hp and torque and diff gears

[DYNOED250]

This is to all the people out there that a smarter than me so so i gues thats every one.


i had an argue ment with a mate who is 4:11 mad. every thing has to have 4:11 gears or its shit.

i dissagrea, i figure it this way a high reving low torque engine eg a rotor would benifit from 4:11 as it would rev up quickly enuf to use them eg, produce wheel spin, and not load up engine.

where as if u put 2.92 s in the rotor it wouldnt have the torque to over come the load on it so it would rev up slowely and not wheel spin and prob not do much at all.


BUT with a high torque engine eg 12 litre cummins truck diesl, if u put it in a car with 4:11 s it would be so damm slow because there wouldnt be a load on the engine as it would be reving up aS QUICKLY AS IT WOULD IN NEUTRAL, and im guesing that it woulnd be using the potential torque or hp from this engine, but if u put 2:1 diff gears in it it, would fly as you would be using the gears to load up the motor and use the torque potental the engine got.

 

[George]

I agree with you..

In the old days we tried all different gears in a 250 cortina (mild job). The conclusion was that with a manual gear box, gears above 2.92 made no differnce on the track. The car was pullung 14.7 ET regardless of gears but was obviously over revving with 3.5:1 and above.
So, I will never use gears above 3.23 in a 250 as it makes no difference..in my opinion anyway! I am using 2.7:1 in my cortina and would go lower to 2.5:1 if I could..The turbo loves these gears!

This may be totally different in a super high performance naturally aspirated build that has less torque down low.??

I believe you select gearing to take advantage of the torque not because your mate has 4.11:1 and his car is sick!!

See Yah

 

[xctasy]

Bascially, you are right.


The deal isn't that 4.11:1's are wrong always. Its that the ideal diff ratio is based on if you have big tyres or small, big kerb weight or small, and if your stall ratio is low or high.

4.11:1 with a 4-speed auto with a 2000 stall ratio would pee over a stock 2.92:1 geared Cortina with a 1650 rpm stall if it could hook up and change gears quickly enough.

In practice, the calcs for net wheel thrust can be worked out on a Quarter Pro program, or by using the formulae from books. You find time and time again a tall first gear and a fairly tall diff ratio work best on engine with big torque.
Overall gearing at 9:1 is best on Cortinas thats a 2.92:1 and a 3.06:1 1st. Or a 3.23:1 and a 351 single rail with a 2.42:1 Ist.

Falcons can go down to 10:1. That's like a 3.23:1 ratio and 3.06:1 1st are best in most hot sixes, cause they are heavier and the bigger tyres are worth a an eighth of a ratio ( needs to be a number 0.13 bigger on a Falc, or smaller on a Corty).

That's why E49 and E38 Chargers had 3.23 or 3.5:1 gears...because first was 2.6 or 2.82:1.

V6 Commodores and OHC Falcons are quicker off the mark with some stock 3.45:1 gears and much taller 1st gears than what they came out with.

A Ford six needs to be geared up like a stock big block Ford rather than a wild small block. A good 250 cube six produces more torque early in the power curve than in the strongest V8's. In the first 50 yards, most sixes pee all over any V8 at the lights or the drags.