3" system

[Glenjo]

Sure 3" is pointless for city driving, but so is a sports car..
I had a 3" and it did lose a bit off the bottom end compared to a 2.5" and was bloody loud, but the top end was great. I ended up changing down to a 2.5" because of noise and large amounts of time spent highway cruising, but i do miss the ol' 3"/

please dont perpetuate myths, unless your car is NA this does not happen

That's just how I saw it, with the 3", the car would hit 10psi at 4200-4500rpm, with the 2.5" (actually 3" dump -> centre muffler, then 2.5" after that) the car would hit 10psi at about 500rpm lower and felt a bit stronger in the lower revs.

I concur. Cuss Cuss, your a wanker. Technicalities aside, the way you make comments to people, your a dead set tool.

[CussCuss]

glenjo, i can deal with your opinion, but i wont be calling you silly names.

Chris, you sure nothing else changed on the car, its just a simple physics thing, back pressure isnt gonna help the turbo spool. Maybe the 2.5" setup even flowed better than the 3" you had.

[skip]

Found it: http://www.racetep.com/starexhaust.htm

We recommend a 2.5” all the way back, no cats. with a 3” inlet and outlet 6” round Walker Ultra-Flo muffler. This is not smog legal and therefore should only be done on cars that are only driven on the track. When driving on the highway always run your cat under the car. We offer High Flow replacement cats for under the car in both 2.5” and 3” diameters. We do not believe in 3” pipe systems for Street Starions. We don’t want to argue with everyone so I will say that… Yes we feel a 3” system will make more power on an extremely modified car running big turbos and big boost… But on a street car it will cause poor off boost driveability and laggy response. 2.5” is sufficient for all street systems up to the high 300 HP levels. We run 2.5” from the Turbo back through a 2.5” catalytic under the car and exit through a 3” muffler. This gives good response and sound while allowing a very free flow system.

[Chris 83JA]

glenjo, i can deal with your opinion, but i wont be calling you silly names.

Chris, you sure nothing else changed on the car, its just a simple physics thing, back pressure isnt gonna help the turbo spool. Maybe the 2.5" setup even flowed better than the 3" you had.

i doubt it, the volume is just louder than standard now, whereas before it was deafening, and the old 3" system was about as straight as they come with only a couple of mandrel bends. The dump is the same as the one i have now. Also the top end now is nothing like it used to be, so I really doubt this 2.5" system actually flows more/better.

Sure back pressure wont help the turbo spool, but surely the fact that the exhaust gasses need to move faster through the smaller pipe would spin the turbo up faster...? A 2.5" exhaust on a 2L low compression engine <3000rpm (below boost) would only create minimal back pressure anyway..

[Alspos]

[quote]We recommend .... with a 3” inlet and outlet 6” round Walker Ultra-Flo muffler. [quote]

rofl

[MrBishi]

I upgraded from the stock exhaust to a 3" unit and noticed no difference in drivability other than more go up high.
Personal experience aside, I don't understand how a larger exhaust is going to effect low rpm driving. Piston goes up forcing exhast gas out, into turbo, turbo spins then flows out exhaust. Surely the easier escape path for the gas the better?

Even on an N/A car I've only ever noticed minor differences in low down torque/drivablity after a free flowing exhaust.

[CussCuss]

thats weird chris, anyway, sorry about how i said it.

The physics is basic, there is a high pressure area before the turbo, this is caused by the turbo, this is the basis of why it works, the turbo is a restriction, creates a high pressure area in the ex manifold, there is a low pressure area in the exhaust after the turbo, so the gasses go thru and push the turbine.

The theory as to why NA cars will suffer down low is sound. But it gets a bit complicated and i cant actually remember all of it right now.
What you end up with say on a 2.5" vs 3" on a 1.6 NA engine for example is that the smaller one will have better low down and not as good top end and the bigger one will have more power, usually the difference is enough to make the smaller one the faster car in a drag race.
Then theres tuned length exhaust systems, pulses etc....

[airbats801]

If you are serious about modding your car, get a 3 inch, there is no comparing the 2, I've ran side to side with 2,5inch systems, and they just dont compare to a 3 inch on the g54b. Not sure about the 2.0

I had better turbo response, and all around power also. The biggest thing I noticed, was at 125mph, and 5krpm on a basically stock engine, my car was still pulling very hard, which usually they hit a brick wall with a stock system at roughly 100.

[WidebodyWoody]

Ok, there is a falacy about more then 2 1/2 inch exhaust on our cars being bad. This is incorrect. You can easily have a 3". They say that you can't have greater then that size because of back pressure. I mean come on, we have a turbo. Back pressure isn't an issue. It is only an issue on NA cars. What a joke.

[skip]

Okay, given that the exhaust on my car is getting done very soon (could be as early as this week, but more likely in a week or two), I have the following question:

Do you guys think its worth me shelling out an extra $200ish for a full 3" exhaust rather than a 2.5" with a 3" muffler for my mainly 'city driven' car when for the extra money I could get a boost controller and some other stuff (don't know yet) ?

(or part payment for the effing paving in my backyard that needs doing next week too :x )

[Chris 83JA]

If you don't mind the noise, then go 3" (in fact you can get em pretty quiet 3" anyway).
If you're going for big power in the future, then you may as well go the 3" now instead of upgrading later.

[Junkers]

do 3" exhuasts use more gas than 2.5's in city driving conditions?

[SpidersWeb]

do 3" exhuasts use more gas than 2.5's in city driving conditions?

My guess: it would use less because the reduced backpressure, means less force is wasted pushing out exhaust matter, therefore more power to the ground with less fuel.

Just guessing because Im bored. I really have no idea.

[Chris 83JA]

do 3" exhuasts use more gas than 2.5's in city driving conditions?

My guess: it would use less because the reduced backpressure, means less force is wasted pushing out exhaust matter, therefore more power to the ground with less fuel.

Just guessing because Im bored. I really have no idea.

My research concurs with that

[GADGET]

Chris what turbo are you running? Seems a bit laggy for stock set-up?