Pontiac introduced their 350 engine as a “me too” in order to compete in the showrooms with the famous Chevrolet 350 engine.

The Pontiac 350 engine is “under square” meaning the bore is too small for the stroke and the bore cannot be enlarged enough to be “over square”. All the best high performance engines are over square, meaning, the bore is larger than the stroke.

The best location you can install a Pontiac 350 engine is in the core pile.

 

well that settles that

I will pull the motor out and put it in the core pile . Thanks !

 

Pertronix ignitions can be a big problem, it's not a question of loving or hating them, this simple is the reality of them.



One common problem is they are designed to run as a replacement for points ignition which use 12 volts to start and then through a resistor either stand alone or a resistive wire they operate on 9 volts. Or they can run on 12 volts as they would when replacing an HEI. The fact of this is they run like crap on 9 volts and don't last very long on 12 volts. That's just the way it is.


The other concern is the 110 psi compression (assuming this is a wet test) is low. There's a ton of reasons why this could be from the cam being out of time to lobes or lifters wiped out to the bottom end just being tired.


The Pontiac 350 came in a lot of versions from grocery getter to wanna be performance engine. The latter came with some nice heads and parts, you should check out the casting numbers and the engine I.D.


It was never a popular engine growing up in the shadow of Pontiac's much larger offerings. Keep in mind if you swap this for a Chevy motor the tranny attachment to the engine is a different pattern requiring an adapter.


I'm not so sure I'd be hasty in scrapping the motor, checking out cam timing for instance is not that hard and in the process will tell you if the ignition is timed correctly to the crank and whether the timing marks are accurate.As far as the pertronix goes I'd put a conventional HEI in there with it's own temporary 12 volt power source to see what happens. Lots of things can be done simply and cheaply to get an idea of whether things are set up correctly or not.



Bogie

 

Most of the problems with the PerTronix ignitions resulted from the installation of a PerTronix module in a stock distributor. You must take all the wobble and extra clearance out of the stock point mounting plate as well as the thrust clearance of the distributor gear. The PerTronix installation instructions did do not address those problems at all, and they still don’t. The best option is to install a complete PerTronix distributor. I checked the gear thrust clearance on my PerTronix Stock Look distributor before I installed it and it was less than .015” . A new stock point type distributor has as much as .030” in most cases. The thrust clearance is not too important with a stock points type distributor but it is critical with a Hall effect magnetic ignition like the PerTronix.


PerTronix ignitions got a bad reputation before PerTronix introduced a distributor with the module already mounted with the gear and shaft thrust clearance at .015”. You should not have less than .015” because the distributor gear and shims require enough thrust clearance for lubrication.

Excessive gear thrust clear evidence, or more than .025”, will cause spark scatter.

 

I have a PerTronix Stock Look distributor. When I check the advance with my timing light on the 8” damper of my Chevrolet 350,, the timing mark is steady at 12 degrees initial advance at 800 RPM idle and 36 degrees total advance at 2500 RPM.

If I had a stock distributor, the timing would be all over the place. That is spark scatter.

 

It's time to begin twisting some bolts and nuts. Pull the intake manifold, heads and front cover. If a master mechanic can't figure it out from the outside, it's time to see what's going on in the inside.

 

"The timing marks are lined up like a Chevy right now , which I think for a Pontiac will have it firing the number 6 plug in this position , which I can work with ."




Pontiac engine times the same as a Chevy 1,8,4,3,6,5,7,2; but the rotor turns in the opposite direction that is counter clockwise to Chevy's clockwise. This of course means the wiring goes in the opposite rotation on the cap from a Chevy.


A complete crankshaft cycle takes 720 degrees or two revolutions. This results in the damper timing marks passing twice a full cycle. You need to know where it is in terms of whether that is number 1 firing and number 6 finishing exhaust and starting intake or number 6 firing and number 1 finishing exhaust and starting intake. Both are at TDC when the timing marks line up but are doing different things.


Another common issue is the distributor gear mesh is off a tooth or more which has you chasing very odd alignments to get the engine to run properly. Down on power and high operating temps go with this and it may display backfire but not always.


Another place to look is low fuel pressure not keeping up to consumption demand. Usually idles fine but just won't go, sometimes backfires but not always.





