Mid Engined possibility.
Discussion
Hello, New to the forum having lurked for far too long,
In a few years time I hope to build my own scratchbuild kit car (bear with me)
Until I have the funds, garage space and expertise Im day dreaming as Im sure many of us do. To that end, Id like some clarification on terms and your input on the feasability of the plan.
Whilst I undersand wheelbase to be from wheel hub to wheel hub, Is the track measured from the end of the drive shaft the centre of the tyre contact patch, or the outer face of the wheel?
Im asking because Im planning to borrow ideas and possibly parts from various other builders and want to know, at the lowest level, weathe Ill need to narrow the spaceframe to keep wishbones the same length or if Spacers or reversed wheels would allow me to "fudge" the finer points to increase decreas my track.
Im hoping to borrow heavily from GT40 replica designs and have a longitudinal engine (LARGE) Rm mounted going to a rear wheel drive with independent suspension.
Boxster gearboxes appear to be the simplest means of getting longitudinal mounted engine power to your rear wheels, Alternativey you could invert a standard Porsche gearbox but was hoping for advice on whether this is actually viable in terms of oil surge, oilling and load bearing when it comes to mounting.
The other option possibly simpler in terms of keeping it agricultural but complex in number of parts involved is jsut to omit the prop shaft from a FW rear drive arrangment, and join the transmission to the face of the diff..... (EEK) is that acceptable?
Ive played with landrovers and decrepit one litre hatches in the past but this project will hopefully have a bit more finesse that those which were all fixed with a hammer and a spanner.
Ideally Id carry over the flappy paddle gear arrangement from a posh gearbox, and have a Japanese turbo engine of some description. for ease of tuning, and availability of parts (hopefully with some clever ECU management to give me the option of high MPG when Im not hooning)
As I said, its all a dream and plans are still being drawn up but I hope someone can assit me.
Dilysi
In a few years time I hope to build my own scratchbuild kit car (bear with me)
Until I have the funds, garage space and expertise Im day dreaming as Im sure many of us do. To that end, Id like some clarification on terms and your input on the feasability of the plan.
Whilst I undersand wheelbase to be from wheel hub to wheel hub, Is the track measured from the end of the drive shaft the centre of the tyre contact patch, or the outer face of the wheel?
Im asking because Im planning to borrow ideas and possibly parts from various other builders and want to know, at the lowest level, weathe Ill need to narrow the spaceframe to keep wishbones the same length or if Spacers or reversed wheels would allow me to "fudge" the finer points to increase decreas my track.
Im hoping to borrow heavily from GT40 replica designs and have a longitudinal engine (LARGE) Rm mounted going to a rear wheel drive with independent suspension.
Boxster gearboxes appear to be the simplest means of getting longitudinal mounted engine power to your rear wheels, Alternativey you could invert a standard Porsche gearbox but was hoping for advice on whether this is actually viable in terms of oil surge, oilling and load bearing when it comes to mounting.
The other option possibly simpler in terms of keeping it agricultural but complex in number of parts involved is jsut to omit the prop shaft from a FW rear drive arrangment, and join the transmission to the face of the diff..... (EEK) is that acceptable?
Ive played with landrovers and decrepit one litre hatches in the past but this project will hopefully have a bit more finesse that those which were all fixed with a hammer and a spanner.
Ideally Id carry over the flappy paddle gear arrangement from a posh gearbox, and have a Japanese turbo engine of some description. for ease of tuning, and availability of parts (hopefully with some clever ECU management to give me the option of high MPG when Im not hooning)
As I said, its all a dream and plans are still being drawn up but I hope someone can assit me.
Dilysi
dilysi said:
Is the track measured from the end of the drive shaft the centre of the tyre contact patch, or the outer face of the wheel?
Strictly speaking, track is measured from where the centreline of the wheel intersects with the ground plane, to the same point on the other side.In plain English (and neglecting camber), that's basically the same as saying centreline of wheel to centreline of wheel.
dilysi said:
...or if Spacers or reversed wheels would allow me to "fudge" the finer points to increase decreas my track
The better way of doing it is to use wheels with different 'offsets' (the distance from the wheel centreline to the hub face), but yes, spacers can be used to give the same effect.dilysi said:
Alternativey you could invert a standard Porsche gearbox but was hoping for advice on whether this is actually viable in terms of oil surge, oilling and load bearing when it comes to mounting.
