timbo Posted November 19, 2005 Share Posted November 19, 2005 I need a bit of advise here guys. The 2.3 I'm building should be good to c.210bhp with max power most likely sub 6500rpm (using std 2.0L cams (8.8lift). I may be able to get my greedy paws on a 6 speed at a hopefully reasonable price. With this i'd use a 3.38 diff. Am I mad going for the 6 speed with this eng? Should I be talking to BGH or SPC for a HD 5 speed? The 6 will give me as follows (calculations are based on 6,500 shift) 1st = 48mph; rev drop to 2nd = 1643 2nd = 65mph; rev drop to 3rd = 1358 3rd = 82mph; rev drop to 4th = 1104 4th = 98mph; rev drop to 5th = 936 5th = 115 mph; rev drop to 6th = 748 6th = 130mph At 79 mph cruise I'm running 4000rpm in 6th. The SPC 5 speed semi helical as follows (3.92 diff) 1st = 47mph; rev drop to 2nd = 2312 2nd = 73mph; rev drop to 3rd = 1393 3rd = 93mph; rev drop to 4th = 1128 4th = 112mph; rev drop to 5th = 845 5th = 129 mph At 79 mph cruise I'm running 4000rpm in 5th. The rev drops aren't that far different except for 1st to 2nd between the 2 boxes. I love changing gear but if the torque is so overwhelming am I wasting my time with the sixer? As anyone any constructive thoughts on this? Also bear in mind I will be upgrading the engine for more power at a much later date and will use the same gearbox as fitted now! anxiously waiting for my new 2.3 SV Link to comment Share on other sites More sharing options...
Paul Formston Posted November 19, 2005 Share Posted November 19, 2005 Hi Timbo why not have A word with Chris at Raceline thay have done a couple of Duratics and im prity sure thay use the B.G.H 5 Speed box, I all ways thougth that you needed a lot of gears ie; 6 on Engines that had no torque like motor bike engines to keep them on the boil but that is not an issue on a caterham so unless you are getting A six speed box for next to nothing I dont see the point, also its an extra gear change so if you put two caterhams side by side one five speed one six speed which one would get to top speed first Regards Paul Link to comment Share on other sites More sharing options...
Myles Posted November 19, 2005 Share Posted November 19, 2005 Talk to BGH. They have many more ratio options than SPC and make a number of mods that significantly improve the capacity of the box (better lubrication for starters...) Rob Grigsby runs a BGH in his Duratec. Project Scope-Creep is live... Alcester Racing 7's Equipe - 🙆🏻™ Alcester-Racing-Sevens.com Link to comment Share on other sites More sharing options...
rgrigsby Posted November 19, 2005 Share Posted November 19, 2005 Timbo I'd go for a BGH 5 speed, you really don't need the 6 speed box. On the road a very rarely get out of 5th gear once I'm on the move, there's enough torque to pull strongly from just about any speed in 5th. On track I think you'll just loose time with the extra gear changes. Rob G www.SpeedySeven.com Link to comment Share on other sites More sharing options...
thinfourth Posted November 19, 2005 Share Posted November 19, 2005 I love changing gear 6 speeder just for the sheer giggle fest it can be yes a 5 speed would make more sense but what the hey The happy handle made me do it Link to comment Share on other sites More sharing options...
rgrigsby Posted November 19, 2005 Share Posted November 19, 2005 One more thing, how much power are you ultimatly aiming for? I think 260bhp/210lbft is Ok with a BGH box but much more and you are probably going to want a dog box Rob G www.SpeedySeven.com Link to comment Share on other sites More sharing options...
paul jacobs Posted November 19, 2005 Share Posted November 19, 2005 How about the uprated 5 speed with a 3.6 diff? The torque should cover the longer ratio without stifling acceleration. Link to comment Share on other sites More sharing options...
rgrigsby Posted November 19, 2005 Share Posted November 19, 2005 I'm tempted by that option, I've got an uprated 5 speed with a 3.92 at the moment and it's a great combination but I suspect a 3.62 would work pretty well as well. I'm not in a mad rush to try it though as I'm happy with the silly acceleration in 5th as it is 😬 Rob G www.SpeedySeven.com Link to comment Share on other sites More sharing options...
