Diff gears and horsepower equiv

[itsagixa]

Yes, i understand diff gears and the relation to engine HP however, what i want to know is if there are 3 VX SS's (not that car matters), all manuals

CAR 1 had stock (3.4?) diff gears
CAR 2 had 3.7 gears
CAR 3 had 3.9 gears

example - clarification

now obviously over a 1/4 mile the car with the 3.9 gears will finish first (unless it hits the limiter in 6th) now the question is how much extra power would the stock car or the car with the 3.7 gears require to keep up with the car with 3.9 gears....

hopefully it makes sense, as i see it if you had stock vx ss with 225kw at the engine it would run 14ish quarter miles, slap 3.9 gears in it and due to the quicker acceleration the time may drop to....lets be generous and say 13 secs...ish

how much extra power would the stock ss require with stock gears to do the same 1/4 mile time

any help would appreciated

 

[itsagixa]

Bump anyone

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[Munz]

You may find an answer by using some drag calculators, I think the equivalent would be around 40hp from 3.9's to 3.7's but not to sure it takes to long to work it out - can be done tho

Drag racing tools 1/4 mile & 1/8th mile conversion calculators

I use 7-10% for converter slip and 1.1 gearbox ratio and 3800lbs for weight

 

[davleigh]

I'm actually keen to see what you find out mate. Keep up posted.

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[itsagixa]

I will run some calculations tonight and post the results

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[Not_An_Abba_Fan]

Diff gears won't have any affect on the actual HP figure, they will affect where the maximum torque is produced but when you apply the formula to work out the HP, it remains pretty much the same.

Example, say you are producing 300 ft lbs of torque with 3.7 gears at 3500rpm, that equates to about 200hp. Change to 3.9's, that's a change of 5%, so now you are producing 315 ft lbs of torque at 3325 rpm, still ~200 hp.

Once you go up in ratio with your gears, you produce more torque lower in the revs, thus the increase in acceleration felt.

 

[itsagixa]

But correct if i am wrong...lets say both cars have 300hp at the engine with 300nm of torque (easy figures) both cars are identical other then diff gears, one car has 3.7's anmd one has 3.9's.....the car with the 3.9's will reach the 400m mark first yes?

now keeping the exact same configuration between the cars except the car with 3.7's now has 400hp and 400nm will it finish first/last?
how much hp and nm would it have to have to do the same time as the car with the 3.9's

what i want to know is how much hp would be required to overcome the difference in acceleration.

 

[itsagixa]

Jeez, its quite complicated.....the calculations are pretty gnarly, ill look at it tommorrow, unless someone can give us an answer or easy way to work it out

 

[Not_An_Abba_Fan]

The difference between 3.7 and 3.9's is only 5%, the difference between 300nm and 400nm is 33.3% so the car with 400nm "should" reach the line first.

Assuming both cars have the exact same torque curve, you would need to have 5% more torque in the 3.7 geared car to achieve the same time as the 3.9 car.

Power is irrelevant.

 

[micky vn man]

how much percent differrnce between 3.08 and 3.9s not an abba fan