A question came up about what size turbo would take a 4" v band style down pipe off the turbo? My car will need a custom made DP and wondering were 4" over 3.5" is to much? I dont think the size matters alot as most the resriction is at the wheel but dont want the extra noise either. Can you put a 4" on a 70MM or is that still to small? By the way I'm talking nonstage heads but flowed Alum. heads.
4" down pipe
- Thread starter chevyII
- Start date
forcefedhatch
Alkyholic
- Joined
- Aug 18, 2004
It's not going to hurt anything going to 4" over 3.5", but you wouldn't gain much unless you're pushing 700+ RWHP.
The guys over on www.supraforums.com have tried 3", 3.5" and then 4" downpipes on a dyno, on the same car. With each size, they gained substantial horsepower. The car was over 600 HP though.
You can never go too big on the downpipe.
Dusty Bradford
Well-Known Member
- Joined
- May 24, 2001
I'm with Louie. Anything over a 3.5 is for looks only. I've been 8.30's @168mph at 3650# with a 4" down pipe. It's way overkill on a 9 second car.
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I have a 5 inch, and I had it made completely for looks and personal preference
but I will add as my new motor was being put in by Brian, I heard him cursing me out from Conn to Long Island. He hated it, the hole size for the reducer was hardly open, it didn't fit back in correctly so had to fabricate the Flange, not sure if that's correct. If anyone wants to see it he has it posted on Facebook.
but I will add as my new motor was being put in by Brian, I heard him cursing me out from Conn to Long Island. He hated it, the hole size for the reducer was hardly open, it didn't fit back in correctly so had to fabricate the Flange, not sure if that's correct. If anyone wants to see it he has it posted on Facebook.
- Joined
- May 26, 2001
There are 2 common ways to reduce flow restriction in a downpipe, or any pipe, and one is to increase the diameter and the other is to minimize bends.
I chose to eliminate the very restrictive 90 deg. bend right at the turbo exhaust. Since the exhaust gas cools very quickly in the DP and needs less volume as it exits the larger diameter that adds very little to restricting the exhaust flow.
Since I was wanting new headers, the turbo orientation was turned 90 degrees which eliminated the restrictive exhaust bend and also allowed fresh air in directly with only a gentle bend there as well, and also provided a direct outside inlet air flow with a ram air affect!
Here is before and after:
I chose to eliminate the very restrictive 90 deg. bend right at the turbo exhaust. Since the exhaust gas cools very quickly in the DP and needs less volume as it exits the larger diameter that adds very little to restricting the exhaust flow.
Since I was wanting new headers, the turbo orientation was turned 90 degrees which eliminated the restrictive exhaust bend and also allowed fresh air in directly with only a gentle bend there as well, and also provided a direct outside inlet air flow with a ram air affect!
Here is before and after:
Nick,
Could also replace a 90 deg bend with 45 deg bend if started bend shortly after the turbo. Yes, you are correct in that elbows do tend to add up to unwanted resistance to flow. Could eliminate the bends over the rear axle and pick up some flow as well. Other than cost, I just don't see a downside to a bigger downpipe if you have the room. The less resistance on the downstream side opens up additional capacity on the upstream side! Having said all that, since when did any of us on this board do what makes sense $-wise? I still like a challenge and I'm spending my kids inheritance!
Conrad
Could also replace a 90 deg bend with 45 deg bend if started bend shortly after the turbo. Yes, you are correct in that elbows do tend to add up to unwanted resistance to flow. Could eliminate the bends over the rear axle and pick up some flow as well. Other than cost, I just don't see a downside to a bigger downpipe if you have the room. The less resistance on the downstream side opens up additional capacity on the upstream side! Having said all that, since when did any of us on this board do what makes sense $-wise? I still like a challenge and I'm spending my kids inheritance!
Conrad
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