Hey guys it is well known that adding a catback and/or headers to a car gives you more horsepower. My question is where is this HP.

1. If you add headers, does it add hp at the crank or does it only take away some of the inefficiencies of the car and bring your rear-wheel hp closer to what you have at the crank?

2. Same thing for the catback.

Obviously, these things end up adding rwhp, but do they only add rwhp(you keep the same crank hp but become more efficient thus getting closer to that hp number) or do they add crank hp(your motor actually makes more hp thus you make more at the wheels)?

 

More power at crank=more rwhp.

 

I freed up like 30-35 rwhp when I put on my longtubes and catback. that was a long time ago though.

 

yeah but does that add more crank hp or does it just give your rear wheels more of the hp that you already had at the motor?

 

Both. Rear wheel horsepower = fly wheel horsepower - drivetrain loss. Drivetrain loss is somewhere around 12% for manuals and 15% for autos. Some will argue that these numbers are a little low and other factors, such at 12-bolt rears and stall converters, will increase that loss but that's the general idea.

 

if one changes as will the other

 

ok. well i guess my question is: does exhaust flow( i.e headers/catback) count as part of your drivetrain loss?

 

no the exhaust flow has nothing to do with drivetrain loss

 

ok so adding a pair of headers will give your engine more crank horsepower correct?

 

lets say if you had a motor on a stand and you put better exhaust and headers on it the crank hp will rise
drivetrain loss is the loss of power due to the motor having to rotate the parts from the crank to your wheels,therefore if you put heavier wheels,driveline,rear end parts then you would see an increase in drivetrain loss and your rear wheel hp will drop


hope that clears it up

 

yes and rear wheel hp will also rise

 

thanks man that clears it up. I just didnt know if headers/catback gave you more crank hp or not. thanks

 

Most of you were missing the point. It IS possible to pick up rwhp without gaining flywheel HP. If you made the driveline more efficient at transfering the power from the engine to the wheels you would pick up rwhp without the motor actually making anymore flywheel hp.

In the case of adding headers and exhaust the engine itself makes more HP as others have stated.