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View Advert WTB: 3.90 LSD and 280ZX Trans Looking for 3.90 ratio LSD diff and 280zx close ratio trans. Thanks Advertiser blodi Date 02/01/2022 Price Category Parts Wanted Year 1981 Model 280zx  

So, if you take what we know from the mechanics readings and we know 4th is 1:1....take 1 divided by the 4th gear ratio that he had (.710) and you get 1.408. Take that 1.408 and mutiply it by the rest of the ratios he gave me...and it lines up pretty well... 1st- 33 Main 19 Counter=2.357-this one doesn't work because his math is wrong, but even if you correct that, it doesn't work out, he must have mis-counted the teeth. 2nd- 28 Main 19 Counter=1.473 x 1.408= 2.075 3rd- 26 Main 28 Counter=.928 x 1.408= 1.307 4th- 22 Main 31 Counter=.710 x 1.408 = .998 5th- 19 Main 31 Counter=.613 x 1.408= .863 Compare that to the wide ratio and it pretty much is dead on: 2010-N3030 3.321 2.077 1.308 1.000 0.864 (wide ratio) Thanks for your help and answers, I think we've gotten somewhere here. So a stock turbo/2+2 clutch should hold the power? Any issues with going to that light of a flywheel and having as large of a cam as I do for idle and low speed driving? Seems now going to a 280x 5 speed and a 3.90 will do exactly what I want compared to what I have. Raise the gearing slighting for 1st and 2nd so they are closer to 3rd and make 5th a bit taller for high speed cruising.

OK, got the car on jack stands, put it into 5th, marked it all and gave the engine one turn over by hand. Drive shaft rotated ~1.15 turns or so. So...it's an overdrive trans. Next, I put it into 1st, marked it all again, rotated the engine 3 times and checked the shaft, it had rotated just under the 3 times, I rotated the engine another ~1/3 turn and it was lined up with the marks again. So...I think we've confirmed that it is a wide ratio with a 3.3X 1st and a overdrive 5th. This matches my driving experience with 1st/2nd being short and 3rd bogging a bit by comparison. Going back to my diff ratio. I'm looking through old images and videos that I happen to have at various engine/vehicle speeds and acceleration through the gears and comparing them to when I plug in the wide ratio gearing, my tires size and a 3.9 rear end to the calculator, and man, they are lining up pretty darn well. Maybe I'm not counting the diff rotations correctly....based on my images/video, the white speedo gear....my high rpm at highway speed....it's all pointing to a 3.9. Here is the wide ratios and 3.9 rear end: Compare that to my images here and notes from a video I found: ~87 @~4400 ~75 @ ~4000- this would be 4th gear. This would have been in 4th given where it was taken, ~51 @ 2900 I have a video that shows me shifting at ~6800 @~38mph then 6800 @ ~58 and topping out in 3rd at 6000 @~84 For comparison, here is the same calculator run but with a 3.54 rear end. Doesn't line up nearly as well.

You can see in my post above that 4 of the 6 comp transmissions actually have 5th as the 1:1. The rebuilder told me 5th was an overdrive gear so I assumed it was one of the top two. However, if 5th was 1:1 and I do have a 3.54 rear end, that would add up to me seeing 4K at 80mph which is what I see currently. I just couldn't get the other ratios to line up to any of those options. Maybe I need to put the back end up in the air, put in 5th and see if the driveshaft rotates exactly once with the engine being turned over once or if it goes a bit further which would indicate an overdrive. I played with this calculator a bit... http://www.vmar.com/java/gear.html Also, my 1st and 2nd gear are both really short and then 3rd seems tall by comparison...another reason the wide ratio seemed to make sense. The other one with a bit more of a gap from 2nd to 3rd is the last comp trans on the list.

1. I followed those instructions. With both wheels in the air and out of gear, the opposite wheel doesn't move. With the car in gear, the opposite wheel rotates the opposite way. I've tested the number of rotations a few times. With only one wheel off the ground, two rotations of the wheel= just over 3 1/2 rotations of the driveshaft. 2. This will have to happen in the Spring when there isn't several inches of snow and salt all over the roads here. 3. Tires are 205 55 15 Dunlop Direzza's, which should be 23.9"

OK, I went back and found a post from 6 years ago when I had the trans rebuilt...here is what the trans guy told me: 1st- 33 Main 19 Counter=2.357 2nd- 28 Main 19 Counter=1.473 3rd- 26 Main 28 Counter=.928 4th- 22 Main 31 Counter=.710 5th- 19 Main 31 Counter=.613 His math on 1st gear was wrong and should be 1.736 if those tooth counts are correct. If you assume 4th is 1:1 and divide 1/.710 you get 1.408. Take that times the numbers above and you get the wide ratio gears....other than first. So that one is a mystery still. Maybe I'm calculating this wrong? What if you assume 5th is 1:1?

