Homer Posted April 27, 2009 Share Posted April 27, 2009 The jspec Auto TT LSD comes with a *02B diff The jspec 6spd TT pre-facelift comes with a *02B diff So, according to the information I have found the ratio on both are the same (3.769), the only difference being that the 6spd diff has the larger ring and pinion (which does not effect final drive ratio) So why do I see and hear people wanting to fit an auto TT LSD to a 6spd car saying it's better suited to track driving (e.g. Ryan.G's build). 1) Are the diff ratios actually the same between the two cars? 2) If so, why do some people recommend the auto TT diff in place of the 6spd one for track cars? Are they wrong? Quote Link to comment Share on other sites More sharing options...
JDModified Posted April 27, 2009 Share Posted April 27, 2009 watching this closely Quote Link to comment Share on other sites More sharing options...
Homer Posted April 27, 2009 Author Share Posted April 27, 2009 watching this closely You know one of the reasons I'm asking It also relates to this and the spreadsheet I'm putting together for the tech section: http://www.mkivsupra.net/vbb/showthread.php?t=181305 Quote Link to comment Share on other sites More sharing options...
TTRickeh Posted April 27, 2009 Share Posted April 27, 2009 I was planning to swap my diff for a TT auto LSD one after reading up on it. I was going by the ratio's posted by Alex on this thread: http://www.mkivsupra.net/vbb/showthread.php?t=92658&highlight=final+drive+diff Quote Link to comment Share on other sites More sharing options...
Dash Rendar Posted April 27, 2009 Share Posted April 27, 2009 Just passing through. Quote Link to comment Share on other sites More sharing options...
Wez Posted April 27, 2009 Share Posted April 27, 2009 Didnt Pigs car have one of the highest tracktive efforts at SRR with the smaller setups? Chassis Dyno Tractive Effort - What Is It? Chassis dyno graphs display both power and tractive effort at the wheels - not power and torque like an engine dyno. Tractive effort is the force being applied at the tread of the tyres and is proportional to engine torque. It differs from torque because it takes into account the gearing of the drivetrain (gearbox, final drive and tyre diameter). Power runs are usually conducted in second or third gear, and the tractive effort graph can be plotted against either engine rpm or road speed at the wheels. Quote Link to comment Share on other sites More sharing options...
JDModified Posted April 27, 2009 Share Posted April 27, 2009 Good info this Quote Link to comment Share on other sites More sharing options...
Dash Rendar Posted April 27, 2009 Share Posted April 27, 2009 The thing that I'm mostly curious about - if the ratios are different - is the unknown over whether the car will be at higher revs in 6th on motorway cruising. The increased revs and spool might have an impact on fuel economy if you do much motorway cruising. Quote Link to comment Share on other sites More sharing options...
Homer Posted April 27, 2009 Author Share Posted April 27, 2009 I was planning to swap my diff for a TT auto LSD one after reading up on it. I was going by the ratio's posted by Alex on this thread: http://www.mkivsupra.net/vbb/showthread.php?t=92658&highlight=final+drive+diff Edited: This is one of the threads that has caused confusion. Alex states the 3.2 diff ratio, but most other sites and epc (that nic posted before) list that ratio on the *03B diff and not the *02B diff installed on the pre facelift 6spd jspec. However, on my epc it's listing the details from Darrens car as having a 3.2 diff ratio. I'm confused, the info posted on various sites is conflicting Quote Link to comment Share on other sites More sharing options...
Terminator Posted April 27, 2009 Share Posted April 27, 2009 (edited) I have kept my auto diff with my V160 box. Using Quaifs calculator, and using my 8500 rpm limit, if I fit a UK manual diff I get a theoretical top speed of 245 mph, with the auto dif it is 212. So the shorter gearing should give better acceleration. I am sticking with the V160/ auto dif combo as I like the way it shortens the ratios. Fuel economy is not a factor at my level of tune. As for revs I estimate I am around 300rpm higher that it would be with a UK manual diff. This info came from the NZ site re vin plate coded 01 (4.083:1), 02 (3.769:1), 03 (3.267:1) Edited April 27, 2009 by Terminator (see edit history) Quote Link to comment Share on other sites More sharing options...
Homer Posted April 27, 2009 Author Share Posted April 27, 2009 Thanks Phil, the codes you mention are what I'd found on other sites and what I beleived to be correct (i.e. auto TT and 6spd TT are the same), but they don't tie up to the posts from Alex, nor my EPC, nor comments from Ryan and a few others here over the years. For the purposes of this thread we're talking aboutn jspec only, the UK's are know to be higher ratio so will just ignore those for now From a logical point of view the number on the axle code should relate to the final drive on the jspec cars but every search reveals another contradiction Quote Link to comment Share on other sites More sharing options...
TTRickeh Posted April 27, 2009 Share Posted April 27, 2009 So what about the 3.133 final drive EU spec? I couldn't see it in Nic's EPC. Do you know the differences between pre-facelift and facelift 6spd diff's? I think I read one was bigger than the other, but is there a difference in final drive ratios? Or am I just adding to your diff confusion? Quote Link to comment Share on other sites More sharing options...
