[Guest]

I believe that the current trend of being satisfied with 3 inch exhaust is crap.
I say we should look into going bigger, 3.5 or even 4 inch.
Someone should dyno their current full 3 inch exhaust, then either a) grab some 4 inch exhaust from somewhere.... or b) run off the turbo elbow, and show me the numbers.
Becausican's website states his cut-off will give you better qt times.
granted he may just be braggin about his product, but people do get cut-offs for a reason.
I'm not saying your average supra owner will benifit greatly from 4 inch exhaust. but I do believe MY supra is faster and will be faster than any other's (with the same mods) due to teh fact that I run off the turbo elbow.
I would buy 4 inch exhaust but no one sells it. I might try making it...
I would buy 3 inch exhaust, but I have my doubts and I believe it will slow my car down and whats teh point in that?
any wanna help me prove that 3 inch ain't jack?

 

[AWIDESUPIE]

Been discussed. Too tired to explain. I am a fan of larger ID. Have some charts and some links etc. "Easy" to do .. even with cats ... do it if you want. Off-turbo performance may decrease ... but on turbo should be a great improvement. I wouldn't run open elbow in my car. Sure oit would be "cool" .. but your engine bay must be getting crazy hot. Any heat damage yet?

I plan on 3.5 to 4inch ID exhaust .. eventually. Was going to be soon .. but trying to organize riorities properly.

 

[Guest]

Wow, you sound angry!

When did anyone ever say you won't make more HP with a bigger exhaust on a turbo car? Or no exhaust at all? But there is a point of diminishing returns with size.

At about 400 HP, this is very roughly how much backpressure you get without any mufflers of any kind.

2.5" pipe = 2.00 PSI
3.0" pipe = 0.65 PSI
4.0" pipe = 0.20 PSI

So you can see, the difference is much more dramatic going from 2.5" to 3", than going from 3" to 4". Reduced pressure losses transfer almost directly to improved engine volumetric efficiency, which transfers into HP.

 

[Guest]

There was a thread a while back about a guy wanting to make 4 inch exhaust, he was flamed like a mother fuck! only the mkiv guys backed him up by calling the mkiii crowd....cheap? something like that. thanks for the numbers shawn dude. I still think that that pressure will result in a decent bit of hp if someone could ever test it. and the farther they go modding the car, the bigger the number would be.
and awidesupie, I had lil heat problems that I could tell, my speedo cable was charred black, other than that, nothing noticeable. When I get my car back on the road, I'll stick my nephew under the hood with a thermostat and see whats going on

 

[chevyeater-on-sf]

Maximum exhaust tubing diameter is a practical concern on a Supra. GROUND CLEARANCE

As for no exhaust, um, I guess if you want every cop for 50 miles chasing you then, yeah, go for it.

 

[becauseican]

Well with the cut out I knocked 2 tenths of a second off my 1/4 mile just by opening it up, the turbo spools up so much quicker. Ask anyone that has run with an open downpipe (3" at least) and they agree that there is a noticable difference when running with just a downpipe.

I think 3" is fine for a stock turbo. Upgraded Ct's and the new SP turbo bigger would probably benifit most from 3.5 - 4" exhaust/downpipe.

4" will be a tough fit under a mk3 especialy a lowered one. Where the pipe goes under the rear crossmember will be the biggest problem. 3.5" will work, Turbo drifter has a 3.5" cat back, he scapes it alot.

 

[Guest]

Yawgmoth, I forgot to mention that once you throw any mufflers or catalytic converters on the pipe, the improvement is even less impressive.

Let's say at 400 HP, we have the following:

2.5" pipe = 2.00 PSI + muffler at 3 PSI = 5 PSI total
3.0" pipe = 0.65 PSI + muffler at 3 PSI = 3.65 PSI total
4.0" pipe = 0.20 PSI + muffler at 3 PSI = 3.2 PSI total

Not that dramatic anymore. You'd have to run more turbo boost with the smaller pipe sizes of course, to get the same 400 HP though.

A cutout seems to be the best of both worlds. Keep your stock exhaust with a custom downpipe/cutout and you'll flow more than a 4" system when you need it and be whisper quiet when you don't.

