Downpipe Discussion
Thread Starter
Melting Slicks
Joined: Jan 2002
Posts: 3,293
Likes: 79
From: Jackson MI
Downpipe Discussion
OK guys, I think I'm at the point of ordering my U-bends for the downpipe on the turbo project. But I'm not 100% sure what to order. The v-band accepts 3.5" pipe and I could get the 3.5" all the way back. But is there an advantage to doing 3.5" then expanding it out to 4" later? I'm planning on running the downpipe to just before the center resonator and splitting that into the stock dual 2.75" out the back, with the mufflers removed of course.
I've got some tight spaces and I think I may just run the 3.5" back and see if I can dump the wastegate else where to make up for the lack of diameter. Which is a shame because there is a perfect spot to do the dump back into the downpipe and keep everything neater.
What do you guys think?
I've got some tight spaces and I think I may just run the 3.5" back and see if I can dump the wastegate else where to make up for the lack of diameter. Which is a shame because there is a perfect spot to do the dump back into the downpipe and keep everything neater.
What do you guys think?
Drifting
Joined: Aug 2001
Posts: 1,500
Likes: 0
From: Holliston MA
Cruise-In VII Veteran
You won't see any advantage doing what you're saying. Optimally you want to have the pipe at the exit of the turbo larger than the turbo exit diameter. Think about what the exhaust gases are experiencing as they exit the turbo. That turbine wheel wants to throw the gas outward radially. After they're thrown outward then you can neck the pipe down as the exhaust cools and the spin slows, or if it's possible to make the pipe fit, run it the same diameter.
Thread Starter
Melting Slicks
Joined: Jan 2002
Posts: 3,293
Likes: 79
From: Jackson MI
I'm trying to figure out if it is worth trying to fit 4" instead of 3.5"
and
If I can't fit 4" would it be worth it to expand to 4" after I clear the engine bay.
In theory less back pressure is always better but I'm not sure if it would buy me anything. Especially at low boost levels when alot of exhaust is going out the wastegate.
and
If I can't fit 4" would it be worth it to expand to 4" after I clear the engine bay.
In theory less back pressure is always better but I'm not sure if it would buy me anything. Especially at low boost levels when alot of exhaust is going out the wastegate.
Thread Starter
Melting Slicks
Joined: Jan 2002
Posts: 3,293
Likes: 79
From: Jackson MI
I don't see how it would help having a foot or two of 4" then going down to 3.5" If I were flowing enough to need the 4" then it would be flowing through that section fast enough that there wouldn't be any loss of heat to make it go through the 3.5" any easier. I'd be better off staying with the 3.5"
Thread Starter
Melting Slicks
Joined: Jan 2002
Posts: 3,293
Likes: 79
From: Jackson MI
hmmmmmm, so you are saying that the air comming out of the turbo isn't going "strait" and uses the extra diameter to correct itself?
Interesting, but the problem of fitting the 4" tubing is still there. How much hp is the extra effort worth.
Interesting, but the problem of fitting the 4" tubing is still there. How much hp is the extra effort worth.
Drifting
Joined: Aug 2001
Posts: 1,500
Likes: 0
From: Holliston MA
Cruise-In VII Veteran
Now you're starting to "see".
It really comes down to if you're going to be maxing the turbo out or not. The down pipe is one of those little places you can see gains if you're at the limit already. If you keep at this long enough you're going to learn that the exhaust side of the turbo often has more affect in making HP than the compressor side.
People have made big power using just a 3.5" downpipe. I've made right around 900 fwhp with just a single 3.5" pipe and no expansion area.
It really comes down to if you're going to be maxing the turbo out or not. The down pipe is one of those little places you can see gains if you're at the limit already. If you keep at this long enough you're going to learn that the exhaust side of the turbo often has more affect in making HP than the compressor side.
People have made big power using just a 3.5" downpipe. I've made right around 900 fwhp with just a single 3.5" pipe and no expansion area.
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Thread Starter
Melting Slicks
Joined: Jan 2002
Posts: 3,293
Likes: 79
From: Jackson MI
Oh, trust me, I've seen what an exhaust side does. going from a .84 ar to a 1.15 ar makes a HUGE difference in the way the car runs and probably a good 150+ hp to go with it.
I've been calling around more and more and I've found a few places that sell 4" pipe with a 4" centerline radius. I think I can get that to fit in my tight space so hopefully I'll be able to make it adapt to the 3.5" vband clamp.
I've been calling around more and more and I've found a few places that sell 4" pipe with a 4" centerline radius. I think I can get that to fit in my tight space so hopefully I'll be able to make it adapt to the 3.5" vband clamp.
Thread Starter
Melting Slicks
Joined: Jan 2002
Posts: 3,293
Likes: 79
From: Jackson MI
I keep looking at the car and thinking, looks like I'm gonna get the 3.5" downpipe and take the 'easy' way out. The install is going to take me half the time if I don't have to deal with the 4", no grinding of the headers and cutting of the wheel well liners and the blower box. And the 3.5" will still get me 600+rwhp from looking at other setups out there.
I can always upgrade later if I really feel the need.
I can always upgrade later if I really feel the need.
Last edited by mn_vette; Nov 16, 2004 at 03:35 PM.