I know the black gear should be correct, that's why it's confusing me. I've checked the rotation ratio several times on the diff thinking something must be off. 3.54 was the stock diff in auto cars, obviously it could have been changed, but the number of rotations always comes out the same. Maybe I need to pop the rear cover and have a look. Even before I changed from the auto the manual, it had the white gear in it. There are 6 different Comp transmissions (see below), mine is supposed to be the one with the stock 280z ratios. I had the trans rebuilt a few years ago and the rebuilder was the one who figured out it wasn't a standard trans due to the synchros and also calculated each of the ratios out for me so I'd know which version I have once we figured out what it was. Looking at an online calculator though, with a 3.54....4K at 80 would be a 1:1 ratio in 5th....so maybe the rebuilder was wrong on the ratios? He told me it was an overdrive trans. Hard to tell now with the trans in the car, but maybe I can mark it and rotate the engine manually to see. The plot thickens I guess. It would explain the high RPM at speed. Still doesn't explain the wrong speedo gear working out to the right speed. I guess I have some homework to do to figure out what I'm really starting with here. Factory Competition Transmissions 77 - 83 There were Factory Competition 5-Speeds available through NISSAN Competiton Dept. There were two overdrive Transmissions, and four with the direct drive (1:1 in fifth gear) #1 #2 #3 #4 #5 32010-N3130 2.906 1.902 1.308 1.000 0.864 (close ratio) 32010-N3030 3.321 2.077 1.308 1.000 0.864 (wide ratio) 32010-N3220 2.818 1.973 1.470 1.192 1.000 32010-N3221 2.348 1.601 1.296 1.138 1.000 32010-N3222 2.192 1.601 1.470 1.138 1.000 32010_N3201 3.321 2.270 1.601 1.240 1.000 (rally transmissions)

So currently, I am seeing about 3500rpm at 70 and 4000rpm at 80. Now that said, I don't know how accurate that is. I know I have a 3.54 rear end. As I said, car was originally auto and I have checked it several times (lifted one rear wheel, turned it around twice and counted the input shaft revelations at just over 3 1/2.) But, I found out that I have a white (3.90) speedo gear in my trans. I installed a correct black 3.54 gear and the speedo was obviously reading way too high. So someone must have figured out the speedo was reading wrong at some point and put in the white gear to get it closer. Would I be better off staying with a 3.54 or maybe splitting the difference with a 3.70? I do a fair amount of driving with it on the freeway and wouldn't mind less RPM. And I'm not hurting for punch in lower gears...1st just spins the tires. Thanks for the tip on the larger clutch/flywheel. Could I run a stock spec clutch with the larger setup and be able to hold my power sufficiently? Ironically, when I bought my trans it came with a Fidanza flywheel that I sold off because I thought I was keeping the stock L24 at that point.

Looking to upgrade the drivetrain on my 71 240Z this year. I want to change out the clutch, flywheel, trans, and diff. My current setup: Engine: L28, 500/300 cam, high compression, triple Weber's, etc.....last made ~200rwhp on dyno. Clutch/Flywheel: Stock spec Exedy clutch/Stock Flywheel Trans: Nissan Comp (steel syncro) wide ratio 280Z trans-standard 280z ratios : 32010-N3030 3.321 2.077 1.308 1.000 0.864 (wide ratio) Diff: 3.54 open diff (car was originally an auto, thus the 3.54) Goals: A bit better throttle response, clutch that holds the power a bit better, closer ratio trans , a bit less RPM at highway speeds, LSD. Current thoughts for new setup: Flywheel: I don't want to lose the drivability too much due to the big cam and this is purely a street car, so this mildly lightened wheel intrigues me: https://www.californiadatsun.com/flywheel/lightened-resurfaced-balanced-steel-non-turbo-225mm-flywheel.html Clutch: Exedy Stage I, would this sufficiently hold my power? Current, stock spec clutch will slip every once in a while if quickly shifting under full throttle/ high rpm from 2nd to 3rd. Just need a bit more grab. Again, want to keep street drivability. I have a really heavy clutch in one of my other cars and don't want to go there. https://www.lmperformance.com/855771/06805a-exedy-stage-1-organic-clutch-kit-nissan-280z-l6-28-2-seater.html Trans: 280zx close ratio seems to fit the bill. Does the 280z clutch and flywheel work with that trans or do I need a 280ZX clutch/flywheel? Rear diff: Looking at doing the Subaru STi R180 diff. Seems most like the 3.90 ratio with the close ratio trans? I know that I need the adapter hubs as well. https://zcardepot.com/products/subaru-r180-swap-billet-axle-set-240z-510?gclid=Cj0KCQiAraSPBhDuARIsAM3Js4q5CMnPC5DVgwnf0LwZQbsZMsb389huRDMDK9EjWpTrE1ZuekVpV-kaApynEALw_wcB&utm_campaign=google shopping&utm_medium=cpc&utm_source=google&variant=39589764792433 It looks like that trans/ diff combo would make 1-4 shorter and closer ratios than my current setup and 5th would be a tad taller? I know there are hundreds of threads on this stuff, but some are 10+ years old at this point and just want to make sure what I'm doing here makes sense before I start sourcing and buying up parts. Any thoughts or other suggestions are welcome. Or if you have parts i might need or might be interested in any of my old parts, let me know. Might be a few months here though til I am ready to swap it all. Anything else I'm missing that I would need to swap? Thanks!

