WFOTC

I see so many 2.5" exhausts for sale but not any 3". I know 2.5" isn't a real restriction for most low boost turbo applications; but, it will help spooling and should give more power than a 2.5".

raamaudio

Mostly you would just make more noise and have a bit more weight to haul around;)


Unless you are building a full tilt monster motor with really big boost, you just do not need a bigger exhaust.


Rick

rlazer5000

^^ I agree, until you turn the boost a significant amount, a 2.5" exhaust is more than efficient. A 3" exhaust is too wide diameter of piping for 8-11 psi and you may begin to lose power because you're not creating enough back pressure.

Give it a little time and I'm sure the manufacturers selling all the turbo kits will begin to make some high horsepower kits that will need a 3" exhaust.

zer0

If you go turbo, get an exhaust cutout that way you can rock an open downpipe whenever you want. No exhaust for a turbo is the best option. Open downpipe for the win!

jct

would that cutout be right at the turbo or behind that cat?

zer0

before the cat on the midpipe.. on or after the spipe.

Gaurenteed to get a CEL though

retrodrive

every cutout I have used had motor failure sooner or later...and I am definetely not the only one having those problems.

WFOTC

WOW,

"agree, until you turn the boost a significant amount, a 2.5" exhaust is more than efficient. A 3" exhaust is too wide diameter of piping for 8-11 psi and you may begin to lose power because you're not creating enough back pressure. "

do you know that with turbos the less back pressure the better, right. saying that you will not gain anything with a 3" exhaust is obsene.

The turbo itself works mainly by the pressure differential before and after the turbo.

zer0

Please explain, I have run Open Downpipe on my DSM for months at a time to no ill affects... ZPI even ran a 12.1 with an open downpipe.

How is a cutout going to kill a motor?


For everyone else..
http://www.quicktimeperformance.com/QTEC/
Goto that site if you want more information on how they work and whatnot.

raamaudio

The cutout motor is what he meant, not the engine;)

A cutout on a turbo car is fine, as long as the location does not effect the tuning and if it does, be prepared to deal with that issue.



WFOTC, big difference between no exhaust(just a tiny stack is best) and having a full exhaust. Since you are going to have a full exhaust on a street car that is entirely different than a race car with no exhaust. Apples to Oranges is the analogy here.

IF you are building a race car, the least amount of exhaust you have the better.

IF you are building a street driven car with a full exhaust, going to big will not help. It is not a back pressure issue, it is velocity and that requires a proper size system.

Bigger is always better is arm chair quarterback, dyno queen, etc, not real world performance;)

Rick

WFOTC

explain to me again...

if you have a turbo equipped car it has a big source of backpressure (the turbo) which works off a pressure differential. A 3" exhaust will help everywhere in the powerband of a turbo car. So wouldn't it be more streetable.

all I know is that I had a 400hp srt4 that I built up over the process of 2years. When I went to a 3" exhaust I noticed a gain everywhere in the powerband.

peteyd

I had several different people including 2 differnt custom exhuast shops i wouldve lost power if I did a 3" exhuast. Dezod/ZPI/Draxas will all tell you 3" is just too much for the tC turbo applications at this time. We are not evos/sti/supra/srt-4 no one is running that high of a boost on a tC. I had 2 differnt exhuast shops tell me I would lose power and sound horrible if i got a 3" exhuast. Including a world famous one called carboys they had the worlds fastest civic at one point in time. Everything they all told me coincided all the same story just differnt wording, they all said 3" is just too much. 2.5" will be more then sufficent for our turbo needs.

raamaudio

Again, apples to oranges buddy, the point is, a big exhaust on a car that is not building big power will cause a reduction in exhaust gas velocity, slowing down the exhaust flowing through it.

Alot of difference between your 400 HP srt4 and the typical 300 HP tC. When you start running that kind of power then you start having a need for a bigger exhaust.

400HP on a street driven FWD is getting to the point of sillyness anyway, so little real use for it as cannot hook up except when heading down the highway at a decent speed already. And major reliability issues or huge engine budget(alot of that depends on how the stock motor was designed)
come into play and few will actually go that route.

