I have L98, ported/siamese plenum, SLP siamese runners, Suncoast Ram Air, Airfoil, T.E.S headers, Catco High Flow Cat, Borla 3" adjustable cat-back

Since new I'v had the full open plate in, Some people were telling me that full open w/ 3" exhaust I was flowing to much. I put in the full closed. its quieter, but deaper now. Think it changed any back pressure, or performance doing that,,,,I seemed to have no top end before, like it couldnt make power, ...seems to now though.

 

3" flow isn't too much, if you lose any low end power you'll pick it up in the high end or maybe it's vice versa, but I thought it was the high end that you'd pick up, but you said that wasn't the case.
As far as backpressure, you don't want any backpressure, the less the better.

 

I think what you want is better scavenging, not backpressure. 3" exhaust on an L98 is fine, TPI is gonna make low RPM Torque no matter what, so its OK to pick up power in other places and extend the range out some more.

Get/borrow a G-Tech and run it both ways.

 

I have a G-tech but I'm gonna leave it like it is for now, those bolts are TIGHT, you need impact to get them off, and I only have that at my friends house (look at my post about Pics of my friends car WORK IN PROGRESS and you will see his house, its HUGE)

 

If you get the chance, post the results.

 

Yeah, I'd be interested too...

 

when I get enough time to do it I'll post.