Homer Posted April 27, 2009 Author Share Posted April 27, 2009 So what about the 3.133 final drive EU spec? I couldn't see it in Nic's EPC. Do you know the differences between pre-facelift and facelift 6spd diff's? I think I read one was bigger than the other, but is there a difference in final drive ratios? Or am I just adding to your diff confusion? No confusion on that, the exports are a different matter, I have all the ratio's on those, it's the jspecs that are confusing things The 3.133 is for the export spec 6spd only. It has the same (larger) casing as the jspec pre-facelift 6spd diff, but the internals are different to the jspec. They are great for high speed cruising and have a huge potential top speed with an auto trans if you have the power to do it (230+ mph IIRC) Quote Link to comment Share on other sites More sharing options...
JamieP Posted April 27, 2009 Share Posted April 27, 2009 When i ran a auto tt diff for a short while the gearing was vastly different, id guess the car would top out at 170-180ish on the rev limit with the auto diff. Quote Link to comment Share on other sites More sharing options...
Homer Posted April 27, 2009 Author Share Posted April 27, 2009 When i ran a auto tt diff for a short while the gearing was vastly different, id guess the car would top out at 170-180ish on the rev limit with the auto diff. Wasn't that an NA LSD diff you had rather than the 02B auto diff? The genuine 6spd diff tops out at 198 mph at 6800rpm on the 6spd, so the speeds you quote (along with the rev limit you had) indicate it was an NA diff rather than a TT one. Quote Link to comment Share on other sites More sharing options...
JamieP Posted April 27, 2009 Share Posted April 27, 2009 Wasn't that an NA LSD diff you had rather than the 02B auto diff? I might have this wrong as it was a long time ago now but iirc the auto diff was the one that was a straight fit (gearing very much closer) the na diff required a different prop? Im sure when Dean (toquicktostop) changed from a auto diff to a manual diff he reported the same and also when going in chingys car its very noticable that the gearing is closer together, he is also on a auto diff. Quote Link to comment Share on other sites More sharing options...
Homer Posted April 27, 2009 Author Share Posted April 27, 2009 I might have this wrong as it was a long time ago now but iirc the auto diff was the one that was a straight fit (gearing very much closer) the na diff required a different prop? Im sure when Dean (toquicktostop) changed from a auto diff to a manual diff he reported the same and also when going in chingys car its very noticable that the gearing is closer together, he is also on a auto diff. The NA and TT auto diffs are interchangeable as the casing is the same smaller one. Only the early 6spd cars came with the large diff casing (like your one should have now), and therefore need a different prop and one of the driveshafts. Chingy and Deans cars are another matter as they are so modified it's a not a good thing to assume they have anything stock left in the drivetrain.. If the diff was changed, was it confirmed as coming from a UK or jspec car? Auto/manual? This was never going to be an easy job to sort out, but it's turning into a nightmare! Quote Link to comment Share on other sites More sharing options...
JamieP Posted April 27, 2009 Share Posted April 27, 2009 Chingy and Deans cars are another matter as they are so modified it's a not a good thing to assume they have anything stock left in the drivetrain.. True, you may have something there, if somebody lends me a auto diff and prop i will happily test it out to see if this is a forum wives tale. Quote Link to comment Share on other sites More sharing options...
Terminator Posted April 27, 2009 Share Posted April 27, 2009 I never realised that the JDM 6's and auto's shared the same diff. Given that so many original Jap owners could choose just about anything they wanted on the car , it is almost impossible to tell what ratio you have in a diff Quote Link to comment Share on other sites More sharing options...
Homer Posted April 28, 2009 Author Share Posted April 28, 2009 Bump. Anyone have any ideas to try and clear this up? Darren is fitting an auto LSD in his car sometime this week, so will be very interested to hear if the final drive turns out different.. Quote Link to comment Share on other sites More sharing options...
Hermit Posted April 28, 2009 Share Posted April 28, 2009 How about an empirical test? The auto box is 1:1 in 3rd gear, and the 6sp is 1:1 in 5th... so if the diffs are the same you'd expect the same mph per revs in each. If the diffs are different, it's by about 15%, big enough to dwarf any innacuracies. My money's on the EPC being correct, but then (from pretty much everything else I've read) I'd expect the ratio part of the code to be '03' for the 6sp... (assuming the car was 6sp when it left the factory...) Quote Link to comment Share on other sites More sharing options...
Dash Rendar Posted April 29, 2009 Share Posted April 29, 2009 I'll be glad to post up some mph figures when I have the auto diff fitted to my 6 spd. (I can't test with the 6 speed diff as the car is off the road until the replacement is fitted.) Quote Link to comment Share on other sites More sharing options...
Ryan.G Posted April 29, 2009 Share Posted April 29, 2009 There is definatly a difference in the ratios guys. I have some logs of Tony's car which has had a 6sp conversion but still has the auto diff... His top speed in 6th at 6800 is only around 180mph. Also another reason im sure is because everytime a supra with a auto diff comes on SRR, the RPM vs Speed always has to be changed alot from the normally supra ratio Ryan Quote Link to comment Share on other sites More sharing options...
TLicense Posted April 29, 2009 Share Posted April 29, 2009 Beat me to it Ryan I found (as has been suggested) about a 15% difference in road speed being reported from the gearbox when I converted to the 6 speed. This definitely suggests that the ratio's are indeed different. Quote Link to comment Share on other sites More sharing options...
Guest 38super Posted April 29, 2009 Share Posted April 29, 2009 I've never heard of a J-spec 6 speed, pre '96, with anything other than the big diff and the 3.266 ratio. The only way to have got the lower auto ratio would have been by factory ordered option. Quote Link to comment Share on other sites More sharing options...
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