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RB26 exhaust sizes - what diameter is optimal?

PSIKO

By PSIKO,
in Engines & Forced Induction

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Steve Grand Master

Steve

Posted
Posted

I might be able to help a bit, even if I only have an rb25

I started out fitting an N1 system, 80mm. Flowed very well, straight through design with minimal bends. Made good power but was LOUD as hell - headache material. I sound deadened the boot, not so bad inside the car

I next got an 80mm Nismo cat back. Also 90mm with a big center resonator. It had more bends than the N1, it killed power and ended up choking the top end above around 290rwkw - it also gave me around 1000rpm more lag and made the car more doughy. But it was quiet.

I tried a 90mm N1 with small resonator on the back - I am sure it actually amplified the exhaust note - it was incredibly bloody loud, so it got take off before I even took it for a test drive.

Lastly I fitted a HKS super dragger, which is 90mm, has less bends than the Nismo exhaust, but not as straight through as the N1. It has a nice burble at idle, sounds angry as hell when you nail it, but is still quiet enough that its not annoying to drive around in, and if you want to just limp around when there are plods nearby, it doesnt attract too much attention.

Bottom line is, you need to compromise. The quieter an exhaust is, the more back pressure, the less power, more lag, doughier off boost.

I dont think there is any harm in going larger rather than smaller, the HKS exhaust still has a few bends (more than the N1) but the 90mm pipe seems to make up somewhat for the bends. Just make sure you have a nice resonator on the back to give it a nice note.

Gav Mentor

Gav

Posted
Posted

HKS gear works for me - bolts up easily, isn't overly restrictive and not droney like some custom made systems I have heard.

On a GTR - you'll be amased at the difference front pipes and terb extensions make as well.

A "Jap-Spec" cat also make a notable improvement to flow and spoolup response. Mr Plod may not be impressed if he finds out, however.

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