Gt3076R Antics , Better Late Than Never .

[Dose Pipe Sutututu]

because 3.5" is more cool.. not to mention for bragging rights

[34GeeTeeTee]

because 3.5" is more cool.. not to mention for bragging rights

Clearly compensating

[skylinecouple]

I guess it's like taking Viagra, the job will still get done, it just makes it easier and as above, bragging rights. You can really get up it.........you know, on the dyno.

[discopotato03]

Well we should put the Viagra eye drops in and take a good long look at this ...

Seriously though Ford changed the game a bit with their XR6Ts because they turbocharged a biggish straight 6 with a Garrett GT BB turbo .

Compared to a base line GTS25T the XR6T is approximately 23% heavier with 60% more capacity , using 1385 Kg vs 1700 Kg .

From memory a Typhoon makes over 300 std where the GTS25T made a little under 200 std so ~ 50% .

The tell all would be to fit a GT3076R to a GTS25T with the XR6Ts exhaust cut up and rejigged under the Skyline and screw the boost up .

Anyhow people are making the numbers (300+ WWasps) with 3" exhausts so it obviously works , I assume that's what Micko used for his 330 odd Kw car ?

The reason I mentioned 3 1/2" is because that's what my dump and front pipe is and ATM it has a 3" bore cat bolted to it (same flange profile) , not a great situation .

It makes sense to use a better cat than a guesses 3" bore 3-400 cpi ceramic one and if a 5" body Venom 200 cell one with a 3 1/2" inlet goes bolt it's all good .

The question then is do I use the tapered cat outlet to reduce to 3" or keep the larger tube size back to the first or possibly second muffler . The big question is drone and noise and I can live without both as much as possible .

I should state my aims which are to give the engine the best volumetric efficiency I can because the theory is that it works as better air pump on and off boost .

Now people like Corky said that the best turbo exhaust is no exhaust because the greater pressure drop across the turbine makes it easier to spin up .

My previous experience with the ancient Subaru EA82T engine was that a 3" front into a 2 1/2" exhaust behind the cat worked well for a guesses 150 max Hp and it wasn't noisy . To put you in the picture we made up an almost equal length header for it and plumbed a dinky GT2554R into it which was if anything a little big . A exhaust of that size you'd think was way too big for a 1800cc four with ONE exhaust port per head/pair of cylinders . Horrible heads with small ports and the siamesed exhaust ones . One engine pipe off each trying to feed the smallest available GT BB turbo , 0.64 AR T hsg because I didn't know a weird 0.56 one existed till too late .

Stone age engine aside an exhaust that by rights should never have worked did - and wasn't noisy .

Any way my RB build has included OS exhaust valves and 256 Tomeis mainly to get the exhaust and heat out of this thing quickly and easily , this is effectively what later engines do because they run so lean and hot that if they don't reject the heat efficiently they cook - literally .

For me this 0.82 GT30 is boarder line a tad big so I need the most part throttle power (torque) I can get in pre boost mode to narrow the gap from NA to forced states . If the engine works better before boost and the turbo can be coaxed to spin up a tad earlier then it's a win I reckon . Of course least exhaust restriction is where power is to be made with the boot in and turbo up to speed .

I think these days that the "tuned" nature of an exhaust behind a turbo is less important than an NA engine is behind its exhaust manifold because of how the manifold and housing is designed to feed a rotary turbine . It's hard to imagine exhaust gas reversion back up the exhaust through the turbine housing and manifold unless they are really huge and or the engine has really big cams . If anything having a small turbine/housing/exhaust off it - is probably worse in every way except heating up the cat for emissions .

Anyway there obviously comes a time when the exhaust gets that big that there is minimal "backpressure" and going bigger doesn't achieve very much .

Realistically tapering down behind the cat is probably way to go because there is probably enough volume in the larger front pipe and hopefully free flowing exhaust to get enough pressure drop across the turbine to wake the turbo up and make adequate street power . The 5" body 200 cel Venom cat is a good compromise IMO (flow/smell) and if it acts as a 3 1/2 to 3" reducer at the same time it's an easy bolt in .

A .

[AngryRB]

Mine has a 3 1/2inch system with one 3inch Xforce oval muffler on the back, doesn't drone just sound like its breathing alot, have a dyno clip if interested.