Bogie

 

Fresh Pontiac 350 runs poorly

I am not going to pull out the 350 poncho motor and throw it in the core pile.This Firebird will survive with the original 350 and will run just great when we locate the problem that was "installed" by the engine builder in Tennesse.
I just located an original point type distributor from a man who bought a 1968 GTO brand new and he is letting me borrow it to test this system out .
Also plan on doing a cranking vacuum test to see what the vacuum is reading while the engine is cranking . If under 5 I think the cam or the cam timing will be at fault . Pontiac builds excitement and I have raced Pontiacs for years , but not everyone likes to keep cars original . Put another LS motor in it is not for me or any of my local hot rod friends .Keep it original and make the thing RUN.Thanks for the help!!!!

 

The optional 1967 Pontiac 350 HO engine that was used in Firebirds was equipped with casting number 670 heads. Those heads were standard on a 1967 GTO and were among the best flowing Pontiac heads produced until the 1969-1970 Ram Air IV heads were introduced.

In 1980, I purchased a 1967 Pontiac 350 HO engine for $300 in a salvage yard. I sold the 350 CI engine for $100 and used the 670 heads on my 1966 GTO.

 

"The timing marks are lined up like a Chevy right now , which I think for a Pontiac will have it firing the number 6 plug in this position , which I can work with ."


Pontiac timing gear is set different then Chevy ! The first pic is Pontiac The second is Chevy!

https://www.hotrodders.com/forum/attachment.php?attachmentid=448433&stc=1&d=1569882076https://www.hotrodders.com/forum/attachment.php?attachmentid=448435&stc=1&d=1569882478

 

Stock compression if I remember correctly was around 9.5 - 10.0 so 110 on a compression gauge is not out of line but a bit low - main thing is that all the cylinders are within a couple of pounds of each other? It could be that the engine didn't have a proper break-in, the rings have yet to fully seat and that's adding to the issues. A leakdown test would go a long way towards seeing if the engine is sound.


You mentioned the ignition which I am not a fan of but if it's providing spark - enough to fire the engine and idle it, then it's functional. I would use a test plug and see what kind of spark you're getting - a nice white/blue is what you want.



You didn't mention the carb - so the question is what kind of shape is it in - rebuilder specials that are based on old cores leave a lot to be desired, Even 20-30 years ago, they weren't all that great and age hasn't helped anything. I would check out the carb real carefully for issues and/or if possible swap a known good one in place.


And don't go in with an assumption that someone else screwed the pooch here. You don't know until you take a look at stuff. Concentrating on one cylinder, you should be able to determine if the valve timing is in the ballpark. Better readings of course would entail degreeing the cam. Verification that valve settings are correct, initial timing is correct and timing advance is right can be checked wiithout tearing everything apart. If you discover something is out of kilter, then open it up as needed.

 

Compression testing doesn’t tell you a lot but how good the starter is.
I’d do a leak down, verify the cam timing, then verify the cam.
I’ve seen several cam gears and cams machined wrong.
A bore scope is an easy way to see what’s inside the chamber.

 

Pester Mousefink, he knows more about Pontiac engines than he lets on. Been so long since a real Pontiac engine has been factory installed there really aren't a lot of folks that are that familiar with them anymore. I just know enough to be dangerous to myself and anyone standing nearby. Most people today have only seen Chevy engines in Poncho's and they ain't the same as the real thing.

Bogie

 

Good old unknown builds. Its a crapshoot.

I have put a couple hundred thousand miles on Pontiac V8s (400, 455) in my time but don't get me wrong... I am a bodyman, not a mechanic. Heres this though. My second 400 was an unknown with smog era heads and "second from the bottom of the page" cam.

It would hardly idle, had vacuum like yours. Early on, aluminum debris from somewhere wrapped itself over a crank gear tooth and it slopped out the timing chain. When I went back together, I advanced the cam via alternate keyway in the gear set. It had been installed "straight up".

Instant 13 inches of mercury, enough to run power brakes. And it ran and tuned as it should from there on out, no more stalling. Other than yeah, common plug wire and timing mark issues theres what these guys are telling you. It is easy to end up with mismatching pulleys and timing marks on a Pontiac, theres that too. FWIW I did know of a guy who could cook up a pretty snotty Ponch 350. He liked Lunati bumpsticks.

 

The Pontiac 670 heads have 2.11” / 1.77” valves. The 2.11” intake valve overlapped the bore wall of a Pontiac 350 and restricted the flow. The large valve Pontiac heads on a Pontiac 350 were useless as **** on a boar.

