diff ratios and combos

[bigmat]

anyone help. i have 18rgturbo setup going in. 180rwkw. w55 gearbox. what ratio lsd would suit for street i have a chioce of 4:1 or 4:3. into ra28. cheers.

[brett_celicacoupe]

depends what you want to do with it.

4.3 ratio will make your car accelerate faster but you will have less top end. its the opposite for the other ratio, but not to any signifcant extent.

[stradlater]

I would have thought 4.1:1 rather than 4.3:1 but I'm no expert.

Some else elaborate.
Take my example.

If I'm drag racing, what's better, a quicker accelerating gear ratio (4.9:1 or something I'm assuming) or a taller ratio like a 3.11:1 or something? Or have I got that completely wrong?

[hypo23]

i would personally go the 4:11, my was making between 200 and 210kw, i have a w58, and a hilux diff with 4:3 gears, and by the end of the quarter i didnt have enough top end speed and was into fifth gear well before the end of the quarter, mind you i was running a very small diameter slick, next outing i will be fitting bigger tyres too hopefully pick up some more top end speed, it was simply running out of puff, my ideal option would be too put some 3:9 gears in, but thats not really a priority at the moment

some food for thought anyway

[brett_celicacoupe]

it also depends on where the powerband is and what sort of speeds you plan to be at. for example a track might have a straight where you just hit the revlimiter 100m before you need to brake. if there is a section like this, it is good enough reason to change to an alternative ratio, lower in this case.

[bigmat]

this will maily be for street driving. low down power with quick spool up of the turbs. just a fun driver but quick of the line. does anyone know the rev range it would sit in while crusing at 60 or 100.

[YLD-16L]

anyone know the rev range it would sit in while crusing at 60 or 100.

You can work it out pretty easily, I made myself an excel spreadsheet with all the gear ratios of my w58 box, the final drive ratio (diff) and the wheel circumference and then all I had to do was plug in various rpm values to see what speed I would be doing in each gear for that rpm.

Google should find some similar online calculators but you'll need to know you gearbox ratios and tyre diameter or circumference to start with.

[brett_celicacoupe]

ratios are here

http://www.answers.com/topic/toyota-w-transmission-1

[Norbie]

Turbo engines love tall ratios, loads up the engine and gets the turbo spooling quicker. IMO even 4.1:1 is too low, I'd be shooting for a 3.7.

[brett_celicacoupe]

agreed, 4.1 -> 3.9 on my car was a big improvement. it actually makes some boost in 1st. with 4.1, 1st was useless

[bigmat]

so has anyone got this combo. 18rgturbo.w55 and 3.9. brett is this what you have?

[bigmat]

forgot to mention i all ready have an rn25 diff ready to go for this so does anyone know if i can get 3.9 lsd for this diff housing

[whatthe?]

Turbo engines love tall ratios, loads up the engine and gets the turbo spooling quicker. IMO even 4.1:1 is too low, I'd be shooting for a 3.7.

Amen brother, when I changed from a 4.1 to 3.7 with W58 in my supra I could actually get boost in 1st gear!

[stradlater]

on that topic then, how the hell do I find out what ratio I have?? I got my center from ARB, it was a 4pinion lsd out of a new hilux or land cruiser.

[bigmat]

just found it in the forums. type diffs in search. but still couldnt find stuff for 3.9 for rn25 housing.