Talon TSI 2 1/2 " Exhaust or 3" Exhaust Which whould i go with?

[l3igl3ang]

Hi im going to do a Exhaust System change and get rid of the stock Exhaust and CAT the shop will charge me $250 for a 2 1/2" full exhaust thats with my own apex muffler but they said a full 3" would be more $'s and i dont have a 3" muffler so how much of a difference is a 2 1/2 from a 3" is it a world of difference?

 

[gob4sho89]

"No. If you are going with different size pipes, you want to go from small to larger; gases expand as they get further from the engine and cool."

WTFWTFWTF

I am pretty sure it is the exact opposite of this....

 

[pboglio]

2.5" exhaust works, 3" is better. I can make a 2.5" exhaust louder than a 3". Its all in the design, construction, quality of components. A cheap 2.5" is going to be loud, so would a 3". Buy a big high quality muffler, a midpipe resonator or bullet muffler, and toss in a high flow cat and the 3" will be very very tolerable and actually sound like a well tuned OEM sports car, not some riced out pile. Only those completely allergic to low frequency sound waves will want to stay clear of a 3".

The upside is your done buying exhausts for the life of the car which is a HUGE saver in terms of dollars. Buy once, buy big, and buy quality and you'll save huge in the long run.

 

[pboglio]

Yes, gasses contract as they cool.

2.5" downpipe to 3" catback has been a great combination foreever on a 16g sized turbo.
Rumor has it that the 2.5" downpipe maintains some low end torque for street driving. This may or may not be true but I've definitely noticed a difference in low end torque when reinstalling my 2.5" highflow cat over my testpipe.

 

[joyfil2001]

No. If you are going with different size pipes, you want to go from small to larger; gases expand as they get further from the engine and cool. A smaller (or in your case same size) DP will help keep the velocity of the hot gases up and improve flow.

That is why a 2.5" DP into a 3" exhaust is common and works well.

You're right.

"No. If you are going with different size pipes, you want to go from small to larger; gases expand as they get further from the engine and cool."

WTFWTFWTF

I am pretty sure it is the exact opposite of this....

You're wrong. Wow, I can't believe how many people have posted wrong information in this thread. Come on guys, the OP could have found his answer via a simple search. And it seems like some of you should use that search button too.

 

[Calan]

Yes, gasses contract as they cool

Correct, but I didn't say anything about what happens to a gas as it is heated or cooled. I was talking about what happens to the gas as it expands

I said:

gases expand as they get further from the engine and cool

As the exhaust gets further from the turbo, it expands, losses pressure, and cools. You want to go from smaller to larger to allow this to happen with as little restriction (backpressure) as possible.

Going from larger to smaller would try to force the same volume of gas into a smaller pipe, thus causing a restriction (as well as causing the gas to heat up due to compression)

 

[DSMunknown]

http://www.dsmtuners.com/forums/new...tter-2-5-vs-3-exhaust-discussions-merged.html

 

[joyfil2001]

http://www.dsmtuners.com/forums/new...tter-2-5-vs-3-exhaust-discussions-merged.html

Thank you. What did that take you, like 2 seconds to search?

 

[JusMX141]

When talking about exhausts, "go big or go home" doesn't apply.

If you're a big fan of boost creep, then a catless 3" turbo-back is for you. It flows so well, the exhaust would rather pass through the turbine housing (as the path of least resistance) instead of exiting through the wastegate. The lower the boost you want to run, the higher the boost level you'll achieve.

If you love to run a consistent boost level between 12 and 18psi on your Small 16G and you're done modding for good, then 2.5" is for you. A buddy of mine ran 12.66 with a Big 16G @ 18psi using a 2.5" Buschur turbo-back on his 1G TSi AWD daily driver, and it was plenty fast for him.

 

[gob4sho89]

I was thinking only in terms of what would keep velocity up, not flow better/have less backpressure. Sorry... I was wrong

 

[ninesixtwo]

As the exhaust gets further from the turbo, it expands, losses pressure, and cools. You want to go from smaller to larger to allow this to happen with as little restriction (backpressure) as possible.