Yes, it's viable - some Ultimas use this box inverted. I believe you have to modify the breather arrangement, for obvious reasons, but other than that it's not a big deal. Try asking on the Ultima forum here on PistonHeads, though - I'm sure someone will be able to give you chapter and verse. dilysi said:
The other option possibly simpler in terms of keeping it agricultural but complex in number of parts involved is jsut to omit the prop shaft from a FW rear drive arrangment, and join the transmission to the face of the diff..... (EEK) is that acceptable?
It's been done before, certainly (I've seen 750 Formula racers that use this arrangement), but it usually makes for a very long engine/gearbox package: a normal longitudinal mid-engined gearbox arrangement has the differential and driveshafts at the front, just behind the clutch/bellhousing, with the main part of the gearbox hung out behind the rear axle line. What you're suggesting would push the whole gearbox forward in front of the axle line and hence push the engine forward too. You'd end up with either an enormously long wheelbase, or the driver pushed far forward, with feet well in front of the front axle line, which is not good in a crash.What you're suggesting is a very major project and no disrespect, but the questions you're asking show that you have a very basic understanding of the basic arrangement of mid-engned cars. I'd suggest you get yourself along to the Stoneleigh kit car show in May and have a good nose round some of the Ultimas and GT40 replicas and similar cars, to get a better idea of how things are put together.
Where in Gloucestershire are you, by the way?
Excellent thankyou very much for that, without appearing passive aggresive you said alot of things that Id thought and im grateful for the help you offered I am in now way offended as Im evidently still learning.
Ive looked around the Ultima pages alot and it was the complications of inverting the Getrag(?) gearbox that put me on to using the slightly "lighter weight" boxster box (lightweight in terms of robustness). The plan such as their is one, is to crib heavily from Ultima/GT40 spaceframe replicas and remove width from the space frame by using shorter lateral braces before clothing it in something less race and track derived. Whilst not looking for a sleeper Im hoping to fit a few litres of blown goodness into something of a gentlemans GT.
Suspension geometry and steering angles are going to be heavily reliant on Stonleigh and club meets I imagine.
Im in the five valleys at the moment, but move around alot with work hence not being likely to get this underway any time soon. There was a firm in the industrial estate down in Nailsworth that did rolling road tunes and GT40 copies who i spent a few months pestering for work experience theyve since folded but if anyone here knows what happened to them Id be interested in having a look at their plans and blue prints.
Ive looked around the Ultima pages alot and it was the complications of inverting the Getrag(?) gearbox that put me on to using the slightly "lighter weight" boxster box (lightweight in terms of robustness). The plan such as their is one, is to crib heavily from Ultima/GT40 spaceframe replicas and remove width from the space frame by using shorter lateral braces before clothing it in something less race and track derived. Whilst not looking for a sleeper Im hoping to fit a few litres of blown goodness into something of a gentlemans GT.
Suspension geometry and steering angles are going to be heavily reliant on Stonleigh and club meets I imagine.
Im in the five valleys at the moment, but move around alot with work hence not being likely to get this underway any time soon. There was a firm in the industrial estate down in Nailsworth that did rolling road tunes and GT40 copies who i spent a few months pestering for work experience theyve since folded but if anyone here knows what happened to them Id be interested in having a look at their plans and blue prints.
It might be worth having a look at the cheetah racing car from the 60s. It was dubbed the Cobra killer, that was technically mid engined, but it was forward of the driver.
The builder/designer made it so that the engine was as far back under the bonnet as possible with the diff bolted directly onto the end of the gearbox. It's a good looking beast and is very cab back with the gearbox right between the potential 2 occupants. I know it is not exactly what you were thinking of, but it does show another possibility and highlights how much space there is potentially wasted around the gearbox area of mid/rear engined vehicles.
The builder/designer made it so that the engine was as far back under the bonnet as possible with the diff bolted directly onto the end of the gearbox. It's a good looking beast and is very cab back with the gearbox right between the potential 2 occupants. I know it is not exactly what you were thinking of, but it does show another possibility and highlights how much space there is potentially wasted around the gearbox area of mid/rear engined vehicles.
