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Old 04-04-2002, 08:03 PM   #1
metoo
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Default Curious: Highflow cat hp vs. no cat hp

Let's say that you have a nice single-cat turbo-back exhaust on your WRX. Then you dyno it. You then decide to remove the hi-flow cat for grin and dyno it again with a non-cat section.

What was the difference?
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Old 04-04-2002, 08:17 PM   #2
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2 dead Penguins

Sorry I couldn't resist.

I wouldn't mind knowing the answer though.

Mike

www.redstarracing.net
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Old 04-04-2002, 10:56 PM   #3
JaMa
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Default 4-5hp

My sources tell me 4-5hp on a fairly tuned WRX, a little more the crazier the car is.

JaMa
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Old 04-05-2002, 09:22 AM   #4
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For a good quality high flow cat, probably ~10hp.
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Old 04-05-2002, 09:59 AM   #5
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On a setup like mine I wouldn't be surprised to lose 20+ HP with a "high flow" cat.
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Old 04-05-2002, 10:37 AM   #6
Greenracer6
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Default agreed

I have to agree with god, I had the cats then lost all of them from the turbo back and it opened up all kinds of power.

The more aftermarket stuff you have, the more the resitrictive exaust will hurt you.
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Old 04-05-2002, 11:44 AM   #7
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On my 2.2L 16V turbo Dodge, I installed a full 3" turbo back exhaust with a high flow 3" cat and Ultraflow 3" muffler. I also installed a "cutout" right in front of the cat. This "cutout" was basically a "Y" which had one outet capped off. When it was capped, exhaust went through the cutout as it normally would. When uncapped, the exhaust took a gentle bend and dumped out right before the cat. This effectively dumped the exhaust right out of the downpipe.

On a Dynojet at only 13 psi of boost, changing nothing else but running out the cutout, I picked up about 13 ACTUAL whp. The turbo also spooled a little sooner as well. (I wanted to run the plots in ACTUAL power without any corrections since they were being run back to back on the same day. I was also investigating the limits of the stock injectors and wanted to see what they would ACTUALLY support without all the correction factors muddying the waters.)

Uncorking the exhaust also had a very nice and obvious leaning affect on the A/F ratio .

Ill post each of the dynos next. I would expect a WRX to show similar, if not greater, gains without the cat.

Last edited by 4sfed 4; 04-05-2002 at 11:55 AM.
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Old 04-05-2002, 11:46 AM   #8
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1991 Dodge Spirit R/T - 2.2 L 16V Turbo - Stock except for 3" turbo back exhaust with cat and muffler - 13 psi boost
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Old 04-05-2002, 11:49 AM   #9
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1991 Dodge Spirit R/T - 2.2 L 16V Turbo - Stock except for 3" turbo back exhaust without cat and muffler - 13 psi boost
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Old 04-05-2002, 01:35 PM   #10
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Great responses!

Next question:
Say that you receive a dyno tune with cat in place, then decide to put in a catless pipe. Are you doing anything bad to your car?
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Old 04-05-2002, 02:33 PM   #11
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Yes, your AF mixtures may lean out more than you want and may increase chance of detonation depending on how close to the edge you tuned with a cat. Also you can advance timing further on a ar with no cats thus increasing power in this manner as well.
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Old 04-05-2002, 03:34 PM   #12
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I just love fluid flow stuff. What I'd love to do is open up my exhaust as much as humanly possible, with several limitations.

= The exhaust pipe may not hang lower than my rear diff. Obviously, it must also clear my rear armor plate.
= I don't want a huge ricer fart tip. Anything larger than the pipe itself is purely cosmetic.
= It must have one high-flow cat, or a section of straight pipe that can be replaced with a cat for inspections.

Noise is not a problem for me! Loud is okay , high performance is better. I'm imagining an N1 style pipe that doesn't hang quite as low as a Kakimoto and has a single 3-4" tip. What do you think?

Oh, and just to get back on topic, here's a plot of both of dyno runs from 4sfed 4's Dodge:
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Old 04-05-2002, 03:52 PM   #13
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Quote:
Originally posted by god
Yes, your AF mixtures may lean out more than you want and may increase chance of detonation depending on how close to the edge you tuned with a cat.
Yes. Look at the A/F plots above and youll see the car ran one full point leaner without the cat. In my case, this was fine as the car loves high EGT's. (Ideal was in the 1750-1800F range.) I ran it as high at 1950F, but the power was notably down.

And no...nothing melted This particular engine design likes to run hot.
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Old 04-05-2002, 04:03 PM   #14
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Heres the same car through the exhaust (no cutout) with 42 lb/hr (about 450 cc/min) injectors (the stock ones used in the previous plots were 32 lb/hr, or about 325 cc/min).

The same 13 psi of boost was held at redline, but I hit 21 psi at 3500 rpm. You can see the obviosu affects on the A/F ratio. (The computer calibration was unchanged.)

I eventually tuned the car to 25 psi at 2500 rpm (4th gear) and 21 psi at redline. But, I never got a chance to redyno it before I cracked the trans case

Most likely it was making 300-310 whp and 350-375 w ft lb. All for $400 in mods!
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Old 04-06-2002, 12:20 PM   #15
Greenracer6
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Default N1 style

Quote:
Originally posted by Kartoffel
I just love fluid flow stuff. What I'd love to do is open up my exhaust as much as humanly possible, with several limitations.

= The exhaust pipe may not hang lower than my rear diff. Obviously, it must also clear my rear armor plate.
= I don't want a huge ricer fart tip. Anything larger than the pipe itself is purely cosmetic.
= It must have one high-flow cat, or a section of straight pipe that can be replaced with a cat for inspections.

Noise is not a problem for me! Loud is okay , high performance is better. I'm imagining an N1 style pipe that doesn't hang quite as low as a Kakimoto and has a single 3-4" tip. What do you think?

Oh, and just to get back on topic, here's a plot of both of dyno runs from 4sfed 4's Dodge:
I had a custum piped 3in turbo back exaust w/ no cats and a N1 up like a Skyline...I'll go take some pics and post in a few minutes..

=bill
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Old 04-06-2002, 01:48 PM   #16
Greenracer6
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Default pics

trying to get this to work...

A'pexi N1, all custum work-3in turbo back

Last edited by Greenracer6; 07-20-2010 at 10:54 PM.
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Old 04-06-2002, 01:52 PM   #17
Greenracer6
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Default few more

side view...

Last edited by Greenracer6; 07-20-2010 at 10:54 PM.
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Old 04-06-2002, 01:53 PM   #18
Greenracer6
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Default one more...

behind..

Last edited by Greenracer6; 07-20-2010 at 10:54 PM.
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Old 04-06-2002, 07:28 PM   #19
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Default Greenracer6

dude, that thing hangs WAY below your rear diff
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