Stick With 3" Or Go 3.5"

[sweetr33]

Hey guys, ive recently sold my hi flow and bought a xtr 35/40 with .63r exhaust housing, i had a 3" full system on the hi flow but exhaust wheel is considerably larger with new turbo and am wondering the backpressure effects of retaining my 3" system over selling my old exhaust and making a 3.5" one for it.. I've noticed that most cars around with bigger hi mount turbo's run 3.5 inch systems. Not sure whether its just what they do or whether same results can be achieved with a 3 inch system. any info would be much appreciated...

[Abo Bob]

Mik runs his GTR with 360+rwkw and a 3" system. I run 270rwkw and 3".

That's not to say there are no gains to be made but I don't think it's a major impediment. How much power are you chasing.

[R31Nismoid]

3.5"

Bigger is always better

[Pauly33GTS-t]

go 3 inch because u dont want the car droning like a c**t.

[R31Nismoid]

Why would a 3.5" drone?

Any exhaust will drone if its not made correctly.

[sweetr33]

interesting, power isnt massive, anything over 400hp i'd be happy but ideally i want 450hp..

[Pauly33GTS-t]

3.5 inch would drone depending on how the bends are done and what metal is used.

[R31Nismoid]

Any exhaust can drone if poorly designed. I've heard 3" exhausts that would give you a headache in 5mins.

Makes NO difference

[mad082]

3.5 inch would drone depending on how the bends are done and what metal is used

my 3.5" on my skyline droned heaps less than the 3" i had on my 180sx. i had a x-force system and left the centre muffler in. but if you were worried about drone just get a good oval muffler for the rear.

as for which size is better, would it 3.5" from turbo back, or only cat back? if it is only from cat back then don't bother, as the front section will still be 3" and that's where the exhaust gas is the fastest. if you are going full turbo back then 3.5".

[djr81]

I have a 3.5 inch system on my car. Can't hear the thing over the tyre noise.

As for sizing it is important to remember that pressure drops of gas flow through pipes are strongly a function of the gas temperature. What does this mean? Well the MOST important bits to get right are the front bits. The least important bit is the exhaust tip...

[Beer Baron]

if you don't want drone dont use thing stainless piping. go for a nice thick piece of mild steel tubing. the sound is much nicer and you wont need great big mufflers to shut it up either (power robbing) as the thick wall mild steel dampens noise too.

[sweetr33]

the turbo has a dump pipe n front pipe already with it, think its about 2 n 3/4 or 3 inch. think i'll just leave it, drone isnt a concern. was more wondering whether retaiing 3" is going to disadvantage my desired power output. cheers

[mad082]

was more wondering whether retaiing 3" is going to disadvantage my desired power output. cheers

no, because you aren't changing the bits that do most of the restricting.

[gtst25]

It also depends on what turbo you're running. My HKS 2835 pros equipped gtst had drone problems from day one of fitting the new turbo. A lot of guys recommended the jasma approved hks hi power silent which is nicely made, stainless and big being well over 3 inches. A few people have said it's so quiet you can hear the tyres and the wind on the windscreen etc. Great. I purchased one and imported it from Japan and it lasted 5 minutes. Horribly droney over the drone zone of 2-3500 rpm. Literally fitted it, drove 100 metres, turned around and pulled it back off. Ridiculously loud.

Sold that and bought a trust pe2 which is ok but I think it might be a bit restrictive. It's 3 inch but I noticed in the centre muffler the tube diameter goes DOWN a wall thickness in size so not a genuine 3 inch exhaust. But the drone is now down to an nice level and it's making ok power 261rwkw on lowish boost 18psi tapering to 16 up the top.

If I did it again I'd look at making a twin exhaust probably 2.5'' with the biggest centre muffler you can fit and two shiny rear mufflers or resonators. The smaller pipe diameter would most likely lift the exhaust note and move the drone zone to a different range while offering excellent flow properties probably better than a 4 inch exhaust system. From my experiences of dropping exhausts turbo cars LOVE the highest flowing exhaust possible - I think there would be a noticable gain if going over 3'' as long as the mufflers flow well too.

Cheers

Edited April 4, 2007 by gtst25

[Marco-R34GTT]

no, because you aren't changing the bits that do most of the restricting.

Such as extractors? Cats? and Mufflers?

[sweetr33]

comes with hi mount manifold, dump/front pipe is one peice about to cat, then from there if i join it to old system will be 3 inch metal cat, pipe all the way to back end where a y piece with twin straight through cannons are. not sure of the restriction. again drone is not a concern for me as car isnt going to be driven everyday i have another car for that purpose..

[mad082]

If I did it again I'd look at making a twin exhaust probably 2.5'' with the biggest centre muffler you can fit and two shiny rear mufflers or resonators. The smaller pipe diameter would most likely lift the exhaust note and move the drone zone to a different range while offering excellent flow properties probably better than a 4 inch exhaust system. From my experiences of dropping exhausts turbo cars LOVE the highest flowing exhaust possible - I think there would be a noticable gain if going over 3'' as long as the mufflers flow well too.

i wouldn't use big centre mufflers. one of tha magazines did a test on a xr6t stock exhaust. they measured the restriction pressure before each muffler. they removed the centre muffler and did before and after dyno tests and gained 17kw, and it was still within the legal sound levels.

now i understand that the power gain may be not 100% accurate, but the back pressure dropped by about 1 bar i think.

Edited April 4, 2007 by mad082

[BOOSTD]

I have an R33 4 door with an RB26DETT which runs a standard GTR system and 244rwkw through an auto with a high stall

I also have a R33 GTR with a 3.5" exhaust that had a resonator that reduced to 2.3" inside and it made 380rwkw. I removed the resonator and it made no more power......

The main restriction is in the cat...the rest of the system doesn't have much effect at street power levels.....

[benm]

Yup it's the Cat + Mufflers that create the restriction + drone.

[RNS-11Z]

Ok, here are my findings.

A supra with a t88, had 3in zorst, up graded to 4in picked up 40rwhp with nothing else touched.

In regards to dronning, apart from poor exhaust design, your rear canon is major contributor. shit canon, small internals = loud and droning.

the larger the canon, more baffles inside canon, the quieter the car, the less droning. also a hot dog helps heaps when car has no other muffler/ resonator on it

h.