That is the ticket and I agree with you exactly. One needs to have the flow to support the 3.5 inch exhaust to have a gain in power but one won't lose power with a 3.5 inch. If anything, if one doesn't have a large turbo, the power band will shift and perhaps the spool will take longer due to less back pressure.

 

I would have to disagree with you in regards to less back pressure causing delayed spool, exactly the opposite. If there is no resistance,i.e. back pressure, then the blades will spool faster, not slower, hence the reason that all the Grand nationals, TD tractors at tractor pulls & race prepped TD trucks. When I added a bigger exhaust and eliminated my muffler on my F250 Superduty, it spooled faster, not slower.
Les back pressure = faster spool.

 

The back pressure the motor normally likes to operate is given to it by the restriction of the turbo in the exhaust system

On turbo cars manifold runner diameter and length make a bigger difference on spool then the post turbo exhaust.

Backpressure after the turbo is 100% counter productive. Because backpressure is restriction of flow.

 

Well, I agree with you to a point. It really depends on how much back pressure /restricion is in the manifold design. I can't speak to the workings on the EVO because I am not as "up to snuff as I should be". I do understand your point though and can't argue intelligently against you.

But I can argue un-intelligently against you that's kinda pointless though !!!

 

Backpressure is the enemy of any turbo...

The best exhaust you can put on a turbo car is the shortest, straigtest, largest diameter exhaust that you can find.

I am a firm believer in putting the largest exhaust that you can find on a turbocharged car as long as price is comparable. The larger exhaust will provide you with not only improved spool, but also maximum horsepower.

With most of the stock Evos your turbine will have a high expansion ratio (~3:1) that means that any backpressure due to the exhaust will only be multiplied by that pressure ratio and applied to the engine as backpressure. So any decrease in backpressure from the exhaust will result in a factor of that decreased at the engine. Anything you can do to increase the ratio of boost pressure to backpressure will result in less pumping losses, lower BSFC and higher power.

 

Wow....

First we do have a 3.5" exhaust for the EVO. We built about 15 of them and are down to 2 left. It has not been a big seller because we do not push it/promote it. The ones we have sold we have installed at the shop as I have never taken the time to build fixtures for them. Same bends etc as our 3" systems.

We just did Tom's car with a 3.5" exhaust on it. Al's car also has our 3.5" system on it, Matt's too etc. etc.

Comparing our shop car or AMS's car in this debate is just useless. First off all AMS's car, our car, Al's car, Matt's car all have GT42r's on them. The outlet of the turbo is 3.5". Putting a 3" exhaust on a car that has a turbine outlet of 3.5" would just make you a retard, plain and simple.

My general rule is if the turbine wheels is smaller than the diameter of the exhaust you are running it into you are probably just fine if the exhaust is designed correctly.

My RS ran 9.97 at 142 with our standard Vband bullet 3" on it. My brothers car made 100 more whp than my car did with that same 3" exhaust on it.

Is it a restriction? I won't say it isn't but I don't believe it is. I have not done any exhaust back pressure testing in years.

Our 3.5" exhaust is very very light. As a matter of fact I'll go out on a limb here and say it is probably lighter than many of the 3" turbobacks that are out there. We had to pay for special tooling to get it made.

In the upcoming weeks/months we are going to do a test of our 3" vs our 3.5" just mostly for our own curiousity. Myself, my brother Dan and Trent all have goals to take our daily drivers past the 150 mph barrier in the 1/4 mile this coming year. We have been talking about the 3" vs the 3.5". Now we need to find out for ourselves.

99% of 4g63 owners, do not need a 3.5" exhaust and certainly not a 4".

BTW, our black shop car runs a 3.5" outlet, not really an exhaust, it exits through the front fascia of the car. We also dump the external wastegate to atmosphere.

That is a good point. Dumping your external gate to atmosphere will free up a lot of extra flow in your exhaust. This is one reason we do not offer our turbo kits with the wastegates re-routed. I hate that.

 

LOL! Well put!

 

Hey Sgt Blamo, where in So Fl are you getting the 3.5 inch exhaust made?

 

at a local shop here in PSL,FL. I'll let you know when he's done with mine, then we'll see how it sounds. Id be happy to give you his phone# and you can call him directly if you're interested. I'll post pics and a brief commentary after install.

 

also, in florida....here's mine:

https://www.evolutionm.net/forums/sh...d.php?t=240739

 

BTW,
I posted this info, soley for the benifit of others, I have no interest in being involved in manufacturing or marketing a 3.5" exhaust. My only point is to show that it can be done, and done @ an affordable price. Granted, they may be really nice looking exhausts, but when it's under my car, who cares what it looks like as long as it holds together, sounds good and flows well. I'm using aluminized metal instead of SS, I've used this same material on my F-250 Super duty to push 430 hp & 780 tq, with well over 110,000 miles since it was installed, so I figure it should hold up just fine on my Evo. You ought to be able to get one made locally for $550-650.