Rate my gearbox

Topics relating to the Lotus Exige S2 (series 2)
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Fonzey
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Since I bought this car I've been rattling around trying to figure out how far I'd like to take it, what I want from it, etc. I think I'm rounding in on a decision and much of the back and forth has been gearbox related.

I don't want to rehash the C64 issues in this thread as they're discussed in pretty good detail here: https://www.exiges.com/viewtopic.php?f=12&t=21267 but I do want to gain some critique on what I plan to do about it, as I know a few here have gone for upgraded boxes either preventatively or as a response to a failure.

I've been flip flopping between leaving it until it blows up and taking it out pre-emptively and being sensible. Due to the costs of the proactive measures I've even questioned whether I have a long term future with the car, and whether selling now and getting the next project is the right move but I'm really struggling to identify a car that ticks all the boxes I get from the S2 currently so I'm now intending to plough on with preventative measures, I think.

I don't have much ambition to raise the power further, so at 280bhp the box may well be safe for the foreseeable but the car is becoming used more and more for track and less and less for road, so if it is going to go pop - I'd rather it didn't ruin a trackday or European trip or whatever. That said, once the box is toughened up a bit, the temptation to push a little more power may be overwhelming :mrgreen:

Anyway, here's the plan:

- Fit Toyota/MR2 LSD, the same that Lotus supplied as an option to some later S2s.
- Fit uprated clutch and lightweight flywheel
- SSC 3rd/4th gear replacements, "semi helical" to try and retain some sensible levels of NHV from the box.
- Komotec or Jubu 5.0 final drive. Komotec is cheaper, so will probably come down to that :mrgreen:
- Toyota C60 Sixth gear

I've done some maths on ratios etc with the different FD, and I've calculated the following:

OEM:
1st 43mph
2nd 67mph
3rd 92mph
4th 117mph
5th 149mph
6th 167mph

Proposed:
1st 40mph
2nd 62mph
3rd 85mph
4th 108mph
5th 138mph
6th 175mph

So the summary being that acceleration through the gears should be marginally quicker, but by adding the C60 6th gear I retain road manners when cruising in sixth, RPM at national speed limit should actually be a couple hundred lower than it is OEM. There are a few circuits now where I'm brushing the limiter in 4th at the end of the straights so these will become much earlier changes into 5th which I guess could be considered a down side - but as I get better as a driver I'd like to think I'll be carrying more speed at that point anyway so the extra shift would become inevitable.

Another alternative which would give very similar gear speeds 1-5 (if my maths are right) would be to emulate @seriouslylotus with the Kaaz gear set and 'yota 4.3 FD but it's a bit more expensive and it's a little more 'racey' at the top end which is better for a dedicated track car, but I do want to retain some road manners.

As for gearbox cooling, I'm still on the fence. I've been logging gearbox oil temps in the second half of this year and I've not seen anywhere near the temps quoted elsewhere on 'gearbox failure' threads so I'm tempted to run without and log my first couple of trackdays with the new gears and make sure the temps have not ramped up drastically. I am only ever going to do short sessions on track which probably keeps things in check. I have priced up the bits needed and it's not a massive expense in the grand scheme, but it's adding more plumbing/weight/complexity which are just additional points of failure - so I don't yet view it as a no brainer cheap insurance.

Let me know what you think, I've not bought anything yet other than the differential, that's going in this winter regardless but everything else is open to adjustment. I'm mainly looking for some glaring problems with my gear ratio maths that may lead to a car that feels awkward to drive at pace, or some alternative products that I've not yet considered.

Hell, even try to talk me out of it if you want and go down the road of treating C64's as consumable parts... the thought has crossed my mind!
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andybond
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Not worth the expense in my opinion of the preventative work.
Especially as the preventative work hasnt been proven as bullet proof.
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Fonzey
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Yep I agree on both fronts, not particularly good value for money for the non-quantifiable level of reliability that it grants.

