dastallion951

Wow read this whole thread, and i know you said that exhaust replaces the downpipe back, umm to be honest unless there's another pipe missing it don't, that looks like it bolts on to the downpipe in place of the front of where the cat flange would be. As far as exhaust diameter, on smaller turbos ie older dsm's that flow a bit less airflow it might not help as much with a 3" exhaust, over a 2.5 or a 2.75 all the way back, kinda the same thing with 2.5" intercooler piping over 3". Now op you gotta ask yourself do you plan on staying with a stock turbo, if your answer is yes then this exhaust system will do. However if you ever plan to go bigger, not saying this exhaust wont be good, but there is a possibility at a 400+ hp level it might be somewhat of a bottleneck, which can rob you of hp on your dyno day. Which then if your tuner recommends a bigger diameter exhaust system you'll be kicking yourself in the a$$ for having to spend your money twice. I say that because ive had to spend money on a few parts twice because i thought they would be good.
Just remember one thing: Look at a fast food place, don't those burgers look good on the commercial, but when you get it in front of you its not the same, long story short pictures can be deceiving.
Good luck and buy the 3".

joseph143

iTrader: (8)

I'm no genius... nor an expert on any level of engine building and modification. but what i can tell you is my stock evo on 91oct at 25psi picked up about 20 hp and a good bit of torque when i installed my cobb 3'' which i still run with the mods in my sig. albeit without tuning.

the one catch in my situation is i was also running the xede with a base flash so i may have just fallen into its real performance range.
either way, i can see this going both ways. i dont see thermal heat transfer or the lack there off having much effect on exhaust flow that far down the pipe. i know at my test pipe my exhaust has never been hot enough to burn me. and the taper in the theorized exhaust is unless i read wrong. after that.
on the flip side maybe the restriction causes a heat pocket which accelerates gases and causes a vacuum effect increase velocity thru out the entire exhaust. idk

All in all the only way to figure this out in the end is 3 pulls on a dyno. 0-1 smoothing... install new pipe... 3 more pulls with 0-1 smoothing
then average the three pulls in order dont mix and match to bias one side or the other.

Gardus

I want to be clear, the Supersprint full exhaust for the stock turbo is 70mm all the way.
The 63.5 mm has been made for regulations reason in the Group N class, where you can't have an exhaust bigger than the stock one.

03whitegsr

iTrader: (8)

It would be interesting to see a good stock turbo setup with 2.5", 2.75" and 3" exhaust, all well made with minimum bends and the largest bend radius you could fit on each with straight through mufflers of equal lengths. In that situation, I could potentially see the smaller exhausts making nearly equal power up top and gaining low end.

The problem though with all these comparisions mentioned is that you could have a garbage 3" and a good 2.5" and the 2.5" could spool better and make more power simply because it's a better design.

Also, I imagine it's going to be setup dependent anyway. A setup that relies more on low backpressure (high overlap cams, a big turbine wheel, and moderate boost) is going to probably act a lot different then something like a stock turbo mild cam setup with little overlap and tons of boost.

cbseven

iTrader: (1)

Well, we may be in luck.

Gardus, do you have dyno comparisons of all three of your systems; 63.5mm, 70mm, and 80mm?

Gardus

I think I do, I need to check in the archives.

EvocentriK

I have an 8, stock engine, stock cams, Ralliart piping and suction pipe, injectors & pump, CBRD 3" vband dump and front + 100cpsi HFC with a BBK Full @ 21.5 psi (for this) and I have a 2.5" ralliart Ti catback and a 2.75" HKS Super Turbo catback that I just did back to back testing with. No difference between the two at all in terms of power and toque. They both go from the 3" cat flange to the 2.5" flange on the catback so this may skew things a little but I'd have thought the 2.75" would flow better as both are straight through systems just different diameter piping. I intend to run the ralliart Ti with a modified cat that tapers from 3" to 2.5" to smooth the transition. A local guy just made 332kw with a dump back 2.75" system so I think I'll be right for my goals on the 2.5" catback and 3" front end. I'd love to see some dyno testing though.

JohnBradley

iTrader: (30)

I forgot to mention that I had employed a different boost control strategy between the 2 that got me better spool as well as some MIVEC changes down low. The ambient temp was a little lower as well.

Chef-j

iTrader: (16)

Going to smaller pipe isnt something i like. Giving back pressure works great on supercharger. Hey when you doing a test, will you also watch EGT as well? Good luck

JohnBradley

iTrader: (30)

Jerry,

There was more to that post that I needed to add and didnt get in before I pressed Post (then I was on the dyno for the last week). I increased spool with an addition 7* of MIVEC advance down low (45* total), some WG spring changes, and the aforementioned cooler inlet temps. I have never seen any advantage to smaller exhaust. I know you arent advocating it, but you cant interpret my data that way either since the muffler didnt add spool just lost power.

General-

We do LOTS OF TESTING. I have tested basically every bolt on combo there is in the last 3 years. For instance, in addition to cam testing, fuel testing, exhaust testing, intake manifold testing, turbo testing, we just got done testing 2 cars with individual EGT probes. It will take me a little while to get all the data quantified and really only will appeal to endurance applications but we dont sit idly by. When I say something doesnt work, I am not going off half cocked, it means we have tried it and learned something.

If this exhaust is actually 70mm ID (2.75) its not the same as running 2.5" ID obviously and all my points, while applicable, have a little more room for variation in a discussion vs generic 3" exhaust.

Aaron

JohnBradley

iTrader: (30)

Huy,

I switched to a 4" downpipe to 3.5" turbo back with 60mm dumps on the testpipe. That is from a 3" to 3.5" with dumps which I had last year.

Backpressure is the devil.

way2qik

iTrader: (5)

This is really not complicated....

With a turbo car, a larger exhaust will ALWAYS make more horsepower with a given set of parts. Even with a stock turbo.

All these "tests" that you guys reference showing the smaller diameter pipe making more horsepower than the larger diameter pipe are forgetting one very important detail... RE-TUNING FOR THE LARGER DIAMETER PIPE.

I promise you I can take a bone stock Evo and put a 3inch downpipe on it with a 3inch exhaust system and make more power with those exact stock parts because I have now reduced backpressure, which is the enemy of turbos. You say, "But the tests show a loss of torque down low!"

Of course that happens. The car has now leaned out due to less backpressure and I guarantee you it wants MORE FUEL THROUGHOUT THE ENTIRE FUEL MAP, but especially in the midrange, where torque gets going... Once you add some fuel to those areas of the map, sit back and watch the torque figures jump right back to where they were and then leave the stock numbers in the dust. Same thing with the horsepower.

Gardus

I agree with you.
In fact, our exhaust are specifically developed for stock cars, no remap or anything else.
That's the reason why we offer the 80mm exhaust as well.

Some backpressure is useful for:
Cars with stock boost and engine management, as they are not able to compensate.
Spool up time.

wshihdnevo

iTrader: (88)