How much HP will I lose with smaller headers?

[Rick Piras]

I'm finally rebuilding my 454. I'm planning to use the full "Edelbrock RPM" motor with the aluminum heads. Thier dyno numbers of 540 HP and 540 lbs. torque were achieved using 2-1/8" primary tube headers. I'm running Hooker headers currently with 2" primaries and 3-1/2" collectors. The car is lowered, and I hate the lack of ground clearance I have, so I was planning to go with "shorty" headers with 1-7/8 tubes. Anyone know how much HP or torque I'd sacrifice if I go smaller?

[MrQuick]

Hi Rick, welcome to the site. Typicaly you will gain a bit of low end torque and loose a bit of top end HP. I'd guess and thats the best I could do HP loss around 10-25 HP.

[Rick Piras]

Thanks for the input. I'm willing to sacrifice a reasonable amount of horsepower (10-20) to gain ground clearance, but if that HP drop is going to be 40-50 that wouldn't justify the motor mods that I'm putting in. The way the car sits now, combined with the headers hanging down make it VERY difficult to clear speed bumps in parking lots, etc. Pretty frustrating. I'm running a 3" exhaust through the X-pipe and all the way to the muffler input where it goes down to 2-1/2", but the main problem is the header collector, and the collector flange.

Would one of those "desktop dyno" programs be able to calculate the difference?