3" is enough

 

Ok, I was unsure about that part tbh, but I did read an article about maintaining gas velocity and something called the scavenger effect and having too large an exhaust is bad. If I'm wrong and an exhaust does nothing to help performance why do drag cars and NASCARs where no one gives a **** about noise even have exhausts if they are nothing but a possible restriction? I'm not trying to be argumentative and if I'm wrong I'm wrong, I just like to know what I'm talking about when it comes to this sort of stuff

 

A lot of it depends upon the engine in question. Like for example on a K series Honda essentially all necessary scavenging is done in the header, about every K series will make the most power open header. A B series Honda typically will lose power with anything larger with a 2.5" exhaust. I'm not as familiar with how the 4G63 does but clearly people are saying there is no benefit moving past a 3" at modest power levels.

 

You need a 5"exhaust and it has to be machined out of a single giant billet piece of beryllium for the maximum thermally efficiency powers. Anything less is not even trying.

 

I was just gonna tell him to settle for a regular Titanium 5". But Beryllium sounds tasty.

 

I was speaking more for turbo cars. I believe on NA cars that some backpressure is better than no backpressure

NASCAR and F1 and such like that is probably a bad example to compare to as they are likely using the exhaust to route air around the car most efficiently and aerodynamically

 

Negative ghost rider. I'm grossly oversimplifying this but if the gas that has already passed the turbo are unable to exit the system quickly enough they end up meeting the next round of gas particles and so on. In an extreme case this ends up killing the velocity of the gases by the turbo and thus its ability to spool. That's why ideally you want the exhaust as large as possible so that you don't ever run into this problem. So the velocity of those gases is important up to a certain point.

To the OP, as others have pointed out is that past 3" unless you are running something ridiculous it won't make much of a difference so if you want to do it to say you did then fine.

 

you guys ever get a weight of your stainless exhausts? I called to order the 3.5" titanium probably a year ago, I guess, but couldn't justify the cost without knowing the difference in weight from my ETS 3.5" stainless exhaust.

 

How does everyone here who has said 3" is enough know for certain that 3" is in fact enough? Are you all just saying it because someone else said it at some point in time?

Although this isn't an Evo, it may be worth reading:
http://www.superstreetonline.com/how...ust-test-tech/

I'm apt disagree with that, but I don't claim to be an expert on the subject. What codgi said sounds pretty right-on though, based on the little I have learned. Too bad Full-Race Geoff is banned from here, otherwise I bet he'd happily post docs, diagrams, and other related info from his engineering books to prove what is true on the topic either way. Maybe someone should email him for an answer...

 

What about all those setups you see the exhaust comes out of the front bumper/front fender area?
It just dumps a couple feet out of the hot side. No time to build up all those gas velocities that everyone speaks of.
My 2 cents of layman logic :-)

 

My buddy here in town ran a 10.1 in his Evo 8 with the exhaust running out of the passenger side front bumper. Said only change that needed to be made was driver mod.

 

True, but what I meant was in terms of backpressure or the gasses somehow helping the turbo spool faster after they're passed through the turbo, of which neither play a part

 

Because you can calculate at what point that 3" is going to be a restriction and years ago this calculation was done on this forum and testing was done and confirmed by several shops at the time. The 3" has worked on successful rally competition cars, track, HPDE and TA cars and even drag cars that went into the high 8s. If it can do all of that without imploding the car it seems to have proven the point. Now with this new crazy 1/2mile and mile stuff going on where folks want to chase GT-Rs, Lambos etc. then you'd need to do the maths again and see. But if the OP is that serious about that kind of stuff it seems best to get hooked up with a legit shop who can answer the question.

 

The OP question wasn't is 3 inch enough... he wanted to know where to buy 4 inch aluminum v band and muffler.

 

What we are saying is 3" is good enough size for weight, power, etc. Its been proven, I'm not saying it because others are mentioning it. There is no need to going bigger.