Excellent thankyou very much.
Not quite what I have been planning but certainly a beautiful car.
Im thinking along the lines of a funny car dragster, But less funny and more practical. Ive been perusing retro-rides as well, and a Karmann Ghia shell with rusted floorpans and a shot through engine can be found fairly cheaply. A beautiful car that was underpowered in its day being given the performance and pace its silhouette deserves.
Louvres and intakes hopefully being in keeping with its already aircooled rear slung engine.
RIGHT enough dreaming, off to smash some books and sketch some stuff out, Im not sure if its called lofting but a few templates have to be drawn up and ill stop bothering you until next time.
Dilysi
Not quite what I have been planning but certainly a beautiful car.
Im thinking along the lines of a funny car dragster, But less funny and more practical. Ive been perusing retro-rides as well, and a Karmann Ghia shell with rusted floorpans and a shot through engine can be found fairly cheaply. A beautiful car that was underpowered in its day being given the performance and pace its silhouette deserves.
Louvres and intakes hopefully being in keeping with its already aircooled rear slung engine.
RIGHT enough dreaming, off to smash some books and sketch some stuff out, Im not sure if its called lofting but a few templates have to be drawn up and ill stop bothering you until next time.
Dilysi
Depends on the kind of power you're thinking of using but all the A4/5/6 2wd Audi gearboxes are ideal for a MR setup. What's more, they're cheap. Some are also used in the Skoda and VW ranges too. TBH some decent engines there too (I'd pick one of the turbo'd units myself) and that makes mating engine to gearbox a cinch.
Boxster is effectively the same as the Audi 012 gearbox, best Audi/Skoda/VW box is probably the 01E, rated I believe to 450Nm.
I considered a scratch build, spent a lot of time designing one but ultimately bought a chassis.
If you want to make it a reality sooner rather than later I would personally pick a decent handling donor for suspension etc. I picked the RX-8 because we both had one and blown up ones go for pennies, you get a good handling car with proper dual wishbone front and multi-link rear, good brakes, EPS (so no trying to route hydraulics to the front of a MR car for power steering) and a load of bits to sell. Do it right, pick the right donor and you get the bits you want for 'free'.
Good luck with the project, don't underestimate just how much planning goes into such a journey!
Feel free to ask as many stupid questions as you like.
Boxster is effectively the same as the Audi 012 gearbox, best Audi/Skoda/VW box is probably the 01E, rated I believe to 450Nm.
I considered a scratch build, spent a lot of time designing one but ultimately bought a chassis.
If you want to make it a reality sooner rather than later I would personally pick a decent handling donor for suspension etc. I picked the RX-8 because we both had one and blown up ones go for pennies, you get a good handling car with proper dual wishbone front and multi-link rear, good brakes, EPS (so no trying to route hydraulics to the front of a MR car for power steering) and a load of bits to sell. Do it right, pick the right donor and you get the bits you want for 'free'.
Good luck with the project, don't underestimate just how much planning goes into such a journey!
Feel free to ask as many stupid questions as you like.
Fastdruid said:
Depends on the kind of power you're thinking of using but all the A4/5/6 2wd Audi gearboxes are ideal for a MR setup. What's more, they're cheap. Some are also used in the Skoda and VW ranges too. TBH some decent engines there too (I'd pick one of the turbo'd units myself) and that makes mating engine to gearbox a cinch.
I must say, I think you'd be better sticking to an engine/gearbox combination from a single donor - designing and building a mid-engined car from scratch with no previous experience is a stiff enough challenge as it is, without the extra problem of figuring out how to mate mis-matched components together.Fastdruid said:
...pick a decent handling donor for suspension etc. I picked the RX-8 because we both had one and blown up ones go for pennies, you get a good handling car with proper dual wishbone front and multi-link rear
Bear in mind, though, that suspension geometry is tailored to match the characteristics of a particular design. For example, the front and rear roll centre heights will be chosen to give a roll axis that's specifically tailored to the weight, centre of gravity and suspension stiffness of the car they're designed for. You can't expect to simply bolt the suspension from an RX8 (for example) onto a rear-mid engined car (or the suspension from an Elise, say, onto a front engined car) and expect it to work - it won't.As an alternative to the Porsche box what about the Audi/VW box. The 2.5tdi box will easily take the torque of a V8 and mounts up to Audi V8/V10 engines with little bother. You could use the V8 Quatro box and blank off the rear take off but that's a bit of a bodge job (even if Spyker do it).