@jonbill you hit the nail on the head! Dropped it down to a .024” gap and she pulls hard and clean! Thank you! Super happy!

I put in new plugs and she certainly revs better. But breaks up now at 6k instead of 5k before. I might try adding timing to see if it has an impact.

I have the MSA upgraded alternator with the internal voltage regulator. I guess I could monitor the voltage gauge. Never had a problem with the pertronix reviving in the past. She’d gladly run up to redline all day. Going to order up some new plugs. Is what I currently have good?

Happy new year and happy uh quarantine to everyone. So, I’m trying to figure out my high rpm sputter. You can see it do it on the dyno video I posted last year. Tried a new coil, wires, put in a new pertronix...nothing. Fuel pressure is steady at 4 psi. Pulled the tops off the carbs and everything looks clean. Maybe it’s the plugs? What plugs/gap should I be running on this setup? Currently running NGK BPR6ES at about .029 gap.

Do you have the ballast resistor hooked up with your setup?

Yeah, that's kind of what I went through back in August.....I had the dizzy installed and bypassed the resistor as instructed...my tach was all bouncy at higher rpm. So I tried hooking the resistor back up and that's when it fried the ignition module on the dizzy. Maybe I need a different coil? I thought I had the correct ohm version...but now I forget what I have in there. I'll have to check.

Yeah, the problem is I can't get my tach out because of my full dash cap blocking it in. Sounds like some people have issues with the swap and some don't : https://forums.hybridz.org/topic/122001-240z-tach-issues-with-280zx-distributor/ Im wondering if there is any dizzy out there that will work with a 240z tach without issue...other than a stock 240z dizzy. Aftermarket?

This is what I used... Car ran great. But the tach was just bouncy when I got on it at all.

Sorry, I meant that I had a 280zx dizzy that I was installing. I did try it with my 240 tach and it's fine until about 3K and then will bounce like crazy.

5 months later.... I finally got around to trying to install the 280z tach here while it’s winter. Quickly realized I can’t remove my stock tach as my car has a full dash cap on it and blocks the tach from coming out. I don’t want to force anything and break the cap or tach. So...anyone know of a aftermarket dizzy that will work with a stock 240z tach? I haven’t searched yet. Also...anyone need a 280z tach or rebuilt dizzy? ?

I installed the new dizzy and got the timing all set. Took it for a spin Friday afternoon and it ran great and pulled hard! But, once you got over about 3.5K, the tach would start bouncing all over the place. So I stopped for gas and reconnected the resistor in an attempt to fix that. Well, I started the car and it died after about 10 seconds. Long story short, I fried the ignition module. Had to get a ride from a friend back home and got the old dizzy and installed it and got the car home. So, I ordered a new ignition module and I guess I'll have to look for a 280z tach to install.

Found a source for both parts and ordered them up today. I did get the car started with the new dizzy last night and adjusted the timing, but realized I couldn't tighten it down with the 240 mount/plate.

Just realized I also need the 280ZX dizzy mount. Do I also need the adjustment plate? Anyone have these?

I checked my timing before swapping the dizzy's out. 20 at idle and 37 at 3K+ So, I guess I did only have 17 degrees in the old one. 280zx dizzy is in but I need to adjust the timing tonight and go take her for a test spin.

So it looks like I'll be going from 24 degress of centrifugal advance down to 17. Since the webers don't use vacuum advance, that's what I get. So I'll probably have to add a bit more timing to it overall to get the same full advanced timing at 3K+.

Ok. Thanks! I also noticed that the dizzy I got has the e12-92 module on it. But it looks like this is fine as long as I only make connections to the B and C terminals. https://www.zcar.com/forum/10-70-83-tech-discussion-forum/116513-e12-92-e12-80-a.html