. To drive home from an event he selected neutral then disconnected the linkage to one box and drove home on one engine two wheel drive
Billiant
RD
[Edited on 10/9/10 by rallyingden]
So if you're considering a twin-engine 4WD setup you have the choice of combining the two engines into a xfer box, then outputting to a centre
diff, or simply driving the two engines to opposite ends. My thinking is that with two 750's, one pointing forward with a flipped diff, one
pointing backward with a normal diff, make a ~200hp/140lbft 6spd sequential 4wd with little more than the added mass of the extra engine and
diff/shafts, which is a nice proposition considering the extremely low price of 750s, plus reduces the wear that you'd normally get dragging half
a ton round with a 750 (not normally a good idea).
But obviously two engines need to be fairly closely controlled or you end up with some odd torque splits. Assuming you maintain the same gears and
shift at the same times, without an Xfer box you should essentially have fairly close match of revs and torque from two identical engines, which
should give you approx 50:50 torque split, and pretty much locked due to the similarity of the engines, almost like a viscous centre diff. Two
seperate engines would have additional costs of two ECUs unless you have them hard-linked where they would act practically as one engine (plus some
harmonic problems).
You would need to have a common gearbox i would imagine. The chances of synchronous gear changes would be tight, though not impossible.
I'd have thought that trying to control the two engine outputs so that they're not constantly fighting each other would be nigh on
impossible for your average 'home' builder.
I know it's been done by the likes of Z-cars, but how successfully? I've not heard of their twin-Busa Ultima since it was finished.
there is a twin engine tiger somewhere
might be worth looking at that for some info
link to tiger click
[Edited on 10/9/10 by tomgregory2000]
Z cars twin engine ZX9R Westy was a party piece.
Take off up to the ton and then switch the second engine on! That was Chris's explanation to me and the two engines could be in different gears
as well.
pros:
woooooooooohoooooooooooo
cons:
how the feck
I'm not sure they would be fighting that much to be honest but I'm hoping we can think it through out loud here. If you have a physical
parallel link on the stick they either both go into gear or both don't. Slow take-off is the sticky point where clutches may be more or less
engaged than their neighbour.
IIRC the zcars one (that was the one on fifth gear wasn't it?) had 2 engines feeding one axle, that's not for me. Essentially if you have 2
axles seperately driven the only time you're really going to have problems is with breaks in traction at one end or the other. If that happens
you're going to end up having one engine revving out while the other bogs, which may be a terminal problem, but that's essentially the same
as an open centre diff, where one end spins out and you have to ease off. Maybe something like the megasquirt rev-rate traction control on each engine
would keep things in tow, automatically throttling back the slipping axle, but I'm nto sure how well MS handles bike-engine rates.
A mate of mine made a twin engine 4WD VW scirroco by grafting the front of one into the back of another. First setup was manual box at one end Auto
box at the other but then he found out that as there was so much wheel spin he could put two manual box's in with a single lever selecting gears.
Off the line it spun the wheels so much that the fact that one set spun a bit slower than the others didn't matter .
To drive home from an event he selected neutral then disconnected the linkage to one box and drove home on one engine two wheel drive
Billiant
RD
[Edited on 10/9/10 by rallyingden]
They'll not fight each other, having one doing more work is the equivalent of one going slightly uphill, the other slightly downhill.
They needn't even be in the same gear or with the same final drive ratio giving you the possibility of an uneven torque split since bike engines
have such a wide rev range. The problem there is over-reving one or wasting the potential of the other. In fact, they needn't even be exactly the
same engine (though you'd get some weird variable torque distribution going on!).
In the real world the main issues will be keeping the gearboxes synchronised and avoiding an accidental overspeed when one doesn't shift up.
The beauty of an engine/axel is obviously 4wd and the ability to use a very simple, lightly built drivetrain.
if the torque balance is such an issue - then why not get two identical engines and detune one. That way you'll always have one engine more
powerful than the other and therefore the torque balance will always be one way in favour. The amount in favour will change through the rev range -
but on a two wheel drive car the torque isn't linear.
