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Discussion Starter #1
Ive been trying to research online but can't really find much. Is there a specific formula or anything I should be considering when deciding what size DP to run? Obviously every car is different, but it seems like most people just run a certain size and end up changing it down the road and seeing how the car responds. My build is a built 2v 4.6, 10:1, TF 38 cc heads with MHS stage 3 turbo cams, edelbrock manifold, and E85. Planning on the turbo setup to consis of a PTE 7675 CEA and CG Fab hot side. The hot side comes standard with a 3" DP, and I will most likely just run open DP. Does anybody have any thoughts if the 3" would be good enough or should I look to be going bigger? Goals for the car are 800+ through an auto.
 

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IMO, For "only" 800hp with your combo I don't think it's going to matter a whole lot whether you go 3" or 4" if you're running open DP. A bunch of people making well over that with a 3" so I would run whatever fits. Where do you plan on dumping the exhaust?

ks
 

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Discussion Starter #3
IMO, For "only" 800hp with your combo I don't think it's going to matter a whole lot whether you go 3" or 4" if you're running open DP. A bunch of people making well over that with a 3" so I would run whatever fits. Where do you plan on dumping the exhaust?

ks
I will either dump it right at the turbo or run it out the front bumper
 

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Watch local rules if you want to race heads up. Around here they ban front exits and sometimes require exhaust to the back axle or behind driver.
 

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Discussion Starter #5
Watch local rules if you want to race heads up. Around here they ban front exits and sometimes require exhaust to the back axle or behind driver.
Thanks for the heads up, this will 99% be a street car though so I'm not too concerned about race requirements. Appreciate the looking out though.
 

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Discussion Starter #6
Since the CEA 7675 has a 3" outlet, would there be any benefit to going with a 3.5" or 4", or would it be most efficient to stick with the 3" to match the outlet?
 

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I don't think I've ever heard of anyone losing power from a too large of DP since it's not being used to scavenge the exhaust. I would think that the larger one would help by eliminating any potential back pressure.

ks
 

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I had horrible back pressure issues with 3 inch down pipe. I had to buy a boost controller that could handle duty cycle to keep the boost from tailing off. Went to 4" off the turbo and all my problems went away.

This is my current setup. I am running custom Lunati turbo cams... 225/229 at .050, .494/.496 Lift, Cut 115 LSA With A 105 ICL

Cold Side With Mishimoto R Line Intercooler, Garrett GT4094R Ball Bearing Turbo 1.06 A/R With Tial "Q" BOV & Dual F35 Wastegates, Swaintech Coating On Hotside Piping & Turbo Hotside Housing,

707 HP on 13 psi.

Good luck with your build.
 

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Discussion Starter #9
I had horrible back pressure issues with 3 inch down pipe. I had to buy a boost controller that could handle duty cycle to keep the boost from tailing off. Went to 4" off the turbo and all my problems went away.

This is my current setup. I am running custom Lunati turbo cams... 225/229 at .050, .494/.496 Lift, Cut 115 LSA With A 105 ICL

Cold Side With Mishimoto R Line Intercooler, Garrett GT4094R Ball Bearing Turbo 1.06 A/R With Tial "Q" BOV & Dual F35 Wastegates, Swaintech Coating On Hotside Piping & Turbo Hotside Housing,

707 HP on 13 psi.

Good luck with your build.
Thanks for the info man. I'm getting complete different answers as to which size to go with, but at the end of the day it's not a difficult swap or expensive change so if its something I have to play around with it's not the end of the world. Just would have liked to address the correct parts up front. If the outlet of the turbo is 3", how would say a 4" provide any different benefit than a 3"?
 

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Thanks for the info man. I'm getting complete different answers as to which size to go with, but at the end of the day it's not a difficult swap or expensive change so if its something I have to play around with it's not the end of the world. Just would have liked to address the correct parts up front. If the outlet of the turbo is 3", how would say a 4" provide any different benefit than a 3"?
It is the power of Pi! The outlet on my Garret is 3". The area of 3" is 7.069. The area of 4" is 12.556, almost 44% increase.

CPRsm uses a initial 5" down pipe on their coyote kits that run in the 1,000 HP range. That make ridiculous power at low boost and going big on downpipe is one of the keys.

I tried running 3" to just the oil pan area and dumping and I still had issues.

Pic of my 3" bell to 4" downpipe.

 

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Discussion Starter #11
It is the power of Pi! The outlet on my Garret is 3". The area of 3" is 7.069. The area of 4" is 12.556, almost 44% increase.

CPRsm uses a initial 5" down pipe on their coyote kits that run in the 1,000 HP range. That make ridiculous power at low boost and going big on downpipe is one of the keys.

I tried running 3" to just the oil pan area and dumping and I still had issues.

Pic of my 3" bell to 4" downpipe.

Good stuff. Thanks again for the info and picture. I think for what my goals are it will probably make most sense to start with a 4" and see how the car responds in the beginning. If I ever need to step down to a 3", which I've never heard of anybody going smaller on a DP, than I can change that no problem.
 

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Discussion Starter #12
About to pull the trigger on the hot side. So if I did go with the 4" DP, how exactly will I get this to work with the 3" outlet of the turbo?
 

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