1. Thanks for the wise "let's wait until the results are in" encouragement. IMO, at the very least, a positive benefit will be that because it will be really loud, it will **** off my domestic friends even more when I hand it to them....

2. This isn't my first rodeo with turbo cars. My experience tell me that less backpressure improves spool-up time dramatically. Take your exhaust off your car and just run a downpipe and see how much faster your car spools up. It is quite a dramatic difference. Well, the only way to decrease backpressure is a) Shorter exhaust, which is why people do front fender exits or b) Go to a larger diameter tubing if you still want to run full length exhaust.

The Mustang pic I attached was my car that I just sold last year. It was a consistent 8sec car all day. It has a Precision pt78gts turbo, '04 Cobra engine, and 3.5inch aluminum exhaust. You can see it under the car in the pic below. The outlet on that turbo is 3.5 inches. The downpipe is 3.5 inches. At the end of the downpipe there is a v-band clamp that holds the straighttube that connects the muffler. BTW, for "mypipeissmalldan" who thinks that "a good 3inch stainless tubing" is "just as light" as my 4inch aluminum, know this - that entire exhaust on that car, including the aluminum muffler, could be picked up using two fingers. That's how light it is.

When I raced the car, sometimes I would disconnect the exhaust so that I was just running the downpipe. The change in spool-up time was HUGE on that car (it spooled much quicker) because the backpressure from the exhaust piping was eliminated.

BTW, I drove that car to consistent 8.70s @ 155mph and this was with only 670rwhp on a Mustang dyno. It went that fast because it only weighed 2600lbs without a driver. Weight makes a huge difference in what a car will actually ET at the track.

But, I'll tell you this, while my Evo will not out-ET this car (at least with my slow-shifting rear-end in the seat...might be a different story with a better driver in the seat), it will out-MPH this Mustang ALL DAY LONG, and that's a fact

 

hey good luck with the aluminum exhaust. let me know how it sounds. my friend custom made one for our ST race car with a 3" vibrant aluminum piece. it's pretty freaking loud just fyi. its pretty durable, with that much power its going to be loud. my friend is custom making aluminum exhaust for kseries cars now, and i was thinking of having him make one for my evo. but after having one and seeing how loud it is, i dont know if its bearable unless its your race only car.
again like most people are saying the stock exhaust doesnt weight as much, so your not going to see those numbers you posted. plus you have to add in the weight of your aluminum piece. i'd say you'll drop roughly 50 lbs from the perrin/cat/ dp to puttin yours on.

 

You might be right on the weight part. I know I'll shed pounds, we'll have to wait to see how much.

As far as the noise goes, my car is a weekend, fair-weather toy. I really don't care how loud it is. If it was a daily driver it would be a different story for sure.

 

I completely agree with your reasoning here. Now the question is "Why is this true?" My understanding is that once hot exhaust gases leave the turbine they immediately want to expand outward. If the turbine wheel is 3inches tip-to-tip and the outlet diameter on the housing is 3inches, and then the downpipe is the same size, the gases will not be able to expand until they exit at the tail-pipe. This WILL cause backpressure in the system.

In lower power cars this isn't that big a deal, but when you are pushing one of these little engines, backpressure needs to be eliminated. Larger tubing allows expansion of the gases and reduces backpressure.

Others have gone fast with 3inch exhaust. I'm not denying that. But all the components need to be considered - especially the weight of the car. I don't know for a fact, but I'm guessing some of the shop cars mentioned that are going 8's through 3inch exhaust are sub-3000lb cars, and probably closer to 2600-2700lbs. Well, my car weighs about 3200lbs. Additionally, I would also be willing to bet that these shop cars going this fast through 3inch would actually go just as fast ON LOWER BOOST through a larger diameter exhaust.

In the end, I made 780whp on 44lbs of boost last year. If I can make that same power figure at 39-40lbs of boost that will be great, because the engine isn't being pushed as hard to make the power.

 

Who cares about your evo, more pics of the mustang!! haha...

 

Here's another one in the stable, B.J. Still have this car.... 1989 20th Anniversary Turbo TA. 12k original miles. Full Stage 2 Buick engine with 88mm turbo. 4inch stainless exhaust with a 3inch electric dump. Car makes 900hp @25lbs on E-85

Again, on this car when the dump is opened the turbo spools much faster than when I close it.

 

awesome work. i'm looking at doing 3" aluminum cat back exhaust also, but the muffler will be at stock cat location. so i have room in the back to have a clean diffuser. also i don't want to run the aluminum pipes too close to the turbo as it might melt under track conditions.

 

I am LOVING the look of that downpipe great job so far!

 

Make sure you run lots of hangars on the alloy exhaust.
If you do not it will sag from the heat, even if it's towards the rear of the exhaust. It still gets very hot.

 

^ yeah, aluminum is a big heat sink. and there's flames shoot out the back between every shift, so i'm sure it's still pretty not back there

 

 

H8rs gonna H8.

Awesome work man!

This evo is your first turbo car right? jk jk

 

I have done it many times.

 

You aren't kidding! LOL!

 

Really? You've driven a manual transmissioned car to high 7s or low 8s in the 1/4 mile?