Alex Wong1697456877 Posted May 3, 2007 Share Posted May 3, 2007 Having tried umpteen gearboxes in VDU over the years, I'm considering a Caterham 6 speeder. I know I know. I've said many times before that this isn't suited to the wide power band of the Vx but I'm tempted by the combination of reliability and quietness. Looking at the ratios, my 3.92 diff is too short. A 3.62 looks better but is there an even taller option? Is the 3.62 crown/pinion expensive or hard to get? Tomorrow, I'll probably change my mind again but the 6 speed looks worth a punt! Link to comment Share on other sites More sharing options...
Tom_C Posted May 3, 2007 Share Posted May 3, 2007 3.62 was standard on many Sierras so shouldn't be hard to find. The XR4x4 had the 3.62 with an LSD IIRC. BTW please give generously to Bundle's Big Charity Walk for Asthma research here Ta. Cheers Tom FH54WLX see here - UPDATED again Link to comment Share on other sites More sharing options...
Allen Payne Posted May 3, 2007 Share Posted May 3, 2007 There's also a higher 3.32 ratio (or something very similar), I believe the SLR race cars used this a few years ago. Link to comment Share on other sites More sharing options...
Alex Wong1697456877 Posted May 3, 2007 Author Share Posted May 3, 2007 Thanks. Done the sums and 3.32 is closer to what I'd like for my car with a 6-speed. I think with a 3.62, I'd be changing gear just a bit too often for my liking. Can anybody else confirm such a ratio exists? How much would it cost to change my diff ratio to this? Mine's a ZF LSD but I assume it's just the crown and pinion that needs to be changed? Link to comment Share on other sites More sharing options...
Tom_C Posted May 3, 2007 Share Posted May 3, 2007 Raceline list the 3.38 CWP set as POA here BTW please give generously to Bundle's Big Charity Walk for Asthma research here Ta. Cheers Tom FH54WLX see here - UPDATED again Link to comment Share on other sites More sharing options...
Alex Wong1697456877 Posted May 3, 2007 Author Share Posted May 3, 2007 Thanks That looks ideal for me if I decide to go for the 6 speed. Edited by - Alex Wong on 3 May 2007 17:44:22 Link to comment Share on other sites More sharing options...
Rob Walker Posted May 3, 2007 Share Posted May 3, 2007 Alex. Phil Stewart will do you an exchange your 3.92 for a 3.62 . he charges around £50 for the swap. The 3.32 ratios are expensive and I have never heard of anyone fitting them to a SLR race car it would be too tall a ratio IMO. Rob Link to comment Share on other sites More sharing options...
Bricol Posted May 3, 2007 Share Posted May 3, 2007 3.92 with a 6 spd and a boggo K-series is real good fun tho . . . 😬 Bri Link to comment Share on other sites More sharing options...
Alex Wong1697456877 Posted May 3, 2007 Author Share Posted May 3, 2007 Hi Rob, OK - you've got me thinking, especially as you're not exactly unfamiliar with big torquey engines! The rational behind the 3.38 diff is that it gives me a nice tall first (anything below 55mph in first at 8000 rpm and I'll be grabbing for second too quickly on a flat out start) and a cruising 6th that is comparable to my Quaife 5 speed with a 3.92 diff. Basically I'm looking to get similar 1st and top gears as a tall 1st Quaife T9, but with 4 gears in between instead of 3. I think that having a 3.92 diff and even a 3.62 will mean too much time wasted changing gear. My Quaife needed 5 gear changes at Curborough on a double lapper and I managed a 59.2 with that. My Elite box had much shorter and closer gears and I did 15 gear changes per double lapper and never got below 59.8. Still, you've got me thinking and I'll look at all the gearcalc results again. Link to comment Share on other sites More sharing options...
Nifty Posted May 3, 2007 Share Posted May 3, 2007 Alex, Phil Stewart will talk you through all the pros and cons etc, particularly since he runs a high bhp VX to boot *thumbup* He convinced me to stay with my current box (BGH fettled 5 speed) and 3.92 diff for my road and track car .... which saved me a few quid .. though he did then take it from me when he fitted the ZF 😬 😬 😬 Keep off the straight and narrow 😬 Edited by - Nifty on 3 May 2007 21:45:14 Link to comment Share on other sites More sharing options...
rj Posted May 3, 2007 Share Posted May 3, 2007 Alex, I know of a Danish scrapyard that has a used 3.38 diff in stock. I don't know much about it though /regin Edited by - RJ on 4 May 2007 06:23:22 Link to comment Share on other sites More sharing options...
