Quote:
Originally Posted by Chance
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.
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When Ford when to the 6-sp transmission they also re-tuned the engine for more torque at lower rpm. My coach (18,000 lb chassis) turns 1800 rpm at 62 mph. Down shifting to 5th at 62 mph gives 2,300 rpm and down to 4th gives 3,000 rpm which is where the engine's maximum torque is produced. Only at altitudes greater than 6,000 ft is it necessary to use the lower gears and to keep up with traffic on the two lane roads.