Thor Forums

[Chance]

Originally Posted by Long & Winding road

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So mine is not bad now - but on the interstate when cruising 75 mph then it downshifts for a hill it can get a bit loud. I try to speed up going down the hills and let off going up to keep it from shifting so much. That helps a lot.

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What I found with my V10s plus all the others I’ve driven in Class C motorhomes is that they get very loud at high RPMs. You probably have 4.56 gears with small tires (for a truck), so the combined gearing is fairly low. At 75 MPH your engine must be spinning close to 2700 RPMs in high gear, which isn’t too bad. However, one downshift gets it up to ~ 3500 RPM, and a dual shift to 4th would go up around ~ 4600 RPMs. On mine with factory doghouse and firewall insulation, 3500 RPMs isn’t that bad, but it gets loud. At 4600 RPMs it’s so loud I’d rather slow down.

If Ford goes with DOHC heads with both intake and exhaust variable valve timing, they should be able to supply more torque at lower RPMs. This should decrease the need of the 7.3L needing to downshift.

Another change that’s coming is the heavier duty 10-speed automatic transmission which will make high RPMs less likely. I expect that the 10-speed will be installed initially in SuperDuty pickup truck line, with motorhomes sticking with 6R140 for a while. Eventually Ford should upgrade motorhome chassis to 10-speed autos. I hope much of this gets sorted out in Detroit next month.