i have a 83 rx7 gs. i want to run pen headers but i was driving my car for a while with out a muffler and recently put it back on and i noticed how much power i was loosing , if i run open heads will i loose a hole bunch of back pressur and loose horsepower? if anyone could help me out i would appriciate it

 

You wont lose power, just your hearing!

http://media.putfile.com/Shootn-flames-19

 

No power loss...better to run open header anyways for drag purposes...but the trick to running open header is make the runners as long as possible before the rear end and then dump them...Lots of noise but lots of fun...

 

how much horsepower would i gain if any

 

i notice quite a power loss when running open headers.

 

Thats simply because your exhaust out-flowed your intake....fundamental gains in horsepower are made from flowing more intake and exhaust.

Do you have any other engine modifications? This may be your answer.

 

also may be a loss in low end power, but a gain in high end??

that would be typical...
with my exhaust attached it feels torquey but it doesn't pull as much up top.
Conversely with the exhaust unhooked it feels weak off the line and is touchy to launch but pulls harder once I get over 4 grand or so.



Can't put an exact number on things... there are lots of variables involved

 

Ok, these "variables" above mentioned are from the bends in the piping, pipe diamter, length of the header, and overall length of the exhaust. The trick is finding out where the exhaust gasses want to go from your particular engine, which is also another variable. My particular (running) engine a stock port 12a, racingbeat underdrive pulleys, aluminum flywheel, holley 465, road race header, and i collected the exhuast via megaphone and ran nearly straight 2 in. mild steel tubing back to a universal resonator. I now know, that although my exhaust flows nearly the same as racingbeat's full dual system, it doesnt make as much power because of the bends in the piping, later collection of the piping, and the fact that power pulse muffler is tailor made for that exhaust and gas flow rate.

My exhaust certainly sounds better than stock and I defineatly felt a huge power increase with the addition of the new carb. My guess is that your power increases my be mild...in different rpm bands. You hardly ever experiance a horsepower increase accross the board. my exhaust power increase is felt for the most part above 5000 rpm, where it sings a sort of tone. and then becasue of the rotary's natural nature, stays hot in the higher rpms as well.

My bet, is that your inexperianced in the art of building exhaust.

 

low end power is loss...high end power is gained...it's hard to say how much horse power he/she lose with or with out the header...without doing some run's on the dyno for the before and after result...So in reality it would only suite you for a few reasons
1. noise pollution is not an issue
2. and if you plan on driving or drag racing everyday...other then that there is no reason to drive open header all the time...