permalink) Old 09-19-2016, 03:33 PM
 
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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!
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post #5 of 92 (permalink) Old 09-19-2016, 04:23 PM
 
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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!
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post #6 of 92 (permalink) Old 09-19-2016, 09:41 PM
 
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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

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post #7 of 92 (permalink) Old 09-19-2016, 10:13 PM
 
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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.
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post #8 of 92 (permalink) Old 09-19-2016, 11:00 PM
 
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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-12348...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

Last edited by bigD; 09-19-2016 at 11:20 PM.
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post #9 of 92 (permalink) Old 09-19-2016, 11:37 PM
 
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"...wanting to install a ram air cam like in the 69 350 ho..."

That cam your referring to is sometimes called an 068 cam. It was indeed used in some 400 ram air engines. Was also used in some 455's. Melling & others sell an 068 clone.

Engine Camshaft-Stock MELLING SPC-7 fits 63-66 Pontiac Catalina 6.9L-V8

The Summit 2801 is sort of a higher lift version of the 068 cam.

https://www.summitracing.com/parts/sum-2801
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post #10 of 92 (permalink) Old 09-20-2016, 01:02 PM Thread Starter
 
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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.

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