mickvonmin
RMS Regular
its only an option on how to lock the 4wd at this stage
awd monster mini project
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sailerbill
RMS Regular
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thanks guys for all your imput but i think its time to move on with this so we will post as we go forward
many thanks Bill
many thanks Bill
stevieturbo
RMS Regular
You could ask why so many people buy 4x4's, yet will never leave bone dry tarmac ?
And locking the centre diff/clutch pack permanently is not a sensible option. It will create horrific understeer.
Nicky
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Much like driving a Freelander with a ****ed viscous coupling which is mounted as part of the prop, whereas its mounted in the front of the rear diff in the CRV. If its seized (or if you deliberately locked it) it would drive horrendously.
It looks like all this talk of changing final drives has confused the original issue, and seems that it isn't easily achievable in this clutch driven 4wd set-up as opposed to that of an Evo or similar. Surely building the desired drivetrain into the car and then working on ratios (when you have a proper understanding of them) if necessary is the right way to go? For all you know, with all the weight of the Mini, the original CRV FD might be perfectly suited to it...?
If you're using the CRV for the reason that's its free or already there, it may actually be more financially viable and practical for driving purposes/getting power down and easier all round as far as fabrication work goes to go and buy a cheap Evo or Subaru and build that into the shell instead. At least that way you won't be turboing an NA engine or trying to lock unlockable diffs and end up with an absolute headache.
Just my 2 pennies worth, but unless you're willing to throw big money at it like any other Mini/CRV build that's documented online, I'd avoid it like a dose of the clap and start off with something already turbo'd with a proper sports car 4wd system.
sailerbill
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- #105
nicky your right i might be thinking of fixing something that’s not broken
may be worth starting with (as you say )what we have and fixing what needs fixed
but all the feedback on possible outcomes are very relevant and will help with the decision on how we move forward
I have the crv now and got the Mx5 subframe today just a set of coilovers to get and some pipe and flat bar
may be worth starting with (as you say )what we have and fixing what needs fixed
but all the feedback on possible outcomes are very relevant and will help with the decision on how we move forward
I have the crv now and got the Mx5 subframe today just a set of coilovers to get and some pipe and flat bar
stevieturbo
RMS Regular
That does make a lot of sense.
I dont think a Subaru front end would be practical though given it's longitudinal layout. It may work, but the engine would need to be right up to the grill. Even then the distance from there to the front axle centreline might still be too great to be workable in such a short vehicle. It may be possible, although driveshaft angles could be very poor.
Evo...unless you get a car with all mechanical diffs, you're still into AYC hassles.
From a turbo perspective....it probably would be cheaper to source a complete vehicle of either of the above though and work from that, than building a kit from a n/a engine
Final drive and gearing in general is still important though. No sense having a car with such short gearing, 3rd gear may as well be 1st gear. It's the 13" wheels that are the killer here.
But as some of the CRV's seem to use a 2.0-2.4 engine...it might just be easier to drop the entire drivetrain in, engine and all and forget the 1.6 completely.
Nicky
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I don't doubt that gearing and final drives is are 2 of the most important factors here stevieturbo, but surely the standard gearing in the 2ltr CRV would be longer than that of a 1.6ltr Civic that the B16 came from, but would it not be brought back down to a suitable ratio by fitting the CRV box to the B16 engine and then putting 13" wheels on the car?
I know if you were to run the CRV box on the B16 engine and fit the standard sized CRV tyres, it would make for a brutally slow accelerating car as the rolling diameter of the CRV tyres would be much much more than the rolling diameter of a set of low profile 13's.
Getting that point across is the reason behind me saying build it and THEN alter final drives if need be, but I can't see there being much of a need, if any.
I know if you were to run the CRV box on the B16 engine and fit the standard sized CRV tyres, it would make for a brutally slow accelerating car as the rolling diameter of the CRV tyres would be much much more than the rolling diameter of a set of low profile 13's.
Getting that point across is the reason behind me saying build it and THEN alter final drives if need be, but I can't see there being much of a need, if any.
stevieturbo
RMS Regular
As already linked. Both the Civic and CRV appear to have final drives in the mid to high 4.x range, which is pretty short.
And altering final drives is not an easy task when you have two to change and there are no crownwheel and pinions available. No gear company has any interest in making a single unit and if you were lucky enough to find one, the cost would be well into 4 figures, maybe even pushing 5 figures. Gear cutting is not a simple or cheap task.