Dobuy Posted November 19, 2005 Share Posted November 19, 2005 I looked at both, but went for the BGH, great ratio's with 3.92 diff. However I have cracked my gearbox case (with 226bhp) so am about to fit an alloy Quaife box as they are stronger. New engine is 270ish bhp so everything is at its design limit. Allegedly BGH are developing an uprated box to deal with this and a bit more, no idea when it will be finished. As to the 6 speed, if you can find one cheap, why not, it has an alloy case already. You truly do not need 6 gears though. Only other problem with the 6 speed is you cannot fit the Raceline bellhousing and engine mounts with it as it has a long input shaft. The Raceline setup is designed to place the engine further back in the chassis, so it has a short bellhousing and engine mounts that place the whole package rear wards. I think Minister will do a bellhousing and engine mounts to suit. Duratec SV, built in Dubai Link to comment Share on other sites More sharing options...
timbo Posted November 19, 2005 Author Share Posted November 19, 2005 Raceline actually do a bellhousing for the long input shaft 6 speed and a set of mounts to suit aswell.... well this is what chris told me anxiously waiting for my new 2.3 SV Link to comment Share on other sites More sharing options...
rgrigsby Posted November 19, 2005 Share Posted November 19, 2005 Just FYI a BGH 5 speed box with an alloy case and lid is actually slightly lighter (1/2Kg) than the 6 speed with it's alloy case. How long till you need to make a decision? can you get out in a Duratec 5 speed car in the mean time? that's probalby going to be the only way to confirm your choice. I'd offer you a ride in mine but it's not going to back for a while and even the it'll be off the road for a couple of months whilst I tidy a few things up. Rob G www.SpeedySeven.com Edited by - rgrigsby on 19 Nov 2005 18:39:28 Link to comment Share on other sites More sharing options...
Budjuggler Posted November 19, 2005 Share Posted November 19, 2005 I'm pretty sure Brent went for the BGH 5 speed in his. I think the perceived wisdom is such that the engine has generous torque thus effectively rendering the 6 speed unecessary - certainly for mainly road use. C7 GON - There is a very fine line between 'hobby' and 'mental illness' Link to comment Share on other sites More sharing options...
Dobuy Posted November 19, 2005 Share Posted November 19, 2005 Raceline actually do a bellhousing for the long input shaft 6 speed and a set of mounts to suit as well Ah, I didn't realise that, as the last time I was talking to Peter he told me about the time he put in a 6 speed, he had to use a spacer between the bellhousing and gearbox. Guess they may have it all developed by now. Duratec SV, built in Dubai Link to comment Share on other sites More sharing options...
Rob Walker Posted November 19, 2005 Share Posted November 19, 2005 The biggest problem with the six speeder is the 1:1 top, even with a 3.62 diff this is too revvy for the 2.3 duratec. The quaife pro box is the best option IMO noisy though. Link to comment Share on other sites More sharing options...
timbo Posted November 19, 2005 Author Share Posted November 19, 2005 Rob, with the 6 speed on 3.38 diff the 6th 1.1 top is the same as 5 speed with 5th 0.87 with a 3.92. So here's the question for 2.3 owners: If you could get a 6 speed at the same price as a 5 speed CR what would you choose? anxiously waiting for my new 2.3 SV Link to comment Share on other sites More sharing options...
rgrigsby Posted November 19, 2005 Share Posted November 19, 2005 The 5 speed, my BGH box has a 0.86 5th gear and I'm going to switch for a .84 or .82 next time it's out as tbh I think it can easily pull it. I've had a 6 speed in my car admitedly with a completly different engine bolted on the front and it's a great gearbox but I really don't think it's necessary. Rob G www.SpeedySeven.com Link to comment Share on other sites More sharing options...
metal mickey Posted November 19, 2005 Share Posted November 19, 2005 Might be worth giving Road & Race a call. I believe Phil is developing a 5spd for use with Duratec's. Link to comment Share on other sites More sharing options...
Rob Walker Posted November 20, 2005 Share Posted November 20, 2005 Timbo I agree top gear will be ok with 3.38 diff but what about the other ratios Link to comment Share on other sites More sharing options...
I.Mupferit Posted November 20, 2005 Share Posted November 20, 2005 As Andy W says, I have the BGH 5 sp as well with a 3.92 diff and I think the ratios are just perfect for my 240 bhp engine which has oodles of torque. I once drove a x/flow with a 6 speed and although the changes were nice, the ratios just seemed to be way too closely spaced for even that engine so I really can't see the point with the Duratec. Brent 2.3 DURATEC SV Reassuringly Expensive R 417.39 😬 Link to comment Share on other sites More sharing options...
dannylt Posted November 21, 2005 Share Posted November 21, 2005 Echo the 5-speed over a 6-speed. I have 250bhp 2.3 with 3.92 diff and a high 2.2 first and it suits the car very well; it certainly doesn't need another gear for either track or road use. The 6-speed is certainly needed for a narrow torque band, but the Duratec pulls strongly from 4k. Link to comment Share on other sites More sharing options...
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