The Audi V engines are also very short (but very wide) so packaging may be easier.
For an example build diary linky
The Audi V engines are also very short (but very wide) so packaging may be easier.
For an example build diary linky
Sam_68 said:
Fastdruid said:
Depends on the kind of power you're thinking of using but all the A4/5/6 2wd Audi gearboxes are ideal for a MR setup. What's more, they're cheap. Some are also used in the Skoda and VW ranges too. TBH some decent engines there too (I'd pick one of the turbo'd units myself) and that makes mating engine to gearbox a cinch.
I must say, I think you'd be better sticking to an engine/gearbox combination from a single donor - designing and building a mid-engined car from scratch with no previous experience is a stiff enough challenge as it is, without the extra problem of figuring out how to mate mis-matched components together.Sam_68 said:
Fastdruid said:
...pick a decent handling donor for suspension etc. I picked the RX-8 because we both had one and blown up ones go for pennies, you get a good handling car with proper dual wishbone front and multi-link rear
Bear in mind, though, that suspension geometry is tailored to match the characteristics of a particular design. For example, the front and rear roll centre heights will be chosen to give a roll axis that's specifically tailored to the weight, centre of gravity and suspension stiffness of the car they're designed for. You can't expect to simply bolt the suspension from an RX8 (for example) onto a rear-mid engined car (or the suspension from an Elise, say, onto a front engined car) and expect it to work - it won't.
Roll centres can be altered although that really does need an understanding of why.
I wouldn't advise using the shocks etc as they are either but I'd personally go pushrod suspension anyway.
The other reason for suggesting the RX-8 is although the engine is in the front its so small and light and far back it makes the car a 50:50 weight distributed MR layout. It has its issues as a donor but honestly don't know of a better one, especially for the money. Everything else is either plain wrong or donors are silly expensive or old/rare.
Saying that you wouldn't go far wrong using TVR parts for hubs/brakes etc. Not cheap but not that unreasonably expensive either.
the footprint of the car is one of the things I am fairly sure I can play with, Ignoring the fact that I am putting the engine at the wrong end, S2000 MX5 Cayman and boxster front subframes all look to be "simple" to remove in one piece wishbones sterring rack brakes and hubs and weld straight into a new frame.
The rear end will clearly be more complex but thats why ive started the dreaming this far ahead of time anyway.
One question on gearboxes, Id imagined that a paddle shift could be fiddled with and removed the difficulty of moving linkage arms around the engine bay, But they are a dark art to me, How many inputs do fancy gearboxes require in order to function properly, I had presumed it just worked off the number of revs the crank was putting out, Or are they heavily reliant on input from the ECU necessitating the same donor for both Engine and Box.
(I ask the stupid questions so other people dont have to)
The rear end will clearly be more complex but thats why ive started the dreaming this far ahead of time anyway.
One question on gearboxes, Id imagined that a paddle shift could be fiddled with and removed the difficulty of moving linkage arms around the engine bay, But they are a dark art to me, How many inputs do fancy gearboxes require in order to function properly, I had presumed it just worked off the number of revs the crank was putting out, Or are they heavily reliant on input from the ECU necessitating the same donor for both Engine and Box.
(I ask the stupid questions so other people dont have to)
Very heavily reliant on engine, indeed some use the same ECU although most now use a second.
I'm certain it could be done but might take a fair amount of time fiddling and making some inbetween circuitry to fool the computer.
Btw, on front ends. Boxster I think use Macpherson struts rather than double wishbone.
RX-8
S2000
Almost identical setups.
I'm certain it could be done but might take a fair amount of time fiddling and making some inbetween circuitry to fool the computer.
Btw, on front ends. Boxster I think use Macpherson struts rather than double wishbone.
RX-8
S2000
Almost identical setups.
