I have an HKS DP sitting here not installed yet. How much power will this really add to my EVO when all I have done right now is a drop in filter and a cat back exhaust? I know adding a DP on my WRX helped a lot, just not sure if there will be similar results with the EVO.

 

It will help quite a bit if you have the cat back already.

What are you waiting for... Install it. P/S your exhaust will get a little louder and you will notice more mid range power.

 

No, it won't help much at all with the stock cat still in place. It will not get noticably louder, nor will it give more power anywhere, because the cat is a major choke point, but the downpipe is not.

Buschur already did this testing and showed no gains.

 

Well, it depends on what you mean by no gains. The dyno chart may have not changed, but there was definitely a difference in on-off-on throttle behavior with just a downpipe. I had to consciously move my throttle application later coming out of corners.

To the original poster:

If you plan on doing a downpipe, it's probably worth it to go ahead an do a HF cat while you're down there. Increase in boost response from the two will be just as enjoyable as any peak power gains.

d

 

No such differences in my car with a downpipe - way too minimal to notice, that's for sure.

 

And I won't throw a CEL with a high-flow right, just with a test pipe? Whats a good one to get?

 

You most likely will unless you get one with a built-in fix. Not sure why you'd care, though. We all get the CEL, and we all fix it with one of the many cheap methods. All the HFCs are good to get, because they are all pretty much the same - very little power and cost a lot.

 

Well then whats a good fix? With my WRX we did some fuse type thing and it worked. I just don't want to stare at a CEL at all.

 

There's several of them - I'm sure you can find several hundred threads talking about them. We don't drive around with CELs. You haven't seen the tons of threads talking about this? Blah.

 

Nah, other than lately I don't get on the internet much. Too busy. I guess I'll try to find some threads soon about this. I don't want to spend a lot of money though either.

 

I already told you above there are several methods, and they're all cheap.

 

the spark plug non-fouler fix works great had it for a couple months now since i installed my TBE and no CEL at all costs less than $4.

 

i noticed a little more power in the mid range with just the downpipe
then added the test pipe later and noticed the tone get deeper and the power grow even more
a quick fix of the CEL courtesy of perrin and you are good to go

 

I have the Perrin o2 sim as well and it works great, no CEL and easy to install.

 

Nice, so far the Perrin sounds the best. How does it work? Is it just a different O2 sensor, or is it something that needs to get sautered in? (I know I spelled that wrong)