Iam thinking of running decat with Factory JCW exhaust but was told that running decat could cause significant bottom end power and torque lost. Is it true?

 

Do you mean you want to run a catless downpipe?

 

Yes decat down pipe.

 

loss in low end? sure, as with any increased exhaust. significant? no. gains in top end? yes. faster spool? yes. bad for the environment? if you're a tree hugger, then i guess yes. (jk on the last one)

 

Iam searching for more bottom end. I guess cat less down pipe will do the opposite. How to get more low end power on mcs?

 

 

I do not think you will see any loss of low end power running catless. The turbo provides plenty of backpressure and opening up the exchaust after the turbo will only give you a faster spool up and more poweracross the whole rpm range. Probably most noticeable on the low end. Send me your JCW cat and call it a day.

 

IMHO running catless will only give you more power over the whole rpm range. Our cars do not suffer a power loss due to lower backpressure because our turbo provides backpressure. Anything done after the turbo to increase flow will only increase power by allowing faster spool up which will give a most noticeable gain on the low end.

 

I see this misinformation a lot. An engine does not need back pressure to make power. It is true that properly designed exhaust for an N/A car will result in some amount of backpressure as a byproduct of the design (tube dimeter/length, etc). It is NOT the backpressure that makes power, but the design of the exhaust. To quote a Garrett turbo development engineer who posted this on NASIOC many years ago "...The backpressure is an undesireable byproduct of the desire to have a certain degree of exhaust velocity..." Again, this is for N/A exhaust design.

For a turbo car, the same is true with respect to backpressure. Note the exhaust in a turbo car is not designed optimize scavenging as in the N/A exhaust. Since the turbo produces boost via an exhaust pressure ratio across it, you will of course have lots of backpressure in the exhaust system upstream of the turbo when under boost. Minimizing backpressure downstream of the turbo really helps due to the pressure ratio and the way it multiplies backpressure across the turbo. To answer the question about removing a cat from the exhaust system, pretty much anything you can do to reduce exhaust backpressure at a given boost level will increase the VE of the engine.

JL

 

Question? If you remove the 2nd cat will it make the exhaust/muffler louder?