Gearbox Ratios To Use With 4.77 Diff

[demuire]

While up at Caloundra for Coastal Challenge and ARC last weekend, I was speaking to Tony (driver of TRD KE70), and he mentioned that he thought the stock gearbox ratios were more suitable to a 4.77 diff for rally and other similar sort of events that had a big variance in speed, and that the close ratio gearboxes were only really suitable for high speed stuff because of the huge 1st and 2nd gears. Or at least that's what I understood from our conversation anyway :)

 

Does anyone (Rob?) have any opinions on this?

[coln72]

I guess it depends on how slow the slowest point of the track/course is and if you have enough torque to accelerate from this speed in first gear.

[demuire]

Hmm, that's true. I suppose I'm looking for something reasonably generic (is there even such a thing...). I'd easily say that most of the events I do (motorkhana, autocross, khanacross) have speeds ranging from 0 - 120km/h, not many exceed that. One thing that does bother me with the stock gear ratios is that even with a 4.11 diff I was hitting the rev limiter reasonably often in motorkhanas (1st gear).

 

I haven't had a chance to drive a motorkhana with the 4.77 yet, am reasonably sure I'll have to use 2nd gear, not sure if I'll be able to get away with just 2nd gear or if I'll have to keep shifting between 1st and 2nd (which would suck)

[coln72]

Yeah, I just tend to rev the ring out of mine in first with the 4.2 gears as it bogs down to much in second if the tyres stop spinning. Time wise for me there wasn't a big difference between first or second on the same test (using first was quicker by .1 of a second or something). I imangine 4.77 gears would make second more usable though.

 

Maybe the close ratio gearset would be an advantage in your case to prevent swapping between first and second.

[demuire]

Yeah 2nd gear with the 4.11 is not really useable for me except for really big flowy tests like Oh What a Feeling and Around the World (?), where I can grab 2nd gear, snap the tail out and keep it going around the course (assuming I don't overcook it and spin) until the last flag when I have to go back to 1st.

 

If only the cost difference wasn't so big between standard gears and close ratio gears! There's meant to be a motorkhana on the 19th of this month, might go out and see how it goes...

Edited June 7, 2005 by demuire

[coln72]

Even on those tests I would keep it in first (the shift light would be on for the whole test though :) ) Have tried using second occasionally but its just one more thing to stuff up, I'm normally to busy just hanging on.

 

I'll either be doing a state motorkhana championship round or a club khanacross on the 19th as well.

 

Another option for you would be to change your diff ratio to a 3.9 or so if you can find one. Be cheaper than a close ratio gearbox.

[demuire]

Heh... No, I kinda like my 4.77 :)

[coln72]

Bugger, I was trying to convince you to get rid of it and give it to me :) By the way, what did you get the 4.77 from?

[demuire]

Bought it from an importer in Perth. Brand new.

[coln72]

I was hoping the you would say that you got it from xyz toyota at the wreckers for stuff all money and that it bolts straight in :)

[demuire]

I wish I could say that too... :) It did bolt in though...

[ancullen]

Just on the topic, here's a link to a little Microsoft Excel calculator I've whipped up for calculating a car's maximum speed in a particular gear. It can be quite handy for when you're working out what gearbox to use. The example you see is for Lola hence the funny wheel/tyre combo and high(ish) rpm.

 

Gear Ratio Speed Calculator

[demuire]

Yup, got one of those. Jamie has one on his site too.

[ancullen]

Bugger, you mean I went and made one up for myself (about a month back) for absolutely no reason??? Oh well, it wasn't that bad to do.