sickbag
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| posted on 21/4/09 at 10:30 AM |
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Crazy enough to work?!?!
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.
Finally back on the job!
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sickbag
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| posted on 21/4/09 at 10:34 AM |
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17 views in less than 3 minutes, who's meant to be working then? 
Finally back on the job!
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antimony
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| posted on 21/4/09 at 10:35 AM |
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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.
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02GF74
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| posted on 21/4/09 at 10:39 AM |
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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. 
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Mr Whippy
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| posted on 21/4/09 at 10:43 AM |
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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
even survived pulling a loaded car trailer too despite the instructions saying not to use it for towing
as for one on a 7, just fit 17inch wheels
Fame is when your old car is plastered all over the internet
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sickbag
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| posted on 21/4/09 at 10:47 AM |
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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.
Finally back on the job!
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sickbag
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| posted on 21/4/09 at 10:50 AM |
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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.
I've already lost 6Kgs off my fat ass this past month, so that should make up for it!
Finally back on the job!
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Howlor
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| posted on 21/4/09 at 10:56 AM |
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Fit some top fuel drag style tyres that increase in diameter with the centrifugal forces so you get the best of both worlds.
Steve
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nick205
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| posted on 21/4/09 at 10:57 AM |
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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.
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sickbag
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| posted on 21/4/09 at 11:04 AM |
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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.
I think the problem is that most of the modern RWD cars are quite powerful, and so the diffs have to be stronger, therefore heavier, to cope with that
power.
The Mazda is a good alternative as they should be more plentiful now, but I don't know what the ratios are. Are they suitable for BEC with
smaller rims (ie. 13 or 14 inch)?
Finally back on the job!
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smart51
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| posted on 21/4/09 at 11:04 AM |
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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?
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MikeR
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| posted on 21/4/09 at 11:35 AM |
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why not incorporate it into the reverse box all becs are soon going to have for IVA .....
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sickbag
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| posted on 21/4/09 at 11:53 AM |
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quote:
Originally posted by MikeR
why not incorporate it into the reverse box all becs are soon going to have for IVA .....
I wonder if a trans-axle could be constructed containing all three components - 2-speed epilyptic (spelling)gears, reverse and diif function - taking
up a similar width, but longer, than a standard diff.
Or even just the reverse and diff functions.
Finally back on the job!
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sickbag
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| posted on 21/4/09 at 11:58 AM |
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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.
Finally back on the job!
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nick205
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| posted on 21/4/09 at 12:17 PM |
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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.
+ I think you'd need some chasis tunnel mods to accomodate/mount the overdrive unit.
All-in I reckon the cost and complexity would be outweighed by the bolt-on-ability of an albeit expensive low ratio Sierra diff.
Do Quaife not produce a low ratio gear kit to fit inside the Sierra diff casing? probably £££ if they do I guess.
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ReMan
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| posted on 21/4/09 at 01:20 PM |
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quote:
Originally posted by MikeR
why not incorporate it into the reverse box all becs are soon going to have for IVA .....
That's been my thoughts.
As much as the Quaifes are apparantly an expensive oil thrower, if you could build a 2 speed and reverse like an overdrive so that you can
(optionally drop the revs by 20% on the motorway, but keep normal gearing for fun
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MikeCapon
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| posted on 21/4/09 at 01:36 PM |
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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]
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sickbag
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| posted on 21/4/09 at 01:45 PM |
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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]
That site is blocked for me at the moment, pretty much every website is! 
Can you post a picture of it? I'd like to compare it to what I had in mind - now I've really thought about it.
Finally back on the job!
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aka Keith
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| posted on 21/4/09 at 02:11 PM |
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I think this is what it looks like, buy my French is non-existant
[Edited on 21/4/09 by aka Keith]
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aka Keith
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| posted on 21/4/09 at 02:12 PM |
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FFS, cannot seem to load pictures, it is in my photo archive under overdrive for BEC
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sickbag
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| posted on 21/4/09 at 02:14 PM |
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Thanks Keith.
Finally back on the job!
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sickbag
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| posted on 21/4/09 at 02:18 PM |
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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?
Finally back on the job!
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MikeCapon
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| posted on 21/4/09 at 02:37 PM |
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Here's the piccy.
 
boite cm
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sickbag
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| posted on 21/4/09 at 02:45 PM |
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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.
Finally back on the job!
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MikeCapon
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| posted on 21/4/09 at 02:53 PM |
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Nope, no chain inside. It's gear drive and the diff is an LSD!
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