*** 4/18 EDIT: For those interested in getting the same 3" DP...you can get one from Hogan Performance. Info here:

http://www.hoganperformance.com/HBodyGM.htm

***4/15 EDIT: Results posted further down ***

Several weeks ago I had Ed Morad send a stock 00+ DP sent to Hogan Performance to get a custom 3" DP made for my 03. Well it'* finally on the way for test fitting!

It'* designed to bolt up to the square flange on the inlet of the stock cat (no welding...complete bolt-up). Unfortunately, the square flange is not standard so it had to be custom fabricated. Anyway, I'm hoping this will allow me to finally drop to a 3.2-3.1 pulley and hit 13s.

I'm going to get "before and after" dynos done to see what gains a 3" DP actually makes. No tuning changes, etc.

I'm no expert by far, but everything I've read is those stock pipes are about as big as the 3800 needs. I doubt you will realize the potential of those 3"ers unless you build up the ability of that engine to suck in, and use, more gobs of air and fuel.

I'll be very interested to see your before and after figures. Keep us posted.

If you already have cam like your sig said, youll definatly feel a difference with the 3" downpipe, at least on the strip.

Youll need to scan to see if a 3" pulley will run fine, 3.2 will run fine with your cam and dowpipe, probably.

that is probably what you need to get you into the 13s if exhaust is having issues getting out.

However the performance from those is noticed more on the GPs

Disagree, i have SLP'* headers with the downpipe and it make a hella difference!
a L67 is a L67, on a GP or on a Bonny.

HIGHLY interested in getting one just like it... can i purchase one, or can i purchase the stock one?

have you seen a side by side comparision of the GPs downpipe vs bonnie?


GP is restrictive as h***

I never said you would not gain performance if you had the supporting mods....Bigger DP goes hand in hand with headers.

My headers are for grand prix, fitted for my bonneville, yes ive seen both, the SLP downpipe (probably the same as for the GP, come 6 inch further than my original. and look smoother.
But like you said, it give performance anyway .

Well I got a chance to get the DP installed today at my buddies shop. When I got there we pulled it up on the Dynojet dyno and got the car all strapped in. (Side note: The wideband 02 was not reading probperly, we couldn't get the torque to register properly and the printer was out of ink. :( Unfortuntely, the dyno graph only shows HP and MPH.)

Mod & Tune info
======================================
As in my sig, I have the 3.3 MPS, FWI, VS Cam, PEMs, 180*, TR6iX@.60 and the stock DP. My tune (via my PowrTuner) for the car is fuel tweaked with stock timing table. (I never bumped timing because I've had trouble tuning out my KR issues at WOT.)


Before DP Install
======================================
We did 3 "before" pulls in 2nd gear. The second pull was dropped because the car downshifted to 1st. The results of 1 & 3 are as follows:

* Pull 1(blue): 232.5whp. I had the normal KR issues (4* spike with 1-3* during WOT.)

* Pull 3(red): 230.3whp. Again more WOT KR. The KR is evident by the dip in the power curve at 80-85mph.


Installation of the DP
======================================
We let the car cool for about 20 minutes and my buddy Steve began removing the stock DP while I sat and watched. The 4 nuts that hold the DP to the cat were rusted pretty good. Steve used a torch to heat them up and they zipped right off...no broken studs.

Install of the new pipe was easy as cake. It lined right up and bolted in fine. We were lucky enough that the gasket on square flange was able to be reused. Started the car up...no exhsut leaks. WooHoo!


After DP Install
======================================
We strapped the car down again on the dyno and let it idle for about 5 minutes to let it warm back up to operating temp. (I did this to ensure it was just as warm as the first 2 pulls.) We did 2 "after" pulls in 2nd gear. The results of pulls 4 & 5 are as follows:

* Pull 4(green): 242.3whp. I had gotten small blips of KR (< 1*) @WOT, but it looks like my steady 2-4* KR issues are gone! Notice the HP increase across the entire power band with it peaking around +10-11whp.

* Pull 5(purple): 243.2whp. Again reduced WOT KR. The dip in the power curve at 80-85mph is gone and has smoothed out. Again, a constant HP increase across the entire powerband.

Summary
======================================
Well I hope this helps provide some concrete evident that a 3" DP is an effective supporting mod. It allows the engine to breathe better allowing it to make more HP and reduce KR. I'm very happy with the results. It was really nice to be able to do "before" and "after" pulls to see what a mod provides.

In the coming weeks, I'll be working on getting the Bonne tuned with dropping down to a 3.2 pulley (maybe a 3.1) and dialing in some more timing. I feel pretty confident 13s are just around the corner.

Here'* today'* dyno graph:
http://www.glovertech.com/BonnevilleClub/3dpDyno.jpg

This is awesome! it really show what i felt with mine

Nice work!