Guest JAMIE T Posted April 25, 2005 Share Posted April 25, 2005 Hey guys, I'm trying to find out what gear ratio's would possibly be in my transmission. It's an RB25DET trans with an OS Giken gear-set. That is all I know, it is what I'm told. I have no reason to believe otherwise. I just don't know what ratio's it is or how to find what ratio's were offered. Thanks. Quote Link to comment Share on other sites More sharing options...
cheftrd Posted April 26, 2005 Share Posted April 26, 2005 OS Gear Set for GT-R/Z32/RB25 ($2000) 1. 2.695 2. 1.703 3. 1.236 4. 1.000 5. Optional 0.826 ($750) Stock is: 1. 3.214 2. 1.925 3. 1.302 4. 1.000 5. 0.0752 Quote Link to comment Share on other sites More sharing options...
Guest JAMIE T Posted April 26, 2005 Share Posted April 26, 2005 Damn, it's looking more and more like my ZXTT R230 diff with the 3.70 ratio is not going to enough gear for the RB. Quote Link to comment Share on other sites More sharing options...
fentin_fury Posted April 26, 2005 Share Posted April 26, 2005 What do you believe a better ratio would be? Quote Link to comment Share on other sites More sharing options...
cheftrd Posted April 26, 2005 Share Posted April 26, 2005 Damn, it's looking more and more like my ZXTT R230 diff with the 3.70 ratio is not going to enough gear for the RB. 3.7 on a 2.6 first is going to be loooong. Quote Link to comment Share on other sites More sharing options...
Guest JAMIE T Posted April 26, 2005 Share Posted April 26, 2005 Yeah, that's what I'm thinking. Damn... Maybe it work out ok and just keep me in boost longer? Probably OK, but not optimal. I think a better ratio would be 4.10's Quote Link to comment Share on other sites More sharing options...
fentin_fury Posted April 26, 2005 Share Posted April 26, 2005 and your comments on the stock geers with the 3.7 - should be quite adequate - don't you think? Quote Link to comment Share on other sites More sharing options...
Guest JAMIE T Posted April 26, 2005 Share Posted April 26, 2005 Probably still alittle tall for a stock RB26. I don't know about rb25's or rb20's. Quote Link to comment Share on other sites More sharing options...
stony Posted April 26, 2005 Share Posted April 26, 2005 you will be about half way thru 3rd!!!!!! by the end of the 1/4 mile. Didnt you buy my rearend setup? Quote Link to comment Share on other sites More sharing options...
Guest JAMIE T Posted April 26, 2005 Share Posted April 26, 2005 Me? No... Quote Link to comment Share on other sites More sharing options...
RB26powered74zcar Posted April 26, 2005 Share Posted April 26, 2005 Matt, Jamie: nubee question here... Does just having the OS grearset alone, make the RB25det trans able now to withstand the HP we want to put thru it ?? Quote Link to comment Share on other sites More sharing options...
Guest JAMIE T Posted April 26, 2005 Share Posted April 26, 2005 That's a good question. I've not been able to find ENOUGH information about it on the web. That's why I turned here for answers. Matt has been a huge help though and I'm sure he'll know. I DO know that this trans came from behind Stony's NEW motor which has dyno'd over 600 rwhp. So, that's promising. Quote Link to comment Share on other sites More sharing options...
cheftrd Posted April 27, 2005 Share Posted April 27, 2005 I've only had one stock RB25 tranny failure, ever. I think it had a lot to do with the rear end failure. The car puts down just over 700whp and likes to tear up R200's in third gear. That's the first gear to get any kind of "traction" at all in this car (275/15 555R's). Anyway, the latest failure locked up the rear hard, just for an instant, probably shocking the hell out of the tranny gears and knocked off a couple of teeth. I've had several OS failures in 700+whp GT-R's, but it's always the main drive gear, which stays stock in the OS (and most other) sets. Keep in mind that a 700hp GT-R leaving at 9,000 RPM with a tripple is a very traumatic experience for the gear. I've also seen the stock trannys live for quite a long time under severe abuse. Another weak point (it isn't) is the input shaft on very high power, high traction vehicles. OS sells an aftermarket one. The final weak point is the center plate. It takes a tremendous thrust load in high power cars and sometimes cracks. There are aftermarket ones available. The gears are the same in the GT-R, RB25, and Z32, so If you're using the Z32 diff, it's not a problem. The 2.6 first will make the gear a little long, but if you have near 500hp+, and are not on drag slicks, it may be a benifit. With a 4.1 or 4.3 on street tires, you ain't goin' nowhere in first or second. Quote Link to comment Share on other sites More sharing options...
johnc Posted April 27, 2005 Share Posted April 27, 2005 In my 240Z with a Quaife trans I had a 2.39 first gear and even with a 4.38 rear gear the car was hard to get going, especially with a 5.5" double disk clutch. Most of the time it involved a small burnout or a stall. It was better with a 4.63 and almost tolerable with a 4.88. Quote Link to comment Share on other sites More sharing options...
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