Cut-outs !

ledgebmx · 08-06-2011, 07:28 AM

Here in NC one of the cars I used to work on had a 3" cutout on a 20b FD. The owner did it for performance, cost and noise reasons. It's expensive to purchase/fab a 4-5" exhaust that is quiet enough to pass noise laws but the 3" exhaust restricted the potential of the engine. He gained around 80rwhp with the cutout open at WOT. I think he dyno'd ~650rwhp @ 17psi all said and done.

I think the biggest factors are exhaust restriction and tuning issues. I would imagine you would tune with the cutout open and just deal with not racing with it closed very often. It's possible to tune for both if you're not running an exhaust that's too small (IE 3" on a 20B). You'd have to keep an eye on the tune but that's a given with these cars!

cewrx7r1 · 08-06-2011, 11:10 PM

Some production sports cars now come with some form of exhaust bypass that open at full throttle. Ferrari and Corvette are two that use them.

RXTASY · 08-07-2011, 05:15 PM

Have a 3" Quicktime cutout on my exhaust.
One of the best mods I have ever done.
Turbo spools quicker and boosts a little higher, plus it sounds wicked as hell!

08-06-2011, 07:28 AM	#1
ledgebmx The Newbie Join Date: Nov 2010 Posts: 10 Rep Power: 0	Here in NC one of the cars I used to work on had a 3" cutout on a 20b FD. The owner did it for performance, cost and noise reasons. It's expensive to purchase/fab a 4-5" exhaust that is quiet enough to pass noise laws but the 3" exhaust restricted the potential of the engine. He gained around 80rwhp with the cutout open at WOT. I think he dyno'd ~650rwhp @ 17psi all said and done. I think the biggest factors are exhaust restriction and tuning issues. I would imagine you would tune with the cutout open and just deal with not racing with it closed very often. It's possible to tune for both if you're not running an exhaust that's too small (IE 3" on a 20B). You'd have to keep an eye on the tune but that's a given with these cars! __________________ Aaron - Auto to manual conversion 93 w/ large streetport, RA Super Seals, GT35R, 1000/1680, AEM EMS, direct-fire AEM smartcoils, M2 Large, Aux inj, Tein Flex, Powerflex, CCW Classics - 18x10's, 99 spec and more. I'll make a build thread soon... Last edited by ledgebmx; 08-06-2011 at 08:56 AM.

08-07-2011, 05:15 PM	#3
RXTASY idahorotary.com Join Date: Mar 2010 Location: Idaho Posts: 135 Rep Power: 16	Have a 3" Quicktime cutout on my exhaust. One of the best mods I have ever done. Turbo spools quicker and boosts a little higher, plus it sounds wicked as hell! __________________ 87 TII-E85-600+ RWHP and climbing Life starts at 2 bar! Come visit my forum! idahorotary.com http://idahorotary.com/smf/index.php

08-06-2011, 11:10 PM	#2
cewrx7r1 The Judge Join Date: Feb 2008 Posts: 196 Rep Power: 18	Some production sports cars now come with some form of exhaust bypass that open at full throttle. Ferrari and Corvette are two that use them.