My understand is the biggest problem is the gear change on bikes. They're a bit agricultural and its far easier to get a miss shift on a bike. At
this point you risk an engine going pop a second or two later. On the tiger twin rear wheel drive car 5th gears tiff blew up one engine as he
couldn't get the hang of shifting both engines. (mates lad was the motec guy who tuned the engines and the comment i heard back was the owner was
rather 'gutted' when he saw one engine go bang)
Sure a guy did twin engine's in a scirocco called it a durocco or something, it was two 16v lumps seperately driving each axle. Went like stink
theres some youtube footage somewhere
http://www.youtube.com/watch?v=eQREhPfA5w4
http://www.durocco.com/
I think the main con is that it's illegal for a road car to have two engines driving two axles independantly!
adrian
quote:
Originally posted by adithorp
I think the main con is that it's illegal for a road car to have two engines driving two axles independantly!
adrian
This is one of those things that gives me a headache (bit like pondering the Universe!).
If one is driving the front wheels and the other is driving the back... and they are not putting down exactly the same power at exactly the same time,
then surely one axle is always going to be turning faster than the other...
So would we get a push-me-pull-you effect and one engine being ragged by the other?
I can get my head around it when you introduce uber-fancy electrickery as we all know that this is a black-art where magical things happen, but I
can't quite fathom it otherwise!
Will follow this thread with interest...
quote:
Originally posted by scootz
I'd have thought that trying to control the two engine outputs so that they're not constantly fighting each other would be nigh on impossible for your average 'home' builder.
I know it's been done by the likes of Z-cars, but how successfully? I've not heard of their twin-Busa Ultima since it was finished.
quote:
Originally posted by matt_claydon
If the throttle's open, they will both be pushing the car forward, if the throttle's closed, they will both be engine braking.
and two engines = twice the weight (engine wise at least)
[Edited on 10/9/2010 by mcerd1]
quote:
Originally posted by iank
quote:
Originally posted by adithorp
I think the main con is that it's illegal for a road car to have two engines driving two axles independantly!
adrian
I've also been told that's a myth based on the crash that nearly killed John Cooper.
Do you have a reference to the law in question?
I would have thought you would need to run both engines from the same ECU to ensure that at least the ignition timing is the same, so the engines
follow the 'same' response. I assume both clutches will be release using the same pedal, assuming you're using the bikes
gearboxes/clutches- This means at some point, even if its only for an instant one clutch will bite and take the whole load of starting the car moving,
until the second one cuts in. I would have thought this would lead to heavy load/unload cycles on the gearboxes and give early failure. On the other
hand, it may be that the first one just starts to put load on the tyres as the second starts to bite, and the boxes may then last a bit better. How
will you prevent the 'missed gear' problems experienced on bikes - if one engine changes up and the other doesnt, it could get messy.
I'd love to see it done though.
Regards
Hugh
quote:
I think the main con is that it's illegal for a road car to have two engines driving two axles independantly!
I cannot see an issue with not having matched engines, 4wd cars do not bias torque 50:50 front to rear, landrovers for instance have an open diff in
the middle so 100% can go to the front or rear with the diff lock out.
Clever jap cars change the bias as you drive, the only problem is making sure you do not over rev one of the engines.
Auto one box manual the other makes the gears very easy, altough car balance will be all over the place on hard bends if it shifts.
I believe the Zcars one had two gear shifts for the bikes engines next t0 each other like fiddle brakes so you could push or pull together, if one
missed a cog you could then just poke that stick, watch the rev counters to confirm they are in sync.
Regards Mark
Getting the perfect adjustment so they both shift up together is going to be the problem. With a single engine and a sequential box you clearly feel
the clunk as it shifts. If you get the clunk from one but the other doesn't quite make it up and over into the next gear (sloppy maladjusted
link, insufficient pull on the shifter, worn barrel... whatever) then you have a problem. You may hear the difference, you may not. If you've
just pulled 1st to 2nd on one box but not the other at max rpm you now have one engine pulling strongly in 2nd rapidly overspeeding the other which is
stuck (making no power on the now ineffective rev limiter) in 1st.
Since it'd be reasonably straightforward to electronically interlock the engines so they'll only run when safe to do so it looks like the
legal issues might be the most intractable problem.
Yep, it did have a twin-stick like boats with two engines. And certainly although my 4x4 does have a 50:50 torque split, most do not, I was just
concerned with some negative handling effects of having one vastly out of whack, however this is effectively a viscous coupling as I say - it allows
some torque bias but not much (only that caused by the slight variation in engine outputs, which will be in single-figure percentages).
Time to ring VOSA I think. It might be twice the weight, but even so mcerd - twice the weight is still only the same weight as a pinto or maybe zetec
powered car but with more power and 4wd. Sure it's not a 1000hp/ton, but I suspect its handling and grip would more than compensate. It would be
nice to have twin torsens to go with it. That could be arranged.
