I didnt say that....how weird.

 

I know, I said it...

 

wow i dont know how that happened

 

Gain weight? Are you kidding me? You think that you are gonna feel the performance difference due to the weight of a 5" system over a 4" system? If its stainless, it'll be like what, a pound of metal?

 

Unlike NA cars (Cars with out a turbos) Turbo charged cars do not need any back pressure for TQ. The turbo it self provides enough back pressure for the motor. The best exhaust to have is the largest one you can fit under the car. Most cases 3in is go enough to flow over 400whp on our cars. The Supra guys run 3.5-4 when making in the 800+ hp range.

Is 3.5 over kill for most people ya but it does not hurt TQ or HP.

Eric

 

Well I disagree with you here. Most of what goes on with ic engines on the engineering lvl are not educated guesses. Those of us that did our 4 or more years in college learning about thermo and fluid dynamics can tell you that pretty much any engine can be explained. I agree with THEGVR. he may not have all the facts, but I think he is generally correct. You need a bit of back pressure to gain maximum torque (and no the turbo does not provide enough, if it does then your turbo is from the 80's because the back pressure caused by most modern turbos is ridiculously low thanks to the genious at work at garrett and I've seen the test results to prove it) and if you make your exhaust completely free flowing (or very close) then you are gonna lose some of that torque. Now I agree with the person that said if you are building an all out drag car that this would probably be a good choice. The bottom line is that if you produce 500 or more ft/lbs of torque then it doesnt matter if you give up a little because you can break your wheels loose at will. But for people with modest lvls of tuning done to their car, 3" is more than large enough. Most people are gonna experience some small torque loss in a 3" system anything larger will further exagerate that loss. I also agree with the person that said "percieved torque is alot differnt than actual torque". Anyway, those are facts not "educated guesses". Also you can't use a V6 or V8 that flows higher volumes for comparison, they can use larger exhaust without torque loss, this isn't the case on our little 4 bangers. Anyway, this is not a flame or an attack on 3.5" exhaust this is just me getting tired of all the BS that gets passed back and forth and finally putting in my 2 cents and for the record I'll repeat an addage that just about an autoxer or road racer has heard before. "HP sells cars, but torque wins races."

 

Like I said if you're building full drag car, then you might reap the top end benefits. Obviously you will be launching the car in the 5k+ range and keeping the car in that powerband, your low and middle range won't matter.

The saying "best exhaust is no exhaust with a turbo" is complete bullshlt. You might see a slightly higher peak hp number with minimal exhaust restriction, but you will definately suffer everywhere else. As someone who has been tinkering with 4G63's for 9 years now, and most notibly, drove over 800 miles home from the Shootout one year running an open o2 dump, I can definately say that without a doubt, turbos need an exhaust system.

 

My car feels much better with this exhaust, in fact my car breaks loose at lower rpms but i think i might as well take it to the dyno and get the questions out our heads. I will try to head to Texas this weekend

 

Let me chime in here. There is definately a difference in low end torque as far as a 2.5 in. downpipe vs. 3 in. It has been dyno proven you give up low end for high end with a full 3 in system on a car not powerful enough to make up for the loss. Now I am wondering if sticking with a 3 in. downpipe but increasing the flow after the cat or test pipe might yield more favorable results.

Shane

 

Aniel Are You Stock?
What Is Your Mods?

 

Are you planning on putting in a flex section on the DP?

shelby

 

You ever wonder why our cars loose boost at high RPM's??? The reason why is due to the backpressure being generated at the turbine housing!!! The backpressure is so high it starts to overcome the wastegate spring. Our turbo is not from the 80's. The small discharge nozzles in the turbine create alot of back pressure. By opening up the exhaust much larger after the turbine housing you alleviate a small percentage of this back pressure, but not much. But the turbine housing does definitely create more than enough back pressure.

I got the 4 year degree and I have had a 4G63 since they came out in 1990. Back from the days of the MDSOG, which stood for Mitsubish Diamond Stars Owners Group. One of the founding members back then, was Mr. David Buschur. He said back then, when 2.5" exhausts were the norm. You can't put on an exhaust too big, as long as you can fit it under the car. I guess he still agrees with that statement, so long ago.. I happen to subscribe to that theory as well.

Brian

 

I havent forgotten about you guys, i still havent had time to take it to the dyno, all i have done to my car at the moment is better intake, 255 fuel pump, boost controller, hks BOV and the exhaust. I got someone working on a fuel management at the moment so im going to wait until i tune it to take it to the dyno.

AJT im using a little section of 3" on the stock downpipe flange and then it flares out to 3.5 so im still using the stock flex set up.

 

What happened to the thing called Pressure Differential? The greater the pressure differential from the boosted side to the non boosted side the faster the turbo is going to make boost, the faster the turbo makes boost the quicker you get to your torque. Is this correct?

 

Sorry.

You are correct.. The pressure differential between the intake manifold pressure and the turbine back pressure creates the low end torque. This is governed moreso by the A/R of the turbine housing than the exhaust behind it. The smaller the A/R housing usually translates into quicker spoolup, but lacks the ultimate flow required for high hp. You can go to a larger A/R housing for more top end but loose bottom end response. It is all a compromise with A/R housings. If your turbine housing was so big, then you might be hurting low end by going to an overly large exhaust, but I dont think I have seen a turbine housing that big on an Evo.

Brian