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Shorter Diff Ratio For F


Jash
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Hey All,

Just not finding my F that snappy these days. Does anyone know if there is a readily available shorter ring and pinion that I can install? Probably looking for something around a 3.7 or 3.9?

Many Thanks,

Jeff

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I found that the ISF has a very similar/almost the same gear ratio to the IS350(which is 4.1) or IS250(which is 3.9) up to 6th gear. The reason why the ISF has a low gear ratio (of about 3.2 I think) is because it has the extra 2 gears on top for highway cruising. When I was comparing gear changes on road from 1-6 with my brother's ISF they were pretty similar.

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I found that the ISF has a very similar/almost the same gear ratio to the IS350(which is 4.1) or IS250(which is 3.9) up to 6th gear. The reason why the ISF has a low gear ratio (of about 3.2 I think) is because it has the extra 2 gears on top for highway cruising. When I was comparing gear changes on road from 1-6 with my brother's ISF they were pretty similar.

It's actually the opposite in terms of your numbers i.e. an IS F with 8 speed g/box could afford to have a low gear ratio of say 4.1 (so that wheels turn once for every 4.1 turns of the diff) for better acceleration - because it has those two extra 'over drive' gears to drop the revs at highway speeds. If you want punch off from the lights with lots of revs and go but no top speed you put in a low or 'short' gear ratio (4.4:1) or you go the other way for a very high or 'tall' 2.9:1 for low revs, economy and higher terminal speed (if the engine has the grunt to rev against the high gearing.

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The gear changes for the IS250 and the ISF are very similar up until 6th gear. The IS350 though has an even shorter ratio.

But for OPs question then I'm not aware of any ring or piston you're looking for but you can always check.

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IS350 ratio or any ratio around high 3s/low 4s will be too short for a daily driver, a few guys in teh US have made this swap and most (all?) of them ended up going back to stock as although it was fun for a while the car hits speed cut very early and it apparently causes the box to behave a bit weirdly because of the 40% difference between wheel speed and transmission speed over the stock ratio.

I have in my possession a brand new crown wheel and pinion kit from a late model Supra diff which according to my research shoudl fit the IS F torsen centre.

The ratio is 3.266:1 which represents about 11% difference over stock, in my experience this should be enough to make a noticeable difference but hopefully will not cause the issues that the IS350 diff causes.

I just need time to take the IS F off the road to fit it....

BTW, this is my thread over at CL - http://www.clublexus.com/forums/is-f/761841-3-266-diff-crown-and-pinion-fit-isf-diff-or-not.html

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Hi Jeff yep doing Racewars, i remember your car from that one-day rally at the Plex we did a few years ago :)

I fitted the headers, it was a bit of a PITA doing it in my shed as you have to drop the subframe but its done. I was going to pull the diff out myself as it shouldnt be too difficult but i'll have to take it to a diff place to get the crown and pinion fitted and set up properly.

Assuming all goes to plan it should give the car noticably more punch off the line which it could do with...

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