RPM/ MPG sweet spot for NA 7.3

[pybyr]

Anyone have any reference data (or know where to get any) that'd indicate the RPM/ MPG sweet spot for NA 7.3-- in other words, the place in the HP and torque and fuel consumption curves that yields maximum output for minimum fuel-per-unit-of-work?

I know that charts of those variables (although I forget the term) are available for industrial and over-the-road truck engines, but have not been able to find one yet for a N/A 7.3 like mine

Thanks

Trevor

 

[icanfixall]

1850 rpm is where I get the best mpg. At that rpm and in doublr overdrive I'm doing 85 mph... I have the gv overdrive and my final drive ratio is 1.96. The mpg is 18.9 and this was done in my 2100 mile trip home from last years rally with the Moose pump. I probably could have done better slowing down and not be in double od...

 

[lotzagoodstuff]

1850 sounds pretty good. If I keep my truck at 62 mph, I get pretty good mileage. If I wick it up to 80 mph and mileage cuts nearly in half (literally). The taller tires helped increase the cruising speed about 2-3 miles per hour, but they are heavier so I'm not sure I gained anything with the 35s (except a better looking truck in my opinion). I can't justify changing the 4.10s as my truck pulls anything I put behind or in it. Not to mention: they are in there, working, and paid for!

I like to get where I'm going, but keeping the R's under 2000 is where you need to be for mileage. I would really like to see somebody put an IDI in a two wheel drive 1/2 ton with like 3.08s and really go for mileage with a lighter weight rig.

 

[funnyman06]

Well actually that has already happened, Mel helped his son put a 6.9L in an F150 and they were getting very good mileage. I think close to 30 on the highway

 

[THECACKLER]

Ditto on the 2000 RPM. If I hold it to 2100 I get 20% better mileage than cruising at 2400. Wind resistance has a lot to do with it as well. Ask the ambulance drivers.

 

[snicklas]

I believe the "sweet spot" is at a point at, or just above the RPM that gives maximum torque. For Example, with my 03 Excursion 6.0, if I keep the RPM's between 2000 and 2250 RPM, I can get almost 20mpg on the interstate, crusing. If I bump it up to the 2500 RPM range, I loose a couple of MPG..... Now this said, the 2-2250RPM range is about 72-74MPH. 2500 is about 80. So for me running the speed limit gives me the best MPG. This is why most of the IDI trucks 50-55 MPH gives the best mileage, as this is about the correct RPM for max torque. Remember the IDI trucks were designed when the National Speed Limit was 55. My truck was designed when the National Speed Limit was 70

On Edit:

Looking at a Ford Manual.... the 7.3 IDI made Max Torque (338lbs) @ 1600 RPM and the 7.3 Turbo IDI made Max Torque (388lbs) @ 1400 RPM. So If you were to stay in the 1800-2000 Range as listed above. This should give you maximum MPG.

 

[david85]

1850 rpm is where I get the best mpg. At that rpm and in doublr overdrive I'm doing 85 mph... I have the gv overdrive and my final drive ratio is 1.96. The mpg is 18.9 and this was done in my 2100 mile trip home from last years rally with the Moose pump. I probably could have done better slowing down and not be in double od...

Yikes! you're getting 19 MPG @ 85 MPH???

I can't claim to do that! Maybe I should get it timed after all.....

Generally I figure anything under 2000 RPM is decent but it depends on net engine loading. Trying to tow a heavy load under 2000 RPM will not help fuel economy.

My testing recently involved cruising at 55 MPH in overdrive. I was able to see a consistent 24 MPG. At 70 MPH, it drops to 20 usually. Something I'm thinking of trying, is to lock out overdrive at 55 MPH to see what sort of drop in MPGs there really is.

 

[RustyBolts]

On the semi engines I've been learning about for the past 10 weeks, the lowest BSFC (Brake Specific Fuel Consumption) is roughly 200 RPM above the torque peak. I can't see where it'd be much different for our old IDI's.

 

[icanfixall]

Mels sons nitemoose got 29.5 mpg traveling home from last years rally... Thats impressive and I told him he should write Jason at Diesel Power Mag about it. That alone wouls sure stir up some interest in our idis...

 

[RLDSL]

If I can keep it below 62 in 5 over ( that's a double overdrive) I can run 18-20mpg interstate and my truck is rather heavy, but if I go over 62 milege drops fast, if I go over 7o I can watch teh fuel gauge drop

 

[LCAM-01XA]

I drive at 1850-1900 rpms as well, that puts me at 55mph which while slower than about everyone else on the highway does get me 15mpg with the big slide-in and right around 20 mpg when running empty.

 

[towcat]

my mileage sucks.
running empty with a car trailer tailgating me, I'm getting 14 and that's behaving myself since I really shouldn't go above 55 in kali with a trailer.
loaded with a car on the trailer, the mileage drops to 12-13. not much of a difference.

 

[gatorman21218]

I thought the speed limit was double nickle on the left coast?

 

[bikepilot]

Nope, most major CA interstates (and some secondary roads) are above 55.

 

[david85]

I thought the speed limit was double nickle on the left coast?

I think thats only if towing a trailer.