Which gearbox?

[wild bill]

Ok My rebuild continues. 

Car is 97 S3 with 2.3 Duratec and currently 6 speed Caterham box. I thought i'd take the box to Road and Race for a refresh although it was fine when last being used, however as it's out currently it seemed worth doing anyway. Having spoken to them it seems parts are difficult to obtain at the mo and someone suggested talking to SP components.

Their suggestion is that the 6 speed is very unsuited to the 2.3 and its true that cruising is at higher revs and changing gear is frequent. The diff i believe from memory is a 3.92. The suggestion is the 5 speed type 9? the cost is not bad considering i'd sell my current box but does anyone have any pearls to impart? experience in use etc. The car is not used for competing but for fast road and touring.

BC i await

[Jonathan Kay]

You can find the current final drive ratio by counting prop shaft turns: wheel turns.

What would your mph/ 1000 rpm be with the current set-up?

You can then compare the options with one of the online calculators (or the downloadable spreadsheet that has the Caterham ratios already entered). Have you already found one that you like?

Previous discussions seem to end up with something like:

1. The six speed box can be a lot of fun.
2. For some people top gear with the six speed box is too short for cruising.
3. First gear with the factory ratios in the five speed box is too short... but there are companies that will fit something longer.

Jonathan

[Englishmaninwales]

I would suggest selling the 6 speed (good demand for them) use the money towards obtaining a Type 9 five speed and refit it with a different set of gear ratios, look at the choice from BGH Gear-tech as one option.  I agree this would be a far better option given the torque characteristics of the Duratec engine, and suit your requirement for fast road and touring.

As above, use a gear calculator eg Quaife. 

Malcolm

[7 wonders of the world]

 

Steve's Tracsport gears are superbly made to his own design, in semi heli format there are 2 1st gear  options either 2.29 or 2.48 and again the same for 5th  .87 or .82

The .82 would offer a relaxed cruising gear for touring whilst not affecting your fun on the twisty bits, I run a 2.29 - .87 in my 2.0 Duratec again with a 3.92 and find the ratios spot on having previously had a 2.48 and 2.38 first, both I found a little too low, I can drop it into first at about 40mph now !

Steve can also build these into he own alloy casing etc which are not to be confused with other ally casings out there, there are neat differences!

The best type 9 gearsets currently on the market.  

 

[L7 FST]

I also have a 2.3 Duratec in an S3.  It has a 5-speed semi-helical type 9 box, supplied and fitted by R&R. I find it a good match, excellent on road and track. As you’ll know, 4th gear is equivalent to 6th in the Caterham box, and I’d advise choosing a ratio for 5th which is reasonably close to that, rather than opting for a kind of overdrive. Aeroscreens has some good advice on all this:  he may be along in a moment...

 

[Drumster]

I can only endorse what 7WotW has said...

I have the 2.29 to 0.87 in my 2.0l Zetec (circa 200bhp & 170 lbs/ft) and it works for me for sprinting/hillclimbing and touring. I find you get a little more whining in 1st, 2nd and 5th but being aero'd and wearing earplugs it's not really a problem.

2nd gear is also longer than the standard 2nd and I would say that the rocket ratios are more evenly spaced out which IMHO makes changing up and down the gears more natural that the standard ratios.

[Drumster]

Evening Stephen (must type faster...)

[AdamQ]

I agree with all of the above.  I recently changed to the Tracsport semi-helical gearkit with 2.29 1st and 0.82 5th with a 2.0 Duratec and a 3.92 diff.  The gearbox was assembled by R&R.

I previously had a BGH sporting close which was a massive improvement over standard, but the Tracsport set-up is a quantum leap further in improvement - simply spot on ...

[David Brown]

Surprised no one has mentioned changing the diff ratio. 3.92 was normally used on the 5 speed and 3.6 for the 6 speed. Had a 5 speed on a 1.6k which I changed for 6 speed and eventually changed the diff ratio. Now have a CSR with 6 speed and lower diff ratio and would never have a Caterham without a 6 speed, it’s just so much more fun despite now having bags of torque. 