 

[mk3supraholic]

Maximum exhaust tubing diameter is a practical concern on a Supra. GROUND CLEARANCE

thats what i was about to say i knew the bigger the better but i was gunna say mines not even lowerd and its almost touching

 

[Guest]

The numbers make sense shawndude, but so does becausican's claim. so yeah a cutout is probably the best solution, however I feel I'm gonna have to lose power no matter what if I get some exhaust on my car. and as for mufflers and cats, I live in iowa, so cats aren't reallyneeded, and i'n sure i'd get a straigh tthrough muffler if that helps.
a 4inch dp with a cut off, followed by 3.5 or smaller catback seems to be what I'd need. I'd be interested to know what the mkiv guys do about this.

 

[dbsupra]

i have 3.5" exh and have never scraped it. i do have the stock baja suspension tho.
dave henry has the hks ti w/ 4" piping. it actually has more ground clearance than the hks drager w/ smaller piping. its all how you engineer it.

dave

 

[OvenRude]

Personally I tend to stay away from the cutout idea, I have heard that when used in the wrong set-up, it can lose power.

I would say 3'' is all you need unless running a real big turbo to offset the new flow.

 

[SuprAng]

why is that exhausts are always such a big deal, i mean honestly gains are so minimal from 3-4, why not look for other ways to make power besides massive deisel engine exhausts... no one said its not worht it, so who are you trying to disprove? run a 10 inch if you can... just make it and move on...

Ang

 

[turbotoy]

Before I built my exhaust I did all the calcs as well, and found it really wasn't worth it to go greater than 3". Modeling a cat/muffler is significantly more difficult, but if you look at just the head loss from the pipe and bends alone, you aren't going to see significant gains by going to 3.5" until you hit ~600 RWHP. I have the Matlab m file saved somewhere if anyone wants to play with it.

 

[outofstep]

Run a standard three and get a cutout. You'll save more money and get the benefits of "no exhaust."

 

[conundrum07]

I run a 3" defcon downpipe, 3" test pipe and 2.5" mandrel catback. I have a 3" electric cutout welded into my testpipe, and with it open it makes a HUGE difference in not only sound, but also spool up time. Having the cutout open also raises my boost by about 3psi.

If you are that worried about free flowing exhaust, you should seriously think about using a cutout. It cost me $190 total, for the welding, flowmaster cutout and the DMH electric valve.

EDIT: And on a side note, you are not going to become considerably faster with a 3.5" or 4" exhaust unless you are making serious power. I raced my friends Supra with identical mods from a 40 roll and he had me by one car. The differences were that he had a full 3" exhaust system and 3 more pounds of boost (my cutout was closed).

 

[[email protected]]

I really don't understand this... If you car makes <600rwhp, 3 inch piping is all you need. Only at ~600rwhp does >3 inch exaust piping yeild substantial power increases. 300-400rwhp supras will see no significant gain.

 

[BLKMGK]

Have yuo guys considered this ->

Oval tubing!

 

[MKIIman]

i have 3.5'' with H&R's....and lets just say ground clearance sucks but here soon i want to go to 4''

 

[adjuster]

Oval tubing works, but so does square tubing.
Nice thing about square is it's cheap. That oval tubing is pricey last time I checked.
Hard part about square or retangular "pipes" are the transistions and curves. Also going from the pipe to the muffler, but a good set of two 2.5" exhaust cans plumbed directly into 4x2.5 square tubing should be an awesome setup. (Flow wise anyway, and at 2.5" height, it would make ground clearance issues a thing of the past. Go 4" from the turbo to the square tubing, then just a straight shot of that to the rear axel, then two 2.5" mandrel bends and pipes to the dual straight through cans with 3" tips, and you have one nice exhaust setup. Kinda heavy though, but square tubing is available in thin wall, you would just want to ceramic coat it to prevent rust....)
(Take a look at those asscar exhausts, they run square tubuing under the car to maintain good areodynamics and ground clearances for the side exit exhaust pipes.)

 

[Guest]

Please correct me if I'm wrong here, but I was under the impression that we go for a larger exhaust diameter to accomodate the natural shape of the exhaust gases, and not for the sheer volume of moving gasses. The exhaust coming out of a turbo is roughly in the shape of a tornado, and as the laws of physics would state, it takes more energy to keep a tornado compact than to let it flow outwards, which dictates the need for a larger exhaust so that the spiral can naturally move faster out of the turbo. The more compressed the spiral stays, the slower it will move out of the exhaust, and the more congested the exhaust piping will be.

So, in the interest of oval piping, wouldn't that cause too much turbulence?