a little hard to help when we don't know the actual performance of the car. It might be exactly where it should be and your expectations are too high, or the thing is a total turd, we just can't tell.

My experience is when a guy does not know specifics like pistons and compression ratio, it is usually not good, i.e. very low. You should do a cylinder pressure test. Also, it would be helpful to know the cam.

There could be several reasons that it is under performing:
1) like Cab said, fuel delivery. It can rob power like no other, and unless you test it, you won't know.
2) Plugged or internal failure of muffler. This has happened to me twice. That is an instant loss of 30 + hp, but every thing seems fine.
3) Low compression.
4) Poor heads.
5) Poor tune


The factory intake is the biggest bottle neck on an already good running 440. It is done at 5000 and getting the motor to go past 5200 is a challenge.

A good set of 915s with some porting, good cam, decent compression ratio and a good tune will result is a car that runs very well, even with factory intake and the 4327 carb.