While sat in the mind-numbing traffic entering Leeds this morning I realised I needed something to think about before my brain shut down.
I started to think about how rare low-ratio Sierra diffs are getting, and what alternatives there are for those that want a BEC over a CEC.
Then I had a thought about using an overdrive unit attached between the gearbox and the diff. stick with me here. . .
I know that these haven't really been used on production cars for a number of years now, but there seems to be quite a lot of stock at
re-manufacturers, etc.
You could buy a relatively cheap high-ratio diff (maybe with LSD), get one of these overdrive units, modify it to work in this arrangement (depends on
version) and instantly have lots of gears to play with.
One option would be to have it switched off in the lower gears for great acceleration, then switch it to 'on' while in 6th for a better top
speed. Maybe mount the switch on the steering wheel for better control.
The one I looked at offered a ration of 0.75 to 1, so an increase of 25%.
Is this a crazy idea that just wouldn't work, or am I on to something here? Or has someone already tried it and published their results.
17 views in less than 3 minutes, who's meant to be working then?
How much would it weigh?
I know you BEC boys are a bit fanatical about shedding grams, so an overdrive weighing more than a packet of crisps may be a non-starter.
yes it would work since this isn't anything new but
1. £££?
2. how many kg?
3. is there space to fit it?
and having more gears in the drive trains introduces loss.
I have overdrive in my land rover whcih gives me 4 reverse gears and 16 forward gears, I tell you, it is damn handy!! 
Caterham have already invented this, called a 6 speed gearbox. 
quote:
Originally posted by 02GF74
I have overdrive in my land rover whcih gives me 4 reverse gears and 16 forward gears, I tell you, it is damn handy!!
I extended the overdrive lever to match the gear one, sooooo cool in traffic The weight wouldn't be too much of an issue as you would gain acceleration due to the higher ratio diff. A bit more weight over the rear axle
might actually benefit traction as well.
I do think this will probably benefit the road going cars more than the track only cars. At least it'll stop the buzzy feeling at motorway
speeds.
I might pop back down the breakers this weekend and have a play.
quote:
Originally posted by antimony
How much would it weigh?
I know you BEC boys are a bit fanatical about shedding grams, so an overdrive weighing more than a packet of crisps may be a non-starter.
Fit some top fuel drag style tyres that increase in diameter with the centrifugal forces so you get the best of both worlds.
Steve
I still think there must be other diff options to get a better ratio
http://www.locostbuilders.co.uk/viewthread.php?tid=106852
The Freelander is already used, but BMW, Mercedes, Audi, Honda (HRV), Subaru, Mitsubishi, Mazda etc all make rear wheel or 4 wheel drive cars - there
must be a suitable diff amongst them some where. Probably lighter than the Sierra one too.
quote:
Originally posted by nick205
I still think there must be other diff options to get a better ratio
http://www.locostbuilders.co.uk/viewthread.php?tid=106852
The Freelander is already used, but BMW, Mercedes, Audi, Honda (HRV), Subaru, Mitsubishi, Mazda etc all make rear wheel or 4 wheel drive cars - there must be a suitable diff amongst them some where. Probably lighter than the Sierra one too.
A 0.75 overdrive would give me another 3 forward gears, would increase my top speed by 18 MPH, would reduce my motorway revs from 6800 to 5100, would
increase my acceleration above 100 MPH on the track and improve my MPG. Brilliant. I'd have to move my speedo pickup from inside the gearbox to
after the overdrive but it would be worth the effort.
Could it be fitted instead of the joint in a two piece prop?
why not incorporate it into the reverse box all becs are soon going to have for IVA .....
quote:
Originally posted by MikeR
why not incorporate it into the reverse box all becs are soon going to have for IVA .....
quote:
Originally posted by smart51
A 0.75 overdrive would give me another 3 forward gears, would increase my top speed by 18 MPH, would reduce my motorway revs from 6800 to 5100, would increase my acceleration above 100 MPH on the track and improve my MPG. Brilliant. I'd have to move my speedo pickup from inside the gearbox to after the overdrive but it would be worth the effort.
Could it be fitted instead of the joint in a two piece prop?
quote:
Originally posted by sickbag
quote:
Originally posted by smart51
A 0.75 overdrive would give me another 3 forward gears, would increase my top speed by 18 MPH, would reduce my motorway revs from 6800 to 5100, would increase my acceleration above 100 MPH on the track and improve my MPG. Brilliant. I'd have to move my speedo pickup from inside the gearbox to after the overdrive but it would be worth the effort.
Could it be fitted instead of the joint in a two piece prop?
The one I was looking at bolted onto the back of the gearbox, with the output shaft directly driving the sun wheel, so . . .
I think you would need to machine the gearbox output shaft to work with your prop, and make up a face plate (with bearing) to enclose the front of the OD.
Lots of work, but do-able.
quote:
Originally posted by MikeR
why not incorporate it into the reverse box all becs are soon going to have for IVA .....
Here you are it already exists. Warning site is in French!
Whole gizmo weighs 25kg
Linky thingy
ETA Blimey. Just seen the price 5000€
[Edited on 21/4/09 by MikeCapon]
quote:
Originally posted by MikeCapon
Here you are it already exists. Warning site is in French!
Whole gizmo weighs 25kg
Linky thingy
ETA Blimey. Just seen the price 5000€
[Edited on 21/4/09 by MikeCapon]
I think this is what it looks like, buy my French is non-existant
[Edited on 21/4/09 by aka Keith]
FFS, cannot seem to load pictures, it is in my photo archive under overdrive for BEC
Thanks Keith.
Looking at theirs you could have it as mid-engined or FWD too. My idea was to keep the arrangement as a front-engined RWD.
Anyone fancy translating my thoughts to actual hardware? With no cost to me?
Here's the piccy.
boite cm
It looks like they're using a chain drive from the gearbox output shaftl - unless I'm looking at it wrong. Not sure I like that.
Nope, no chain inside. It's gear drive and the diff is an LSD!