Fastdruid said:
Roll centres can be altered although that really does need an understanding of why.
...but if you alter the geometry to move the roll centre, it will alter other elements of the geometry at the same time. If you know what you're doing/what your objectives are, it's almost always better and simpler to just pick a suitable front upright, then design the rest of the geometry from scratch, using fabricated wishbones.Fastdruid said:
Saying that you wouldn't go far wrong using TVR parts for hubs/brakes etc. Not cheap but not that unreasonably expensive either.
Have you driven a TVR?! Their front upright/steering geometry, in particular, is an object lesson in how not to do it!! No, not driven one but they can be easily changed, top and bottom joints are bolt on so could be extended/moved fairly easily for whatever geometry you want.
Although you really need to decide on wheel size, track and wheelbase first because so much of the geometry is driven from them. You can fudge it to a certain extent later but better to start off right.
Although you really need to decide on wheel size, track and wheelbase first because so much of the geometry is driven from them. You can fudge it to a certain extent later but better to start off right.
Fastdruid said:
No, not driven one but they can be easily changed, top and bottom joints are bolt on so could be extended/moved fairly easily for whatever geometry you want.
I have (I've owned a Griffith 500) and believe me, the suspension/steering geometry is the one thing you wouldn't want to replicate.You appreciate, I assume, that far from being expensive, custom-made components, they are in fact modified Ford Sierra/Granada parts?
The front upright is modified from the Sierra strut upright. You can use conical spacers to extend the top and bottom ball joint positions to some extent, certainly, but that presupposes you know what you're doing - and even then you're stuck with a fixed steering arm that dictates some of the geometry. I've never come across a car (either the TVR's or the numerous kit cars that have used the same approach) that has managed to make the Sierra upright work very well, when modified in this way for use with a double wishbone suspension - the basic geometry just isn't suited to it. You always seem to end up with either dead, lifeless steering with insufficient self centring, or else sufficient self-centring but steering that kicks back and tramlines all over the place (TVR).
The rear uprights/hub carriers are fabricated (albeit using Ford hubs, bearings and brakes) but the rear geometry on the Griffith/Chimaera generation cars had a very nasty flaw in that the roll centre location was poorly controlled in some combinations of suspension movement, such that you could occasionally experience a sudden shift in weight transfer when, for example, you traversed the crest of a camber in the road while accelerating to overtake (ask me how I know: I did an analysis of the geometry myself after scaring myself s
tless on a couple of occasions). Suffice it to say I wouldn't be rushing to replicate the rear geometry, either.Fastdruid said:
I was thinking tuscan s, alloy uprights, jeep hubs. TVR branded AP racing callipers. At the front anyway.
Different, but similar geometry problems - again, I think you need to drive the car before recommending them. The Tuscan is similarly prone to tramlining and directional instability.I'm told they finally sorted the Geometry for the Sagaris (it's one TVR that I haven't had the opportunity to drive yet), but you won't find many of those breaking for spares... and in any case you'd still have the problem that it's a front-engined car, whereas the OP requires something suitable for rear mid-engined weight distribution.
Just uprights/hubs, not geometry!
For example, here are some on a GT40 replica.
Top and bottom are bolt on so could be swapped to change the geometry of the upright itself, KPI/SPI & ackerman are all changeable. Castor is from the wishbones.
Unless you want it to handle like a TVR there is no reason it should.
For example, here are some on a GT40 replica.
Top and bottom are bolt on so could be swapped to change the geometry of the upright itself, KPI/SPI & ackerman are all changeable. Castor is from the wishbones.
Unless you want it to handle like a TVR there is no reason it should.
Sam_68 said:
I did an analysis of the geometry myself after scaring myself stless on a couple of occasions). Suffice it to say I wouldn't be rushing to replicate the rear geometry, either.
Sam,tless on a couple of occasions). Suffice it to say I wouldn't be rushing to replicate the rear geometry, either.What would you suggest the geometry (KPI, caster, trail, scrub) should be and what do you think was wrong (as in too much of X and not enough of Y) with the TVR set up?
I would have thought that using MX5 hubs for a smaller car and Corvette hubs for a larger car would provide a good ready made solution.
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