Delete gearbox?
Discussion
I'm slowly putting together a trackday/fun car based loosely on a Kitten chassis. I'm looking to keep and modify the front suspension, lose the original engine and gearbox, move the front seats forward a little (and replace them) and put something big and torquey behind them.
A number of engines look nice, particularly the 5.0 V12 from BMW's 7-series, but they all suffer from Long Drivetrain Syndrome; the engine is long, the gearbox is just as long, the propshaft (which can be shortened or even deleted) is looooong, even the diff has a long nose!
Stick all that in my little chassis and I'd end up with a cross between a Group C Sportscar and an aircraft tug!
So I started thinking about ways to shorten it.
The obvious answer, of course, is a transaxle. Sits behind the engine, not too long, drive comes out of the sides near the front so my wheelbase doesn't end up longer than a 750iL donor.
Trouble is, most are weak - they won't put up with 330 lb/ft of torque. And those that will are made by/for Porsche, and are expensive.
I thought further - I have 300 lb/ft of torque from 1,000-6,000 rpm. The finished car should weigh around 500Kg. Do I need a gearbox?
If I take the standard autobox, cut-and-shut it so that all that remains is the torque converter driving the output shaft and connect that directly to the OE diff, I then have a 'drivetrain' capable of driving the rear wheels from rest to 1900 rpm.
Assuming the torque converter is not especially unusual in its operation, this should give wheel torque from 1900 ft/lb at standstill to 900 at redline - my e30 325i peaks at 2300 lb/ft in 1st gear, dropping to 480 lb/ft at the top of 5th.
Have I missed anything (apart from no reverse gear!)?
Has anyone tried anything like this?
Does anyone know someone willing and able to butcher a perfectly good ZF autobox in this way?
Have I finally lost it
?
Any answers appreciated
A number of engines look nice, particularly the 5.0 V12 from BMW's 7-series, but they all suffer from Long Drivetrain Syndrome; the engine is long, the gearbox is just as long, the propshaft (which can be shortened or even deleted) is looooong, even the diff has a long nose!
Stick all that in my little chassis and I'd end up with a cross between a Group C Sportscar and an aircraft tug!
So I started thinking about ways to shorten it.
The obvious answer, of course, is a transaxle. Sits behind the engine, not too long, drive comes out of the sides near the front so my wheelbase doesn't end up longer than a 750iL donor.
Trouble is, most are weak - they won't put up with 330 lb/ft of torque. And those that will are made by/for Porsche, and are expensive.
I thought further - I have 300 lb/ft of torque from 1,000-6,000 rpm. The finished car should weigh around 500Kg. Do I need a gearbox?
If I take the standard autobox, cut-and-shut it so that all that remains is the torque converter driving the output shaft and connect that directly to the OE diff, I then have a 'drivetrain' capable of driving the rear wheels from rest to 1900 rpm.
Assuming the torque converter is not especially unusual in its operation, this should give wheel torque from 1900 ft/lb at standstill to 900 at redline - my e30 325i peaks at 2300 lb/ft in 1st gear, dropping to 480 lb/ft at the top of 5th.
Have I missed anything (apart from no reverse gear!)?
Has anyone tried anything like this?
Does anyone know someone willing and able to butcher a perfectly good ZF autobox in this way?
Have I finally lost it
?Any answers appreciated
Final question first: Yep, you've lost it.
Have you missed anything? The only obvious thing I can think of is how you actually intend to stop? How do you disengage drive from the torque converter if you've cut away the rest of the autobox mechanism?
Your torque calculations are probably OK, and if you could build a 500kg car with that sort of torque, you probably wouldn't need a gearbox, though as others have said, you'd need to look at the how the torque converter is supplied with fluid if you don't want to cook it in seconds.
But...
The standard Kitten chassis and suspension is completely unsuitable for that sort of power/torque.
The supension geometry, brakes, wheel bearings etc. on the standard kitten chassis are completely inadequate and are aslo tailored to a different weight distribution.
Your weight estimate of 500kg is woefully optimistic. That would be very light for a simple 'Seven' type with a small car engine in it; my Sylva (which is one of the lighter kit-cars) weighs in at 508kg with a 1600 Crossflow.
You'd be better starting from scratch with a chassis design...
Since you mention the word 'Kitten' though, I'm sure that fellow PistonHeader JWB will be along any time soon to tell you how to do it properly. He built a very well engineered Kitten for drag/street use with a Rover V8 and autobox, but the only bit of Kitten left was the bodyshell - everything underneath was specially fabricated (to a very high standard).
Have you missed anything? The only obvious thing I can think of is how you actually intend to stop? How do you disengage drive from the torque converter if you've cut away the rest of the autobox mechanism?
Your torque calculations are probably OK, and if you could build a 500kg car with that sort of torque, you probably wouldn't need a gearbox, though as others have said, you'd need to look at the how the torque converter is supplied with fluid if you don't want to cook it in seconds.
But...
The standard Kitten chassis and suspension is completely unsuitable for that sort of power/torque.