I'm still thinking through the missed gear scenario. If the selector travel is controlled, in fact limited, by the entry of the gear into its
location (as I've had it described, I've never done it on anything but a 600cc on an engine dyno) then you press and wait for it to drop in.
Now if two are linked together a few things may occur:
1) Press and hold, one will mesh, the other meshes slightly later, stick moves into place - all good.
2) Press and hold, one meshes, the second has fallen past the point that it'll mesh so never meshes, neither engine achieves a gear.
If the lever motion is controlled by the action of the gears meshing, it's an all-or-nothing affair, or rather both or none unless your
adjustment is out of whack. I'm not sure how tight that tolerance is. This could make it a pain to drive, but it's fairly easy to cut spark
during the shift to aid meshing and ease the load on the box. But I'm guessing on the details of this due to lack of experience with them.
[Edited on 10/9/10 by coyoteboy]
[Edited on 10/9/10 by coyoteboy]
Maybe one (or would it be two) of the electric shifter kits would minimise the missed gear changes?
I ecu controlling two engines sounds difficult but maybe MS would be a better idea.
quote:
Originally posted by tomgregory2000
there is a twin engine tiger somewhere
might be worth looking at that for some info
link to tiger click
I'd only have 1 ecu to 2 engines if you have a solid crank or output linkage and guaranteed gear selection, then it would effectively act as one
engine. Otherwise it's got to be a pair, the risk of running the wrong timing on one that's slightly out is too high. I may be able to
re-write a chunk of the MS firmware to do some of the between-engine-difference monitoring but writing twin-engine encoders would be a whole re-write
of the code, and not even possible on the MS1 (not looked at MS2 in that much detail). They're not expensive enough to warrant that level of time
expenditure.
[Edited on 10/9/10 by coyoteboy]
quote:
Originally posted by coyoteboy
I'm not sure they would be fighting that If you have a physical parallel link on the stick they either both go into gear or both don't.
I think Chris from ZCars told me, in order to get the 4wd twin engined car to turn and handle there were £10,000 worth of electronics required.
The last time I spoke to Chris and was talking about twin engines and the like he said forget it, have a single mid engined lightweight powerful bike
engined you will go quicker around a track and it will be cheaper and much more reliable
Cheers
David
Sure, but we're talking about minimising mis-shifts, not eliminating them entirely as that's as open to operator error as it is mechanical error, but I suppose it's just one of those things where you have to do it to quantify it. The twin shifter idea makes sense in that you can feel with each half of your hand when each engine drops in. If pneumatic/electronic shifting could 100% eliminate mis-shifts I could do that with some ease, I'm already working on a similar system but it's as yet untested.
minicooper -it'd be interesting to discuss it with him and exactly what those electronics are and the reasons behind it. I'm not saying
he's wrong, far from it, but I'd like to hear what he has to say with technical discussion so I could make that decision myself. We're
not talking a machine for racing, it's more of a "I'll do it because I can and for fun". I can probably create all of the required
electronics myself, as part of the fun. I won't do it if it's significantly poorer than a cheaper and simpler alternative of course, but
currently it looks about the same price as a decent 1ltr+ mid engined car.
[Edited on 10/9/10 by coyoteboy]
The Fifth gear episode on the Tiger is HERE btw
getting them in sync in a strait line is one thing, but what about when you turn a corner ?
then all 4 wheels need to turn at different speeds and the front axle needs to go slower than the rear (as its on a slightly smaller radius)
If you really must have two engines, it'd be much simpler to have both of them connected / geared together driving a central diff....
and even simpler again to just use one big engine...
There have been loads of twin engined cars on the modded car scene since the 90's, like Mk1 golf, mk3 golf, R5GTT, MK4 escort pickup effort etc
etc and they all worked with separate engines and gearboxes. All of these were road reg'd so I don't think it's illegal in any way.
The mk3 Golf even had a 2.8VR6 in the front, and a 2.9VR6 in the back, so definately a mismatch but I don't think it matters. The more powerfull
engine helps the less powerfull engine to accelerate, like removing weight would help it accelerate. There isn't really a constraint on how fast
an engine can reach its limit, so the more powerfull one helping it get there quicker doesn't hurt at all.
The one's I have seen have all had the twin gear levers that can be locked when both engines are to be used.