Alex Wong1697456877 Posted May 3, 2007 Author Share Posted May 3, 2007 Hi Nifty, I did talk to Phil and I'm aware as to how good a close ratio 5 speed is with the 3.92 diff. As mentioned above, the fastest my car's been was with that setup. My worry with any T9 box is in the strength of the synchros. The dog box is an option but I'd prefer helical gears if I can have them but they're only available with synchros (Unless you go for the very expensive Quaife sequential helical 6 speed). The dog box is less than road friendly at slower speeds and making the car friendly to other drivers is important to me. The Quaife SC box isn't too noisy but as part of my devolution plan, a nice quiet gearbox is starting to appeal! Maybe it's a backlash against the Elite box which was very noisy. I've pondered this conundrum for months and still can't decide but it seems clear that the Caterham 6 speed is the most reliable synchro helical option and the Quaife 5 speed dog box is probably the strongest box at the moment and would give me a slightly faster car overall. I have bought back my SPC Quaife 5 speed and it is superb (although I haven't seen it for a few years) I should get it back soon but being a clubman box, I'm a bit worried about it being suitable when I next give the engine a tweek. I'm hoping to sell this on when I get it to help fund the next box. I need to get this all sorted soon though. Le Sept is not far off and the weather's been rather good of late! Basically, I've got to the point when I realise I've thought too much and should just make a choice and go with it. At the moment, I think the 6 speed is worth a punt. I just want to get back to enjoying the car on the road and the track. I'm sitting in my garage where my PC is and I've had enough of seeing my car on stands with no engine in it. ☹️ Alex Edited by - Alex Wong on 3 May 2007 23:34:09 Link to comment Share on other sites More sharing options...
Paul Gibb Posted May 3, 2007 Share Posted May 3, 2007 Hi Alex , My contribution FWIW Assuming that you are running 22"rears, that your Caterham 6 speed is direct top, and that your rev limit is between 8500 - 8750, the 3.92 diff should be spot on for your car (as it is for mine (which as a fellow Vx luddite you are welcome to try) running the Quaife seq 6 speed with direct top ). You will be geared for 130mph + and will never max out in top on a UK circuit. Both Arnie & Mark have run big Vxs in the past with the Caterham 6 speed box, so don't worry about the final drive just get on & enjoy driving your car . L7 FUN Link to comment Share on other sites More sharing options...
Alaskossie Posted May 4, 2007 Share Posted May 4, 2007 Alex, I certainly cannot speak from experience (since I have my first-ever Seven arriving in kit form at the end of this month!), but I have gone against the flow and have ordered the Classic with 6-speed CC box and 3.38 rear end with ZF l/s. I will be powering it with a 2.3 Duratec from Cosworth USA (244 hp) and it will primarily be used for fast road work, not the track. Distances are vast here in Alaska, and I wanted something that would not cause the engine to spin its little heart out on long drives. I have been told that the 3.38:1 diff was a diesel Sierra option and is very uncommon; it was pricey for me, at $1200 extra. We'll see if I've made a big mistake..... Why doesn't Caterham offer a different ratio package for their fine 6-speed, with an o/d 6th gear, suitable for the Duratec range now being installed?? Seems like an obvious solution, but perhaps not? Tom Meacham Alaskossie Link to comment Share on other sites More sharing options...
Rob Walker Posted May 4, 2007 Share Posted May 4, 2007 Alex, I fitted 3.62 diffs in two big 2.3 Duratecs both running 5 speed quaife boxes and 22" rear tyres but these engines are rev limited to 7200rpm and had massive torque from 4000rpm. I can`t say that I personally liked the 5 speed ratios especially the tiny difference between 4th 1:1 and 5th .87:1 seemed pointless changing gear on track. I have just fitted a 2L Duratec into my own car retained the Caterham six speed box and run 22" tyres and the 3.62 diff is spot on with this engine but again its not really what you would call a revver 7500rpm. I would have to agree with Paul Gibb if you have 8500-8750rpm at your disposal then the 3.92 diff would best suit the Caterham six speeder. It will be tiresome to drive on long runs though. Link to comment Share on other sites More sharing options...
Alex Wong1697456877 Posted May 4, 2007 Author Share Posted May 4, 2007 Hi Paul, My engine has standard rods and crank. I do have a set of steel rods on the shelf but won't be fitting them just yet - so max is only about 7500 rpm. I agree that with a 3.92, overdrive is never needed on a UK circuit but it would be nice on the road. Tom - I'll be very interested to see how you get on. I think it'll be fine and very good on the road. Rob, I think your engine isn't very different in character from mine and I hear you're going VERY quickly these days! . OK. 3.62 it is then. (If I go for a 6-speed.....) Thanks! Link to comment Share on other sites More sharing options...
Rob Walker Posted May 4, 2007 Share Posted May 4, 2007 Alex, Second thoughts as a compromise I would probably fit a 3.62 diff along with the sixspeed, you will have enough torque to pull it and it will be nicer to drive on the road. The R500 was supplied with the 3.62 diff and has less torque than your engine. Your engine should also last longer. I do like the Caterham six speed box Rob Link to comment Share on other sites More sharing options...
