pontiac straight eight

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willy knight

Active member
Joined
Mar 1, 2011
Messages
33
Location
Ohio
How good of an engine is this Pontiac straight eight and are the olds and buick engines the same and or interchangable?
I have seen some straight eights on bonneville cars that appear to have overhead valves (mine is a 1949 pontiac flathead)that say buick.What years did they produce those and did only Buick do that?
Does someone make an adapter to put turbo 350 behind a straight eight?
 
Not really sure of what bolt.pattern they used o them. But GM had a Trans called a BOP for Buick Pontiac Oldsmobile and some were universal and also bolted to Chevy blocks. I don't think Chevy ever did thesame though with the th 350. Mine is a 200r4 behind an Oldsmobile 307.
 
To my knowledge the Olds, Buick and Pontiac straight 8's are different animals. Buick was the only GM straight 8 with overhead valves, they resemble a Chevy 6 with 2 more cylinders. Nash did make an overhead valve, 16 spark plug straight 8, the only other ones that come to mind are even more rare - Stutz and the ultimate straight 8 - Duesenberg.
 
Had a Pontiac I-8 years back. 268 cid I think--had a 4 speed automatic--came out of a hearse. It had cracked valve seats, and I had to have new seats installed. Ran fine, just no powerhouse. I think it'd be fun in a bucket or something to show off the uniqueness of the thing--otherwise just a typical antique engine.

PA41
 
manual

I would suggest a manual trans over an auto with the straight eight. This is due to about 95 - 100 hp. Takes much more power to turn an automatic.

I wish I had been lucky enough to have gotten a 1949 Pontiac with a manual transmission, which I would think most of them had, but I did not.I would have to find or fabricate pedals,linkages,Z bar,Pivots for the Z bar ,Etc.
On the other hand one of the posts on here suggested checking at http//www.transmissionadapters.com so I did.Bob there told me they have an adapter to put the Chevy turbo 350 on a straight eight.Since I have been collecting car stuff for over 35 years and have 20 to 30 GM turbo transmissions and most are Cevy ,it would be easier for me to go this way.He said the adapter would be around $975.00.
This will be worth it if the motor is a long liver.I am trying to determine from the stories here if it is a long term motor.I have heard they had crank issues because the crank is so long.
 
I wish I had been lucky enough to have gotten a 1949 Pontiac with a manual transmission, which I would think most of them had, but I did not.I would have to find or fabricate pedals,linkages,Z bar,Pivots for the Z bar ,Etc.
On the other hand one of the posts on here suggested checking at http//www.transmissionadapters.com so I did.Bob there told me they have an adapter to put the Chevy turbo 350 on a straight eight.Since I have been collecting car stuff for over 35 years and have 20 to 30 GM turbo transmissions and most are Cevy ,it would be easier for me to go this way.He said the adapter would be around $975.00.
This will be worth it if the motor is a long liver.I am trying to determine from the stories here if it is a long term motor.I have heard they had crank issues because the crank is so long.

It could be said that all straight 8's have issues due to the length of the crank... some manufacturers made 9 bearing cranks like Packard, Nash, and some others. The big thing about them is they are not meant to do high revs - even the best ones experienced some crank flex, it's the nature of the beast. Also they are mostly long stroke / small bore compared to V8's so that adds to the crank harmonics.
That being said, there are things that can be done to keep them alive on todays roads. #1 - have the rotating assembly balanced - best thing you can do. Also Egge Machine pistons are much tougher than the stockers, give it a healthy overbore, they are thick wall block castings and can easily take an 0.80 overbore for more cu. in. Use a PVC valve and draw thru the carb instead of the old road draft tube, this will really cut down on the sludge. Modern oils are far superior to what these engines had when new, synthetic would be the best choice. Another important mod is to drill the oil pump and main oil galley in the block for fittings to send the oil to a remote filter first for full flow filtering, a bit of machining and a couple plugs to install but well worth it . All these old engines only had a small amount of oil going thru the filter, most of it went straight from the pan into the oil galleries.
 
I would do some research and talk to someone at

either TCI transmission or other aftermarket trans builder that could advise you which torque converter to use behind that motor.... I remember that with the early vega motors they used a turbo 250 trans and the torque converter worked well with the low HP motor.... I don't think they had over 100 or 110 hp either.... weight of the car, rear gear ratio and trans and torque converter type is critical in how the vehicle would perform.... just don't want you to waste a lot of time trying to make something work that might not fit your build.... even the old chevy diesel pickup and passenger cars with the 5.7 diesel had different rear end ratios than the norm and both used high stall converters to get the motor up to the power levels it needed to pull those things...350/403/455 olds V8 swaps worked really nice in those vehicles and you could use all the brackets, pumps and everything off the motor as the 5.7 diesel was nothing more than a reworked 350 old motor.....junk, but none the less.. they did run for a while.....LOL
 
road draft tube

What did the road draft tube do and would I have to seal it off? Thanks for the info also.

It could be said that all straight 8's have issues due to the length of the crank... some manufacturers made 9 bearing cranks like Packard, Nash, and some others. The big thing about them is they are not meant to do high revs - even the best ones experienced some crank flex, it's the nature of the beast. Also they are mostly long stroke / small bore compared to V8's so that adds to the crank harmonics.
That being said, there are things that can be done to keep them alive on todays roads. #1 - have the rotating assembly balanced - best thing you can do. Also Egge Machine pistons are much tougher than the stockers, give it a healthy overbore, they are thick wall block castings and can easily take an 0.80 overbore for more cu. in. Use a PVC valve and draw thru the carb instead of the old road draft tube, this will really cut down on the sludge. Modern oils are far superior to what these engines had when new, synthetic would be the best choice. Another important mod is to drill the oil pump and main oil galley in the block for fittings to send the oil to a remote filter first for full flow filtering, a bit of machining and a couple plugs to install but well worth it . All these old engines only had a small amount of oil going thru the filter, most of it went straight from the pan into the oil galleries.
 
What did the road draft tube do and would I have to seal it off? Thanks for the info also.

The road draft tube mounts to one of the tappet covers on the side of the block and ventilates the engine when the car is moving - air going past when driving draws the crankcase air in the vent cap and out of the road draft tube. At low speeds, it's ineffective and when stationary not at all, often with old engines using this system you will see smoke coming out of the vent when idling (more so if the engine is tired and has worn rings or valve guides). Remove the road draft tube and install some sort of plug that you can install a PCV valve into, then plumb it to the carb base like a modern engine. Now the crankcase fumes will be drawn through the intake and burned. Also this is tied to engine speed, the higher the revs, the more it draws. As a bonus, it will pollute less too. :)
 

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