I don't understand how a larger downpipe could be beneficial with smaller downstream components. Aren't you limited by the capacity of the downstream piping?

 

It still works because you are still relieving a restriction. On a turbo it's all about the pressure diffrential from one side to the other. The larger downpipe allows a greater pressure drop across the turbo. It allows the turbo to spool faster. And even though the rest of the exhuast is not opened up anymore it still makes a difference. Stock is somewhere around 2" so it is a considerable change in size.

ChillinEvo8
If your not going to stop at just an exhaust, which no one ever does, then your prolly better off with the 3". I think there are other posts in this forum that document there is no actual loss on a dyno, it is just percieved. Really on the grand scale would you give up a slight bit off boost to gain much more on boost? Most people aren't putting around off boost in this car.
HKS's pipe probably is better on a stock car but judging from your signature, an exhaust is not the end.

IS2000
No it does not fit. You can buy thier brace to fix that problem. naturally. Some have reported shimming the braces to clear. Pick your poison, but who wants to go backwards, your trying to improve the performance of the car. Some people leave the braces off. I got the brace because I wanted the RMR exhaust parts. Flanged is much easier to work with and IMHO they make good ****.

 

for those of you who missed my previous post, no mod parts would have stayed on my car had I needed a warranty repair. ALL parts would have been removed, including the AFC and the harness extention which is what all aftermarked electronics will be tapped on to. I've modded my last two mitsubishi's and never had a problem with warranties. I've also wired a few other eclipses for friends and removed parts for warranty repairs. Friend broke 2 trannys and got 2 new trannies

 

,

I can't see a 3in losing power over a 2.65. This is why. On NA cars (cars with out a turbo) some back presure is needed to help the motor with TQ. But on turbo cars the turbo it self creates back presure (lag) to help the motor with TQ. Any why to help the turbo spin faster or free-er will help performance. But do you need a 3in on the stock turbo. I don't think you do unless you are looking to make over 350hp. But then again a 2.65 would not have a gain over 3in. Now the quetion is why is hks making a 2.65 instead of 3in. Well I think it's for fit more then anything else. With a 3in downpipe you have to space the tie bars to clear the piping. So instead of including extra hardware (extra cost) hks choose to run the fatest pipe that clears witch is why the odd size of 2.65.

Eric

 

Noit exactly true......turbo cars need backpressure as well, unless we are talking about a very large turbo.

Try it.....remove your exhaust and do a run on a stock Evo.....power down low will stink, though up top will improve.

Why is HKS doing it the way they are? A few reasons, but I would say that a big part is because for most people, the power than a 2.65 inch downpipe can support (upwards of 400) is more than most tuned Evo's will see. Not to mention the clearance issues.

The fit and finish on the HKS downpipe is hands down second to none......

 

,

I don't buy that you lose any power or tq with a bigger down pipe. Low or High. I will 2nd that the HKS downpipes fits great and 2.65 is fine for most user aplications. Just this past weekend I have seen all kinds of setups on a dyno and 3in catless makes the most power even on a stock turbo 13g TD04. 16g would love it.

Email me if you would like to see dyno sheets.

 

Anybody have a link to where the HKS exhaust for the EVO can be purchased? Thanks!

 

hmm the finish doesnt really matter cuz its underneath the car anyways and im droppin it with some tein flexs.. now as for the fit ... as long as the flange is the right size isnt that all that really matters for the fit? other than the fact that some 3'' are having problem clearin our bar?

 

Turbo cars do not need or benefit from any type of backpressure. All upper limits to pipe diameter, in a turbo car, are dictated by: Cost of bending, fitment or noise concerns. Removing an exhaust all together at the turbine outlet yeilds losses due to boundry layer separation caused by a non-gradual transition in effective pipe diameter at the point where turbulence is most deletorious (at the turbine discharge) to turbo performance.

Just my 2c,
Shiv

 

Let me see if I get this right:

Stock Evo exhaust system according to Claudius is 63mm. The HKS downpipe is 65mm. That's a measly 2.56in. I'm quoting HKS JDM downpipe, not sure if USDM is any different?

Can a 2mm increase in diameter (with 'straighter' exhaust path too I assume) yield a noticable power increase? Take out your rulers and see for yourself how small 2mm is.

I have been looking for JDM downpipe upgrade. Curiously, most are 70mm (2.75in): Fujitsubo, Apex'i, Cusco (CP9A)

A couple are 65mm (2.56in): HKS, Monster Sport (CP9A)

So far I only found ONE 76.3mm (3in) solution: Marche (www.cs-marche.com)

Any Evo experts would like to comment on this? Is CLEARANCE the big issue for not making bigger diameter downpipe in the Evos? Sorry if I'm hijacking thread (although I think it's kind of relevant...)

 

The factory exhaust, while ~2.5" at most places, has a lot of crush bent sections to it which make it pretty compromised as far as flow goes. It's worst at the downpipe section which it is literally squashed flat in a couple of places to clear the underbody cross braces. One approach, which we did, was to adding spacer blocks to drop the underbody braces an inch. This allows a full, mandrel bent 3" downpipe but does reduce ground clearance a bit. However, I don't think this will be an issue unless one lowers the car 3 inches or so which, in that case, performance isn't really the biggest priority

Cheers,
shiv

 

As Shiv pointed out hardly any 3 inch downpipes which should tell you something there. Tuners are making huge HP without them so why do you need it. 2 things to throw in. Another reason for a downpipe is it reduces the bends in the piping improving flow. Last if your seriously looking for more HP also consider replacing the turbo outlet pipe into the downpipe. Sizes run from 65 to 76.3 MM. Expect good returns for you hard earned $$$ with it.

 

Actually, our testing has showed benefits of having a 3" downpipe over 2.75". I suspect this benefits are even greater when comparing 3" to 2.5" or 2.6". These benefits are even there even at stock boost levels (which, at 20psi, isn't exactly conservative by OE standards). All things equal, the closer you get to the turbo, the more important it is to have minimal backpressure and exhaust gas turbulence.

Regarding the turbo outlet casting, we are currently running a dual dump set up on our shop car. It keeps the wastegate flow separated from the main exhaust flow several inches longer than the stock piece. We've documented slightly better boost control when running off a simple MBC which is not surprising given the changes. Still haven't been able to quantify any significant output gains. The stock casting is actually quite nice with very smooth transitions. The downside of replacing the factory casting with such a tubular dual dump piece is the installation which is really a bear. Involves taking out the turbo, manifold and radiator/fans. Also involves triming a stud and lots of drilling and extraction if any of the studs breaks

Cheers,
sihv

 

Shiv..I did not mean to say remove the exhaust completely, but rather, removing the cat back section....I have personally run a few Evos this way purely for testing purposes, and just as on the WRX's, the loss down low was very prominent, though power up top did improve a bit.

it would be interesting to see an independant test of the downpipes out there on a single car, single dyno, single day, just for comparison puroposes.

 

But it might be if it is a mandrel bent system versus the stock crush bent. Remember, were talking volume, not length. The stock system might not be a consistent diamter across the board, but the aftermarket one may be. That 2mm over just four feet of pipe assuming two mandrel bent systems would mean a difference of 12 sqaure inches. That might be noticable on a dyno.