cat delete questions? does it cause power loss....

[pearbmw325is]

thinking about custom making new pipes from the bottom of the stock headers going into my UUC exhaust. doing so will delete my cats and resonator. what size piping should i use. Last i have heard people having power loss when running test pipes. should i just delete the resonator and leave the cats to not have this power loss. I have a e36 328is auto. i also understand that i will not pass emissions and have a check engine light on.

[SQ Bimmer]

Didn't read thread, but I am here to say that it doesn't cause power gain.

[Rob Levinson]

Removing catalytic converters on a street car is not recommended.

http://www.uucmotorwerks.com/html_te...ps/catless.htm

[BMDub325]

Getting a performance cat loses only around 1 hp and 1 ft/lb or torque in comparison with no cat, so that's what I would recommend.

[GeekRide]

thanks Rob, that was an excellent read.

[tokbandit]

something else you might want to read.....and was posted in another thread by xveganxcowboyx

Back pressure does not increase torque, nor does reducing back pressure reduce torque. The scavenging effect which you referenced has nothing at all to do with back pressure. It has to do with the total volume of the piping and the high and low pressure zones created by exhaust pulses. In simple terms as an exhaust pulse moves through the exhaust system it creates a vacuum behind it which helps to pull the next exhaust pulse away from the engine. Notice that this is a method of REDUCING back-pressure. Slower engine speeds have longer spaces between exhaust pulses which is why scavenging can help create better power at low revs. Smaller diameter piping greatly increases the scavenging effect at these low speeds. The loss of low end torque in some aftermarket exhaust comes from increasing the diameter/volume of the pipe, which reduces the scavenging effect. The increases up high come from the fact that the exhaust flows more freely (read: has less back pressure) than the stock systems smaller diameter piping. At higher engine speeds scavenging is minimal since the exhaust pulses are so close together and exhaust restriction determines power.

The two common choices are:

1. Stock size piping which reduces back pressure by using mandrel bent pipe, fewer bends, less restrictive mufflers and cats, etc. This will maintain low end torque and may yield gains across the board.

2. Larger diameter piping which also uses Mandrel pipes, etc to reduce back pressure. This may sacrifice some low end torque but may yield larger power gains at higher revs.

The horror stories of large low end losses mostly come from poorly deigned and overly large exhaust systems. It seems most of the aftermarket systems for these cars are designed fairly well engineered and provide good flow without using massive piping and all seem to provide reasonable numbers.



I'm afraid my attempt to simplify this issue at 2:30 in the morning may not be as clear as I hoped. Here is a good explanation that is not hard to follow. http://www.dsmtuners.com/forums/freq...kpressure.html