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Discussion Starter · #1 ·
I am looking into a new exhaust at the moment. However, what are the maxinium horse power a certain bore of an exhaust can take on a GTR.

For ease, lets use a single turbo with a 85mm (HKS) downpipe/collector.

Exhaust option:
A) 80mm exhaust with middle silencer
B) 80mm exhaust with no middle silencer (straight pipe)
C) 90mm exhaust with middle silencer
D) 90mm exhaust with no middle silencer

The question is, say for a car of this spec to put out 600bhp, what would be needed in order to flow 600bhp? Can you get away with a smaller pipe if no middle silencer is used? How much "backpressure" does a middle silencer add?
 

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Nocturnal,

I have an RB28 with a T04Z. The HKS downpipe is 76mm and the wastegate joins back into the downpipe. I then have an 80mm decat and did have an HKS Kansai pipe that went from 80mm to 90mm half way along.

On the Dyno it wouldn't allow any more than 600bhp. Changing to an HKS Ti muffler 102mm it jumped 30bhp instantly without any other changes. With a few more changes its now running more power that was unavailable with the other system.

Going to 100mm means the system is a fair bit louder!

Therefore an 80 going into 90mm will allow 600bhp. I don't know if an 80mm all the way would. The Kansai system has a centre silencer with an 80mm pipe going in and 90mm coming out.

Rgds
Nito
 

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Discussion Starter · #3 ·
Thanks for the Info NITO.

Just wondering, since the HKS 102mm Ti exhaust goes from a 85mm flange and then into a 102mm pipework, that mean it still start at 85mm. Well, the the downpipe is only 75mm anyways.

Here is an idea for thought. What if you split the pipe work right after the decat simillar to what Nismo/Kakimoto does and run it into 2 muffler? Of couse, Nismo and Kakimoto is made for twin turbo set up so they don't have to split it, they just take it from each turbo.

But the Idea is if we do the following for a single turbo setup:

75mm downpipe --> 80mm Decat --> 2x 75mm pipe work --> 2x 75mm inlet Exhaust Muffler

I wonder how would that do? Would that flow as much as a 100mm pipe work? Anyone who know something about gas flow physic that can help out here please. :thumbsup:
 
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