Well thanks to the graph in this thread I know I won't be messing with the cat on this car since apparently it barely makes a difference.

Which is good news because messing with the cat is almost always a headache with CELs and emissions testing, etc.

 

Ok, I may be misintepreting the methodolgy of these tests, but it seems that you ran a full 3" downpipe and catback and switched from the stock cat (I think its ~2.5") and a 3" test pipe and 3" high flow cats? If that's so, perhaps the bottleneck in the setup using the stock cat partially accounts for the torque and power difference. However, the 10 WHP difference with those mods doesn't seem that huge.

 

I don't think you guys are really seeing/appreciating the improvements that are actually represented by these graphs.
Yes 10 hp is not huge, but 10 here 5 there, before you know it you have some really impressive power gains.

The most impressive aspect of this test is the truly significant improvement in turbo response. Also keep in mind that these gains will become more pronounced as you increase flow with higher boost/power levels.

The Random high flow cat used in this test was also 2.5", I now have a 3" Random cat but I have not tested it yet. I am getting cams (272/272) this week and have a stand alone ECU with higher boost. I will try this test again, I am sure the improvements will be significantly better with this new setup.

Perhaps looking at the graph this way will give you a better perspective.

 

I'm defintely seeing your gains (especially in the low-mid portion of the rev range), but I had figured they would be bigger with those mods. However, the use of the 2.5 inch random cat partially explains that. I guess as with many stock parts on the car, the EVO's cat is a pretty decent part (considering it has to meet a higher emissions control threshold than an aftermarket unit).

I know its not going to affect many people choices, but I think it would be interesting to see some actual emissions test results from the various different set-ups.

Thanks again for the tests and graphs, its been an interesting read.

 

I recently re-installed my original cat because the test pipe made my car so dirty. I felt the big power lost, my brothers who were familiar with my car also felt it. in fact, they thought my turbo was broken. I just re-installed the test pipe again and am very happy now.

 

welcome to the world of turbo cars. less restrictive exhaust after the turbo means faster spool up and more power everywhere. the engine has more than enough back pressure from the crappy evo 8 exhaust ports, turbo manifold and turbo

 

It is, this Random cat is the only one I have tested that actually showed a noticable improvment. I am going to test the 3" version soon, that should be be even better.

The 2.5" Random does pass emmissions, I am not sure about the 3". I had the 2.5" on my car with the stock ECU for 3-4K with no codes (no cel's) and OBDII scanner also showed no hidden error codes. I have had a stand alone ECU for most of my time with the 3" Random so I cannot say for sure on that one. I need an emmisions sticker soon so I will find out if the 3" is going to work. I will let you know.

Butt dynos are a bit subjective, but I could certainly feel the difference from the stock cat to the test pipe. IMO the Random cat feels more like the test pipe, so it was a good compromise for me.

 

What other high flow cats did you test? I also expect the 3" system to be better, but I would really like to see it compared to a stock cat setup with an aftermarket 2.5" or similar size downpipe and a 3" catback. I believe David Buschur said the two most restrictive part of the stock exhaust are the downpipe and the catback.

I checked Random's web site and I believe they said their 2.5" and 3" cats were EPA and CARB certified. However, it seems the main variant in terms of catlytic ability is the amount of precious metals used in them, which are of course quite expensive. I think in general, to keep the cost down, most aftermarket cats will use close to the minimum level required. However, this is pure conjecture, so I shot Random an email to see if they can provide any hard data.

 

It was a custom made 3" with a high flow Catco core, (see pic).

All I can tell you is that a test pipe was one of the very first mods I tested on my car. With everything else being stock I measured a good 10-15 WHP just from the test pipe. That's actually not that much compared to other turbo cars where removing just the cat in some cases has been good for 20-30WHP. That just shows how good the stock exhaust system system really is.

 

Yep, it just goes to show you that the 30 WHP + gains for the aftermarket turboback exhausts are pretty realisitc.

 

About the comment saying jdm rally teams using stock bov....not 100% sure in this particular situation, but all sanctioned racing bodies have some sort of limitations or regulations. Maybe one of the requirements was use of stock bov, unlikely but maybe. Just like Honda racing in Japan, the N1 group is very limited on modifications and don't allow use of a non-oem airbox. Could be a similar deal here.

 

Wow, last post in this thread was over 2.5 years ago.... and the thread was started just a bit over 3 years ago.

Keith

 

The 3" model uses the exact same core as the 2.5" model. (Heard this from Random Tech when I called to ask about the two cats.)

 

My IX was tuned w/ TBE+Random 3" cat, MBC, stock intake, stock BOV. Netted 340whp/342lbs. Yes, Random does flow very well and it feels as good as testpipe. I tried both and could not tell the diff via butt dyno. My awd dyno was on dynoject. Random is very good piece!

 

but that 2.5" in/outlets going to be a major bottlenecks! get a true 3".