I was running 0-70 in 8 seconds in nearly 100*F weather in a 5800# truck with a 5.6L engine and 1 3/4" primary headers. It got out of its own way pretty quickly.
http://www.youtube.com/watch?v=lELdtvmah2A
I also towed with it, plenty of low-midrange grunt over stock.
The Express has Thorley Tri-ys and gained noticeably as well even shifting at only 4,900-5,000 rpm in Tow/Haul mode.
Doug Thorley even used dual 3" pipes to mate the headers to the factory Express van exhausts. I reduced from 3" to 2.75" to 2.5" at the cats and used a dual in/single out muffler.
The van has a huge gearing disadvantage compared to the 5spd in the Titan yet it still pulled down a respectable ~8.xs 0-60 and 11 sec 0-70. For a 6,200 lbs beast with only a 3.73 gear and a 4L80E it is not short on torque by any means. The 4L80Es tall 2.48 1st and 1.48 2nd gear ratios are like having a 3.00 rear gear with a 4L60E in first and a 3.23 in 2nd and the 60 lbs stock 13" torque converter also doesn't help the off the line jump very well either, despite having a dual stator and 2,200 rpm stall speed. When you go WOT from idle it kinda lags, hesitates for a second, then takes off like a proded bull!
http://www.youtube.com/watch?v=-6DZhPN7VHQ
Finally the 99 Burb....0-80 mph in 13 seconds on an uphill onramp in 90*F weather.
http://www.youtube.com/watch?v=LYdyu501Z4Y
Like I said I think I have a little first hand experience at making these engines run pretty strongly.
I also had both 1 1/2" long tubes and 1 5/8" tri-ys on the same engine in my G20, the larger tri-ys blew the smaller headers away from off-idle through redline.
When I put the healthy TPI enging into the G20 I was glad I had the extra headroom to make more power.
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