I guess under engine braking there could be an issue with one axle slowing at a higher rate than the other but when you consider a std road car, there
is only ever 1 axle slowing or speeding up so that's as much of a mismatch as is possible.
Look it the history books of the result of John Coopers twin Mini, I believe he spent some time in hopital as a result of his attempt at a twin engine setup.
quote:
getting them in sync in a strait line is one thing, but what about when you turn a corner ?
Hmm and maybe something like a GSXR600 with a slipper clutch as a possibility to limit some of the effect of one engine pushing the other ?
it would be a real engineering challenge as a home build and if you want to build it then go for it
I just can't help thinking it would be cheaper and easier to just stick a turbo on the one engine......
You're probably right, it would be simpler. Sticking a turbo on things is not necessarily easy thought, any of the lightish-weight engines that
can be turbocharged require significant modification to do so (cost of the engine again really to lower compression etc) and then have clutches and
gearboxes that can't cope with 2x the power output etc etc.
I have a possible donor for a normal car engine option that I can easily get to 300hp, but it's not 4wd. And not sequential.
What's a sensible, cheap bike engine I can get to ~200hp without significant internal mods and then a subsequently unreliable timebomb of an
engine, and then not have traction problems? Genuine question, not having a go!
I dont think the engines fighting each other is that much of an issue, in every 2wd car the unpowered axle is fighting the driven one all the time,
seems to work ok so far!
I know it's not just quite that simple but if one engine is'nt putting quite the same power out as the other it'll just not be pulling
quite as hard as the other.
If you picture a car being moved without the engine running with one bloke at the front pulling & another at the back pushing, if the one at the
back pushes harder than the one at the front pulls then the rope from the front bloke doesnt suddenly go slack & the car catch him up, he's
still contributing to moving the car but just is'nt working quite as hard.
And if the bloke at the back finds out he'll be pissed off but that probably wont happen to the engines!
I've just thought though, one thing that would'nt be so good would be if say the front engine suddenly died (snapped a throttle cable?)
while you were powering out of an opening corner, you front wheels get engine braking while your rears are pushing hard = brown trousers
[Edited on 10/9/10 by hillbillyracer]
Twin engine set ups are very common in Autograss racing, I think its class 10 cars!
I'm sure Google will prove a great resource for this!
I believe there are even specific suppliers of the components to link to engines and transmissions who sell to the Autograss boys!
Yes very popular in Autograss, but there is no 4wd class (they're fast enough with 2wd!) & all engines must drive through a common connection of some sort before driving the wheels.
OK so there's been some fairly decent discussion here, I like the fact that there have been a few negatives thrown at me so what I'm going to do is go away and try to summarise them all, along with weightings, against other power units (V6, highly strung 4pot, single large bike) and make a decision on which to settle on and design around. Thanks to all for taking the time to argue through it with me!
thinking today about the problem of them ending up in different gears, and theres a fairly simple solution. Have both engines with their normal rev
limiter via their own seperate ECUs, and have an additional rev limiter that would look at both engines, and if EITHER hits the limit, cuts the spark
to BOTH engines, thus preventing one being over revved.
Resync by having a seperate lever that only changes gear on one engine. This could be combined with a flat shifter on each too, if you have money to
burn.
Torque bias can be sorted simply by having the two throttle cables connected to different points on the accelerator, so one engine gets a little less
gas than the other. Make it adjustable and im sure with an afternoon on track you could set it up well.
Then turbo both.
My layout of choice would be a normal locost chassis, with one engine backwards in the normal engine bay powering the front wheels, and one in the
front of the passenger footwell driving the rear wheels. Still leaves room to scare a small passenger!
IVA seem to be happy with a twin-engine setup even if it's one per axle, providing I can fill in all the boxes on teh application form!
look up russ bosts original furore two engines two wheel drive each engine one wheel (no direct connection) nothing trick just a split double gear stick.both engines completly seperate. worked real good.
quote:
Originally posted by Canada EH!
Look it the history books of the result of John Coopers twin Mini, I believe he spent some time in hopital as a result of his attempt at a twin engine setup.
a mention was made of massive torque steer with the engine set up to drive one wheel on the furore original No such thing one engine off half the performance (on either engine so drive shaft length made no difference at all, if my finances eventually permit twin engines is my prefered way can be done and has been done and very simply, and proved to work.although one at each end would give so massive traction and big big smiles.