questions on 8.1 motor in 2004 Chevy truck

[Kegracing]

All,
I posted in the support section, but we don't get much traffic down there.

Looking at a 2004 Chevy dually with the 8.1 gas motor and Allison trans.

What is considered high mileage on these motors? (assuming good condition, good service, not abused, filters oil etc all taken care of correctly)

Known problems with these motors?

thanks
Ken

[Alan Roehrich]

I have a 2003, I love it dearly. Wouldn't trade my 8.1 for any diesel of any type or brand.

Some of them have slight piston slap when cold. Don't rev it up cold. It won't hurt a thing.

Some of them use a little oil, maybe 1 quart in 3000-3500 miles. The vast majority of them are actually sucking some oil from the lifter valley under the intake manifold due to the design of the PCV system. It is not getting oil past the rings, or past the valve guides and seals. It's simply picking oil up through the PCV system built into the intake that has the pick up in the wrong location, and a serious lack of baffling.

The PCV system design will cause deposits to build up on the plugs, usually at 25-30K miles they'll look a little rough. Change them, the deposits can cause enough resistance to create a misfire, and could cause enough load to kill a plug wire or coil pack.

I use 20W-50 Royal Purple in mine, and because it is a 2 wheel drive, I use an AC PF 932 two quart filter. My truck will be down maybe 1/2 quart or a little more between oil changes.

At 96K miles I replaced my plug wires with Taylor wires to resolve a slight misfire under acceleration. And I went back to the GM AC Delco double platinum plugs.

It's a tough big block that makes really good torque, with proper maintenance it should go 200K+, and possible 300K+ before needing anything serious.

If you live in an area where they don't require emissions testing, or at least don't look at the exhaust, at least get rid of the catalytic converters, better still, put a nice exhaust system on it, and get the ECM tuned. Power will increase considerably, but so will fuel economy. You can also put a GM 180 degree thermostat in it, big blocks don't like to run hot.

[Kegracing]

Thanks Alan.
Appreciate the excellent feedback.

Ken

[Rusty Davenport]

One of my best friends has several of these trucks that roll everyday....he is in a REPO business and they have cars hung on them everyday ......they must be hardcore tough original motors and at least three of them has turned 250,000 with store brand CARQUEST oil changes and filters......amazing trucks no joke

[Mark Howes]

Running the 2004 8.1 Allison combo in a motor home. Lots of power. Hauls motor home and trailer up and down the hills as fast as you want to go. Only 40.000 miles so far so sounds like lots of life left

[Alan Roehrich]

I'm behind on my projects, but I'm actually developing a kit to convert the 8.1 to adjustable shaft style rocker arms, under the stock valve covers. If you're keeping the stock camshaft, you can use 1.8:1 rocker arms for a little boost in power. If you're changing cams, you'll probably want 1.7:1.

The intake manifold can be modified to solve the PCV problem, and also for about a 30HP gain, by cutting it open to remove a baffle or two and doing some porting. The stock PCV system inside the intake manifold is closed off, and the PCV system is run externally at the oil filler tube (you won't want to add oil with the engine running).

My personal truck will be getting a set of Hedman headers and 3" true dual exhaust.