exhaust.... what makes more power?

**EVL LS1** · 11-18-2005, 11:32 PM

i've heard over and over during the years that less restriction makes more power... is this true?

my current truck has four.. yes four damn cats on it which i plan to replace in december with two high flow cats... it has dual exhaust with a huge ass 50 gallon barrel for a muffler (only thing connecting the dual 2.5" pipes) yesterday i had the muffler removed and two pipes welded in to make it have duals. the truck sounds great now but someone on another board said i'm loosing power now.

i'd appreciate an exhaust expert to chime in please =0) thanks

**FastAssZ** · 11-19-2005, 01:10 AM

more flow equals less back pressure, less back pressure equals more hp but less TQ and less flow causing more back pressure equals more TQ but less HP........ if im wrong someone please correct me but as far as i am concerned that is how it goes

**FastAssZ** · 11-19-2005, 01:11 AM

so by taking out the 4 cats and putting in 2 high flow and cutting the exhuast off as you said above will give you more HP but less TQ

**EVL LS1** · 11-19-2005, 01:22 AM

thanks for the reply. i've always thought of the need for backpressure is really a myth
well,not so much a myth but played up more than it really is

The less back pressure the better.

The reason why smaller diameter pipes create more torque at lower RPM is due to exhaust velocity. With larger pipes on the same set up it takes more RPM to create the same velocity. Power band moved up. Its the same concept with cams. More duration doesn't kill torque, it just moves max output up in the RPM range

this is what i read in another thread and that's how i always thought of it as. right now the truck has two cats per manifold side and two 2.5" pipes all the way to the back. there was a huge muffler connecting the two pipes together (2 in and 2 out) but i removed it yesterday and put two pipes in it's place.

the truck is suposed to be 340 bhp @ 4500 rpm / 425 lb-ft @ 3250 rpm stock btw

**SteveC** · 11-19-2005, 05:45 PM

I can only speak about the LS1 engine, and my belief is that you want at most .5 lbs of back pressure, that you do not want 0 lbs.

I do not know why, however I have had reputable exhaust shops tell me this.

SteveC

BlackHawk T/A · 11-20-2005, 12:54 AM

Originally Posted by FastAssZ

more flow equals less back pressure, less back pressure equals more hp but less TQ and less flow causing more back pressure equals more TQ but less HP........ if im wrong someone please correct me but as far as i am concerned that is how it goes

Wrong...the more restriction you remove from the system the further up in the powerband you move the power to...just like adding higher flowing heads and a higher performance cam. It has the same effect. You really aren't losing Torque just moving it up in the powerband so it may feel that way.

A restrictive system may be great off-idle but at higher RPMs will really choke the engine.

quicky06 · 11-20-2005, 06:50 PM

the reason why you need back pressure is to slow down the exauhst. in a high reving engine (especially one whos sprayed) if the exauhst leaves the piston to fast it can act like a cutting tourch. an by slowing it down you can prevent this.

**Ric** · 11-21-2005, 07:40 PM

Originally Posted by quicky06

the reason why you need back pressure is to slow down the exauhst. in a high reving engine (especially one whos sprayed) if the exauhst leaves the piston to fast it can act like a cutting tourch. an by slowing it down you can prevent this.

If this is true, then could you just use a much bigger pipe than needed, and reduce the velocity of the exhaust without the backpressure??? It'd keep what you described from happening and flow better, too.