JM Performance

I talked to F-Max today and they said that the F-Max downpipe comes in 2.25" because thats the size of the exhaust housing, and any bigger would cause pressure problems that would actually take away power.

Does this make any sense?

BoostinDC2

correct me if im wrong but i dont think it makes sense. have u ever dropped the exhuast on a dyno run it gains like 30hp just by unbolting the exhuast.

JM Performance

^

Also, he didn't say that a large exhaust would be bad, just an overly large downpipe.


[Modified by 00SilverLS, 10:13 PM 9/30/2001]

Reverend

ok, they told him that "You would loose power and could get reversion into the turbo" Or something to that effect.

Anyway, I've always heard that there is no such thing as a turbo car with an exhaust "not restrictive enough" - I was always told that tubo cars can use as much freeflow of air as possible, and to restrict airflow is to restrict only power.

Please, someone who understands what this guy said please explain it to us

dbman96

The only thing I can think of is that there is a very big static pressure drop associated with transition from a small opening (turbine outlet) to a large plenum (3" downpipe) so if the downpipe is significantly larger than the outlet from the turbine it can actually slow down the flow. Which is why I think ARTurbo has such a good thing going with those 2.5" -> 3" transition downpipes.

DIRep972

iTrader: (1)

I kinda doubt that, tell that to dusty womack who runs a 4 1/2 inch Down pipe of his turbo.. and gained like 50hp.. hes the blue supra on turbo a few months back

b18bvudoo

it better NOT be 2.25". I'm expecting 2.5". guess i'll give em a call tomorrow.

JM Performance

no real advice?

dustin

I honestly think that is a load of BS. If you ran NO downpipe whatsoever you would see amazing gains in power. There is no way any sort of "reversion" could occur because you are going from a place of smaller cross-sectional area to larger.... The only way reversion can occur is if the original port is too large. This is not even an issue, because there is no way exhaust could ever "revert" back past the turbine wheel.

People usually talk of reversion at the head/manifold union. You do not want the head ports too large or you can get reversion of exhaust back into the cyls when the valves are still open... and lose power.

Dustin

liam821

My downpipe broke in 1/2 *again* the other day by the flange which connecst to the turbo. I drove it around just like that for the rest of the day. The turbo spools DAMN fast!!

liam

2latev8

Some of you guys are right but if you do away, or go extra big with the down pipe you WIll loose power on the lower portion of the powerband cause of no backpressure, at the same time gain power on at high rpm cause the exhaust gases have less exhaust restriction. Trust me you need SOME back pressure. My downpipe is only 2.25 inches.

BoostinDC2

yeah i dont see how a big DP would effect performance. if u think about it the turbo is actually another muffler.

JM Performance

so what would you think about the 2.25" downpipe and a 2.5" cat and exhaust?

BoostinDC2

that will be fine. wht turbo kit are u getting

JM Performance

read the post......F-Max

Reverend

If you think about it, fingernails are like little helmets for your fingers.

JM Performance

<U>WTF??!!</U>

DamonBoost

I have drag III kit and just ordered thermal 3" exhaust. should i get the 3" downpipe from arturbo or just leave what i have on there? the one that came with the kit.. would i get a noticable gain in power??

BoostinDC2

u might was well if your getting the 3inch cat back u might was well get the 3inch DP