# Engine advice.



## Hank_ (Jun 11, 2016)

A little background. I just picked up a 1969 Lemans convertible. I had one of these cars years ago and am excited to have this one. The motor in this car is seized and as I am gathering parts to rebuild this rusty beast and I have come across what seems like a good deal on at low mile 400. They say it is out of a 1969 pontiac grand prix "1969 400, 350 HP engine, #62 Heads, Complete / original carb to pan". The price I could purchase the complete running engine is far less than I can build a 400 or rebuild my 350. As I research this motor it is a high compression motor somewhere around 10.5:1. Is this motor going to be run on high octane pump gas? I don't want a bunch of grief dealing with the high compression issue. If this motor would work I would like to get it and put it in and be done with it. Any information would be great. This is a great web site with tons of information. Great to have a Pontiac again. Watch for a build thread to begin this fall.

Thanks,
Hank


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## thor7726 (Sep 2, 2012)

I'm no expert, but I was told that to run 93 octane without wrecking anything it has to be close to 9.5 compression ratio. I was also told that Pontiac literature listed compression ratio numbers where a little higher than what they really where back in the day so you might be closer to the 9.5 than you think. Butler does sell thicker head gaskets for around $260ish that would lower the compression ratio with only having to take the heads and intake off. Again, I'm no expert. Good luck with the cool new Lemans!


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## Hank_ (Jun 11, 2016)

Thanks for the response. I also see a stock 455 out of a 1974 for sale near by. Not sure what kind of performance to expect out of a 1974 MY vehicle though. I know my 74 Firebirds were low horsepower engines due to emissions. I will see if I get some more information and I will check out Butler Performance also.

Hank


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## oldskool (Apr 26, 2015)

If both engines are good, I'd go with the 455. It's low compression, so will work with pump gas. But, it has more stroke, so will have more low rpm torque, than the 400. :smile3:

The 400 has some good parts--same as a '69 350hp GTO or 330hp Bird. But, with that much compression, you'll need some octane booster. :frown3:

Torco is the cheapest good booster. It's $22.75 per qt.

https://www.amazon.com/Torco-Accelerator-32oz-Best-Additive/dp/B004ZO3VN0


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## Doug68gto (Mar 8, 2016)

I would look into 400 and see if it hasn't been open up. 69 motor un touch is highly unlikely running good. IMO stay away from thicker head gasket quench problem read up on it and gas additive pain int the ass. Again only my opinion. Do a complete compression test on both motors and see what you have. Keep CR down under 9.5 if you want to run iron head on pump gas. You can do a budget rebuild on that 400. Depending on condition for less than you think if your will to do some of the grunt work. You won't know until a machine shop gets in there and sees what you got.. Don't try to go cheap it will cost you more in the long run. Best luck keep us informed.? Doug


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