ok here is the problem, I have a Isuzu 5-speed tranny hooked up to my v8 engine. When I'm on the highway doing about 70mph someone comes up beside me and wants to see what my car can do. I step on it and they pull away from me. I can hear they have an auto trans and I can hear it downshift. How hard would it be on the engine and trans if I downshifted to 4th gear.
Thanks,
Matt

I do it all the time when some PITA won't let me pass them on the freeway. 4th at 70 should only be about 3.5K rpm or lower.

If you really want to find out what it will be at just start off on an open road accelerating and watch the max speed/RPM's when you leave fourth. That way you control exactly where you shift without blowing anything up and you will know at what speed you can safely downshift

Like he said, you just have to know the max speed for each gear so you know when and when not to downshift without blowing up the motor. My Ferraro with 4 speed, always gets downshifted if im under 70 and want some pickup quick, like on a two lane.

i do it all the time in Ling.

------------------
Buddy - there are two "G"s in my name
Ling = 84SE-350-N2O-Poly-Mr.Mike seats-Sequential turn signals-short shifter
Julia C = 85GT stock (mostly)
KCFOG
got a broken stud?
car doesn't crank over?

If you want to be safe, you double clutch

Into neutral, clutch out, rev up, clutch in, downshift, clutch out with revs up.

With v8 torque, double clutch is good insurance.

With me it is 4th to 3rd. I normally revup before I drop the clutch on 3rd but I am running a v6.

I used to do it when provoked back when I had the Sunbeam Tiger. 4th to 3rd, 3rd to 2nd at 70, Nail it (Not a heck of a lot left,but the 2nd to 3rd shift would really lanuch.)

What is the purpose for double clutching?? Can someone explain?

Double clutching is old school for trannies that had no synchro's. Where you had to match rpm to speed. I have no idea how that would apply to this situation.

It keeps the RPM's up and makes the shift into the gear easier and keeps the engine in its powerband when you engage the clutch in the next (higher or lower) gear. Either way, it better matches the RPM's of the engine to the speed of the wheels/axle. Lets you get a lot more power on the upshift and not beat on your motor on a hard downshift. The draw back is that since you are slipping the clutch at higher RPM's, it eats up the clutch much faster than normal driving.

Why do you need to 'double clutch' though?? Other than when doing it for braking, etc, you bring the rpms up when downshifting naturally. It prevents the jerk when u let off the clutch, and in racing, its good to keep the engine speed up when going thru the turn, even though slowing down.