mark kibort

got it. so, it might shift all the gears up or down.... probably more up and make them taller because the other rear end gear boxes actually dont have the shorter gears.......... remember, i havent argued the gear boxes just change shift points, ive just provided the information of why that is ....... the gear box is just an optimizer for HP to the wheels for any speed range.

so, if i can find a 5th gear, i can save two gear boxes, rather than just one. the one i have now, just needs the dogteeth hubs/synchros right ? *(and possibly shift forks for its inability to not select one gear at a time when it gets really hot)

I know its not going to be cheap, but i have to do it, so it will be done.

just trying to find the best solution........ aside from not buying a cheap S4 with a 5 speed and ditching the car and parting it out.

mark kibort

jim, the 5th gear is 21 teeth. the gear below is 33 teeth .63 reduction. i dont know what that means. I thought 5th was 1:1. ill have to look at the gear box to see how the ratios play out with the layshaft, etc.
so, you are saying that i can find a 5th gear of 21 teeth, but there are different matching gears below that might work. (sorry for the Noob question, but ive never really done much with the internals of the trannies)


EDIT: so, it looks like the 5th gear set determines the layshaft ratio, for which all the gear ratios are multiplied by. so, the 2.2 boxes have a 1.5714 ratio, and the 2.63/2.72 boxes have a taller 1.4545 ratio. So, if i found that 5th gear, it would make my 2.2 even talller in all gears but 2nd..... 8% taller hmmmm that might be a good thing. 127mph in 3rd gear for all the long straights.... no need for 4th, and i could start using 1st for all 2nd gear turns and get great launches. going though the HP range for all gears would actually be an advantage. any track faster than 127, unless i was able to get to 170mph on a straight, would be a disadvantage. Andersons beast would have benefited with this for cal speedway, and then the normal 2.75 would be better for him at tracks like laguna/sears. Thats how you determine what gear boxes will be best. look at the track speeds, power curves, and select the best ratio. lower is not always better. its relative!

James Bailey

In 5 th the power NEVER goes to the layshaft....it is 1 to 1 however all the gears are still turning they are just not locked up to the pinion shaft One reason why power losses transmission stress and heat are much lower in 5 th because the power does not have to make a 180 turn inside the gearbox, the layshaft is not being pushed out of the gearbox. 5th is just locked to the front of the pinion shaft. Power straight in and straight to the ring gear.

mark kibort

Got it. thanks...... Yep, that's right ..... one less stage of reduction, one less factor effecting efficiency. it would be interesting to see the difference on the dyno in 5th gear. even a run to the max speed of the dyno , would be interesting just to see the loss difference.

Rob Edwards

Mark, here are all your gearset ratios, part numbers, and interchanges among gearbox models.

Anderson has used 5th gears from a G28.13 listed on the 928intl website. No idea whether he's actually got any on the shelf but at this point I would buy first and ask questions later. (Shoulda been asking back in December, but I digress....)

mark kibort

Thanks .

calling mark next!

mk

mark kibort

Mark- do we have any 5 gear sets in used inventory?
Greg - if i drop off my transmission, how long would it take to fix it if all it needed was the 5th gear replaced and possibly new syncrhos. ( i know, best case)

PM me if you dont want to talk about it in a public forum.

SCCA is seriously considering having the 928 approved to run in GT2-ST class (ex- wCGT /STU class)
If i do it, i will absolutely need some new stuff. new transmission and the suspension rebuilt are first on the list.

this would be a hoot ! It will be a chance for the 928 to get on national TV again!

Mk