They all seem to leak a little, I actually found a 2-3HP increase on the dyno by changing the DV on back to back runs. It's long, but this thread explains it in detail.
https://www.evolutionm.net/forums/sh...threadid=24611

 

I wonder why all the EVO VII and VIII JDM race/Rally cars use the factory DV then? I have seen alot of set ups and I have never seen a after market DV.

Maybe yours was defective. And I do understand that the turbo working less with no leaks witch would equel a little more power.

Thanks
Eric

 

That could be, I don't know any one else who actually bothered to test the stock DV. I would be interested to see others try the same test. That is mainly why I put so much detailed info out. I wanted to make sure I wasn't missing something and hopefully get confirmation of my test results.

It's not hard to do, all you need is a 1 1/4" to 1/4 or 3/16" male to male adaptor (hardware/plumbing supply) some 3/16" vacum hose, a tee connector, and a compressor.
Remove the DV including the hose going to the intercooler tubing, leave that hose attached to the DV. Install the 1/14" in the hose and clamp it down, then connect a vacum hose via a three way tee to the adaptor, the DV actuator nipple, and your compressor. Adjust your pressure accordingly and turn it on, does it leak?

I think you will find that it does, because it is very difficult to get an air tight seal without using rubber. I was a little suprised at how much air was actually leaking, and that I could see a HP difference on the dyno.

I have been around long enough to see many highly educated, experienced, reputable, individuals and companies make mistakes or just over look some simple little detail. So just because the JDM Rally team did not upgrade/replace the DV does not necessarily mean to me that there is nothing to be gained there. You never know, perhaps next year there will be an upgraded or different DV from JDM.

Kind regards,

Eric

 

Oh I'm sure it could have bin over looked. But if there spending some money moddifiying there cars for racing why would they not just change the DV. That's what I find odd. Most off these cars are stock Turbo BTW. There might be a reason that they were designed to leak a little. I like the ??? why first.

 

I think this may be correct, let me try to explain.

The stock DV uses a relatively heavy spring tension. If it sealed completely I believe you would get excessive surging especially at part throttle/light load. The spring tension is actually much much higher than what is actually needed to keep the valve closed under full boost/WOT, even with after market modifications and much higher boost. Other DV valves I have seen are nowhere near this stiff and can leak at WOT with higher than stock boost levels, this is not the case with the stock EVO DV.

I have found that a softer spring tension (compared to stock) with a rubber sealed valve actually reduces part throttle surging improving drivability, and seals better making slightly more power.
The spring tension I use is also more than enough to keep the valve closed under WOT at ridiculously high boost levels, far more than the stock turbo could ever put out.
There is a down side though, the valve makes a high pitched squeeking sound when lifting at part throttle. This noise does not bother me, but many people do have a problem with it. If you increase the spring tension you can get rid of the noise, but then you get compressor surge drivability problems.
Do you think that a high pitched squeeking sound every time you you lift off the throttle would be acceptable in a production car?

So if your Mitsubishi what do you do? Well increase the spring tension for better throttle response, higher boost, and less noise. Then by designing it to leak a little you minimize the surging/part throttle drivability issues. Yes you give up a slight amount of HP but there is always some comprimise.

So yes the stock DV will work with much higher boost so it's not really necessary to replace it for higher boost HP modifications. I found that you can pick up a slight amount of HP and actually have better part throttle drivability, as long as you do not mind the noise.
This is why I suspect the stock EVO DV is the way it is. It is only a slight improvement in HP and drivability, and then you have the added noise. So this mod may not be for every one, and you can certainly still make a lot of HP with out changing the stock DV.
Does that make sense?

 

Yes it does .

 

Where can I get a Random High Flow Cat (3 inch)?

 

I ordered mine direct from Random http://www.randomtechnology.com/, part #703007 retail price is $302.17. Any performance shop should be able to order it for you, also from what Random told me no one has it in stock yet.
I just got mine the other day and have not installed it yet. I will be doing some dyno testing in the next couple of weeks for this 3" version along with my new Power FC, butt dyno acceleration and drivability impression along with features and tunning ability is awsome. I will be posting impressions pros/cons with dyno graphs for both of these items in the next 2-3 weeks. Stay tunned.

 

Yeah Silver let us know if you get that check engine light from the 3"random.It took about 400 miles for me when i went from the 2.5" to the 3".

 

Oh I am selling my 2.5" Random cat (asking $180). This would be a great upgrade for some one with a 2.5" or stock exhaust system. I had it on my car for about 6 weeks and no cells. PM me if your interested. I also have another slightly used custom 3" high flow cat for sale $100.

 

Well, unfortunately or fortunately depending on your perspective, the Power FC does not care about emmisions, it won't throw a code even with a straight pipe. I already have the Power FC installed and tunned it on the street. The car just drives and pulls soooo much better, I don't think I can force myself to drive around with the stock ECU any more. I can't I won't

Random did say that there is a possability that the 3" cat flows so much more air that it might throw a code. They were supposed to do some work on that, and I did notice that this new 3" cat seems to have a slightly heavier coating than the old 2.5" that I am running now. I did snif test the 2.5" cat just out of curiousity and it does pass emmisions, not as good as the stock cat but good enough to be acceptable.

Actually with an OBDII scanner you can actually see if there is going to be a problem long before the ECU throws a code. The ECU can see the problem immediately but it just waits a while before it throws a code. Since your 3" cat is probably just barely out of spec it waits much longer before it reports the error.
I suppose I can reinstall the stock ECU long enough to run an OBDII scan and see if there is a problem.

I have about 3-4K on this 2.5" cat and it has absolutely no problems with ECU emmision checks.

 

SILVER SURFER,

which DV do you use and/or recommend?

thanks,

 

I use the Greddy type-S with one spring, (they come with two installed). It makes a slight chirping noise when lifting at light throttle, other than that it works great. I have also tested the Forge DV and IMO it is also a good choice. A couple of people have had problems with both of these valves, but for most they seem to work great. That seems to be the case with just about every product, if you know what I mean.

 

Thanks for all the great info Silver Surfer. I will be getting the Random 3" cat.

 

whats the difference between random 3" and ultimate 3" is it the same.. and isnt' ultimate cheaper???