Possible milage tuning

J

JAS3+390

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Oct 19, 2011
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Hey guys about six months ago I finished up a 12v ppump conv in a square body Chevy dually crew. Here's a lil rundown of what I've got... Complete rebuild bored .020 over factory cam and bottom end. 4k gsk with 60lb springs and fire rings. 5x12 sticks and a phatshaft 62. Behind it is a nv4500, Chevy 205 case and a Dana 70 with 4.56 gears. Primary use is hauling farm equipment/hay and daily driving. I've got about 12k miles on it so far and am averaging about 11-12 mpg. Planning on running 20 degrees timing and some afc mods but what else can I do to attempt to improve my milage?

Thanks in advance. Josh
 
Is that 11-12 mpg towing? If so that's pretty good already, if not your doing something terribly wrong.
 
I think the 4.56 gears have something to do with it.. kick them to 3.55's or 3.73's should do much better..
 
Fill it up and go on a 100 miles round trip non stop unloaded.

Do that to get a mpg baseline. Hard to get a good baseline when the conditions are different everyday

Short trips and pulling things are not going to net to much better than what your seeing most likely.

What is the timing set at now? Could have slipped and with your crawling gears your not in your sweet stop on the highway.

Ah one last thought... what size tires are you running?
 
Towing runs around 9-10 mpg depending on load and wind direction ..ha. I'm running 315/75/16 tires (bout 34.5 inches tall). Timing is just standard factory setting. I'm sure the gears are what's killing me the most just don't have to coin to swap gears and carrier right now... Especially front and rear. I think timing and afc work will help but will it honestly be that noticeable? Will I lose significant towing power jumping gear ratios that far? As high as diesel is now I hate to be buying so much of it I just don't wanna lose the strength I have pulling to get a mike or two better on mpg ya know.
 
4.10's with your tires will be a good compromise..
I bet your truck is done by 70 in overdrive..
Timing will help, afc tuning and some pump work will all help drive ability, and mileage in the long run..
Just make a single change at a time, drive the same when calculating so you don't do too much at once... A nice methodical approach.
 
With 4.56 gears and 34.5 inch tall tires that puts you a 2000rpm going 60mph in 5th gear. Perfect for towing in my opinion.

Timing will help the most since it is still at the factory setting and probably has slipped even lower than stock.

on edit: 4.10 gears at 2000rpm in fifth would put you at almost 67mph.
 
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Thanks for the info thus far. I've hit 101mph on GPS and I'm sure I was knockin on that four grand(scary I know)! What kind of pump work should I look into? Will 20degrees be a good setting?
 
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