# More Horsepower from Stock 400 4V in 1971 GTO



## Harry1971 (Jul 28, 2018)

I own a stock 1971 GTO with 117000 documented miles, all original local car. Engine has been at some point in 2000's been overhauled and runs strong. 

My question is with a complete stock GTO and most all original, I want to increase the horsepower back to where it should be before the 8.2:1 compression drop in 1971. What can i do that keep the vehicle from straying too far from its originality per se a stage 3 cam, replacing the carbeurator and manifold and would headers make a difference given the true dual exhaust set up on the car now? Any ideas


----------



## bigD (Jul 21, 2016)

Several ways to increase performance. More compression & a better cam are 2 ways.

Tuning your ignition with the correct timing curve, can help quite a bit.

A correctly built Q-jet & iron intake is hard to beat.

Obviously, the easiest way to increase compression is to use the '70 & earlier smaller chamber heads. But, if you wanna keep the original heads, you can have some shaved off of 'em. Then , if you have the cheap Fel-Pro head gaskets, you can use the FP #1016 gaskets, which are only .039 thick. 

One of the small Voodoo cams will increase cylinder pressure, which will increase low & mid range power. 

Voodoo Hydraulic Flat Tappet Cam - Pontiac V8 262/268 - Lunati Power

Most say the Ram Air manifolds are better for street driving than headers. 

If you got lots to spend, you can rebuild the shortblock using a stroker assembly. That can give you an instant 455 or more cubes, 400hp & near 500 torque, using your original block, heads, carb, intake, & a decent cam. Can't see any difference from the outside.

https://butlerperformance.com/c-123...es-stroker-kits-400-blocks-406-495-cu-in.html


----------



## Nicholas (Jan 16, 2017)

Harry1971 said:


> I own a stock 1971 GTO with 117000 documented miles, all original local car. Engine has been at some point in 2000's been overhauled and runs strong.
> 
> My question is with a complete stock GTO and most all original, I want to increase the horsepower back to where it should be before the 8.2:1 compression drop in 1971. What can i do that keep the vehicle from straying too far from its originality per se a stage 3 cam, replacing the carbeurator and manifold and would headers make a difference given the true dual exhaust set up on the car now? Any ideas


Some good ideas from bigD. Like you, I have a '71 GTO with the original 400 motor, TH400 trans. and 3.55 gears. The motor has been rebuilt at one time and I'm assuming it's .030 over. No idea of the CR. Stock heads, intake and carb. Ram Air exhaust manifolds. A Lunati VooDoo 702 cam as described in the above thread. The engine runs very well. Oil pressure at 50 lbs. Stays in the 180-190 temp. range, but plain and simple, it's slug. Difficult to get out of it's own way, at least for me. I'm not too disappointed in it because I knew '71 was a pivotal year for compression which could equal performance. I bought the car knowing that and because it was a body off frame resto. Never had one of those before. I have a '62 409/380 hp engine, and I know it's not fair to compare this to the GTO, but I do. So if I want go fast performance, I take out the 409. For a comfortable ride, it's the GTO. I'm not sure what I am going to do with this car yet. Sell or hold onto. If I keep it, I'll be looking for a 400 engine to put a stroker kit in. That should certainly give me what I'm looking for. I'll put the original motor on a stand. don't want to launch that one. If this car performs well enough with the stroker motor, might just sell the 409 LOL. Please keep us posted on what you decide to do and the outcome. I'd be interested. Thanks.


----------

