T67 25g Dump Pipe Size

[Ke55pig]

So im going to redo my dump pipe on my 25 neo to neaten it up its curently a bitsa of stainless and mild.

Im going to redo it in stainless.

Is everyone running 3" or could i benefit from 3.5" ????

[iruvyouskyrine]

3" is fine if external gate

[Ke55pig]

Fine or best option ?

Want to do it ounce do it right.

Curently 350 at 17

[Dale FZ1]

If there is sufficient room to fit 3.5 inch, then run it.

Not much sense to that idea if you are running a 3 inch system though...

[GTSBoy]

Not much sense to that idea if you are running a 3 inch system though...

Yes there is. Biggest dump volume* is always better, regardless of whether the exhaust gets smaller afterwards.

*within reason of course. No one is talking about a 6" dump here.

[Ke55pig]

Well i have room for a 4" dump but i think that could be over kill.

My exhaust is only a 3" blitz nur spec type r.

So it will have a step wen it goes into that but if that's not a issue i will opt to go bigger then 3 to allow for future mods

[Ke55pig]

The difference in this dyno sheet is e85 and changing my exhaust from a straight through 3" with twin rear pipes to the nur spec type r so i do beleive that the sytem is restrictive most likely the rear cannon section

[WMDC35]

I'm using 3", hasn't been a restriction as yet but if I was going in there I'd go bigger

[Ke55pig]

Wmdc35 is that exhaust or dump ?

I dont beleive my dump is a restriction but i think 3.5 would be better but i do think my exhaust is a restriction.

I will drop the exhaust next time its on dyno see if i gain all that power up top somethings restricting that.

[scotty nm35]

How do you know if an exhaust is a restriction? Unless you can somehow drop the dump at the turbo flange... otherwise the dump might be the restriction.

Bigger and straighter it is the better usually. Larger diameter at the dump and dropping half an inch around where the cat usually sits seems to work well for me, with the least bending possible.

[r32-25t]

It's a Japanese exhuast, so they will have been nice enough to include a free restrictor in one of the mufflers

[Ke55pig]

Yea thats a good point i dont no if the exhaust is the restriction but as u can see on the dyno it dives across and masde the same it did on 98 up top makeing me think its the exhaust as thats what got change with the tune.

It only has a centre round hotdog muffler thing rear muffler/cannon seems to hold 3" through it.

So it is ok to have a stepp in the pipeing doesnt cause funny flow

[rx-line]

Did you say you went from one exhaust to another but also changed your fuel to E85?

[Ke55pig]

Correct

[Ke55pig]

Normsly e85 makes condistent 30 kw more over entire range as u can see here uptop it flattens out

[Ke55pig]

So i spoke to the guy who does my fab he would prefer to do it in 4" instead of 3.5 is there any downsides to this ??. And do i just let it step from 4 to 3 at exhaust or ramp it down vefore itbhits the exhaust. ????

[GTSBoy]

Never* step change any pipe, especially a reduction.

*if you care about flow

[Ke55pig]

Yea thats what i thought ill just do a reducer on end of the dump.

Im hoping that the full 4" dump will compensate for the restriction in the exhaust it self.