lost torque after cat removal..
lost torque after cat removal.. Every-so-often I'll run w/o cats and have always put them back on due to the loss in torque. These are the cats that are part of the FLP system and the loss of torque is really noticeable when their off.
I've heard that high-flowing cats aren't supposed to make a difference, but if that's the case should the difference be that great? Or, would I get it back plus some if I get it retuned.
I've heard that high-flowing cats aren't supposed to make a difference, but if that's the case should the difference be that great? Or, would I get it back plus some if I get it retuned.
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From: Cypress, TX USA
You would need some "high-flow" cats to gain some of your torque back. All the cat's do is build up that back pressure and release it to the rear wheels.
Without cats you have nothing to build up the back pressure, therefore you lose you torque.
So the question is?
Do you want more rear wheel hp? if so get rid of the cat's..
Or Do you want more torque to the rear wheels?-If so leave your high flow cats on.
Without cats you have nothing to build up the back pressure, therefore you lose you torque.
So the question is?
Do you want more rear wheel hp? if so get rid of the cat's..
Or Do you want more torque to the rear wheels?-If so leave your high flow cats on.
Originally Posted by XtinctHawk02
You would need some "high-flow" cats to gain some of your torque back. All the cat's do is build up that back pressure and release it to the rear wheels.
Without cats you have nothing to build up the back pressure, therefore you lose you torque.
So the question is?
Do you want more rear wheel hp? if so get rid of the cat's..
Or Do you want more torque to the rear wheels?-If so leave your high flow cats on.
Without cats you have nothing to build up the back pressure, therefore you lose you torque.
So the question is?
Do you want more rear wheel hp? if so get rid of the cat's..
Or Do you want more torque to the rear wheels?-If so leave your high flow cats on.
So, even after getting re-tuned for a less restrictive exhaust/possibly a leaner afr, one couldn't expect to get all/most of the torque back?
Thanks for the reply, btw.
Hahahhaha here we go again. Backpressure is a myth, it doesnt "build" torque. Backpressure just moves your torque band lower in the rpms, so you "feel" it more. Resonant scavenging is what you want. You want exhaust velocity. The way the exhaust waves move through the pipes determines your torque band. Open exhuast will always give you the most torque, hp. if you put your cats on, you can feel your car drop off at higher RPMs due to reduced exhaust velocity. Straight pipes cut to a specific diameter is what you need. You can put bullets but you will gain the most. 2.5 for stock cube motor, and 3 for big h/c or big cubes. trust me, its only SOTP feel. Put it on a dyno n youll see you have more torque and more hp, its just higher up in the band where you need it while your racing 
Originally Posted by ohhiitznik
Hahahhaha here we go again. Backpressure is a myth, it doesnt "build" torque. Backpressure just moves your torque band lower in the rpms, so you "feel" it more. Resonant scavenging is what you want. You want exhaust velocity. The way the exhaust waves move through the pipes determines your torque band. Open exhuast will always give you the most torque, hp. if you put your cats on, you can feel your car drop off at higher RPMs due to reduced exhaust velocity. Straight pipes cut to a specific diameter is what you need. You can put bullets but you will gain the most. 2.5 for stock cube motor, and 3 for big h/c or big cubes. trust me, its only SOTP feel. Put it on a dyno n youll see you have more torque and more hp, its just higher up in the band where you need it while your racing
That post (reply #6) is what really led me to ask this question.. Your response btw, is alot easier to understand. Thanks and I'll try it and dyno..
Backpressure on the power stroke would aid
torque - under very specific conditions. The
exhaust pressure would have to be higher
than the cylinder pressure, the exhaust valve
open. But this is not how the power stroke is
set up. The exhaust valve may open before
BDC slightly, more on a "big" cam, but by BDC
your crank angle has really cut the cosine
torque contribution to about nothing.
Backpressure on the exhaust stroke -steals-
torque, a negative shaft torque is taken to push
the gas out against any backpressure.
Reduced backpressure equates to more cylinder
emptying, then more cylinder filling. This will
increase dynamic cylinder air, pull back spark
timing unless corrected. It will pull in a bigger
charge with less dilution, possibly making a
faster burn, maybe not wanting more spark
anyway. The true VE at higher loads will go
up but the PCM knows nothing, this will likely
change transient throttle mixture by the SD
tune. Anyway, you have multiple mixture and
timing effects that come from a change in
exhaust efficiency and the PCM needs to be
educated.
But the pressure as a simple actor, is not
giving torque.
torque - under very specific conditions. The
exhaust pressure would have to be higher
than the cylinder pressure, the exhaust valve
open. But this is not how the power stroke is
set up. The exhaust valve may open before
BDC slightly, more on a "big" cam, but by BDC
your crank angle has really cut the cosine
torque contribution to about nothing.
Backpressure on the exhaust stroke -steals-
torque, a negative shaft torque is taken to push
the gas out against any backpressure.
Reduced backpressure equates to more cylinder
emptying, then more cylinder filling. This will
increase dynamic cylinder air, pull back spark
timing unless corrected. It will pull in a bigger
charge with less dilution, possibly making a
faster burn, maybe not wanting more spark
anyway. The true VE at higher loads will go
up but the PCM knows nothing, this will likely
change transient throttle mixture by the SD
tune. Anyway, you have multiple mixture and
timing effects that come from a change in
exhaust efficiency and the PCM needs to be
educated.
But the pressure as a simple actor, is not
giving torque.
Man.. my eyes are still glazed.. With all due respect, can you please simplify?
moving forward, what about dyno's of before and after.. I've always liked pictures.
moving forward, what about dyno's of before and after.. I've always liked pictures.
Last edited by AVB; Aug 1, 2004 at 12:26 PM.
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Originally Posted by jimmyblue
Maybe the problem is the torque to noise ratio, the
same sound level that used to mean hard acceleration
now corresponds to less.
Quantitative comparisons are better.
same sound level that used to mean hard acceleration
now corresponds to less.
Quantitative comparisons are better.
