I have a 3" downpipe and I wanted to get 3" catback. The exhaust shops here are giving me a hard time about it.

First off, they are saying that 3" won't even fit under the car.

Secondly, they are saying that 3" would be overkill for my car, that I would actually lose hp with it. (funny cause it was a huge gain for my talon)

Third, they are saying that to bend the 3" pipes the way they need to be they will put horrendous kinks in the pipe, which will make the 3" piping pointless anyways.

Lastly...I'd like to get a resonator, but they are telling me that my ground clearance will be too badly affected for a resonator, cause the resonator will be around 4 1/2" in diameter.



So, BS or not BS? Is 2.5" or 3" better? Is there a 3" kit available? Resonator...yay or nay?

 

They are 100% right.

The reason you gained power on a turbocharged car is because post-turbocharger, you're not following the same laws of exhaust velocity and scavenging like you would a naturally aspirated vehicle or a supercharged vehicle. The optimal exhaust system for a turbocharged car would be as wide as possible and as short as possible (open downpipe), this is for optimal power.

The smaller the exhaust system on a turbocharged car, the more backpressure is being created and the pressure going back towards the engine causes slight disruptions with the turbine trying to spin as free as possible in a single direction slowing down response time.

If you put a 3" exhaust system on, you'd cause a slower exhaust velocity build up and slower scavenging effects at lower RPMs. You MIGHT make more peak HP but your power band would narrow out (or become peaky).

As far as fitting, if they knew what they were doing, they could make a 3" exhaust fit.

Adding a resonator would keep the tone down alot. I've heard a 3" on a ss/sc and it's louder than a fat guy screaming as he's falling off the empire state building.

The longer the resonator, the deeper and quieter the tone. Otherwise, you'd sound...well...obnoxious.

 

Hmm. Ok well that all makes sense.

I guess one more question, lol. I already bought a Magnaflow muffler thats 3" in and out. Will it be stupid to have that flanged onto 2.5" pipe?

 

They can do it, it's not that big of a difference. It won't hurt anything either.

 

at what HP is a 3" necessary for the Cobalt?

 

He has Stage 2 and if i was him i would be going with a 3" catback.

As soon as you drop on a smaller pulley.

There's a huge thread about at what hp you need a 3" exhaust. I think it was at 300crank horsepower which is 268whp.

 

Its been shown mathmaticly that once you hit the 300hp mark is where the 3" piping comes into play. Below 300 your killing your low end and losing HP over a 2.5.

Its been shown on here a bunch of times. Adam sumed it up for you.

 

TY guys.

 

You're not going to lose horsepower with a 3". You'll lose low end torque but will make it up as top end horsepower.

 

i can put my car on a lift take pics, and prove that 3 inch fits. of course. im not exactly stage 2 anymore. with the type of racing i do, it is needed

 

I have 3" and I love it!

 

unfortunately you made the same mistake I did by buying the 3" DP first. While the debate between 2.5" vs 3.0" will rage on I think my 3" exhaust is great but u will lose some low end but gain some high end.

IMO you want a 2.5 Dp and 3" or 2.5" exhaust, because after the DP it doesnt matter what size ur exhaust is as long as its 2.5"+. Just my 2 cents.

 

hey vibrant makes a 3" catback system for the cobalt, and dont listen to people who say you will loose low end power thats bs they have this weird thing about back presure there just dumb, if they where right it would mean a small exhaust would be the best lol so go with the 3 thats wat im getting

 

Do you understand what exhaust velocity or what intake / exhaust resonating is?

I love how you say that people are dumb for saying that about 3" exhaust systems when you don't even have one and the testimony from people who have a 3" exhaust say exactly the opposite.

Bigger isn't always better. Yes, sometimes a smaller exhaust system is best for a wider powerband.

 

im sorry trebek, can you rephrase the question in the form of a cheeseburger?


in short. no.

 

"I'll take the rapist for 400"

 

i've got it.

team thread jack. "we will **** up any thread"

 

Rofl

 

I'll take "the ***** mightier!"

 

3" would be fine.

The physics of the exhaust on a naturally aspirated engine and a force induction engine are completely different.

The whole concept of scavenging from a smaller exhaust with higher velocity is to scavenge the cylinders during valve overlap.

A good forced induction engine shouldn't have any overlap, or at the least a very, very small amount. Scavenging the cylinder isn't practical in a force induction engine.

Is 3" necessary? Probably not, but the same adverse effects of an exhaust which is too large on a naturally aspirated engine won't apply.

 

But they still have overlap none the less.

The most important part is understanding exhaust velocity.

But I agree with what you're saying though.

 

for the few of us that are pushing over 270 to the tire. we benefit from it. the others. don't.

 

Yes. Understanding exhaust velocity and pulse waves is what it's all about.

As far as turbo engines go, that's your game. I'm not very familiar with turbo engines and how exhaust velocity and pulse waves play into those. I'm not that educated on the effects of those things on the turbine.

I would assume velocity is very important but pulse waves not so much. The pulse waves won't reach the exhaust valve in the same manner as a naturally aspirate, or even a supercharged engine so all pulse waves (I'm assuming) would be lost regardless (or for lack of a better term "scattered").

 

im running 2.5 dp with the clear image header and the hahn catack, i agree that the low end is a little weaker but luckily my 2.5 stuff makes up for most of that. and it will fit quite easily.

 

Why would you run a 3" exhaust after a 2.5" downpipe? Biggest waste in the world.

Ideal setup for S2 cars would be....

1 7/8th Header
3" downpipe
3" catback