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Discussion Starter #1 (Edited)
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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Discussion Starter #2
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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ex-Super *********
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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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Discussion Starter #5
Our cars resonate at 4-5k and I wonder if that has anything to do with it.
 

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Icy Hot Stunta
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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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Discussion Starter #7 (Edited)
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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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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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-

Every converter has to use a brick that has at least 400 cells per square inch.

Any less and the converter will not get EPA approval, both Car Sound and Random Technology are using the same 400 cells per square inch, so one brick can not outflow the other...


The difference must then be in the casing-

1. Have you got the groove???



The brick is a brittle piece, so it has a rubber- like cushioning mat that cushions the monolithic catalyst. (the brick)

This rubber- like mat is about 1/8th of an inch thick.....

If you look at a Random converter, it has a smooth body so that mat sits out in the open...with the exhaust gas hitting it causing the air to not flow smoothly.....



The Car Sound converter has grooves built into the casing, which lets the matting sit recessed into the casing. This means the exhaust is not hitting that 1/8" piece causing turbulences.

Not only does this allow the air to flow smoother, but it helps to protect the matting from the exhaust flow which will eat away at it and it keeps the brick in place when the metal of the converter body expands as it gets hotter.....

2. You have to see it from the right angle-

If you look at the two converters side by side, you will notice that the RT has a lot sharper bend where the casing decreases and increases from the actual exhaust piping.....

If you look at the exit side of the converter- what flows better-

air hitting a 15 degree angle or a 45 degree angle- sharp curves in the case cause less flow......

(not only does the more obtuse angle cause an easier exit for exhaust out of the converter, but upon entering the converter, it gives more room for the air to spread out, reducing emmsions and providing more even wear on the brick)

3. Get connected-

Look at where the inlet and outlet pipes are welded into the converter body......

Instead of using a butt weld, which causes a ridge where the two connect, Car Sound uses a 1/2" overlap, which means that the place where the body connects to the piping is smooth....

the overlap also provides a better surface area to weld on as well making it a stronger weld.

Those are three of the main reasons a Car Sound converter will outflow a Random Technology-

Again, we all must use the same 400 cells per square inch, so the real difference in flow is created with the casing-
cheap prices:

http://exhaustproslinc.com/brcarunconwi.html

Carsound/Magnaflow affiliated companies.

-Ron
 
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