8.1 Engine Mods

[RULER]

So are these big gains in mileage and power done with stock exhaust and regular fuel??? If not what modifications will need to be done?? For those improvements

[Alan Roehrich]

You can gain a pretty fair amount with just tuning, Ed is correct, the factory tune is abysmal. There are tunes that use the different grades of fuel. It's still a big block Chevy, it likes timing, and timing likes octane.

There are people gaining substantial additional power and fuel economy with headers and a free flowing exhaust.

There are a couple of people modifying the intake by removing a substantial restriction, some are adding a bigger throttle body, and killing the EGR, as well as relocating the PCV system, because the PCV system will literally suck oil out of the lifter valley.

The intake and exhaust work has shown another 30-50 HP, depending upon how much intake work is done, and depending upon your use and driving style, another 2-3 MPG. If you constantly use the added power, you won't help fuel economy at all.

I have been developing a bolt on adjustable rocker system, but it is on hold right now. The plan is to have both stock ratio rockers for those upgrading the camshaft but not replacing the pistons, and 1.8:1 rockers for those keeping the stock camshaft.

[stock1080]

Please keep me in the loop. Have a 1999 3/4 pickup I want to use to just tow my trailer to races. I never thought there would be any help for that thing. jeff

[Ed Wright]

My GM Calibration Engineer ("tuners" on the internet) friend told me about what all they had to go through to get that engine past EPA. No timing, and a 60 second P.E. Mode delay. Like the power valve on your Holley carb not opening until you had the gas pedal on the floor for a minute. They had to keep them out of P.E. (Power Enrichment mode) during the drive cycles in the EPA testing. Shortening that delay, or setting it to zero, is a mileage killer for people with poor driving habits. I have ridden with people that move their right foot all the time. Their mileage will be lower than other's everytime.

[Adger Smith]

Ed, Do you have to do the tune on the truck or can I just send you the ECM?
Mine is a 2002 1 ton.
Hope your wife is doing better..

[Bob Don]

I'll be following this thread. I have a 2002 2500hd 8.1/Allison for towing.

[Ed Wright]

Originally Posted by Adger Smith

Ed, Do you have to do the tune on the truck or can I just send you the ECM?
Mine is a 2002 1 ton.
Hope your wife is doing better..

Yes, Adger, you can just send the ECM. People do every day.
If you have the Allison transmission, the gains won't be as impressive. The Allison has so much Torque Management programmed in it's computer (TCM) to protect it, that thing calculates the torque output, and tells the ECM to pull the timing back to protect the transmission. I had one truck with that transmission, and hated it. The 4 speed 4L80E trucks are much faster, use less fuel, and tow trailers better. Performance gains with the Allison are not nearly as noticeable. On my chassis dyno, the Allison trucks gained very little. I towed with a gasoline motor home a few years ago, with an 8.1L & 4L80E, it towed my trailer easily, and never an issue.

[Adger Smith]

Yes, Ed mine has the Allison 1000 Trans.
I read an article about "Limp Mode" in the transmission if you modify the engine and the two computers don't communicate.