SpitfireS

Incubus Posted on Jul 6 2006, 11:21 PM
Try reading all the posts next time

Fongu

I'm too lazy to make a graph to show exactly what's going on, but essentially there are going to be speed ranges that favour 4.57 gears and speed ranges that favour 4.1 gears. Depending on which speeds you drive the car at, will determine what acclerates faster. Depending on how many shifts you require will also determine what is faster. That's why gearing changes are application specific.

Here is an example without any numbers, I'll let you calculate them yourself.

0-a mph - both cars in 1st gear, 4.57 faster
a-b mph - 4.57 car shifts to 2nd, 4.1 car still in first --> 4.1 car faster
c-d mph - both cars in 2nd gear, 4.57 faster
e-f mph - 4.57 shifts to 3rd, 4.1 car still in 2nd ---> 4.1 car faster
etc......

Overall, 4.57 gears are faster than 4.1 in general applications because you're moving more of the "engine's accleration potential" into the lower speed ranges where people typically drive, and that normal drivers do not optimize their shifting like on a track.

Wisconsin S2k

Also not true.

While there may be moments (such as a 30mph roll) where the stock car is in 1st and the geared car is in 2nd, allowing the stock car to be slightly faster (the gearing advantage is not very big) and be able to pull a bit, that advantage is completely negated by the shift at 41mph that the stock car has to make that the geared car does not.

in a straight line race, no matter what starting speed, the 4.57 geared car wins, period, hands down. the only exception to this is if you START the race at about 105mph, the math figures that both cars are about the same so you'll likely end up in a near tie with a slight advantage to the 4.57 car getting to its top speed first.

mikegarrison

There are two reasons for this:

1) gas mileage -- a "super-overdrive" gear (like the Corvette sixth gear) can give great gas mileage at highway cruising speeds

2) even if the gear is sized for best speed performance, the top gear should have some margin over your best expected level straight speed. This margin is so you don't run out of revs in case you are going downhill, have a tailwind, are drafting, etc.

But if you only care about 0-120, then yes, you will get your best performance if you adjust your gearing so that your gears are used in the range of 0-120. (120 being chosen arbitrarily for this example.)

Wisconsin S2k

^^ tracks are definitely going to determine what gearing is best for what track. !!

Johnny Sack

i have pulled a local memebers 4.57'd car from a 70-110 run putting about a half car on him. over 75 i'd say that the 4.57's have lost their advantage.

SpitfireS

versionJDM Posted on Jul 8 2006, 09:28 PM
Starting @ 70 you would both be in 3rd right?
You would both have to shift to 4th, the 4.57 even to 5th to get to 110.
So the extra (slow?) shift costed him the "victory".
IMO if you guys would have done a 70-120 you would have lost

xviper

70 to 110 can be done in 3rd (starting @7000rpm) and 4th for a 4.10 car.
70 to 110 for a 4.57 car is best done from 4th (starting @6000rpm) to 5th gear.

A 1/2 car difference at those speeds isn't a real indicator of which car performed better. If either of you had farted while shifting, it could have gone either way.