jgkurz Posted August 19, 2003 Share Posted August 19, 2003 Hi all, I'm working on a Z project where I need a differential that has a taller gear than the current 3.15 R200. I've seen a lot of posts on Corvette and R230 IRS diffs, but they all seem to have ratio's in the 3.5 - 3.7 range. Any suggestions? Thanks! Quote Link to comment Share on other sites More sharing options...
Guest Aaron Posted August 19, 2003 Share Posted August 19, 2003 I think scottie's vette rear is a 3.07, and there was tread recently discussing the ford IRS (Mustang, TBird, Cougar). It was mentioned that it had ratios as high as 2.15. The R230 is available with 3.54 (Q45) and 3.7 (300ZXTT). There is also a gearset availablt that is something like 4.1. Quote Link to comment Share on other sites More sharing options...
jgkurz Posted August 19, 2003 Author Share Posted August 19, 2003 Awesome. Thanks!!! Quote Link to comment Share on other sites More sharing options...
jgkurz Posted August 19, 2003 Author Share Posted August 19, 2003 I have searched every forum that would contain this info and cannot find any reference to a 2.15 ratio. Can anyone point me in the right direction? Thank you. Quote Link to comment Share on other sites More sharing options...
Scottie-GNZ Posted August 19, 2003 Share Posted August 19, 2003 John, what ratio are you needing and what application requires such a ratio? Just curious. Quote Link to comment Share on other sites More sharing options...
johnc Posted August 20, 2003 Share Posted August 20, 2003 The highest Nissan ratio I've ever heard of was a 3.08 used in a Japan only R200 truck diesel application. The highest domestic ratio I've heard of is the 2.64 in the rear end of my 1964 Lincoln Continental. Quote Link to comment Share on other sites More sharing options...
Mike C Posted August 20, 2003 Share Posted August 20, 2003 2.41 and 2.56 are common in 8.5" 10 bolts, but as far as IRS setups, the 84-92 Corvette is commonly fitted with 2.73 gears when automatic trans equipped, and the late 70's through mid 80's Jaguar IRS usually have gears in the mid 2's. You might be able to buy 2.15 for a Ford 9 inch. The only thing that would use a gear like that is a Bonneville type car. FWIW, the Jag and 'vette IRS are NOT NHRA legal because of safety concerns since the half shaft is a locator for the suspension and not just a power transfer device. Tom's differentials has an NHRA legal safety device for the 63-82 'vette setup that adds a redundant locator from the wheel to the diff in case the half shaft breaks. Quote Link to comment Share on other sites More sharing options...
jgkurz Posted August 20, 2003 Author Share Posted August 20, 2003 Mike C got it right. This is for a 1980 280ZX L28 turbo I am going to take to Bonneville in 2004 or 2005 if all goes well. Yes I said 1980. The engine is obviously not original. The car belongs to a friend of mine who built it and raced it until 1990. The car has been in storage since that time. The car runs in the F/BGT class where the record was set in 1990 at 222mph by a Japanese team with a 300ZX Twin Turbo. I kind of wish it wasn't a Nissan... Our car has gone 226mph with a home grown fuel injection that required too much attention while driving. I don't want to be driving at 200mph and have to mess with tuning the EFI. Basically, everything was a knob, switch or lever to manage the fuel mixture. I am in the process of refurbishing the engine, chassis and safety componants. My hope is that adding my Electromotive Tec3 to this car will get us a few more HP to get the record back. The other problem is we need a taller gear. The current setup uses a Chevy 4spd truck transmission with 4th being an overdrive. All Nissan transmissions broke, and I do mean all. Everything from the T-5 to the Datsun transmissions were used. Nothing would hold the power once the car was in overdrive. The truck transmission has held up better than any other setup. I'd rather be using a T-5 in 4th gear with a Corvette IRS diff. That way the driveline and pinion gear wouldn't have to spin at 11,000 rpms or more. So back to the diff question. The Corvette diff looks promising. Has anyone done this swap? Quote Link to comment Share on other sites More sharing options...
Guest Aaron Posted August 20, 2003 Share Posted August 20, 2003 I'm sorry. I misquoted. Thats what I get for trusting my memory. Here is the post I was refering to, but 2.73 was mentioned, not 2.15. Again I am sorry for misleading you. Quote Link to comment Share on other sites More sharing options...
rags Posted August 20, 2003 Share Posted August 20, 2003 jgkruz, Scotty has done the Corvette swap. http://www.turbobuicks.com/members/scottiegnz/vette-irs-swap.htm Is the R200 that you currently have going up for sale? I'm very interested! Quote Link to comment Share on other sites More sharing options...
jgkurz Posted August 20, 2003 Author Share Posted August 20, 2003 Aaron, No problem on the 2.15 post. At least it got the thread started... rags, Sorry, but the 3.15 R200 won't be for sale. Thanks for the link. Regards Quote Link to comment Share on other sites More sharing options...
johnc Posted August 20, 2003 Share Posted August 20, 2003 If you can't find the rear gear you want, can you go with taller rear tires? Quote Link to comment Share on other sites More sharing options...
jgkurz Posted August 20, 2003 Author Share Posted August 20, 2003 John C, We are using the tallest possible tires right now. I don't think there is room for taller tires. Part of the problem is the car sits so low. I'm encouraged by the possibilty of using the C4 diff. We would probably just fabricate in the center section and still use the ZX suspension. Quote Link to comment Share on other sites More sharing options...
