This stuff is covered in the owners manual. Different engines shift (or should be shifted) at different speeds (RPMS actually).
Also, some even have a little lite to tell you when to shift.
For Napier.
It doesn’t matter what sort of box one is operating-----the first need is to get the iron rolling.
Even the most exotic auto boxes still begin motion in the lowest gear.
Synchro mesh wasn’t designed so much for making shifting easier------it was made to keep the un-dextrous operator from having to drop the gear box every other day to remove the scrap metal that once was gear teeth.
Take any car you can get your hands on that has an automatic tranny[three speed]------find an open stretch of road----put the thing in D--------acellerate SLOWLY but at a steady speed--------and as the motion increases note the shift points of the transmission.
First shift at 9/12 mph-------second shift at 15/20----then you’re in drive.
That’s what the designer intended------anything else is playing with fate--------and a possible couple of grand.
Drive on!
When to shift? When the horsepower curves of the two gears cross over. Here’s the deal:
Picture a graph of horsepower on the y-axis and vehicle speed (NOT rpm) on the x-axis. Assuming that you are holding a constant throttle, there will be five identically shaped curves on the graph, one for each gear (for a 5-speed, of course). Each curve will cross over the curve for the gear above it. This is where you should shift. Notice that doing so will put maximum horsepower to the ground FOR A GIVEN THROTTLE SETTING. This last point is important: always shift for maximum horsepower to the ground. Think this is only for drag racers? Not at all. The horsepower curve is different for different throttle settings (the ones you see in car mags are done at full throttle). Because the horsepower curve varies with throttle setting, the crossover points will vary with throttle setting as well. Therefore, the shift points depend on throttle setting. Higher throttle settings (when you want to accelerate quickly) result in crossover points at higher vehicle speeds, which most drivers intuitively do. Notice that shifting at higher vehicle speeds at a low throttle setting actually results in slower acceleration. So, how do you determine crossover points? By vehicle acceleration, mostly… maximum horsepower means maximum acceleration (once again, maximum acceleration for a given throttle setting). Tachometers are really decorative items, so don’t bother with them (in the old days, you needed them to synchronize the gears for downshifts, but those days are long gone). Fast dragsters don’t even have one, and slower dragsters use them because they are run at full throttle all the time (they run with a fixed power curve, and thus have relatively fixed shift points). The key to remember is to shift when the rate of acceleration is lessening, i.e, you’re over the horsepower peak. Once you are at the desired vehicle speed, keep upshifting as long as the engine is not unduly struggling.
For Barber.
You’re right!
BUT!
The average operator of the average machine has to learn to shift by “ear tach”.-----or elbow tach.
He has to develope a sense of velocity----and have a feel for underspeed and over speed.
The ‘showroom’ vehicle isn’t usually equipped with exotic instrumentation.
The average driver is in a showroom cream puff-----and there’s the trouble.
You can’t use a run-of-the-mill four banger like it’s a Masseratti without ultimately enriching the local shop man through ignorance.
Note:----ignorance meaning a lack of specific knowledge,—no offenses intended.
Too many drivers seem to think that because their little shoebox has a loud muffler anbf a whiny countershaft it’s a formula one.
'least that’s my opinion.
Ezstrete has now left the area!