I'd be wanting a final drive in the mid 3.x range. Maybe 4.0 at the absolute highest. And if it was turbocharged and making some decent power, absolutely lower than 4.0:1
And altering final drives is not an easy task when you have two to change and there are no crownwheel and pinions available. No gear company has any interest in making a single unit and if you were lucky enough to find one, the cost would be well into 4 figures, maybe even pushing 5 figures. Gear cutting is not a simple or cheap task.
I'd be wanting a final drive in the mid 3.x range. Maybe 4.0 at the absolute highest. And if it was turbocharged and making some decent power, absolutely lower than 4.0:1
mickvonmin
RMS Regular
again, only one final drive would need to be changed but i'm clearly incapable of explaining it.
sailerbill
RMS Regular
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this sounds like bait mick
mickvonmin
RMS Regular
i'm just upset cause I explained it as best I could several times.
stevieturbo
RMS Regular
explaining and understanding are very different things.
mickvonmin
RMS Regular
maybe you could enlighten me?
explain please
stevieturbo
RMS Regular
It's already been very clearly explained.
I'll try and simplify it even further.
Take a single solid axle.. right wheel is your front FD, left wheel is your rear FD. As the diff in the middle is a LSD, or hydraulic VC as in the case of the CRV, no slippage or variation is allowed.
When both wheels are the same size, all is well. What you are proposing is changing the diameter of a single wheel. It simply will not work. They will be trying to turn at different speeds except they are locked together by a central shaft, so something has to give.
In the CRV case, it will destroy the centre diff unit.
stevieturbo
RMS Regular
Or to look at it another way.
Nobody in their right mind would fit 10" wheels to one axle of their 4wd car, and 20" wheels to the other. That is basically what you are proposing by changing the final drive in a single axle.
As coog says, the only vehicle you'd get away with this, is one with a fully open centre diff. Even then it would be bad though, as the diff unit itself would be working very hard to cope with the very different input/output speeds
Nobody in their right mind would fit 10" wheels to one axle of their 4wd car, and 20" wheels to the other. That is basically what you are proposing by changing the final drive in a single axle.
As coog says, the only vehicle you'd get away with this, is one with a fully open centre diff. Even then it would be bad though, as the diff unit itself would be working very hard to cope with the very different input/output speeds
mickvonmin
RMS Regular
good theory steve but irrelevant. normally id let this go cause i'm lazy that way and have no ego whatsoever when it comes to forum ***** talk but i'm doing some pretty drastic mods to bills mini so I cant have him loosing faith. if you'll remember, the confusion is over whether or not 2 final drives need to be changed to alter overall gearing ratios, the answer is no, this can be seen in the sketch below, I'm not out to make anyone look silly unlike yourself but please show me where, if you are correct, is the 2nd FD to be found.
I will give both prop cwp's a theoretical ratio of 3 to1 (in reality they areis a difference of 3% , I think this is to keep the hydraulic pumps primed but could be wrong). if we take the FD out of the equation all together, for every rotation of the diff, the front shafts will obviously turn once and the prop turn 3 times, at the rear diff, the 3 turns of the diff will again turn the rear wheels 1 rotation( same as the front). all of this can happen without even taking the FD into account as all it does is turn the diff at a ratio of gearbox countershaft rotation. regardless of what final drive is in the gearbox, for every turn of the diff, all 4 wheels will turn 1 rotation and the prop turn 3 times.
I will give both prop cwp's a theoretical ratio of 3 to1 (in reality they areis a difference of 3% , I think this is to keep the hydraulic pumps primed but could be wrong). if we take the FD out of the equation all together, for every rotation of the diff, the front shafts will obviously turn once and the prop turn 3 times, at the rear diff, the 3 turns of the diff will again turn the rear wheels 1 rotation( same as the front). all of this can happen without even taking the FD into account as all it does is turn the diff at a ratio of gearbox countershaft rotation. regardless of what final drive is in the gearbox, for every turn of the diff, all 4 wheels will turn 1 rotation and the prop turn 3 times.
But are you usng the MX5 back end???
You will have to match the FD on the mx5 diff to that of the honda front diff
The stock stuff straight from the CRV will work, no doubt about that. I was also reading there that the CRV uses a slightly different PCD on the Crownwheel bolts than the other hondas, and as such it isnt just a simple swap out for the CWP as you then have to bolt on the prop CWP, so something to look into there too.
