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go from 3" to 4" exhaust?

Old 02-28-10, 10:18 AM
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go from 3" to 4" exhaust?

hello guys!

Last year i dynoed my car at 23psi and made 529rwhp with a t78 powered full bridgeport engine.

at that point i thougt the backpressure became to high, the EGT's began to rise, and couldnt get the boost higher. i'm running a 3" exhaust, with 2 mufflers and the wastegate welded in to the downpipe..

soooo.... would i see more power(at hte same boost), and faster spoolup with a 4inch exhaust?

regards,stig
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Old 02-28-10, 10:32 AM
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From what ive heard its not so much a hp increase(maybe a couple rwhp unless you running a huge port and turbo and the 3in causes restriction) as its a increase in spool time you see. Im going from 3in to 4in myself as soon as i get it back from the body shop but for the better spool time.
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Old 02-28-10, 11:24 AM
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my ports is pretty big, full bridge, and equal size on all 4 ports.
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Old 02-28-10, 11:26 AM
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What you'll find is that it mainly helps come on boost quicker. It should free up some hp how much will depend on the setup. The main thing is though quicker response so more power sooner. Medium sized wastegates can have a harder time controlling boost also.

~S~
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Old 02-28-10, 11:30 AM
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i've got a 60mm wastegate bolted on it, i hope that can handle it

zero r: I've sent you guys an mail about a 4" exhaust system!
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Old 02-28-10, 05:30 PM
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1. This will cause additional noise. Do you think you will get tired of it, not now but two or three years from now?

2. What about the police? Will the additional noise attract too much attention? I have a few friends from Norway and I know Norway is also really bad for inspections and alcohol laws.
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Old 02-28-10, 06:00 PM
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Any thoughts on a BNR stage 2? 4 inch too large? The reason I ask is because the previous owner had larger turbo and a 4 inch. He sold the turbo and I bought the car with a 4-inch exhaust still hanging. Engine is street ported BTW and I will use a 3inch downpipe to start

-mike
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Old 02-28-10, 09:40 PM
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As previously mentioned, you would see no HP increase, just spool time decrease.

If you can handle the extra noise, 4 inch on BNRs would not hurt. However, that is a bit much.
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Old 03-01-10, 12:44 AM
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The noise i can handle, no problem, and if it get to bad, a change in mufflers can do a huge difference. the inspections up here are pretty bad, but the car goes much more on the track that on the road, so its more important to me to get backpressure down, get the EGT's under control (its rising under longer runs) and maybe gain some spool. more power is a bonus, and if everything looks fine, I'll bump the boost up a bit too!

i guess i'll go with the xcessive LIM at the same time, to even the EGT's and flow, then its dynotime again Love the Dynapack, a friend got one, so i get free dyno-time! was on it a couple of times last year
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Old 03-01-10, 08:34 AM
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Originally Posted by WaachBack View Post
As previously mentioned, you would see no HP increase, just spool time decrease.

If you can handle the extra noise, 4 inch on BNRs would not hurt. However, that is a bit much.
I just did a recent dyno test and JUST taking a RB catback off a car yeilded 10rwhp across the board @ only 16psi( and that is with an open vent wastegate). I would suggest he would see at least double that power increase on his setup, especially since his w/g is rerouted.
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