Edited March 15, 2014 by AngryRB

[Mick_o]

Thats correct disco my car had a 3" exhaust and was also very quiet and drone free

[KiwiRS4T]

My system is 3in all the way with a resonator in the middle and a cannon on the back - no drone. My 100 cell 5in Venom is welded in to the front pipe. You can cut the cat to achieve 3 1/2 in size and go 3and 1/2 in all the way to future proof the system (although 3in will do for your current goals).

[Dale FZ1]

Put 3.5" tails on the cat and neck down after that.

Again, the experiences with 3" full systems count for something but you have options of going up a size for when you're ready to be bait for excess noise.

[wolverine]

^^yeah what Dale says

No smell with my 100cell cat so that is a non issue.

[discopotato03]

Ok so what combinations of oval mufflers are we using in 3" systems , bigger can area better IMO so do any off the shelf use all the available space ? The quieter the better .

Also I'm keen to lose the 5 inch or whatever Jap rear outlet for a 3 inch one .

A.

[KiwiRS4T]

In general the oval mufflers will be quieter than the cylindrical ones but check the interiors - a lot of big brand name Japanese mufflers I looked actually reduced to 2 1/2 in at some point although they had 3in inlet and 4in outlets.

[discopotato03]

Magnaflow are doing 5x11x22" ovals in 76mm , would these fit an R33 mid and rear or too long ? Mine has a lock bar rather than rack at the back if that makes any difference space wise .

Cheers A .

[GTScotT]

Disco make sure your flanges do not have different ID's. I note you said the dump tube was 3.5" to the cat but you did not mention if it reduced down before the flange or if you have a 3.5" flange bolted to a 3" flange.

I have a 80mm dump into a 76mm cat which bottlenecked power badly.

[discopotato03]

So much reading on exhausts . I searched to see if the Japs did anything and all I came up with was Kakimotos that looked good but had a few surprises inside . A cannon is out , hate the look , but why do they try to rip everyone . At one stage I bought a second hand Evo 6 HKS Silent something and it's plain to see they think everyone wants the BIG look . They start out with something like 63-70mm from the cat to the mid muffler/hot dog then step up again from there to the rear muffler/cannon in 80mm . The rear muffler has conical entry and exits in its perforated tube so nothing like 80 anyway . The outlet is something you'd nearly get your head in , the big one ...

If you have to change exhaust diameter it makes sense to start out large and end up smaller IMO , some hope of the gas cooling and shrinking and maintaining velocity through the mufflers - in theory . I see zero logic in having tube increases after mufflers because losing gas speed there is a backwards step .

I think the path is 3" tube with 3" mufflers , plenty big enough for the power and no idiotic gas speed increases / decreases for lunatic value ...

A .

[discopotato03]

GT yes the go will be to use the cat "cones" as a reducer ie 3.5 in and 3 out , bolt on solution .

A .

[steve200b]

I have one AES rear round muffler 3in and it's 97db has a deep note as well

[GTScotT]

Buy my zaust, Disco.

80mm with oval muffler and tip au naturale (no viagra/extensions needed).

[discopotato03]

The measure up shows that at the back a 6 x 11 x 20 oval will fit , the mid one is 5 x 10 x 16 but they don't reckon anyone does a 5 x 10 .

KiwiRS4T you mentioned that your Venom 5" body cat is welded into your front pipe , is your cat in the std location or further forward ?

The reason I ask is because in the US they sometimes flick the cat a use a "resonated cat pipe" to help shut evos up .

Also Buschur offers a "diff back" pipe for Evos that has a 7 x 14" round Magnaflow instead of an oval . The claim is that round work better than ovals because of the depth of the packing above and below the straight perforated tube .

Thoughts ? Cheers A .

[Ben C34]

That's interesting,I have read that oval works best. I suppose an oval would work over a wider frequency range due to the difference in thickness, whereas a round one would be likely to be more efficient at silencing a narrower frequency range.

[discopotato03]

Was back at Kirrawee mufflers this afternoon to look at the Xforce cat I wanted ordered , 4.5" OD 3.5" bore 200 cel one they normally use on XR6Ts - looks very adequate ...

They've also ordered in mufflers and the rear one is huge , from memory 11 x 6 x 20" long . They reckon they can get it in - just with a couple of tight radius 3" mandrel bends .

The middle one looks the part too , not as deep as I'd like but between the 3 "cans" they reckon it'll be very quiet and flow well .

At the time they had a GTR on the hoist with an interesting looking 4" exhaust on it , custom mufflers and they think it will be quiet too . Hmmm .

I just need time to get the work done and fingers crossed it will uncork this GT3076R and make it come alive .

A .