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View Full Version : Chevy 8.1L Modifications



don johnson
11-23-2004, 10:20 AM
FYI.... All you Chevy 8.1L owners. I just completed a succession of modifications and documented the dyno results of each. Here were my findings;
Test- 2005 Suburban 4 x 4 8.1L
Stock= 262 HP and 386 ft lbs torque at the rear tires
Added Gibson Shorty headers and cat back= 14 HP and 27 Ft lbs of torque increase
Added Volant Cold Air Induction= 6 HP and 9 ft lbs torque increase
Added Westers tuned computer= 56 HP and 63 ft lbs of torque increase
In total picked up 76 HP and 99 Ft Lbs which maxed at 338 HP and 485 Ft lbs at the rear tires
The Westers tune was by far the biggest add on. Lyndon Westers custom programmed my computer in 4 days and the tune was set up to compliment the headers and cold air. A huge plus of the Westers is the reprogramming reduces the torque management and removes the speed limiter. We are taking the Sub to the river this weekend so we will get a great idea of increase in MPG but just driving around town it seems to have gotten an increase in MPG.
The Westers tune was a huge improvement. The car passes with ease without downshift now and is simply a lot more fun to drive. It drives like an 496 CI motor should now!
For the hell of it I also dyno'ed an Hypertech handheld reprogrammer to compare a handheld/ flash reprogrammer to the Westers custom tune and can tell you that the Hypertech sucks by comparison! The Hypertech did pick up 17 HP and 24 ft lbs of torque. However, not even close to the Westers... Both tunes were set to run on 91 octane.

Havasu Hangin'
11-23-2004, 10:39 AM
Nice job, Don. My 8.1 Sub needs some help, too. How's the noise level with the headers and duals?
Let me know how the trip goes on the mileage.

cdog
11-23-2004, 11:30 AM
Thanks for the info. I did headers to my 96 3/4 ton work truck and they were noisy. I did a programer and a flowmaster on my 03 sub with the 8.1 and it helped quite a bit. Mostly what helped was the shift points in the tranny. Stock the trans short shifts and the 496 is so de-tuned that it does'nt make the torque to pull thru the gears. If they just put the allison in these damm things they would be great! My MPG is a little better than stock but I did the RV settings so I do not have to buy 91 octane.

don johnson
12-03-2004, 06:29 AM
Nice job, Don. My 8.1 Sub needs some help, too. How's the noise level with the headers and duals?
Let me know how the trip goes on the mileage.
The shorty headers were a little louder but hardly perceptable.
Over the Thanksgiving weekend drive the Westers tune raised average MPG from 9.5 to 10.9. Huge increase. What a difference in driveability. This thing really scoots now! Shift is firmer and it now shifts where it should. It will also leave 2 huge patches of rubber off the line if you want....