S47zz Posted May 5, 2007 Share Posted May 5, 2007 Had a 3.54 in my car, but was too low, now with 3.9 car is much better, I don't have a 6 speed just a type 9 5 speeeder. - 2 litre TB'd zetec But working the ratios out 5-6speed if you had a 3,9 then with a 6 speed 3.3 -3.4 sounds OK Link to comment Share on other sites More sharing options...
rj Posted May 5, 2007 Share Posted May 5, 2007 ISTR the R500 was originally supplied with the 3.92 diff, but this may have changed when the max revs were brought down to a mere 8600 rather than the 9200. Guess this was a choice that had to be made by the first owner... /r Link to comment Share on other sites More sharing options...
Alex Wong1697456877 Posted May 14, 2007 Author Share Posted May 14, 2007 S47zz, that's what I kept thinking. Well, I've gone for........ a 3.38. Did the sums again and again and it just looks right to me. Phil Stewart seems to think it'll work well. It's still shorter than a Quaife 5 speed with a 3.92, apart from 6th is a bit taller than 5th on the Quaife. So this gives me a slightly shorter 5 speed and a motorway gear which I think suits my needs, and a tall enough set of ratios to allow the torque of the engine to express itself. When I find out it's pants and the car is gutless with it, you can all say I told you so!!! Edited by - Alex Wong on 14 May 2007 10:09:56 Link to comment Share on other sites More sharing options...
S47zz Posted May 14, 2007 Share Posted May 14, 2007 Alex All you can do is try you 3.38 I'm sure it'll be good though *thumbup* Just wish I could afford a 6 speed, would gladly refit the 3.54 Link to comment Share on other sites More sharing options...
Jason Plato Posted May 14, 2007 Share Posted May 14, 2007 Ohhhhhhhhhh 3.38 I'm running a 3.62 and the 6 speeder with the duratec revlimit @ 7450 rpm and the combination is fantastic . The engine stays in the power band at 5500 > 7500 all the time and yet you can still tootle ( ] along on the road in 5th all day long I would think a 3.38 would be too long a ratio and make the car feel sluggish ? Link to comment Share on other sites More sharing options...
Alex Wong1697456877 Posted May 14, 2007 Author Share Posted May 14, 2007 Maybe I'm just getting old Dave and would prefer a more sedate ride! 😬 If you look at the gearcalc results for a 5 speed quaife on a 3.95 and compare them to the 6 speed on a 3.38, you'll see why I'm giving it a go. I liked the Quaife with the 3.95 very much. I've got 2 days to decide (the diff is in the post on it's way to Phil.) I'll post the numbers when I get a mo but 3.62 looks too short to me. 1st looks way too short for a flat out start and I doubt it can be used once you're on the move. With the 3.38, 1st is taller but still shorter than the quaife with a 3.92. 5th is shorter than 5th with a 3.92. So if you look at them as 5 speeds and ignore the 6th gear, I've still got a shorter, closer box with the 6 speed and a 3.38 than I had with the Quaife with a 3.92, plus I get a cruising gear which I suspect will never be used on track apart from at the 'ring. Please tell me if I'm making a big mistake but I can't see it. Edited by - Alex Wong on 14 May 2007 18:04:40 Link to comment Share on other sites More sharing options...
Alex Wong1697456877 Posted May 14, 2007 Author Share Posted May 14, 2007 What I had GearCalc v2.0.0.3 Copyright ©2001, Peter Ogden Gear Ratio, Speed and RPM Calculator Gear set: Ford Sierra Type 9/N Quaife 5 Speed High 1st Gear 1 2 3 4 5 Final Ratios: 2.040 1.540 1.210 1.000 0.870 3.950 RPM Limit: 7600 RPM @Peak Power: 7250 Tyre Diameter: 22.00 in Gear Mph per 1000 RPM Mph @7250 RPM Mph @7600 RPM -------------------------------------------------------- 1 8.12 59 62 2 10.76 78 82 3 13.69 99 104 4 16.57 120 126 5 19.05 138 145 Edited by - Alex Wong on 14 May 2007 18:16:00 Edited by - Alex Wong on 14 May 2007 18:16:53 Link to comment Share on other sites More sharing options...
Alex Wong1697456877 Posted May 14, 2007 Author Share Posted May 14, 2007 What I'm going for GearCalc v2.0.0.3 Copyright ©2001, Peter Ogden Gear Ratio, Speed and RPM Calculator Gear set: Caterham 6 Speed Gear 1 2 3 4 5 6 Final Ratios: 2.690 2.010 1.590 1.320 1.130 1.000 3.380 RPM Limit: 7600 RPM @Peak Power: 7250 Tyre Diameter: 22.00 in Gear Mph per 1000 RPM Mph @7250 RPM Mph @7600 RPM -------------------------------------------------------- 1 7.20 52 55 2 9.63 70 73 3 12.18 88 93 4 14.67 106 111 5 17.14 124 130 6 19.36 140 147 Edited by - Alex Wong on 14 May 2007 18:16:17 Edited by - Alex Wong on 14 May 2007 18:17:08 Link to comment Share on other sites More sharing options...
Recommended Posts
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now