3" downpipe HP limits
Thread Starter
TECH Regular
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Joined: Feb 2005
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From: brunswick, ohio
3" downpipe HP limits I have changed my combo I am limited to a 3" dp without more mods.
365" turbo short block,
AFR 225 heads 72cc, 9to1cr
-11cc wiesco pistons
H beam rods polished stock crank,
ls6 intake, Z06 cam
1.8 yella terra RR,
single turbo PT76GTS, 4" intake, 3" dp .96 ar turbine, .75 ar comp.
COS3 efi live OS instock computer
60# injectors
Mostly street car AWD 4L80E
How much power can I make on low boost, 10-12#
How bad will the 3"DP choke my hp?
will it be mostly at high rpms?
THANKS
365" turbo short block,
AFR 225 heads 72cc, 9to1cr
-11cc wiesco pistons
H beam rods polished stock crank,
ls6 intake, Z06 cam
1.8 yella terra RR,
single turbo PT76GTS, 4" intake, 3" dp .96 ar turbine, .75 ar comp.
COS3 efi live OS instock computer
60# injectors
Mostly street car AWD 4L80E
How much power can I make on low boost, 10-12#
How bad will the 3"DP choke my hp?
will it be mostly at high rpms?
THANKS
Last edited by sparkwirez06; Jan 12, 2009 at 09:47 AM.
I've always been under the impression you can safely run up to close to 1000 crank hp before any problems should arise. Especially if its dumped. Otherwise a very free flowing exhaust.
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Teching In
Joined: Jun 2006
Posts: 22
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From: Charlotte, NC
I built a viper that made 1460 rwhp with 3 inch downpipes. Went to 4 inch, and it picked up 30 ft/lb torque down low and 25 peak hp. Don't be scared to run the 3 inch. The bigger pipes help, but not that much, especially below 1000 hp. At low boost(around 800 rwhp), there wasn't much difference.
I built a viper that made 1460 rwhp with 3 inch downpipes. Went to 4 inch, and it picked up 30 ft/lb torque down low and 25 peak hp. Don't be scared to run the 3 inch. The bigger pipes help, but not that much, especially below 1000 hp. At low boost(around 800 rwhp), there wasn't much difference.
Teching In
Joined: Jun 2006
Posts: 22
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From: Charlotte, NC
I understand you point you are trying to make, and that the vehicles are considerably different. I am simply trying to make the point that big pipes,or pipe, make more power, but are not the holy grail of endless horsepower. If you put it on the dyno it won't make as much, but it will still put up a good number.
Thought I'd just continue this thread rather than start a new one..... What's the thoughts on a 4" DP with a 3" in the middle to get through the K member and then back to 4"? Or is it a bottleneck is a bottleneck is a bottleneck?
I have a 3" outlet on my setup off the turbo, 3" thru the k member, and steps up to a 4" pipe at the firewall thru a dynomax bullet turned down at the axle. Its pretty droney and loud under accel, been thinking about running a 3" e-cutout right behind the firewall in the stock cat. location and running a normal 3" catback behind that to keep it tame when not ripping on it. If anyones interested in my 3" to 4" setup I'll make a good deal on it.
TECH Addict
Joined: Jul 2005
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I'm running a 3" downpipe that's about 5' long with 2 45's in it. From there, it's 3.5" all the way back, over the axle, and through a Magnaflow. I've run 146 in the quarter at full weight at 17 psi boost from a T76GTS. Backpressure numbers were only around 34 psi, which is quite low for 388 cid on the 76GTS. Doing some math tells me I'm over 900 fwhp on the 3".
Nice. I bought my v-band and elbow this morning to take to my guy. I thought about just kicking the 4" back as far as possible for now and then work with getting it back with a muffler later. Sounds like a 3" intermediate probably won't make much difference.
OK my stuff has been mostly welded up. We've gone with a 3" down pipe that makes a 90 off the turbo then pretty much straight back from there to underneath the pass side rear. I may just leave the muffler off.
Last edited by dhdenney; May 20, 2009 at 05:50 PM.