If I'm off in actual rpm vs. speed, I'm open to correction, but I don't think I am.

As for being "off in [my] assessment of effectiveness a bit", I don't know exactly what you mean here.

I agree that lower 1-4 gearing will give a benefit in acceleration from zero to most speeds (possibly depending on whether an additional upshift is required to get there). But from rolling-start acceleration, it will totally depend on what the beginning speed and ending speeds are. In some instances the AP1 trans will be quicker.

But again, we're talking minor differences here.

Main point for posting in this thread was to discourage swapping a perfectly good AP1 trans for an AP2 trans because the difference in performance is going to be pretty small (4% lower 1-4 gearing, 2% taller 6th gear).

 

[QUOTE=ZDan,Jan 12 2010, 03:51 PM] If I'm off in actual rpm vs. speed, I'm open to correction, but I don't think I am.

As for being "off in [my] assessment of effectiveness a bit", I don't know exactly what you mean here.

I agree that lower 1-4 gearing will give a benefit in acceleration from zero to most speeds (possibly depending on whether an additional upshift is required to get there).

 

Knew we could clear it up

FWIW, here's how I arrive at 8700 at 64mph with the AP1 trans:

tire diameter = 24.8", working rolling circumference ~.97 * 24.8" * pi = 75.6" = .00119 miles/wheelrev
64mph / .00119mi/rev = 53,656 wheel revs per hour = 894 wheel rpm

wheel rpm * diff ratio * overall trans ratio = engine rpm

For AP1 in 2nd gear:
engine rpm = 894 * 4.1 * (2.045*1.16) = 8698rpm

That should be fairly damn close for low-load cruise, but doesn't account for slip under acceleration. So I'll concede that under full throttle acceleration in 2nd gear, AP1 engine rpm is going to be closer to 8900rpm at an actual vehicle speed of 64mph.

 

Here this link will help the OP. put in your Final drive ratio and this will help shed some light on what your speed is in each RPM.

http://www.turnzero.com/technical_resource...gear_calculator

 

[QUOTE=ZDan,Jan 12 2010, 05:40 PM] The point is, if you are lower-geared you have to upshift sooner.

 

Numerically higher gearing is LOWER (or shorter) gearing. Numerically lower gearing is TALLER. AP1 1-4 gears are TALLER than AP2 1-4. Likewise, a 4.3 diff would be LOWER geared than stock 4.1. TALLER gearing => lower rpm at a given speed (as a TALL person will make fewer steps to cover the same distance as a shorter person).

A minor and sometimes confusing point...

I've never noticed any notchiness of my AP1 trans on the street (unless it's pretty cold and the car's not warmed up) or at the track. But this does seem to be a not-uncommon complaint.

Comparitive lap times would be helpful! It isn't uncommon for a slower gearing setup to feel faster and vice versa.

Agree that 4.10 are generally a bit tall (i.e., numerically LOW) as far as maximum performance for an NA goes. With additional power, taller (numerically lower) gears make more sense as you have found.

Yup, from a stop, gearing wins.
I don't doubt this. Equal car vs. equal car with 4.10s vs. 4.77s, it will depend on the initial speed. Wouldn't be surprised you pulled 2 lengths if the starting speed favored 4.77's. But with equal cars/drivers and simultaneously hitting the throttle, 4.10's will beat 4.77's if you start at 57mph. 4.10 gears will have you in 2nd gear at 7770rpm making ~190hp to the wheels, 4.77's will have you in 3rd at 6520 making more like ~170rwhp. At that speed, the gearing advantage is with 4.10s.

My position is that if acceleration from a dead stop (or very low speed) is a priority for you, then gearing is an excellent choice. If you're doing autoX or track days, where acceleration from zero never happens, gearing is less attractive, and at some tracks/courses can make you slower.

Mmmm, booost...
One o' these days

 

Your right on that one mixed my words up