The supension geometry, brakes, wheel bearings etc. on the standard kitten chassis are completely inadequate and are aslo tailored to a different weight distribution.
Your weight estimate of 500kg is woefully optimistic. That would be very light for a simple 'Seven' type with a small car engine in it; my Sylva (which is one of the lighter kit-cars) weighs in at 508kg with a 1600 Crossflow.
You'd be better starting from scratch with a chassis design...
Since you mention the word 'Kitten' though, I'm sure that fellow PistonHeader JWB will be along any time soon to tell you how to do it properly. He built a very well engineered Kitten for drag/street use with a Rover V8 and autobox, but the only bit of Kitten left was the bodyshell - everything underneath was specially fabricated (to a very high standard).
Ian Oddie built a ford citrine yellow (read sh**ty yellow) cossie powered Kitten that was in CCC mag before its demise iirc. There was also a rally prep firm that built a purple spaceframed bike engined single stage rally version as a showcase for the companies deign/fabrication talents (superb actually). for me the thought of a short wheelbase, narrow, light car with a large heavy engine would seem a handling and packaging nightmare, but fair play to you fella :-)
Thanks for the replies (even if they do rather piss on my bonfire 
)
It looks like a number of rethinks are in order, the biggest is that I thought a TC was a sealed unit - aah, complications
Looking at this diagram, something may be possible; it looks like the gearbox oil pump lives just behind the TC....
As regards stopping, a TC is a form of fluid flywheel and replaces a clutch. An automatic car can be brought to a halt in any gear, though it will have a tendency to creep forward, it can be held stationary by hand if the engine is merely idling.
Whatever I do, at the end there won't be much Kitten left. Actually there isn't much now - I have a chassis with front suspension, steering and front brakes; no propshaft, rear axle or bodyshell.
Ideally, I'd build the engine/diff/rear suspension as a self-contained fabrication that could be attached to the existing chassis, which would be stiffened by a rollcage/spaceframe. The front suspension can be modified fairly easily to suit a change in weight distribution - it's double wishbone with coil springs over shocks - but the standard drum brakes would definitely need uprating. The hubs are Mini, so a wide range of options exists.
)It looks like a number of rethinks are in order, the biggest is that I thought a TC was a sealed unit - aah, complications
Looking at this diagram, something may be possible; it looks like the gearbox oil pump lives just behind the TC....As regards stopping, a TC is a form of fluid flywheel and replaces a clutch. An automatic car can be brought to a halt in any gear, though it will have a tendency to creep forward, it can be held stationary by hand if the engine is merely idling.
Whatever I do, at the end there won't be much Kitten left. Actually there isn't much now - I have a chassis with front suspension, steering and front brakes; no propshaft, rear axle or bodyshell.
Ideally, I'd build the engine/diff/rear suspension as a self-contained fabrication that could be attached to the existing chassis, which would be stiffened by a rollcage/spaceframe. The front suspension can be modified fairly easily to suit a change in weight distribution - it's double wishbone with coil springs over shocks - but the standard drum brakes would definitely need uprating. The hubs are Mini, so a wide range of options exists.
Now the bonfire is out why have you discounted a transaxle?
I have an Ultima which uses a standard Porsche G50/20 6 speed. My Chevy V8 engine ran 508bhp and 527lbf/ft on the engine dyno and the 'box is fine.
I believe a G64 may be stronger and an Ultima owner in the US is running 1030hp with this box but it may have been modified.
Unless you want to run silly power numbers a secondhand G50 at £1800-2K will do the job.
Steve
I have an Ultima which uses a standard Porsche G50/20 6 speed. My Chevy V8 engine ran 508bhp and 527lbf/ft on the engine dyno and the 'box is fine.
I believe a G64 may be stronger and an Ultima owner in the US is running 1030hp with this box but it may have been modified.
Unless you want to run silly power numbers a secondhand G50 at £1800-2K will do the job.
Steve
getting a TC to work standalone would be ball ache. IF you have access to extensive engineering facilaties it may be possible to shorten an autobox right down to just after the front pump. But having built several autoboxes, you are looking at awful lot of work - and for what for? - A single speed gearbox with no reverse and no neutral. Sack it.
you can get automatic transaxles that are for v8's, search for 4T60 and 4T80.
you can get automatic transaxles that are for v8's, search for 4T60 and 4T80.
v8ian said:
another thought, what about removeing the tailhousing completely, get the output shaft shortened to where it comes out of the box, and get it splined to suit a flange or Muff cplg, this will enable you to bolt the back of the box to the diff, could be an option
Or just get a 4x4 version of any popular GM transmission - as they have a very short stubby output shaft - as they bolt directly to the transfer box.Steve_D said:
crisisjez said:
Didn`t the Renault 25 box lend itself to transaxle mounting?
Yes it did but was prone to input shaft failure at much lower torque figures than the Porsche 'box can take.Steve
As the op has`nt made an engine choice perhaps he`d be better off with a high HP screamer with low Torque.
Would certainly keep the weight down.
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