RPM's

[G_whizz]

Hello all...

Ok, so with my 05 G35 MT.. hypothetically speaking of course...

If I want to get from point A to point B the fastest... at what RPM's should I be shifting through all the gears 1-6. Think of how you could get the best 1/4 mile time!

And go......

[Q45tech]

You multiply the engine torque in pound feet at each rpm by the total gear reduction including tires [ratio] to arrive at a instanteous acceleration.So many pound/ft moving so many pounds of car weight. Peak acceleration in most cars occurs between 20-30 mph...........whereever torque peak rpm occurs in 1st gear then progressively slows down.

What graphing all this usually shows is you shift just before the redline in each gear ----------really depends on the closeness of gear spacing.

Automatics have wider gear spacing but always shift beyond the so called HP peak rpm before redline to avoid hitting rev limiter as they age and take longer to shift.

[G_whizz]

Ok, that is a super detailed reply! Thanks for your advice. Any way someone here could "dumb" it up for me?

1st gear= ? rpm2nd=? rpm3rd=? rpm4th=? rpm5th=? rpm6th=? rpm

[j1stande]

I would say split the max hp rpm and max torque rpm.....in other words

about 5,000rpm

best of both worlds

[joe603]

Just don't go over 4k and drop the clutch, ever...our cars have a safety device that will not let the clutch engage. It can even do it while moving...Sucks!

[C-Kwik]

I would say split the max hp rpm and max torque rpm.....in other words

about 5,000rpm

best of both worlds

You should be shifting at the point at which the curve for the gear you are in crosses the curve for the next gear up. It's hard to see in the diagram Q45tech posted, but it was more to just give you an idea of what he meant. Shifting at 5000 RPM would be less than ideal if you're looking for the best acceleration. If you look at the graph, it shows 1st gear would probably put you at redline for a shift point. 2nd is slightly less. 3rd less is slightly less than 2nd. Of course this varies from car to car as different motors have different HP curves and different gear ratios so you would need to get your motor dyno'd or find one for the same motor(and mods) and essentially do the math or graph each gear scaled to your vehicle speed to determine where each curve crosses the next.

Splitting HP and Tq peak RPM's isn't going to be the best solution. Torque peak represents the point at which peak acceleration will occur for a given gear. The peak HP is the point at which the motor can most effectively multiply torque to the wheels. Generally, most motors will accelerate the fastest by keeping the motor at least above the torque peak to a point somewhere past peak HP. Most trannies will drop RPM's well below peak Torque if you shifted midway between peak torque and peak HP which would make you slower than you should be. Understanding that trannies are no more than torque multipliers and lower gears multiply torque more, the key to acceleration is to use the lowest gear possible until the point at which the next gear would provide more torque.

[Q45tech]

Take a dyno torque curve and multiply it by the gear ratio [transmission x diff] and correct for tire loaded radius;

Say 220 lb/ft x 3.54 [1:1 x 3.54] x {12/12 [tires]= 1} = 779 lb/ft with a 3500 pound car .....................779/3500= 0.2225714 G instantaneous acceleration

With a 3.54 [1st gear] and the same torque, the acceleration would be:220 x 3.54 x3.54 = 2756.952 lb/ft /3500 = 0.7877 G

Study the rpms of an AUTOMATIC transmission you will see that each shift drops the rpm to roughly equal the torque peak rpm [~4000-4400] and doesn't shift until after the so called HP peak rpm.

The only reason to NOT take it always to the redlineline is you might mess up and hit the rev limiter causing you to lose time.