You will have to match the FD on the mx5 diff to that of the honda front diff
The stock stuff straight from the CRV will work, no doubt about that. I was also reading there that the CRV uses a slightly different PCD on the Crownwheel bolts than the other hondas, and as such it isnt just a simple swap out for the CWP as you then have to bolt on the prop CWP, so something to look into there too.
mickvonmin
RMS Regular
mx5 hubs, subframe and wishbones. i didnt bother looking into differnent FD's as we are happy with the ratios from the crv box after finding out they are the same as what we have at the minute so thats news to m, the lowest standard honda FD i know about is 4.26, compared to 4.4 or whatever its hardly worth the effort.
My understanding is that you believe you can run the rear diff without changing the CWP because it will work at a 1:1 ratio of the output from the front CWP output ring. This would be the case if the ratio was 1:1 from the front output CWP to the rear input, but it isnt.
The MX5 WILL be either a 4.1: or 4.3:1
The CRV rear diff was 2.529:1
The CRV front diff was 4.562:1
so there is a set ratio for the output crownwheel on the front diff (most likely 1:2.529), allowing it to provide the rear diff with few enough turns to keep the 2.529:1 diff at the same speed as a 4.562:1 in the front.
What you are going to get with the MX5 4.1:1, is the back end turning at just under half the pace of the front, therefore causing massive binding issues in the transmission.
So basically the following:
engine turns gearbox
gearbox turns front diff approx 4.5 times
- front wheels turn once
- propshaft turns approx 2.5 times
propshaft input to rear diff (2.5:1) approx 2.5 times
- rear wheels turn once
or with MX5 rear end
engine turns gearbox
gearbox turns front diff approx 4.5 times
- front wheels turn once
- propshaft turns approx 2.5 times
propshaft input to MX5 rear diff approx 2.5 times
- rear wheels turn just over half a turn as it requires 4.1 or 4.3 input rotations to complete one output rotation.
As I mentioned before, personally I would be leaving ti all CRV for ease of install, although, if you happen to find an old RT4WD Civic Shuttle, use the rear diff out of one of those. They have the same final drive as the CRV rear diff, only you can lightly modify any D-Series LSD to fit in it which would suit your needs down to the ground.
The MX5 WILL be either a 4.1: or 4.3:1
The CRV rear diff was 2.529:1
The CRV front diff was 4.562:1
so there is a set ratio for the output crownwheel on the front diff (most likely 1:2.529), allowing it to provide the rear diff with few enough turns to keep the 2.529:1 diff at the same speed as a 4.562:1 in the front.
What you are going to get with the MX5 4.1:1, is the back end turning at just under half the pace of the front, therefore causing massive binding issues in the transmission.
So basically the following:
engine turns gearbox
gearbox turns front diff approx 4.5 times
- front wheels turn once
- propshaft turns approx 2.5 times
propshaft input to rear diff (2.5:1) approx 2.5 times
- rear wheels turn once
or with MX5 rear end
engine turns gearbox
gearbox turns front diff approx 4.5 times
- front wheels turn once
- propshaft turns approx 2.5 times
propshaft input to MX5 rear diff approx 2.5 times
- rear wheels turn just over half a turn as it requires 4.1 or 4.3 input rotations to complete one output rotation.
As I mentioned before, personally I would be leaving ti all CRV for ease of install, although, if you happen to find an old RT4WD Civic Shuttle, use the rear diff out of one of those. They have the same final drive as the CRV rear diff, only you can lightly modify any D-Series LSD to fit in it which would suit your needs down to the ground.
stevieturbo
RMS Regular
good theory steve but irrelevant. normally id let this go cause i'm lazy that way and have no ego whatsoever when it comes to forum ***** talk but i'm doing some pretty drastic mods to bills mini so I cant have him loosing faith. if you'll remember, the confusion is over whether or not 2 final drives need to be changed to alter overall gearing ratios, the answer is no, this can be seen in the sketch below, I'm not out to make anyone look silly unlike yourself but please show me where, if you are correct, is the 2nd FD to be found.
I will give both prop cwp's a theoretical ratio of 3 to1 (in reality they areis a difference of 3% , I think this is to keep the hydraulic pumps primed but could be wrong). if we take the FD out of the equation all together, for every rotation of the diff, the front shafts will obviously turn once and the prop turn 3 times, at the rear diff, the 3 turns of the diff will again turn the rear wheels 1 rotation( same as the front). all of this can happen without even taking the FD into account as all it does is turn the diff at a ratio of gearbox countershaft rotation. regardless of what final drive is in the gearbox, for every turn of the diff, all 4 wheels will turn 1 rotation and the prop turn 3 times.
If the CRV gearbox is as you have drawn it, then yes you are correct. It's a weird setup though. I guess that's why they moved the centre diff to the rear then, instead of up front as most 4wd setups.
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