Which precups?

[HillBilly2]

I'm begining the rebuilding of a mid 80's 6.2. I am looking for max mpg instead of power. There was a page here with pics of the different precups but I cannot find it now. Can anyone explain the markings on the precups? The ones in these heads have two dots. The guy I am using to check the heads has a few cracked one I could get some from if necessary but I do not know what I'm looking at. Thanks

[Robyn]

The cups with the largest ports were used in the 6.5TD engines and they were fro power.
For mileage you want the early 6.2 cups with the small port.

There were 1 dot 2 dot 3 dot. diamonds and a whole slew of stuff including no marks at all
The little ports are slightly larger than your index fingernail.

If the heads on your current 6.2 are usable use them. The cups will fit across the line I believe so go for it. Just be sure you have a matched set.

The small port gives a higher velocity to the gas flow as it exits the cup into the cylinder and this results in better mixing of the fuel and air.

I had an 82 GMC Jimmy (Blazer) with a stock 6.2 it had 120K on it when IO bought it. That little creature would consistently get 24-26 MPG on the Hwy.
stock tire size with the 700R tranny and 3.42 gearing in the butt end.

Good luck

Robyn

[More Power]

You can read more about precups here: ;)
http://www.thedieselpageforums.com/tdpforum/showthread.php?t=26336

[HillBilly2]

Thanks Guys, I appreciate your responses. I finally found the pics in the "6.2 Diesel Engine Volume II". I knew I had seen them somewhere.

fwiw, I fit into scenario 2 of the mileage quest. I usually run in cruise control. When the engine is complete it will be getting a rebuilt Banks sidewinder.

If the heads test OK, just use them with the two dot cups or try to find others? If they fail, what to do then? Moot point until i hear the verdict I guess. My engine guy is backed up and the suspense is killing me.

Thanks again!

[More Power]

It's splitting hairs to choose between the various small port cups. There is a big difference between the NA & TD cups. Whether small or large, it's important to use a matched set, along with heads that have a matching casting number.

I put 40,000 miles on a 6.2L with a Banks Sidewinder, after having run the 6.2 for 170,000 miles NA. It was a big deal... :D

Jim