MPG gains/radials,singles,Zenith,etc....

[DMgunn]

Hello, guys.

I've been researching the archives tonight only to find that my new 5-ton (M139 gasser)is destined to disappoint me where fuel-mileage is concerned. Does anyone here have real-world first-hand experience with before and after effects of the following changes (with regard to mileage)?

1)- Changing from 14.00 bias duals to 16.00 radial singles
2)- Zenith carburetor
3)- locking hubs (and t-case disengaged with air-line mod)

My thoughts are that a change to 16.00-20s would be a great benefit because of reduced RPMs at any given speed and MUCH less rolling resistance. I have yet to see someone post any results despite the fact that there seem to be a lot of guys running this configuration. Am I the only one concerned about mileage? Once I go with the 16.00-20s, checking the mpg gain will be at the top of my "to-do" list, right behind "Stand back and admire all that tire".

Any replies from people that have actually made these changes (even to diesels), and not just read about them somewhere, will be greatly, extremely greatly, appreciated.

Thank you in advance for your help.

 

[Recovry4x4]

DM, I think you are right about the dissapointment. Even if your mods double your fuel mileage, it will still be only 4 MPG for the beast. On a good note, in low range it can pull houses from the foundation.

 

[cranetruck]

Hello, guys.... I have yet to see someone post any results despite the fact that there seem to be a lot of guys running this configuration. Am I the only one concerned about mileage? Once I go with the 16.00-20s, checking the mpg gain will be at the top of my "to-do" list, right behind "Stand back and admire all that tire".

Any replies from people that have actually made these changes (even to diesels), and not just read about them somewhere, will be greatly, extremely greatly, appreciated.

Thank you in advance for your help.

IMHO, the mpg thing is mostly academic since most folks don't really drive the vehicles long distances, where 1 or 2 mpgs would matter. It's a hobby, and fun to add features that make the trucks look good or behave better. I have found that most of the changes carry side effects with them, considering the original design goals.
Most mods regarding radials I have seen are not that great for higway driving anyway. Off-road tires are used, which may not have the greatest wet pavement characteristics and improving mpg figures are the primary end.
Patrick (OPCOM) uses commercial truck tires in the front, which I think IS an improvement for higway driving, although I would also free up the tandem axles (which I don't think Patrick did). Then again, he runs dual 1100's in the rear, which looks very good but adds unsprung weight, so who know what this mod does to mpg figures. He has posted his mpg results and they don't differ a heck of o lot from standard.

Bottom line, experiment and post results!

Using homemade bio and veggie oil type fuels is my way to "improve milage".

 

[Towman2277]

RE: Re: MPG gains/radials,singles,Zenith,etc....

Hey man, I have a M328, which is the M139 chassis but with the bridge truck flatbed, and I get 5 mpg on the interstate. The biggest improvements i've done is "free up" the stock oil-canister breather assembly, and I've shortened the 20' exhaust!! BIG Improvements!! I've got singled out 14:00's, and it makes a world of difference versus the dual setup, BUT with the larger 16:00 and added "un-sprung" weight of the tires, it will have about the same acceleration, if not slower, then the 14:00 duals, but you will have overall higher top speed, if you have the power to pull the rpms. Another big improvement is to be 100% sure your valves are adjusted precisely! It may run well, but I promise with a correct valve adjustment, that baby will sing!! I didn't feel any difference from a well-tuned Holley versus the Zenith....just no gasser valve on the Zenith! Hope it helps...... !

 

[OPCOM]

RE: Re: MPG gains/radials,singles,Zenith,etc....

Mileage "improvements" are usually small. A truck of this weight will not get any kind of "good" mileage without the help of Mr. Fusion. Tweeking for a place that puts the gasoline engine in the position where it produces the most torque is usually where the best fuel economy is found. So if the gasser has a peak torque at 2200RPM, then that is the RPM where you should try to do most of your driving if you want the best economy (I do not have the torqque curves). If the speed does not suit you, then wheels and tires and maybe gears in some cases can be changed. If you can deal with slower acceleration, then bigger tires should help. I changed tires to the larger size to reduce engine RPM, not to make MPG.

 

[area52]

Re: RE: Re: MPG gains/radials,singles,Zenith,etc....

Hey man, I have a M328, which is the M139 chassis but with the bridge truck flatbed, and I get 5 mpg on the interstate. The biggest improvements i've done is "free up" the stock oil-canister breather assembly, and I've shortened the 20' exhaust!! BIG Improvements!! I've got singled out 14:00's, and it makes a world of difference versus the dual setup, BUT with the larger 16:00 and added "un-sprung" weight of the tires, it will have about the same acceleration, if not slower, then the 14:00 duals, but you will have overall higher top speed, if you have the power to pull the rpms. Another big improvement is to be 100% sure your valves are adjusted precisely! It may run well, but I promise with a correct valve adjustment, that baby will sing!! I didn't feel any difference from a well-tuned Holley versus the Zenith....just no gasser valve on the Zenith! Hope it helps...... !

So how did you "free up" the stock breather? Where did you find the proper procedure for adjusting the valve?

thanks

 

[DMgunn]

RE: Re: RE: Re: MPG gains/radials,singles,Zenith,etc....

I am curious about that breather work as well......as far as the 16.00s are concerned, I am aiming primarily for a lower cruising rpm.......lots of open spaces (flat and boring) here in ND, and I think that this apparent torque-monster should have little trouble with the additional diameter. As far as unsprung weight and inertia, I find it difficult to believe that single 16-20s could carry more mass than dualled 14s. I will expect a modest loss of acceleration due to reducing my efffective gear ratio, of course.

The only personal experience I can use that relates to this is my old work/play truck. I went from 33x12.50 radials to 35x12.50 radials, with 4.10 gears and a small block, and noticed no differences in perceived power whatsoever. Then I went to 35x14.50 bias belted Swampers, and went from 11 mpg to 8.5 mpg with no other changes, and the truck drove like a person walking with 3 lbs. of clay on each boot. Gutless and sluggish. Had to turn the steering wheel half a second earlier before it would respond in a turn. Couldn't even pull 5th gear against the wind. But boy, would she float in saturated stubble and sod............but anyway, back to this topic.

Now if I apply that example to this truck, but on a different scale, I would have thought the improvements in mpg would be significant. Is the drivetrain just that inefficient? I will not disable any of the axles, even by removing a driveshaft....if I wanted a highway truck, I would have bought one. Had hoped for 8 mpg, but I can live with 5 or so, I suppose. Hell, I can live with .5 or less - still not going to sell my new "baby", just want to drive it more than that would allow........sheesh, looks like I just wrote a novel...