Phantom Posted August 20, 2003 Share Posted August 20, 2003 If you're willing to run a GM auto then try the GM T56 manual. I have that in my car and the .5:1 6th gear with a 3.70:1 R200 LSD and 24.9" tires calculates out to 240 mph at 6,000 rpm. That should be good enough to get your record back. Quote Link to comment Share on other sites More sharing options...
jgkurz Posted August 20, 2003 Author Share Posted August 20, 2003 The current transmission is a GM truck manual 4spd with a OD 4th gear. We thought about using the T56, but are not confident the 6th gear OD will hold the power. So far the GM truck trans has held up better than any other. I'd much rather use a T56 since it shifts much easier. Our trans options will grow significantly if we are able to use a 1:1 4th gear. Most transmissions in 1:1 don't use a cluster gear in 4th which is much stronger. Maybe we could go back to the T-5 if all we needed was 4th gear. So using a tall diff and a 1:1 trans would be ideal. Another problem is when you use the OD in the trans rather that a tall differential your driveline and pinion RPM increase. I believe, spinning the driveline and pinion at 11,000 RPM will greatly increase the chance of failure. The engine goes thought the 5th mile at around 7200 - 7500 RPM. Quote Link to comment Share on other sites More sharing options...
Phantom Posted August 20, 2003 Share Posted August 20, 2003 Talk to Craig Taylor at http://www.taylor-race.com. He can set you up with a 3.36:1 LSD R200 and build you a "crash box" tranny like the NASCAR guys use that will give you a 1:1 4th gear that will run you over the 220 mph mark. All it takes is money. Quote Link to comment Share on other sites More sharing options...
jgkurz Posted August 20, 2003 Author Share Posted August 20, 2003 Talk to Craig Taylor at www.taylor-race.com[/url']. He can set you up with a 3.36:1 LSD R200 and build you a "crash box" tranny like the NASCAR guys use that will give you a 1:1 4th gear that will run you over the 220 mph mark. All it takes is money. We are using an R200 with a 3.15 ratio. With the OD tranny we have a theoretical top speed in the area of 225MPH or so depending on tire selection. ---Correction on the redline---. The 5th mile RPM is between 7200 and 7500. If I can fit the C4 2.59 diff then use a 1:1 car 4th gear transmission we will be good shape. Having more forward gears will help get the car accelerated in the critical 1st and 2nd miles. With the long throws, the truck trans is a pain to shift at 200mph... Quote Link to comment Share on other sites More sharing options...
Scottie-GNZ Posted August 20, 2003 Share Posted August 20, 2003 That is correct. The C4 IRS was available with a 2.59: ratio. Although the car is a ZX, let me know if there is anything I can do to help. As for the NHRA rule on IRS, I am still confused. If anyone has a 2003 rulebook, could you please quote what it says about IRS. Here is the only thing I can find on the web: "A long-standing rule that requires any car with independent rear suspension (IRS), weighing over 2000 pounds, and running 10.99 or quicker to replace the IRS with a conventional rear-end housing has been modified. For 1999, only those IRS designs which utilize a lower control arm only (like a 1963 to 1982 Corvette) will have to comply with the above requirement. If the suspension utilizes both upper and lower control arms, the IRS may be retained regardless of weight or e.t." Note that the revision was made in '99 and the specific reference to a Corvette is for the C3. Why not also spell out the C4 if it did not comply? OTOH, I wonder if they would consider mine compliant with my mod connecting the hub to the Z shock tower with a coilover? Really does not matter since I do not intend to compete in events where those rules would enforced. Quote Link to comment Share on other sites More sharing options...
Mike C Posted August 23, 2003 Share Posted August 23, 2003 A better choice might be a C3 corvette diff for adapting to the Z suspension. It has significantly less of the mounting involved with the cover. Check out Tom's differentials for some pics and other misc info. The "truck" 4 speed is for all intents and purposes a Vega trans. It should have a 3.5 first gear. They flip the 3-4 shift arm so when you think you are putting it in 3rd, it really goes direct, then when you shift into "4th" it goes back through the cluster to a OD gear setup. The Saginaw is reasonably strong in terms of continuous torque rating, just don't dump the clutch! I have a friend running a Ford version of this. A toploader 4 speed with effectively a 1:1 3rd gear and an OD 4th. He is running it behind a build 262 6 cylinder in a 55 Ford customline. The 3 speeds with BorgWarner electric OD couldn't take the torque of the big six even though they were regularly installed behind the 292 and 312 Y blocks. Check out Dutchman motorsports as they sell an IRS based on a 9" center, you might be able to buy just the center or modify a housing and have short axles fabbed. The Dutchman uses inboard brakes like the jag. But it does give you the freedom to run virtually any gear ratio, and a spool is an ideal traction device in a Bonneville car. Is their a penaly for running a solid axle? Does it bump you classes? Quote Link to comment Share on other sites More sharing options...
jgkurz Posted September 13, 2003 Author Share Posted September 13, 2003 Is their a penaly for running a solid axle? Does it bump you classes? There is no penalty for running a live axle vs the original IRS. I would stay in the same class. You are correct about the spool. It's so hard to get traction in the first mile. Quote Link to comment Share on other sites More sharing options...
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