Hey guys, so this is the third season with a turbo on my car and I'm thinking I need to make some changes.
First here's the setup:

GMPP 350 crate engine (330hp rated)
Stock vortec heads
Stock cast rotating assembly
9.1 compression
212/222 @ .050 hyd flat cam
ARP head studs
Perf RPM intake
650 Demon - blow through
Holset H2E turbo
Intercooler
4" exhaust full length of car with flowmaster race muffler
700r4
Vigilante 9.5" converter 3200 stall advertised - flashes to 3000
Moser 9" 3.25 gears with true trac
M/T Drag radials 255/50/16 (26" tall)
Full interior plus stereo, sound deadening, turbo stuff, etc

I'm running 10 psi, timing at 19 degrees, AFR 11.5-11.9 at WOT. I was hearing detonation (very faint so can't say for certain) so I backed timing down to 19, usually I have had it a couple degrees higher.
Last night I ran a best of 11.8 @ 118 - 1.76 60' at 10 psi

Two years ago I ran 11.55 @ 123 - 1.87 60' at 10 psi and 20-22 degrees timing.
The only two differences back then were that I had 3.42 gears in the 10 bolt and only had 4ft of open 4" exhaust off the turbo. Heck I could trap 118 on 7psi back then.

The reason I went with 3.25 gears was with the 3.42's I was at 6100 through the traps at 122mph and I wanted to bring it down some. My combo is out of steam at those rpms so I figured it would help. I thinking my converter is slipping too much on top end and gearing it up might just be a band-aid.

My exhaust has got to be affecting HP, in addition to the extra weight. I went back through old videos and I was still trapping 120 on 8psi when I switched to 3.23's in the 10 bolt before swapping in the 9". I bet the 9" might eat up a little.

What does everyone else run for rpms/trap speed and with what size tires?

I think next time to the track I'm going to remove all the exhaust and run my stubby out the side and compare.


Anyone have similar experiences with adding more exhaust or a muffler?
Thoughts on getting my converter tightened up and maybe gearing it back down some?

 

get that thing on a dyno and check the power through the mufflers verses open. U will get idea of the power that is dropping off.