That said, I'm (obviously) still not ruling it out. I think it's a given that with the 3rd/4th and FD addressed that the weakness just moves along the chain a bit but the fact is, it HAS moved the weakness on a bit which might mean buying me another season/year/decade of trackdaying.

It's about doing what I can with a budget I'm comfortable spending. If I don't spend it on the gearbox, I'll only spend it on something stupid like carbon fibre or worse, my pension :lol:

It sounds insane to type it, but having my third gear go pop at a trackday would actually make my life easier... as it would justify the decision :roll:
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andybond
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You = me

I am not even convinced that the 3rd/4th gears will shift the problem, if you read long enough there are reports of these failing.
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Elahrairah
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andybond wrote: Wed Oct 21, 2020 3:05 pm Not worth the expense in my opinion of the preventative work.
Especially as the preventative work hasnt been proven as bullet proof.
This Kyle.
seriouslylotus
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No gearbox oil cooler fitted to my car, It doesnt need it.
The different ratios and helical angles in the Kaaz box means it creates MUCH less heat (Less friction I assume)
Heat and driver abuse are the worst for failures IMHO, Then torque.
oli748
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Sticking the LSD in is 100% worth it. Interested to know which lsd you're going for.

Mine ( S2 S) frequently spins up an inside wheel on track.

I guess whilst the box is in bits changing the 3rd 4th would be a good option.
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andybond
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seriouslylotus wrote: Wed Oct 21, 2020 7:22 pm
Heat and driver abuse are the worst for failures IMHO, Then torque.
Any idea on what temp figures are considered dangerous @seriouslylotus ?
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Fonzey
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andybond wrote: Wed Oct 21, 2020 3:43 pm You = me

I am not even convinced that the 3rd/4th gears will shift the problem, if you read long enough there are reports of these failing.
SSC/Holinger claim they've never had a 3rd/4th gear failure, at least not reported to them. Final Drive, Synchro and input shaft failures are all next in line from what I can gather and I'm not aware of any cost effective mitigations for the synchros and input shaft.

This isn't about making the box bullet proof, as I don't think that's possible - it's about deciding how much I'm comfortable spending and then getting the most robust box that I can out of it. The temptation to run my OEM till it pops is still lurking in the background, but I really don't want to aggro, cost and drama of it failing in style at a trackday - because knowing my luck it'll be on a sighting lap of a Spa weekend or something like that :roll:
oli748 wrote: Wed Oct 21, 2020 7:29 pm Sticking the LSD in is 100% worth it. Interested to know which lsd you're going for.

Mine ( S2 S) frequently spins up an inside wheel on track.

I guess whilst the box is in bits changing the 3rd 4th would be a good option.
Yep I've found the same, the open diff is really struggling at this power. I spent a bit of time at Croft altering my approach a bit and I've got to be honest I did manage to 'drive around the problem' by the end of the day and I could now make an argument to say that the differential probably wasn't losing me too much time (if any) BUT it felt like it was sapping the fun out of a couple of corners, so I'm still very much intending to lob the LSD in, regardless of what I do with other components.

I picked up a second hand Toyota LSD, they came in the UK spec Mk3 MR2s and it's the same unit that Lotus offered as an option on later S2 cars. They come up fairly regularly on eBay for £250-£300.
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My SSC 3/4th had plenty of abuse from 340hp and were absolutely fine. The syncros and bearings need replacement.
The FD was also SSC.
Friends have said that the thing that gets the car to come alive is a very close ratio gearbox. I didn't do that
I agree with the celica 6th. More manners driving to the track
I never needed 6th on track. At the end of the Kemmel straight I was just about to hit the rev limiter in 5th, same at the end of Lavant at Goodwood. I read that as 154 on the speedo, so your 149 OEM estimate is probably right.
Ultimately you chase speed and the journey is fun. Many of us have done it, then you run out of love for the car as it is so altered from the road car you bought.
Graeme
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