I had my cat back installed today. The first 90 miles of use were positive and negative.
1. I felt my car stronger in high rpm 5000rpm to 7000rpm.
2. I felt the turbo spooling later. With stock exhaust at 3000rpm the car jumped forward. Now just at 4000rpm.
Maybe I have to disconet the negative terminal to have a proper adjustment, I don't know.
Everyone including Ralliart showed me me positive results on the torque side, saying that with a free exhaust the turbo spools earlier, improving the torque.
3. My car is hotter than before. maybe a lean condition
4. More turbo lag.

It would be nice to have some opinions about the results and if possible dyno charts to end with these doubts.

Obs: just a cat-back. Ralliart maker. 65mm mid pipe, 106mm tail pipe. No other mods

 

How big is 65mm in inches?

 

about 2.5 inches

 

wow...all of what you said (except for the part about your car pulling harder between 5k-7k) should be the opposite! your spool should be slightly increased, your engine should run cooler due to the hot gases escaping faster, and you should have less lag (more flow)! i dunno man, the only thing i can say is i have a 3" turboback and i have had a quite different experience.

 

the stock muffler has a spring loaded diverter in it which gives you a little more back pressure when cruising, and when it's in boost the exhaust pressure pops it open. the extra back pressure gives you a little more torque off boost, which is lost when you go with a hi flow cat back.

 

I have some positive news.
In my first G-tech run after the cat-back my car is 0.6 seconds faster to 60 and 17WHP stronger.
I didn't measure 0-400m because I'm with brand new front pads.
I have to do more runs to be sure.

I think that the ecu is adjusting the air/fuel ratio.

One more week and I will post the final impressions

 

Have it tuned or flashed for the catback, and report back. Just bolting on a catback means little without adjusting the ecm A/F parameters.

 

I guess that the stock ECU has the ability to adjust for small mods, like a cat-back and a drop in air filter. Maybe I'm wrong...

After the low temp thermostat I will install the Ralliart ECU. Let's see what they can give me.

 

An evom member, i think his name is Cole Trickle, got an A/F flash on a stock evo and gained 15 hp.

Then he added a catback, gaining another 12 hp.

Then he got the a/f custom tuned for the catback. He gained a big fat 2 hp.

 

isn't the back pressure from our turbo's more than enough to make any other down stream mechanism to have any negligble effect on torque as far as back pressure is concerned???

 

Weird results...
Today I did another g-tech run; It is a 3th gear from 2500rpm to 7000rpm.
After the cat back I got 22WHP more and 24lbs more with a much better toque and hp curve. BTW, all results of the meter were better.
Unfortunately I got a resonace in 5th gear from 3000 to 4000rpm... Is it normal?