Final drive gearing

[PeeBee]

Something is not right with this conversation. The equation of Power relative to torque is P=2PiNT/60000 where power is P, Torque in Nm, N = rpm, Pi=3.1416. If you maintain the Power and change the rpm, the Torque is affected. I dont see how you can go from 31" to 33", be happy with the driveability and not realise the issue is the impact on the avail torque as you are probably sitting at a different spot on the torque curve. Swapping diff ratios is only going to land you back where you started - I think, as others have suggested, you look at the power component of the equation to get better driveability as the torque curve will change to compensate.

[mihit]

Something is not right with this conversation. The equation of Power relative to torque is P=2PiNT/60000 where power is P, Torque in Nm, N = rpm, Pi=3.1416. If you maintain the Power and change the rpm, the Torque is affected. I dont see how you can go from 31" to 33", be happy with the driveability and not realise the issue is the impact on the avail torque as you are probably sitting at a different spot on the torque curve. Swapping diff ratios is only going to land you back where you started - I think, as others have suggested, you look at the power component of the equation to get better driveability as the torque curve will change to compensate.

Yeah... TD42 has about eleventy billion torques so the 33s don't bother it much. I think it actually puts it in a much nicer driving range (for what I do).

Does push EGTs if you try hauling up hill at low revs...but it'll still do it though.

[timbo2410]

Soooo ... do I get from this conversation NOT to look at dif ratio and to go for higher horsepower?

[mihit]

Soooo ... do I get from this conversation NOT to look at dif ratio and to go for higher horsepower?

-Always- go for more horsepower

[pollenface]

Soooo ... do I get from this conversation NOT to look at dif ratio and to go for higher horsepower?

Personally, I would change diff ratios to match the tyres.

[timbo2410]

so what ratio would I need?

[nipagu7]

some 3 ltr's have 4.3's ( early di's , i think ) , most have 4.11's check your compliance plate on the firewall near the brake booster . i think it is listed as the trans axle code . if you put on 33's and you have 4.11 diffs , changing them to 4.3's will put you back to standard gearing . if you have 4.3'you will need to go to 4.6's to get back to your standard ratios .

[pollenface]

so what ratio would I need?

depends on your vehicle/engine/gearbox combination which I encourage you to share with us

[timbo2410]

I thought I had .. patrol wagon, 3 litre .. 5 speed manual