That is the main problem with the Pontiac 350......unlike a Chevrolet 350, the bore of a Pontiac 350 is too small in relation to the stroke and is still too small even if it is bored .060”.

 

I talked to the late Monk King about why my 1969 Firebird 400 spun rod bearings. Monk was the Pontiac man in the sixties. He told me I should quit driving my Firebird 400 like it was a Chevrolet. Monk King said I was turning the RPM it too high with a Crane solid lifter camshaft, 4-speed and 4.33:1 Safe-T- track and was starving the rod bearings of oil.

I switched to a Crane hydraulic lifter camshaft with Ram Air IV hydraulic limited travel lifters and had no more spun rod bearings.

In conclusion, I was turning the Pontiac 400 too high. My SB Chevrolet driving habits are hard to change.

 

Poor runnig Firebird

Don,t forget if using a points style dizzy it has to be right on no. 1

The best place to start is the timing and change out the dizzy. Since you have done a leak down and compression check and have 110 all around I am thinking the timing is off. If you already have the front tore down then set timing at gears and drop in dizzy and go from there. otherwise I would pull up tdc with the valve cover off to make sure the you are firing no.1 and drop in the dizzy and fire it up to see if it runs and timing can be advanced or retarded with that causing the motor to ping or idle up and if that shows no change in performance then I would check timing marks. Those old Pontiac 350s were like the 348s. either they crawled or screamed. Good Luck
Murph

 

Distributor Rotor set to fire on #1 cylinder at TDC
Dot on cam sprocket on top
Dot on crank sprocket on top

I have seen the cam/crank firing illustration in early Pontiac Shop Manuals that shows firing on #1 cylinder when the dot on the cam sprocket at the bottom of the cam sprocket. That is 180 degrees out of time if the distributor rotor is set to fire on #1 cylinder. That illustration was corrected on the 1967 and later Pontiac Shop Manuals.

 

I am with Johnsongrass. Degree the cam .That will tell you a LOT

 

Pontiac fresh motor runs badly

well , Thanks for all the good input on the engine specs and timing and distributor set up , etc ........
I have other jobs this week so I will get back on this next week , and I just learned of an interesting Vacuum test done on a motor that is cranking over at 200 rpm with just a fresh battery and a good starter .This is supposed to give the service tech an idea of how the engine is breathing relater to cam size or bad cam timing .......
Leave in the spark plugs , Close off the carb plates ! Close up the PCV hose , and plug any possible vacuum ports .
Hook up vacuum gauge to a good location on the intake , somewhere in the main runner area , I will use the brake booster hose to hook up the gauge.
Crank the motor over for 15-20 seconds and see the Vacuum reading .If it at 5 inches , I am told that the cam and the cam timing is probably not the reason this 350 runs poorly and when it does run it only has 8.5 inches of vacuum .
I just tried this test on my ole Chevy L82 small block and it came up to 5 inches . Opening up just the smallest port during this test and the vacuum reading dropped to 1 ......ugh ...
Anybody out there ever try this type of test , if it really is accurate that would be pretty cool .
Also now have an original Pontiac points distributor to try in place of the Petronix that is in there now , but maybe the tech who has set this up just has the Distributor way out of wack .
Thanks for all the assist !!!

 

Pontiac fresh motor runs badly

Well after all my effort to help out this guy for Free!!! his customer got frustrated and towed his car out of the shop on Saturday last !!

I love a challenge but never got the chance to put my hands on this Pontiac 350

Oh well ,Still learned alot from all of you !

 

First thing is to find #1 top dc ,pull #1 spark plug, should be marked on intake , but standing in front its first plug on drivers side. Pull plug , stick finger in the hole and crank motor over(bump) till air pushes out hole then look at timing mark. That's done, now,follow #1 plug wire back to the disturber, mark,remember distributer turns cc and cylinders are #1,3,5,7 drivers side and 2,4,6,8 pass side make them right/correct, make sure the rotor is pointed to #1. Now remove valve covers (i think the lifters are miss adjusted) and re adjust the valves, do all the ones that the manual says to on #1 tdc then turn motor and follow the manual to do the rest. By finding #1 and verifying timing mark you should be able to set the timing correctly and check the advance with a timing light and a tach. ONLY then should you go into the timing chain and gears !!