Knuckle Headed Move

[jesus_man]

I'm not sure if the electronics will permit it, but I havent tried it to confirm... If you end up downshifting manually, you can mechanically overrev the engine as well. IE, downshifting into 2nd gear at highway speeds. There is no fuel/timing for the limiter to cut, and the drivetrain is taking the engine past the redline. I would guess (but not certain), that the ECU prevents a manual downshift that would take you past the redline.

This seems to be an industry standard. My diesel F-350 is a manual tranny rig. The only way I can over rev the motor is by downshifting into too low of a gear. I have protection on acceleration, but there is nothing for deceleration.


I could see how momentum could carry an engine past the redline, but I would be very surprised if it's more than 1000 rpms. What's the redline on the V8 again?

J.D.

 

[jpljpl]

This seems to be an industry standard. My diesel F-350 is a manual tranny rig. The only way I can over rev the motor is by downshifting into too low of a gear. I have protection on acceleration, but there is nothing for deceleration.


I could see how momentum could carry an engine past the redline, but I would be very surprised if it's more than 1000 rpms. What's the redline on the V8 again?

J.D.

I'm not sure what the redline is... That would definitely be a handy piece of info for this discussion.

I'm more curious to see if overrevs are logged, and what the dealer would say if there is an engine issue related to the overrev, would it be covered under warranty.

I too would be surprised if you could get 1k over redline just based on inertia/momentum. The internal friction at that RPM level would be pretty high. At 7500 RPM, you're talking 125 rotations a second.

But there is definitely a limit to what the 'limiter' can do.

 

[jpljpl]

This seems to be an industry standard. My diesel F-350 is a manual tranny rig. The only way I can over rev the motor is by downshifting into too low of a gear. I have protection on acceleration, but there is nothing for deceleration.

J.D.

Not that it's applicable here, but most rev-limiters dont work when an engine is spinning backwards either. ie, at the track during a spin. Mostly mechanical over-revs, but some high speed spins result in cars going backwards very fast, all of a sudden. Sometimes traction takes over and again, you can overrev that way too. Hence "2 feet in when you spin".

If you try hard enough, you might be able to get the end around on that big F-350.

 

[jesus_man]

If you try hard enough, you might be able to get the end around on that big F-350.

While I often do the occasional power slide in my truck, I hope I never see what happens with it goes backwards in that situation.

I never thought of over revving and engine backwards, like a stock car that gets spun backwards. But all of my primary cars/trucks have been manuals and I have been a couple accidents. Each time, my engine was still running after the accident because I do push both pedals instinctively.

I looked at the tach on my wife's LR3. While it tops out at 8,000, there is no indication where the redline is.

J.D.