Full Exhaust Overhall.

[Nee-san]

To the men of fire and steel of SAU.

The picture above shows my HKS front pipe for my R32 GTR

The two turbo pipes measure in at ~ 70+ MM each whilst the merged part measures in at ~80+ MM.

Now here is my problem.

I will have a set of HKS split dumps to go off the back of my 2860-5's to dump into this pipe, after this however I plan on running a "venom" 500 series cat (3" inlet and outlet and 5" body")

Link here: http://www.venomexhaustworks.com.au/products.html

This will meet up with my HKS exhaust which is roughly the same size upto a medium sized muffler which then goes to a 4" pipe, terminating at a HKS cannon.

Now my goal is to hit 400AWKW and anything over being a bonus, will this system give me what I want in terms of making the most of the turbos (as I will need to for this sort of power)

I have my concerns obviously, hence I"m putting the question out there.

Yes I know the general rule of around 1" for every 100KW after say 2.5"

I'm looking for literature, peoples experiences first hand etc.

Cheers,

Mitch.

Edited March 28, 2011 by Nee-san

[SiR_RB]

i think that 3" cat would be too small, especialy since the front pipe merge to 80mm, you dont want that getting squeezed down to 76mm at the cat

i would go 4" cat and either full 3.5" or 4" cat back

[R31Nismoid]

needs to merge much more than 3.1 inches (80mm).

you'll need a new front pipe setup made.

also as stated, 4inch inlet/flange on the cat to suit the 4 inch exhaust.

[Beer Baron]

The short 80mm pipe after the twin 70mm front pipes is a bit of a problem, but not too bad as by that point gas has already expanded a lot and velocity is lower anyway, still if you really want every bit then cut off the 80mm pipe, replace it with a 90mm+ pipe ending with a 4inch Vband flange. get a BIG cat with 4inch in/out and put Vband flanges at each end, then run 4 inch cat back exhaust (3.5inch will be ok too in a pinch).

other option, is cut off the 80mm bit and run twin 70mm system the whole way.

personally I'd replace the HKS dumps too. they are pretty small. a set of tomeis are much bigger and allowing the gas to expand as quickly as possible is the aim of the game. you are asking for 400kw from what is on average a 350kw set-up. you really need a decent exhaust to make that happen.

[Nee-san]

This is cementing pretty much what I had thought myself, thanks guys

Is there anywhere I can buy an off the shelf front pipe of the required size, say 3" merged into 4" then 4" the rest of the way back ?

Failing that I will get my workshop to make me up an exhaust and sell the one I have, it's sad because this is a pretty nice sounding setup I have and already makes 330kw

PS

Beer Baron,

I have been eyeing off the Midori dumps for ages so I guess this is an excuse right ?

[Nee-san]

any of the big horsepower twin turbo guys got anything to add

?

[XRATED]

I made 400rwkw with trust dumps and down pipe, 3.5" exhaust and a (now found out) restrictive 3.5" rear muffler.

If I stay with low mounts, my next exhaust will be, trust dumps- custom 3.5" down pipes- twin 4" cats (on v bands)- custom burns stainless 2x 3.5" inlet, 4" outlet center muffler- burns stainless 4" inlet custom rear cannon.

X2 HKS dumps probably should go.

Good luck.

J.

[BoostdR]

I currently have 2x3" into 3.5" Makes 455awkw. I put twin 3" side pipes on and it makes another 80kw

If you can pick up a Apexi N1 dual, it would be a simple mod to run twin 70mm.

having sais that a single 4" has about 10% more flow over twin 70mm

pie x Radius , squared = area of a circle(pipe)

[Beer Baron]

yep, just goes to show how much power there can be if the exhaust is a restriction.

I don't know of any off the shelf front pipes bigger than the current model HKS drag front pipes. they are twin 70mm (or 75mm i forget) into single which is at least 80mm (could be bigger). it's the biggest I've found. most are twin 60mm or sometimes they quote 70 but when you measure them that's 70 OD not ID.

the best off the shelf cat back exhaust on the planet for a GTR is the trust power evolution which is 94mm and comes will all V-band flanges (except to connect to the front pipe which is normal 2 bolt flange), comes with a 'fake cat' which is actually a big resonator, with the 2 bolt flange on one side (to meet normal front pipes) and a v-band on the other (to meet the cat-back). it's all straight pipe and just has one rear cannon which is HUGE and is 4 inch (well 3.75 really) all the way through it. no restriction at all in that set-up and perfect for big power.

sadly trust will only make them in batches so need to order 10 or 20 units or some such. and are special order. I don't think they've made any for about 5 years or so. I still have one brand new in it's box, but i'm saving it for a rainy day. it's a nice piece of gear.

[paulR32gtr]

I have grabbed some Midori 76mm dumps + 90mm Midori front pipes being the biggest I could find.

Dumps are really nice, much like the older Tomei ones but a bit bigger I think, designed to mate up with the front pipes without any reduction.

Only thing that surprised me is the front pipe for the rear turbo tapers down slightly after the join with the dump - see pics. Not sure if this is by design due to them actually analysing the gas flow, or to make it easier for them to merge at the collector.

[BoostdR]

Will be for clearance. The gab in between is needed to actually get to the inner nuts, plus the chassis rail contains the outright size of the outer pipe.

[paulR32gtr]

Yeah cool was thinking that might be the other reason. Won't be an issue at my power level anyway.

[Nee-san]

Ok at this point my system is going to look like this:

Midori 3" dumps

Midori Front Pipes OR Custom front pipes, can they be made any bigger then 3" ? if so 3.5" to a 4" merge

Following this, into a 4" inlet 5" body cat.

then straight pipe to a rear 4" muffler at the end ?

peoples thoughts ?

Is getting twin 3 inch system all the way to the back worthwhile ?

It seems it could be taking BOOSTDR's experiences into consideration.

the Full N1 mega twin system is a possibly Hmmm, hard choices.

[R31Nismoid]

You dont need bigger than 3" (76mm) front pipes dude. Even 2.75" (70mm) is ok if it's going into 4".

The bigger you go the more drone/noise you have to counter muffler wise. Not a problem if you don't care but 3" front pipes is more than enough. 3.5" is going too far i reckon for front pipe size.

[KING87]

Don't forget about pentroof pretty sure they do a twin 76mm into a 90mm.

Nice looking bit of kit.

Kakimoto twins would be unreal also but very loud i would assume.

[BoostdR]

some twin 3 to 4" here for $50

Ebay link

[Nee-san]

Hahaha, thanks mate, but thats me that bid on that yesterday LOL !

[R31Nismoid]

The trust/greddy was not 3" into 4"

I had them myself, its 3-3.25" with 70mm front. I had my trust ones modified to be a full 3.5" merge back in the day.

I'd be asking to see measurements mate to back up sellers claims as they aint like that factory

[Nee-san]

Hmmm,

thanks Ash, I will definitely get onto him as I didn't think there were any off the shelf 3" into 4".

Cheers guys.

[Beer Baron]

yeah of all the main off the shelf front pipes the 'new' HKS ones (easily picked as flanges are welded to the pipes on the inside of the flange, not around the outside like normal) are the biggest. most others (trust included) are between 60 and 70mm twin pipe into 70 or 80mm single.

twin 3 inch system is a good idea. it flows about the same as a single 4 inch, but does't hang as low to the ground as single 4 inch. it is also possible to make it a bit quieter than a single 4, though both can be quiet with the right mufflers. the downside is it'll be heavier.