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Discussion Starter · #1 ·
Hi everyone, I was just wondering what other 240/260/280Z Turbo(280ZXT conversion) owners were using for a diff ratio? I have used the 3.36 which I didn't like and the 3.7 which is pretty nice with my stock ZXT engine. However, I do have upgrades planned and I wonder if a 3.54 wouldn't be better. BTW I am going to be using an R200 LSD, but it has 3.9 gears on it now(I will likely switch the ratio). My friend who also had a 240ZT was running the 3.9 diff with a comp tranny, but he seemed to have to shift the thing like crazy(all the time). My new project car will pretty much be a weekend warrior and mostly play around at autocrosses, may even check out a legal drag race or two. I have a pickup, with AC :), as a daily driver now. I am tired of fearing the police whenever I go out. Not that I go out to break the law, but they always manage to pull me over some **** thing or another. The last time it was for having a parking permit hanging from my mirror. The time before that was my exhaust was too loud(bored policein Daly City). Tired, tired, tired. Oh well, I just hope they're there when/if I need them. Don't hate em, just that they discriminate against Zs or sports cars. Well if anyone with a 1st gen Z with the turbo conversion has experimented with the different gear ratios, I would sure would like to here from them. Only turbo owners need apply, normally aspirated is a different beast(but any info is welcomed).
Thanks,
Tim Deesen
71' 240ZT
73' 240ZT(project 99')
CA "TS 240ZT"
 

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Discussion Starter · #2 ·
<b>RE: Diff ratio for 240Z Turbo? Anyone try 3.54?

I have used both the 3.36 and 3.54. I am planning to run a 3.70 for daily use. I think you need to choose you gearing based on your projected power output. Generally, turbo motors like more gearing, 3.55-3.36, to stay in the power band longer. I would think that a turbo motor with less power would benefit from a 3.70-3.90 gear, while a high hp turbo motor would benefit from a 3.36-3.70. When I was running the 3.55, I raced "BOOST" who was running a 3.90 gear. In 1st we were dead even, but when we swithced to second I started to pull away. It was weird to hear him have to shift while I was still pulling through 2nd gear. Boy I like to ramble on. To make a long story short, I would stay between the 3.55 and 3.70 gears. Get a G-meter and measure which one gives you faster acceleration, 0-60 and 1/4 mile.
 

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What are the options for a LSD rear? I thought they used different ring gear bolt sizes which prevented you fom swappping gears? I'd like to try lower numeric gears than the 3.7 I currently have in my LSD. I'd like to really load the turbo down for drag racing. Autocrossing is probably a different story, might want to keep the revs up more there.
Either way I'm not going to give up the LSD to change gears.
greg
71 240z
 

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Discussion Starter · #4 ·
For LSD gear sets check you main gear bolt size

I haven't done the conversion of the gear set on my LSD yet, but I have one LSD that has 3.7 gear set and another that has a 3.9. I think the LSD clutch units use a 17mm bolt(~12mmthread) on the main gear where as other R200s(earlier) may use a 14mm bolt(10mmthread). I am pretty sure you can get the right gear set out of an 86-88 300ZX(not verified yet). I am going of of speaking to someone who has an LSD and was thinking the same thing. If anyone has a Nissan Motorsports catalog, you can see what I am talking about. They sell two different limited slip R200 assemblies one having the 10mm and the other the 12mm(note this is in the 300ZX/Z31 section) bolts shank diameter. I think the later 86-88 Z31 300ZX may have the larger gear sets. You should do a visual ID to see what you have on your main gear. I am pretty sure I will pop in a 3.54 gear set as the 3.9 doesn't allow you to use the boost as much(too much shifting). I will also beef up the breakaway of the LSD to around 80ft lbs. I also plan on boosting to around 12psi this summer with an intercooler and installing a Centerforce Dual friction on a lightened 240mm flywheel. When I have been autocrossing with the 3.7 LSD I almost felt as though a 3.54 would be better so I could keep it in first nearly all of the time. **** the rev limiter to ****, that thing is out the door. I am going to disable it!
Later,
Tim Deesen
71' 240ZT
73' 240ZT(summer project)
CA "TS 240ZT"
 

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Which tranny is everyone using?

I plan on doing the turbo conversion in a couple of weeks, and I have been debating which tranny to use. I have a Borg warner and a 5spd from an 82' n/a. I don't like how the Borg-Warner shifts at all. How different are the two trannys geared, and could I just switch to the Datsun unit for now? I don't have the money for an LSD right now, but that B-W with the high stock gears of the 240 seams a little rediculous.
 
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