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Julian West · 08-20-03, 06:42 AM

Lee,

I've also been doing alot of research on this! Here's what I've learnt so far! please bear in mind this is only research & I haven't quite got round to cutting up my chassis!!

Inverting the gearbox is a very attractive idea, as it measures up like it was made to fit!

As Malcolm sias, there is only one person in the club that has done this.

As standard (with the R21T) the crank C/L is 70mm higher than the driveshaft output C/L. If you invert then you could retain the same driveshaft angles & lower the engine 140mm.

With Armandos GT40 sump at 165mm deep, you'll find the bottom of the sump would then be flush with the botttom of the chassis. Perfect!

FWIW inverting the trans was a common mod in Hillman Imps & there are a few about. I'm told some older forumla Renault single seaters used an inverted UN1, but I've never seen one.

Ultima use the Porsche G50/60 'box and or the 996 (getrag) 'box, both inverted. There is a breather mod they use but other than that I'm not sure exactly if there are any internal mods.

If you have even deeper pockets a Pantera ZF can be inverted by Roy Butfoy in CA.

I've thought long & hard about inverting the R21T, but do not have the confidence with the oil control, especially as I'm using DB's Quaiffe upgrade (V expensive!). Overall I'd have concerns as to how the lifespan of the trans may be affected by inverting. It may last for ever, or it may pop in 5 minutes.... I don't know!! An external transmission oil pump and/or cooler may help, but it's extra plumbing, complexity, weight, cost, etc.

So if you don't want to invert, the trade off is more extreeme driveshaft angles.

Basically, I've learnt that driveshafts can do 'high angle, low speed', or 'low angle & high speed', but not both!

The 'Off-road' 4X4 chaps use outrageous driveshaft angles when they're driving up & over mountains, etc. However it's all at relativeley low speed. In our application wheel speeds are much higher.

I found a company that can supply CV joints that (they say) will happily cope with 20 deg & more. These are pretty pricey, but are used in World chapmionship rally cars, where they need alot of suspension travel & high wheel speeds, combined with bucketloads of BHP.

So using some basic geo (as Trevor suggests) & a bit of trig, I calculated that allowing for full bump (75mm) putting the driveshaft at 20 deg, the crank C/L could be placed 195mm from the chassis underside, with the engine & trans dead level. I guess if you're happy with a bit less suspension travel, or a bit more driveshaft angle you could go lower. Also I guess it's V unlikeley you'll ever be at full droop whilst on full throttle!

As I mentioned, I haven't put any of this into practice yet. I'm getting the hacksaw out soon!!

Hope this helps!

08-20-03, 06:42 AM	#4 (permalink)
Julian West Julian West 7 Tenths Join Date: Dec 2001 Location: Devon, UK GT40: GTD Posts: 750 Rep Power: 14	Re: Low Engine C of G / Inverted Gearboxes Lee, I've also been doing alot of research on this! Here's what I've learnt so far! please bear in mind this is only research & I haven't quite got round to cutting up my chassis!! Inverting the gearbox is a very attractive idea, as it measures up like it was made to fit! As Malcolm sias, there is only one person in the club that has done this. As standard (with the R21T) the crank C/L is 70mm higher than the driveshaft output C/L. If you invert then you could retain the same driveshaft angles & lower the engine 140mm. With Armandos GT40 sump at 165mm deep, you'll find the bottom of the sump would then be flush with the botttom of the chassis. Perfect! FWIW inverting the trans was a common mod in Hillman Imps & there are a few about. I'm told some older forumla Renault single seaters used an inverted UN1, but I've never seen one. Ultima use the Porsche G50/60 'box and or the 996 (getrag) 'box, both inverted. There is a breather mod they use but other than that I'm not sure exactly if there are any internal mods. If you have even deeper pockets a Pantera ZF can be inverted by Roy Butfoy in CA. I've thought long & hard about inverting the R21T, but do not have the confidence with the oil control, especially as I'm using DB's Quaiffe upgrade (V expensive!). Overall I'd have concerns as to how the lifespan of the trans may be affected by inverting. It may last for ever, or it may pop in 5 minutes.... I don't know!! An external transmission oil pump and/or cooler may help, but it's extra plumbing, complexity, weight, cost, etc. So if you don't want to invert, the trade off is more extreeme driveshaft angles. Basically, I've learnt that driveshafts can do 'high angle, low speed', or 'low angle & high speed', but not both! The 'Off-road' 4X4 chaps use outrageous driveshaft angles when they're driving up & over mountains, etc. However it's all at relativeley low speed. In our application wheel speeds are much higher. I found a company that can supply CV joints that (they say) will happily cope with 20 deg & more. These are pretty pricey, but are used in World chapmionship rally cars, where they need alot of suspension travel & high wheel speeds, combined with bucketloads of BHP. So using some basic geo (as Trevor suggests) & a bit of trig, I calculated that allowing for full bump (75mm) putting the driveshaft at 20 deg, the crank C/L could be placed 195mm from the chassis underside, with the engine & trans dead level. I guess if you're happy with a bit less suspension travel, or a bit more driveshaft angle you could go lower. Also I guess it's V unlikeley you'll ever be at full droop whilst on full throttle! As I mentioned, I haven't put any of this into practice yet. I'm getting the hacksaw out soon!! Hope this helps!