R32 GTR Nismo Front Pipe match for Dump Pipes

[I BMC I]

Hey all,

I'm a long time forum reader, but have only just signed up.😬

I have a simple question and hopefully one or some of you can assist.

I don't believe I found a definitive answer by searching, possibly as its not a common question or even possible.

Question:

I have a Nismo Front pipe, I believe the inlet is twin 2.5inch pipes into 3inch outlet.

I am presently removing factory twins to replace with -9/GTSS twins.

Naturally, this has made me consider upgrading/replacing the R32 GTR dumps.

I appreciate it's debatable if it's worth doing from a performance vs cost perspective when sitting around 300kw mark, but I thought I should explore anyway for due diligence.

Seeing as my front pipe is 2.5 inlets, what dump pipes would be suitable?

They all appear larger than 2.5inch, does this create an issue when bolting together or do I simply end up with an internal step down (lip)?

The closes match is the HKS ones, but from what I understand these are not recommended due to design/performance constraints.

In a perfect world, I would opt for a HPI dump or Tomei, but hence my question I am not sure if it's possible with a 2.5 inlet front pipe.

With all things considered, it makes me think to not bother with any, as I'm not interested in replacing my Nismo front pipe to accommodate dump pipes.

Perhaps factory dumps are the best for my intended purpose/power level of 300kw - 320kw?

On a side note if anyone has some 34 dump pipes, please can you kindly message me? 🙏 

Thanks in advance.

[Duncan]

It's been a really long time since I've looked at the standard dumps, and you didn't mention a measurement for them, but from memory they are very small and probably one of those deliberately easy to fix restrictions that the car came with to keep it to "206kw". I remember the R34 ones were better but don't have their measurement handy either

I'd change them out for sure, the HPI ones are good price/performance and give a 76mm outlet, which I can see is larger than your 63mm front pipes but I don't see that causing a problem, the front pipes will just be the restriction.

[I BMC I]

Thanks for reply Duncan, really appreciate it. 

I believe the 32's are 54mm. The 34's are possibly 60mm from what I have read. But, don't quote me on that one.

Thank you also for confirming re dumps into front pipe as far as sizing is concerned.