# Cat losses 15 whp ?????? with VE



## 98sr20ve (Oct 6, 2002)

I dyno’d my car about a month ago with a test pipe and with the stock cat. I lost 15 whp at 5000rpm with the stock cat vs the test pipe but about the same peak hp. I did about 15 runs with the test pipe and then put the cat on and did 2 pulls. I don’t know why I would lose so much HP with the cat in place especially at 5K rpm. Does a cat need to be super hot to be efficient. Would only 2 pulls be enough to warm up the cat? Would a High Flow cat be any better? Here is a picture of my dyno. One pull is with the sr20ve cams and it nets 180whp, the other is with the sr16 cams and it nets 185whp the third is the sr16cams but with the cat and it losses about 15whp at 5k. Any ideas? I need to quiet my car back down so a cat or a new resonator is going back in its place.


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## 98sr20ve (Oct 6, 2002)

Sorry about the size of the picture. Ignore the red graph that was with the sr20ve cams on a different day.


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## Mr SEntra (Oct 7, 2002)

Steve, nice runs man. Sorry I don't have any advice. I wish my DE could make that kind of power right now.


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## PatScottAKA99XE (Apr 30, 2002)

Steve,
Couple of ideas I have thought about concerning cats: I wonder if maybe the internal shape of the stock cat has anything to do with it, not nessarly the flow capabilities. Would the interior diam. change cause any turbulance disturbing flow in certain RPM ranges( mid in your case)? Would a cat that has less dramitic wall changes help any? This is something I would like to see investigated, but I have neiter the money nor the facilities to check it out right now.


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## 98sr20ve (Oct 6, 2002)

Our cars resonate at 4-5k and I wonder if that has anything to do with it.


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## morepower2 (Apr 19, 2002)

98sr20ve said:


> *Our cars resonate at 4-5k and I wonder if that has anything to do with it. *


Where is your cam switching point? Maybe that might have something to do with it.

The more duration you have, the greated the senstitivity to back pressure. Tap your header collector and measure your backpressure. If its more than 2.5 psi you are losing power.

It might have something to do with your cam switch point and intake and exhaust manifold resonance as well, VE is highest near the torque peak.

Genraly so called aftermarket high flow cats don't flow better than stock but I personaly think the Magnaflow ones are better, their shell is actualy designed on a flow bench.

Mike


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## 98sr20ve (Oct 6, 2002)

morepower2 said:


> *Where is your cam switching point? Maybe that might have something to do with it.
> 
> Mike *


My cams switch over at 4300 and 4900 rpm. I still lose power after the cam switch. I was thinking I might be able to tune some of it out but dyno time is getting expensive.

PS Thanks


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## JustinP10 (Apr 30, 2002)

Dumb idea, but would something like a G-tech be able to help you "tune" the switchover. If you enter your car's weight (or at least a constant number) you could use the hp feature of the g-tech to see when is the best switchover. If the hp drops on the g-tech when the cams change then up the rpm point, if it jumps up a lot, then try lowering the switchover a bit. 
I forget the refresh rate of the g-tech though. I'm thinking you'd probably have to do this in a higher gear, like 4th or 5th on the highway to have the rpms move slow enough under full throttle to accurately see the hp figures change on the lcd readout. 

Just an idea?


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## edo (Nov 26, 2002)

> Genraly so called aftermarket high flow cats don't flow better than stock but I personaly think the Magnaflow ones are better, their shell is actualy designed on a flow bench.
> 
> Mike


Borrowed from a post by a Magnaflow rep:



> Random technology vs Car Sound High Flow Converters- why Car Sound Flows better
> 
> First of all the facts-
> 
> ...


cheap prices:

http://exhaustproslinc.com/brcarunconwi.html 

Carsound/Magnaflow affiliated companies.

-Ron


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## Guest (Dec 6, 2002)

wow good website thanks for the tip


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