Going from larger to smaller would try to force the same volume of gas into a smaller pipe, thus causing a restriction (as well as causing the gas to heat up due to compression)

Going from larger to smaller diameter piping keeps the exhaust travelling in pulses, which in turn keeps the velocity of the exhaust up, and the backpressure down. Fast, hot exhaust gas will be restricted more by colliding with slow turbulant exhaust than it will from the smaller diameter piping. The reason that a 2.5" to 3" DP is common is because every single O2 housing available has a 2.5" opening.

 

[tkelly27]

I have to eat my words. I'm hitting overboost with my big16g and there is nothing I can do about it aside from adding exhaust restrictions. I'm going to have to put on a muffler to (hate to say this) go faster. I guess I could port my wastegate, or just get rid of the fuel cut, but I need a muffler to pass emissions too.

It requires more pressure to get the same amount of gas through a smaller pipe. Also, for a given fluid in a given pipe, a higher velocity requires a higher pressure drop through that pipe. Velocity has it's place pre-turbo and in a naturally aspirated engine, but turbines run on pressure drop and heat. All pulses are generally considered null and void post turbine.

 

[Ludachris]

At 350 h.p. there is a difference between 3" and 2.5" exhaust. From a roll the 3" exhaust makes more torque and hits more violently. The noise level of the 3" takes some getting used to so that is probably a consideration.

HP level is not the only factor involved there - it's also dependent on what other components you're using (turbo/downpipe/O2 housing/cat/etc), how the exhaust is designed, the muffler type, etc. That will all affect throttle response, hp, and torque to some degree. It's not as simple as saying that if you have 350whp a 2.5" would be best for you. Altitude also plays into it.

With that said, most people not putting down more than 400whp would be fine using a 2.5" exhaust - a few of the big vendors have done tests and showed little difference between the two sizes on their shop cars. The difference would typically be minimal. This is all covered in the Tech Guide > Upgrade Paths. I'm assuming everyone has read through that, right?

 

[Boosted98gsx]

As the exhaust gets further from the turbo, it expands, losses pressure, and cools. You want to go from smaller to larger to allow this to happen with as little restriction (backpressure) as possible.

When Gas cools, it CONDENSES, meaning taking up less volume than a gas at a higher temperature, which is why it loses pressure....

So theoretically you want to go from larger to smaller as the exhaust progresses to the rear of the car. But it's such a negligible difference, a straight diameter pipe works just fine.

 

[DSMunknown]

I went with a 3" on my talon. There is a huge difference in price going from 2.5 to 3 unlike 2.25 to 2.5". But the rarity of a 3", the sound of the turbo through the exhaust, and the power is well worth the money. And with a 3" cat and full exhaust race gas is like nitrous on a turbo car.

F.Y.I.= They can swell a 2.5" pipe on one end to connect from the muffler to the 3" pipe. I have a 2.5" inlet apexi N1 muffler as well.

Pretty naive statement, if you ask me.

 

[knochgoon24]

At 350 h.p. there is a difference between 3" and 2.5" exhaust. From a roll the 3" exhaust makes more torque and hits more violently. The noise level of the 3" takes some getting used to so that is probably a consideration.

And if noise is a problem, get a shop to make one up for you. I bought my 3" of a guy who had it welded together custom for him. It's actually nice and quiet, even at 75mph on the highway. The muffler might have some part in that too. It's not some el-cheapo looking fart can.

 

[pboglio]

Here is a before and after of a 20g on 21 psi with a 2.5" vs. 3.0" exhaust. You be the judge if its a worthwhile mod:

Edit: Couldn't get the image to load for some reason.

If anybody has some boost creep they can lend me I'd appreciate it, I'm running a T28 and need all the creep I can get.

 

[jerseydiver84]

3inch woke my car up a lot with only a few minor mods at the time, but i would say go with the 3inch for future goals you want to reach the 2 1/2 in would restrict your long term goals if thats the route you wanted to go.