Adrian Bridge Posted January 2, 2019 Share Posted January 2, 2019 Hi - advice and wisdom pleaseI have a 1996 1.6 K supersport (138 bhp) with 6 speed gearbox and I assume 3.62 differential. The 1:1 final drive and resulting high revs is tiring when touring. Wheels are 14 inch with 185/60 H tyresI am not an engineer but am keen to look at after market crown and pinions available that are higher ratios than the 3.6. Road and Race transmissions can achieve longer gearing with a 3.36 and 3.14 giving a 7% or 13% drop in revs for a given speed (approx cost to get this work done £720)Everything is a compromise I know: while a 7 % drop in revs hardly seems worth the expense of going for the 3.36, I am worried that going for a 3.14 ratio would excessively limit acceleration. Has anyone done this before? Your thoughts would be appreciatedAdrian Link to comment Share on other sites More sharing options...
TomB Posted January 2, 2019 Share Posted January 2, 2019 Semi-seriously, Ive just taken out my engine & 5 speed gearbox. I have a 3.92 LSD rear diff in the car. Would a swop to this drive train be of interest? Id like a 6 speed/3.62 drivetrain, but cant justify the cost of buying separately a 6 speed box and the diff work. Just a thought. Link to comment Share on other sites More sharing options...
DJ. Posted January 2, 2019 Share Posted January 2, 2019 I think going for a very long final drive with the six speed box could give you a very long first gear that would be a pain in traffic. Link to comment Share on other sites More sharing options...
rj Posted January 2, 2019 Share Posted January 2, 2019 And you'd loose the idea of the close ratio box if you make 6th an "overdrive" Link to comment Share on other sites More sharing options...
Wrightpayne Posted January 2, 2019 Share Posted January 2, 2019 Personally having had both 5 and 6 speed boxes in my 1.6K supersport I think the 5sp (std ratios) and 3.9 diff is better suited to touring and 6sp and 3.6 diff better for track days / shortish rapid blats.6 speed always commands a premium price wise over a 5 speed.Ian Link to comment Share on other sites More sharing options...
Area Representative Richard Price Posted January 2, 2019 Area Representative Share Posted January 2, 2019 Adrian,Are you sure you already have a 3.6 diff?What sort of revs are you seeing at what speed?With 14" 185/60's and a 3.62 diff , you should see just short or 75mph at 4k rpm in 6th, where a 3.92 is closer to 70mph.A 3.38 would give around 80 mph at 4k rpm, and a 3.14, 86mph. (alnng with the potential to pull 60mph in 1st gear....)By contrast, a normal 5 speed with a 3.92 diff gives around 85mph in 5th gear at 4k rpm.If cruising revs are a major concern, then a swap to a 5 speed 'box would look far more sensible.Actually, swapping your 6 speed for a BGH modified 5 speed with taller 1st 2nd & 3rd would look to be a good compromise. Link to comment Share on other sites More sharing options...
Adrian Bridge Posted January 2, 2019 Author Share Posted January 2, 2019 HiThank you all for your advice.I note with interest your comments Richard. I should have made some records when I last drove the car but I am pretty sure the revs exceed 4,000 rpm at 75 mph in 6th so I may not have a 3.62 diff after all. Food for thought.Next dry day I'll go out and check.I don't really want the hassle of changing the drive train (or the car) at this this stage but may need to think again.Adrian Link to comment Share on other sites More sharing options...
Alastair B Posted January 2, 2019 Share Posted January 2, 2019 Another thought IIRC you could get an overdrive higher gear put in as a replacement for your 6th gear so that you keep the sprint close ratios for gears 1 to 5 then select 6th for motorway cruising, this could be a 13% longer gear for example, again Road and Race will be able to advise. This way the box gets an overhaul if you are unsure of the provenance. I’m sure a gearbox aficionado will be along to confirm or otherwise this option as being practical. Link to comment Share on other sites More sharing options...
Alastair B Posted January 2, 2019 Share Posted January 2, 2019 Another thought IIRC you could get an overdrive higher gear put in as a replacement for your 6th gear so that you keep the sprint close ratios for gears 1 to 5 then select 6th for motorway cruising, this could be a 13% longer gear for example, again Road and Race will be able to advise. This way the box gets an overhaul if you are unsure of the provenance. I’m sure a gearbox aficionado will be along to confirm or otherwise this option as being practical. Link to comment Share on other sites More sharing options...
DJ. Posted January 2, 2019 Share Posted January 2, 2019 I was under the impression that sixth is 1:1 because that is direct drive as fourth is in the 5 speed box, so I don't think that is an option unfortunately. Link to comment Share on other sites More sharing options...
Alastair B Posted January 2, 2019 Share Posted January 2, 2019 Ignore the double post and the incorrect info. The 6 speed is in effect a direct drive and results in the 1:1 gearing and cannot be changed as is linked to the box design. You probably already knew this. Link to comment Share on other sites More sharing options...
EEK Posted January 3, 2019 Share Posted January 3, 2019 Some relevant information here,https://www.lotus7.club/forum/techtalk/which-gearbox-2I went for different diff, see post 10 in above link Link to comment Share on other sites More sharing options...
Wrightpayne Posted January 3, 2019 Share Posted January 3, 2019 Caterham online stores have 3.38 recon diffs (non lsd) on clearance at £358. Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted January 3, 2019 Member Share Posted January 3, 2019 Adrian: Private Message sent.Jonathan Link to comment Share on other sites More sharing options...
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