I am not putting down big power, I love it as much as anybody, I just happen to love having a reasonably fast car that I can drive anywhere and actually use the power in almost any situation

I have run setups with a 3" downpipe and used a proper long taper cone to reduce it to 2.5" 3 ft or so down the system with really good results, even on my 1.8 Matrix, spooled up very quickly and made good power all the way to redline, and was quiet, which I prefer so I can have more fun driving instead of making noise so I get attention;)

The tC is a bit more difficult to do a 3" downpipe on due to the nasty S pipe. With just a 2.5" pipe there are alot of clearance and heat issues to be concerned with. Already we are right by the alt and AC pump, then right under the oil pan, and up in back by the intake manifold.

I looked this over very carefully and into NASCAR style ovalized piping to go under the crossmember as well as the idea of sectioning the crossmember and welding in a passage for a 3" pipe. I can do these things well enough but I decided for the amount of power I am going to run and the proven dyno and track results with the proper turbo size it is just not worth the extra effort. If it was, I would do it, already have hundreds of hours into things nobody will even see but us but they are for real performance. Things like the entire chassis being filled with structural eurathane foam, all factory deadening removed(redeadend our way, saved alot of weight and far quieter than stock), three bins out in the shop of excess wiring, connectors, studs, seat belts, bolts, nuts, brackets, etc, that are generic in nature to building assembly line cars that really do not need to be there. Carbon Kevlar roof, etc, etc. In other words I will do whatever it takes to make this car as low in weight as possible yet stronger than originially designed(welded in roll bar for now, 6 point cage when we can get more time to finish it off) The tranny is apart right now as we are installing an LSD, aluminum flywheel, 6 puc sprung clutch, our version of proper motor mounts, we build out own short shifter(better than any you can buy and located perfectly for me

Just saying all this to point out we understand real performance that is of real use.

If a 3" exhaust was worth the trouble we would glady build our own, we have always built our systems from intake to exhaust and love doing so.

But, we are picking up a nice sponsorship on a great 2.5" system and it will do the job just fine(with a few little tweaks though, can't leave anything untouched, lol

Rick

peteyd

You talkin to me Rick or the other dude? And you are right dead on about the spipe thats the one issue every shop said. It COULD be done would they recommend it NO. But if I wanted it done they would do it. Is the tC worth running 400whp? In my opnion no. In my opnion and this is strictly my opnion the tC shouldn be no more then 330 maybe 350whp TOPS. I feel that a 2.5" exhuast is more then sufficant to handle that type of setup. Plus once you get past that amount of power anything 400+ is just no longer a tC in my view, look at the jotech tC its 533whp they had to lift the whole engine and move it to make everythign fit! Thats just not a tC anymore in my views.

raamaudio

Nope, not you peteyd, you get it

Jotech tC is just another dyno/trailer queen of little use in the real world except bragging rights and advertisement, which has it's place in business but not in actual use of something you plan to drive on the streets.

Of course it sounds fun to have that much power and we are considering it in a couple of years, once we get all we can out of our FWD in SM class autocross, Solo I, hill climbs, track days, etc. Then we are very much considering 450-500WHP but to use it, an AWD conversion, if we determine the system we would put together can take the abuse, if not, then drop it down to a more reliable level, so we can drive the damm thing, alot and hard, not just post how big our cajones are because we have huge power.

Rick

WFOTC

I kinda understand where you guys are comming from now. 2.5" should be enough to handle up to 3XX hp.

and yes 400 FWD hp was worthless. On the street I would break loose as soon as I stabbed the throttle anywhere in 1st and 2nd and come loose in the the top of 3rd. a duel stage boost controller would of helped.

engifineer

Great info above by rick (as usual)...

Another disadvantage of having lower velocity exhaust gas (due to the larger exhaust) is that slower gas cools more while still in the system... cooler gas is more dense.. which is harder to move.

paul_dezod

Gentleman, let's not forget the A/R of the exhaust side of the turbo has a big part in exhaust backpressure, but for the most part raamaudio hit it home.

raamaudio

Thanks guys, I was almost ranting, did not mean it that way, just have alot of feeling about what we should or should not do to our cars for real performance that we can use effectively

Weight is the number one real enemy of performance, why I sometimes compromise effciency of building power over the added weight penalty it may bring.

Then I try to blend appearance in a clean, quality, funtional fasion into the real performance design, not always easy. Things we do would include an intercooler big enough to do the job required, small enough to save as much weight out over the front axle as possible(or anywhere else for that matter) yet big enough to look cool, then I paint the front black to keep the popo off my **** but polish the top so it looks nice from under the hood

Rick

peteyd

^^ RESPECT!