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Old 08-07-2004, 01:23 PM   #1
ImportVenom
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Member#: 34204
Join Date: Mar 2003
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2004 WRX
WR Blue

Default WRX Cobb stage 2 - stock catback vs Sti catback (almost 1 sec difference)

Hey all, I'm running a Cobb stage 2 with just an HKS downpipe. I did some runs with the stock catback, and then some runs with a stock STi (USDM 04) catback. The results are very surprising. I've been told that the stock STi catback was still really restrictive, but why did it make such a big difference? Keep in mind this was done at a track at over 5000 feet, and the density altitude was around 7500 feet both nights.

Night 1 (Stock WRX catback + HKS downpipe):
Conditions: 77 degrees F, 32% humidity, 30.14 baro press => 7561 feet density altitude
Best ET = 15.49 @ 91.3 mph with a 2.14 60 foot time and a 9.99 1/8 mile time
Best MPH = 91.5 mph
Average ET ~ 15.55 sec @ 91.2 mph

Night 2 (Stock STi catback + HKS downpipe):
Conditions: 75 degrees F, 43% humidity, 30.17 baro press => 7445 feet density altitude
Best ET = 14.60 @ 95.3 mph with a 2.0 60 foot time, and a 9.4 1/8 mile time
Best MPH = 95.7 mph
Average ET ~ 14.70 @ 95.0 mph

I was consistently running 14.6 to 14.8 on the second night with the stock STi catback. How could the stock STi have made such a huge difference? My boost levels are hitting a peak of maybe 14.5 psi, dropping down to 10 psi by redline. I was getting much better 60' times with the stock STi catback. Any thoughts on this? The biggest thing is my mph jumped nearly 4 mph with a stock Sti catback. From what I understand, the mph is most important in determine how much power you have. I can't believe it made such a huge difference. Cobb said the Sti catback was minimal in flow difference compared to the stock WRX catback.
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Old 08-08-2004, 11:20 AM   #2
GameOver
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different technique used ?!?
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Old 08-08-2004, 02:44 PM   #3
drees
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Tuned with Enginuity

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No idea, is it possible to switch back to the stock catback again and try again to verify results?
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Old 08-08-2004, 03:45 PM   #4
ImportVenom
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Quote:
Originally Posted by drees
No idea, is it possible to switch back to the stock catback again and try again to verify results?

It is...but I'm kinda lazy

Maybe next time I'll try running without a catback at all, and see if it makes any difference? My theory is that the stock STi catback flows well enough for the amount of power I'm making. If I take off the catback completely, that would be the most power possible right? One car was doing that at the track but ran with a stock downpipe still - he ran a best of 15.2 I think.
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Old 08-08-2004, 06:58 PM   #5
elhalisf
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This is kind of outside the scope of the topic, but I have been trying to search for 1/4 miles with the Cobb Stage 2 and I dont understand how you were running only 15.2 with the cobb stage 2? Did I miss something? Please inlighten me. Thanks
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Old 08-08-2004, 08:38 PM   #6
ImportVenom
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Quote:
Originally Posted by elhalisf
This is kind of outside the scope of the topic, but I have been trying to search for 1/4 miles with the Cobb Stage 2 and I dont understand how you were running only 15.2 with the cobb stage 2? Did I miss something? Please inlighten me. Thanks
Altitude, plus the fact that I don't dump the clutch. There were two other WRX's running 15.1 - 15.3 with full turboback, intake, and boost controller. They also didn't dump the clutch, but slipped slowly. I'm convinced that the Cobb ECU will run about the same speed-wise as a car with a boost controller, except that running the Cobb ECU is much safer supposedly (although I've read reports of people running really lean as well as really high EGT's).
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