increasing the DP/MP size...is it worth it?
10-04-05, 09:27 AM
#26
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I always understood that going to a larger diameter exhaust piping would often have the effect of increasing top end horsepower and decreasing low end power/torque.
I would suspect that the bigger turbos that flow more air would be able to create more power with a larger diameter exhaust. Not sure if it would help or hinder with a smaller turbo.
I would suspect that the bigger turbos that flow more air would be able to create more power with a larger diameter exhaust. Not sure if it would help or hinder with a smaller turbo.
10-04-05, 09:44 AM
#27
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10-04-05, 09:56 AM
#28
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Originally Posted by SPOautos
Oh yea!!! Well I have a full 9" to the tip!!!
Oh wait...nevermind....wrong discussion
yea yea yea, I just had to
hahaha
Stephen
Oh wait...nevermind....wrong discussion
yea yea yea, I just had to
hahaha
Stephen
10-04-05, 06:05 PM
#29
Originally Posted by alberto_mg
I always understood that going to a larger diameter exhaust piping would often have the effect of increasing top end horsepower and decreasing low end power/torque.
I would suspect that the bigger turbos that flow more air would be able to create more power with a larger diameter exhaust. Not sure if it would help or hinder with a smaller turbo.
I would suspect that the bigger turbos that flow more air would be able to create more power with a larger diameter exhaust. Not sure if it would help or hinder with a smaller turbo.
But the idea is simple you want as little backpressure as possible on the turbine.
10-04-05, 07:45 PM
#31
I tried several exhaust sizes on the same engine and turbo set-up as I was battling boost creep.
On my S5 hybrid tubro with clipped "P" trim exhaust and 60-1 HiFi compressor and 60mm external WG I found the larger exhaust REALLY improved the very low rpm power as boost came on earlier but did not feel like it impacted power at all once the WG was open.
-First I had the JIC spec 90 which is a reverse velocity stack off the turbo to 80mm (~3") pipe for the 1st bend and then merged to 90mm (~3 1/2") for the remainder of the exhaust with one muffler at the end. All mandrel bends, 4 bolt flanges etc.
It started getting into boost before 1,500rpm, 2-3psi by 2,00rpm, 8psi by 2,500rpm and full 17psi by 3,500rpm. It has so much low end power I usually cruised at ~1,00rpm in 5th and could kick the rear out with power on oversteer in 25mph corners at this rpm. With the tip silencer in the low end power was about the same, but it killed the top end power.
-Then I put on the RB turbo back system. Cheated radius cut off the turbo to 80mm pipe, cheated radius cut to 80mm presilencer, cheated radius cut out of presilencer, split to 2 60mm pipes to 2 mufflers.
The low end suffered badly as I couldn't even drive under 1,500rpm now without it stuttering/bogging. Boost came on now ~2,000rpm and full 17psi boost ~4,00rpm. After 4,00rpm it felt the same as Spec 90.
I also ran the RB 2.5" downpipe and presilencer with the Spec 90 catback section once while I was working on the wastegate set-up. It REALLY killed the spool. As a matter of fact, even without ANY wastegate opening on the system at the time it couldn't achieve full 17psi boost! Though, interestingly it felt almost as strong psi boost per psi boost as the other systems in the top end.
On my S5 hybrid tubro with clipped "P" trim exhaust and 60-1 HiFi compressor and 60mm external WG I found the larger exhaust REALLY improved the very low rpm power as boost came on earlier but did not feel like it impacted power at all once the WG was open.
-First I had the JIC spec 90 which is a reverse velocity stack off the turbo to 80mm (~3") pipe for the 1st bend and then merged to 90mm (~3 1/2") for the remainder of the exhaust with one muffler at the end. All mandrel bends, 4 bolt flanges etc.
It started getting into boost before 1,500rpm, 2-3psi by 2,00rpm, 8psi by 2,500rpm and full 17psi by 3,500rpm. It has so much low end power I usually cruised at ~1,00rpm in 5th and could kick the rear out with power on oversteer in 25mph corners at this rpm. With the tip silencer in the low end power was about the same, but it killed the top end power.
-Then I put on the RB turbo back system. Cheated radius cut off the turbo to 80mm pipe, cheated radius cut to 80mm presilencer, cheated radius cut out of presilencer, split to 2 60mm pipes to 2 mufflers.
The low end suffered badly as I couldn't even drive under 1,500rpm now without it stuttering/bogging. Boost came on now ~2,000rpm and full 17psi boost ~4,00rpm. After 4,00rpm it felt the same as Spec 90.
I also ran the RB 2.5" downpipe and presilencer with the Spec 90 catback section once while I was working on the wastegate set-up. It REALLY killed the spool. As a matter of fact, even without ANY wastegate opening on the system at the time it couldn't achieve full 17psi boost! Though, interestingly it felt almost as strong psi boost per psi boost as the other systems in the top end.
10-06-05, 02:14 PM
#34
Stupid question.Is there any advantage to be had running a larger DP tapered down to the rest of the exhaust? i.e. 3.5inch DP tappering to 3inch exhaust.cheers
Last edited by The Griffin; 10-06-05 at 02:20 PM.
10-06-05, 02:28 PM
#35
Stupid question.Is there any advantage to be had running a larger DP tapered down to the rest of the exhaust? i.e. 3.5inch DP tappering to 3inch exhaust.cheers
Yes, but that is a good question!
The exta volume of the downpipe will reduce backpressure during the critical spool up time.
Be careful to make the reduction from DP size to rest of system smooth as too fast a transition can cause turbulence that will further reduce the working diameter of the pipe at the reduction.
My 3.5" turbo back with the muffler tip silencer in place restricting the outlet to ~2" with a design to create a reversion at the end still spooled MUCH better than RB 3" turbo back.
The further back the restriction the better.
Yes, but that is a good question!
The exta volume of the downpipe will reduce backpressure during the critical spool up time.
Be careful to make the reduction from DP size to rest of system smooth as too fast a transition can cause turbulence that will further reduce the working diameter of the pipe at the reduction.
My 3.5" turbo back with the muffler tip silencer in place restricting the outlet to ~2" with a design to create a reversion at the end still spooled MUCH better than RB 3" turbo back.
The further back the restriction the better.
10-06-05, 08:28 PM
#37
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Originally Posted by Zero R
Ha! Mine isn't straiiiiiiight back but it is ok.
10-06-05, 08:35 PM
#38
I was going to run two, one in the middle as a presilencer then another one in the rear. We'll see how it goes. Those pics are a little misleading, one it looks much bigger in person, and two it actually sits higher up than that. There was no hangers yet in those pics other than on the muffler itself.
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