18.1 Cr

[quickv6]

My old truck just past 534,000 on the clock. I built a new engine at about 400,000 with steel splayed caps etc. Since the old beast just wont die I have never installed it. She is really getting tired so its time to consider the swap. The new engine is an 18 to 1 engine. When I built the engine I towed heavy often so power was a concern. Now I drive more than tow and occasionally tow heavy. The avg fuel mileage on the original 1994 engine is about 18mpg and sometimes I have gotten close to the 20 mark. This MPG with 4.10 gears. The truck has enough power as is for what I do. I am considering tearing down the new engine and bumping the CR back to stock as I am pleased with my current performance and MPG. I still have the stock CR pistons from the original build. I would like to hear from guys that have gone to 18 to 1 CR engines. What happened to your fuel mileage? I am now more concerned with mileage than an increase in power. If I can keep the same mileage or close and get more power in the process that's great. I just don't want to go backwards to that 13 or 14 mpg mark. Little more about the new combo is listed in the sig. I plan to purchase a chip from Kennedy Diesel. The engine in the truck is a plain Jane vintage 1994 6.5 turbo with a ton of miles. (so much for the guys that told me these engine were crap when I bought the truck. This has out lived everyone of my friends Cummins and power Strokes.

[Robyn]

Personally I would leave the fresh engine all together and run it as is.

The 18:1 arrangement is not going to cause any real issues and will add that bit of insurance when you do have to tow and work the engine hard.

Hope this helps.


Missy

[TAG]

I did not notice much difference when I switched. If anything, mileage went up a little. I get a pretty consistent 19.5 mpg in the summer in all around driving, but my commute is 30 miles one way on the interstate. In the winter, it goes down to 14-17 depending on how long I let it run before I go home at night. These numbers are with 373 gears & 285 tires. The combo I have does everything better than the original engine, & towing is no comparison.

[Robyn]

The 6.5 has never been a great mileage getter.

The addition of the turbo, the heavier fueling to get more power, plus the change to the precups (larger ports) and the super sweet mileage that the 6.2 N/A engine were noted for, went away.

20 MPG with a 6.5 turbo is possible, but the 24 Hwy miles that the 6.2 used to get are not there.

Missy

[HH]

I have an 18:1 engine and get anywhere from 17 - 19 with my K3500 with 4:10 gears.

[quickv6]

Good info. I am going to do a gear change. Really thinking hard on 3.42s. I had a 93 6.5TD 3/4 ton truck that pulled better with the 3.42s than my 94 does. That truck also eclipsed the 20 MPG mark. 75 mph on highway I would get 23 and change. Was a 2wd regular cab truck.

[16gaSxS]

I changed to 3:42's about 180K miles back on my C2500 Standard duty. I have towed 5,000 lbs a lot (hauling water) i have towed 20-26 travel trailers from Yuma AZ to Montana about 7 times no problem. I would tow 7,000 without a second thought. I have a canopy on the truck and bug defector set the cruise at 75mph and get 19.8 mpg all day solo on winter #2 and 20.2 mpg on summer #2.:) I hope this helps.

Rather than change pistons what about changing the precups to the smaller higher MPG style???

[JohnC]

With an auto it'd probably be fine. Mine was a standard and the gears were too far apart to tow much more than 5000 lbs, and a bit of a pain towing anything. Granny 1st was too low and 2nd was too high to start off with a load. Great mileage, though!