I’m doing an sr swap and I have a buddy that has a 4" exhuast for sale for my s13.
I was just wandering if anyone is running one, is too big, can a 3’ downpipe be attached to it?
thanks.
GT Greg was running a 4", ask him
GT’s exhaust was amazing.
Its actually for sale right now.
This exhaust actually has a converter, converts from 3" dp to 4" exhaust. Exactly what you are looking for.
they are really lowed with out silencers!
yup its for sale.
buy my shit.
its dirt cheap
GT
I’m currently running one right now N/A bahh ha ha…
People thought it was loud with my turbo, ooeee!
4" is a bit overkill if it’s any of the nissan t25/t28 series of turbos.
If you have a bigger turbo, it might be good. I think greg had a hks gt28rs or something?
4" is the way to go if you can afford it, Brand new those exhausts are over a grand…
That they do indeed fcuk…
Well woth the investment. 
Just so everyone konws and to make this clear to all (I have had this argumet with many machanics) When you have a turbo car There is no such thing as an exhaust piping being to big. With turbo cars you don’t need any back pressuer even for your low end.
YOU: But Justin thats not ture!
ME: The back pressure is built up between the cylinder head exhaust ports though the manifold to the turbine!!!
IF you run with no exhaust you will make the most power but will also probably start a fire. (900C coming out is damb hot)
So everyone just rember that and when you go to a shop for a 3" or bigger exhaust and they say thats to big. They don’t know what they are talking about and probably only like raw muscle cars (there is nothing wrong with that)
Just though I would shair.
i support every word he said
Er, you’re going to sacrifice power with lack of back pressure and loss of
heat due to large pipes.
From what I gather…
For mild setups (250-300rwh) you want at least 3" to 3.5".
Anything more then that go to 4" (or something).
A few reads:
http://webhome.idirect.com/~trini/car/muffler.html
http://www.nsxprime.com/FAQ/Miscellaneous/exhausttheory.htm
http://home.att.net/~jroal/perftheory.htm#Exhaust
Someone learn me on this if I’m mistaken…
heh… well, what if it physically can’t fit 4" 
on my frist project car (turbo colt) 3" was the absolute max (and I still have issues) because of how the rear suspension is setup. there is no way 4" would fit. unless I removed half the supports in the rear.
and I’m jumping on the “no exhaust is a good exhaust” boat for turbo cars. what gets the turbine spinning is the difference in pressure between the two sides of the turbine. eliminating pressure on the outlet side would allow it to spin more freely ie boost faster and harder.
but then again when you get into the whole exhaust pulsing business things may be different.
and Gonad… isn’t loss of heat desirable? to an extend obviously, you don’t want the thing running chilled but at the same time you don’t want it running at 900C.
If 4" won’t fit out the back I know what I would do. Gangster side exit, honestly if your running enough power that you want 4" do dual side exit and watch as people cower when your toss flames out of it lol.
Your exhaust temperature isn’t going to be 900C from tip to tip. It’s
obviously going to cool down. So yes, there is some level of heat you
want to retain throughout the stream.
The benefit of hot air vs cold air is less resistance. Low resistance
means the velocities remain high. You start cooling things down and you
will lose that velocity, and thus preventing the gases from escaping fast enough.
I suck at science/physics but this is what I gather from reading so far.
Pipe Sizing
We’ve seen quiet a few “experienced” racers tell people that a bigger exhaust is a better exhaust. Hahaha… NOT.
As discussed earlier, exhaust gas is hot. And we’d like to keep it hot throughout the exhaust system. Why? The answer is simple. Cold air is dense air, and dense air is heavy air. We don’t want our engine to be pushing a heavy mass of exhaust gas out of the tailpipe. An extremely large exhaust pipe will cause a slow exhaust flow, which will in turn give the gas plenty of time to cool off en route. Overlarge piping will also allow our exhaust pulses to achieve a higher level of entropy, which will take all of our header tuning and throw it out the window, as pulses will not have the same tendency to line up as they would in a smaller pipe. Coating the entire exhaust system with an insulative material, such as header wrap or a ceramic thermal barrier coating reduces this effect somewhat, but unless you have lots of cash burning a hole in your pocket, is probably not worth the expense on a street driven car.
I beleve he is talking about a NA engine. Trust me go to a dino and you will see. As for pressure on the back side of the turbo (that would slow it down) the manifold is spining it up and then its going out. think of spining a wheel on a car in the air. Now add resistance? its just like adding back pressure to an exhaust.
As for the heat leaving the exhaust and keeping the exhaust that might be right but shorten it or take it away and you don’t have that problem any more.
I dont konw I stick by my staitment 100%
but jjm_240sx… with what you just said… you’re agreeing that no exhaust is the best exhaust. (no exhaust and big exhaust are different now)
you’re complaining about the cooling down process and entropy and all that… but if there was no exhaust at all then the gases would never get a a chance to cool down in the system would it?
the same reason no exhaust is the best exhaust is the same reason why jet planes don’t have 50" tail pipes hanging out the rear.
although I will agree that given engine size, turbo size, etc, etc, there is an ideal exhaust system (if one is required). to small and it’s can’t flow properly… to big the gases will end up banging into each other and slow things down (like you were saying).
damnit… someone needs to just get on a dyno and shut us all up heh. or write to SCC haha.
Jet engines work ‘slightly’ different than car engines. :?
heh, yeah, but a jet is basically a really, really fancy turbo.
it’s even possible to power a vehicle with a regular automotive turbo (it’s been done) check this out http://www.badbros.net/jetbike.html
took a turbo off a big truck and now it powers a small bike. pretty cool hack.