Quote:
Originally Posted by jannnda
2600 rpm at 65mph? On my 31Z (V10) at 65mph I am just a little over 2000 rpm. I also have never gotten 8.5 mpg.
Really nice looking rig BTW.
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The RPM difference is likely “not” due to V8 versus V10. For many years Ford specifications called for lower gearing on higher-capacity motorhome chassis.
A quick look at motorhome specs indicate yours is on 18,000-pound GVWR while his is on 22,000-pound GVWR chassis. That GVWR difference in the past changed the rear axle gearing by 25%, which would explain his higher RPM compared to yours. I’d bet Ford still uses same axle gearing for different GVWR, although I haven’t found 2021 detailed specs yet.
In that light, that he’s getting 8.5 MPG at 65 MPH on a heavier motorhome while running 25% higher RPM speaks well of 7.3L V8 fuel economy compared to V10.
It will be interesting to see what the V8 does on 16,000- or 18,000-pound GVWR chassis with taller gearing. It should do a little higher MPG under similar conditions.