[EEK]

I've gone the "other route" to get effective overdrive on the 6 speed box. Car is a 2.0 Vauxhall with about 265 hp. It had Caterham 6 speed box with 3.62. As I use car for longer trips then I was looking for something that cut the revs in 6th. So fitted a 3.18 diff, it has made 6th an overdrive, and I do need to remember to change down for the faster overtake, so car is a bit different. that being said 60 mph in 1st is now possible.

[7 wonders of the world]

The torque band on the Duratecs is wide enough to cover wider ratios, the 6 being originally design for more peaky low capacity 'K' s and is now used by Caterham marketing as an upgrade path as more gear must be better !

[Jonathan Kay]

Surprised no one has mentioned changing the diff ratio.

I was waiting to hear what's currently fitted!

:-)

Jonathan

 

[Jonathan Kay]

2nd gear is also longer than the standard 2nd and I would say that the rocket ratios are more evenly spaced out which IMHO makes changing up and down the gears more natural that the standard ratios.

What's the full set of ratios, please?

Thanks

Jonathan

[7 wonders of the world]

Bill STR its a 3.92

 

Full ratios here:

https://www.tracsport.com/gearkits

 

[Jonathan Kay]

Thanks

Jonathan

[Drumster]

For comparison

My old standard type 9  - 1st 3.36, 2nd 1.84, 3rd 1.225, 4th 1, 5th 0.82

Tracsport rockets ratios  1st 2.29, 2nd 1.61, 3rd, 1.225, 4th 1, 5th 0.87

[Alan Reeves]

I changed the diff of my previous 260 CSR to a 3.14 with a 6 sp box.

Effectively the same as a 3.62 and 5 speed box...

Transformed the car for the road where is was so undergeared , B andC roads just flicking between 3rd n 4th

 

 a 3.92 and 6...now that is seriously undergeared 

[wild bill]

Thanks for all the help guys. Any further thoughts welcomed. I haven't had a chance to DC the diff ratio due to swimming and hip hop classes (my 8yr old daughters NOT mine!) and now the smell of sausages and falafels has distracted me but i'll get toi the garage asap

[7 wonders of the world]

You could always ask steve to rebuild your final drive with one of his Trasport LSD's too....... 

[ChrisC]

Anyone ever tried this with a BMW diff?  120d automatic is a 3.15, maybe better than the 3.64 for a 6 speed.

[Alan Reeves]

I’ve not heard if anyone using a different bmw diff

 

[wild bill]

Quick update, sorry for delay but dealing with kids and dementing parent sidetracked me.

I thought there was a tag on the diff top with the type stamped. Took the boot floor out to look and ....nothing so i have no proof that the current diff is a 3.92 just a vague memory from previous rebuilds. The LSD was put in by Kendricks i believe in 2003 a year before i owned the car. With a 2.3 Duratec 190 lb foot of torque and around 240 bhp  so my undertanding is 2.29 1st but what difference does a .87 or .82 final make in terms of the use i'd put it to.

Will ring Steve today and get on with box and deal with diff later when its on a ramp. Trouble with SP is lead times but at least it's getting wintry and i can hunkjer down in the garage.

[anthonym]

I view the 5 speed as a three speed box, so the all the fun is in the gears sixspeed. HOWEVER, I don't do motorways for which I use a trailer, and I don't do tracks except the Nurburgring "slowly", I drive a K so keeping it on the cam is fun. I haven't tried the tracspeed which does sound interesting (my five speed is a BGH in a BDR and I dislike it with a passion); I could do 60 in first if not for the limiter at 8,750. AND I don't compete, I do mountain twisties and not much else. Since you ask - I plan to put a sixspeed into my BDR (169bhp)  with a 4:1 open diff (already installed) and see what that does.. when Rob gets to it.

[anthonym]

I view the 5 speed as a three speed box, so the all the fun is in the gears sixspeed. HOWEVER, I don't do motorways for which I use a trailer, and I don't do tracks except the Nurburgring "slowly", I drive a K so keeping it on the cam is fun. I haven't tried the tracspeed which does sound interesting (my five speed is a BGH in a BDR and I dislike it with a passion); I could do 60 in first if not for the limiter at 8,750. AND I don't compete, I do mountain twisties and not much else. Since you ask - I plan to put a sixspeed into my BDR (169bhp)  with a 4:1 open diff (already installed) and see what that does.. when Rob gets to it. I rather fancy the Quaif 7 speed... 

Anthony