exhaust bigger not better

[raywong]

I am just watching discovery turbo right now, a documentary about a race team called "Fall Line". they race with e92 M3, they showing how to modify the cars. the first thing they did was to remove the cat, resonator and muffler. the head engineer was surprised it lost 15hp, so he fabricated smaller diameter pipes to gain hp. the smaller diameter pipes speed up the exhaust gas flow to reduce back pressure. there's is a fine balance between restriction and gas velocity.

[FVM3]

i dont know headers and pipes but deleting cats does gain hp

[NJBMWM3]

With turbo cars the bigger the exhaust the better. It enables the turbo to spool up faster. With an NA engine that is not the case they need some back pressure.

[Addicted2M]

Primary Cat delete shows gains in our cars dyno proven. no tune just p cat delete +10-15hp and 10-15tq, with tune +30-40hp, 15-30hp.

[Lorde]

Originally Posted by NJBMWM3

With turbo cars the bigger the exhaust the better. It enables the turbo to spool up faster. With an NA engine that is not the case they need some back pressure.

For turbo cars...True, up to a certain point. Then the law of diminishing returns comes into play.

[Taunto]

Ya I can see this. Your engine can only push out so much gases. Only way that it would gain any hp is if the engine was say built or had cams or such.

Like said above this is why it works on Forced induction cars.

Addicted2m would you mind posting a dyno chart of one of these gains on your cars if possible. Would like to see this. Is this gain from Cat-removal with a tune? or just cat removal and dyno run? In theory Cataylic converters now-a-days flow extremely well and help force air out of the exhaust due to the gases being compressed through the mono-loth,pladium and plantinum.

If running high horsepower or high intake strokes where the engine needs to push out as much gasses as possible then the cat does cause a restriction. Mainly why you see almost all drag cars running open headers.

I also perfer the smell of a clean burning car rather than that raw fuel smell you smell from old muscle cars - just my personal opinion

[Gearhead999s]

Originally Posted by raywong

I am just watching discovery turbo right now, a documentary about a race team called "Fall Line". they race with e92 M3, they showing how to modify the cars. the first thing they did was to remove the cat, resonator and muffler. the head engineer was surprised it lost 15hp, so he fabricated smaller diameter pipes to gain hp. the smaller diameter pipes speed up the exhaust gas flow to reduce back pressure. there's is a fine balance between restriction and gas velocity.

This means nothing to us as the E92 M3's that race in that series have to run a inlet restrictor to reduce their power to equalize the performance to the other cars in the class.

[Addicted2M]

http://www.turnermotorsport.com/p-13...t-delete.aspx#

Here is Turners dyno chart showing results with the primary cat delete + TMS Tune. Alot of members here have done this and see performance difference. Turner doesn't make up fake numbers they use all the performance parts they offer.

[raywong]

I think there is hp gain from deleting the cats on most car. but I wont be surprised to see hp lost if the cats, the resonators and the muffler are all removed.

back pressure is bad, it can only slow down the engine combustion cycle. The exhaust gas travel thru the pipe in series of pulse(wave), each wave generates a pulling force on the next following wave. if the pipe gets too big, the wave is destroyed, you get turbulent air inside the pipe blocking the flow, the engine need use part of the hp to fight the back pressure...

[Taunto]

Thank You addicted. And i would also believe any dyno numbers that tuner motor sports puts up. They are a very great business and knows there stuff thats for sure. Cool to see the gains tho, thanxs for the info.

[///Matthew]

[Singletrack]

This thread is like a meteor shower of misinformation. RUN FOR COVER!