FWD to AWD conversion

[Rokita]

i have FWD car in which engine is mounted in transverse, im planning to make AWD conversion there are available AWD gearboxes that fit my engine but those use electrical clutch before rear differential to turn on AWD only when needed
thats not what im looking for
i need all wheels to be powered all the time since this gearboxes dont use any central differential running this setup with "welded" clutch on rear diff will probably destroy the gearbox

my idea was to take existing gearbox and mount engine longitudinally

what are your thoughts can it work or trying to is just waste of time?
because for me it sounds like it really could work
im not concerned about weight balance because i would adres it when fitting a roll cage and since driver is on left side it evens the balance enough
gearbox linkage will be changed to hydraulic

 

[BrianPetersen]

Spot check. It appears that the rear axle ratio in a Honda CRV (don't know/care which generation) is 2.529:1. This is not the same as the final drive ratio in the transverse front-drive transmission - because the drive to the rear is taken from another set of gears driven from the front differential housing after the front transmission's final drive, with (presumably) a 2.529:1 speed-up ratio built into the front transmission to correspond to the 2.529:1 reduction ratio in the rear axls, so that (nominally) all four wheels are driven at the same speed (not counting the intentional slippage in the clutch that is actually used to supply torque through the rear drivetrain). This set-up is very typical of AWD systems that are based on transverse front-drive powertrains.

Better choice ... Seems that there is a VW Haldex rear differential assembly with a 27/17 tooth count, 1.588:1 reduction ratio. That is starting to get within the realm of plausibility when combined with taller gearing inside the transmission. It's still going to end up way shorter than stock but it's within reach of something that "could work".

 

[LionelHutz]

Has the use and speeds been specified? Tire sizes? Off-road guys do what is being proposed, I have a neighbor who found that 4.xx differential ratios still didn't give enough reduction.

 

[SwinnyGG]

I think you are in for a rude awakening unless you find appropriate 90-degree final drive and diff assemblies with extremely tall (ideally 1:1) final drive ratios.

For reference - by my math in whatever transmission gear is 1:1 (usually 4th in a 5 speed trans) with a 23.5 inch tall tire, back-to-back 3.2:1 ratio gives a wheel speed of 108 mph at an engine speed of 10,000 RPM. 10,000 RPM in 1st gear using a sensible 1st gear ratio is around 22 mph.

Calculate your ratios OP before you go too far down this rabbit hole.

Has the use and speeds been specified? Tire sizes? Off-road guys do what is being proposed, I have a neighbor who found that 4.xx differential ratios still didn't give enough reduction.

per OP this is a Honda Civic, not a unimog.

 

[Rokita]

I calculated everything and it looks like that

speed at 6500rpm on 1st gear is 46km/h
with longer ratios, crv differential + bigger wheels it would drop to 30km/h

6500rpm on 5th gear is ~200km/h
after modifications it would be 120km/h

since i want to increase redline of my engine from 7800 to 11000 it would be
5th 206km/h at 11000rpm

not ideal but i would for sure have A LOT of torque

i personally had no luck in finding shorter final drive differentials
haldex is a bit too big to fit in my design
but with 1.588 final drive i would actually go faster than fwd setup
5th 213km/h at 6500rpm

after talk with u
If I decide to go AWD I will keep it transverse by going the shorter way of swaping CRV power train

but talk is yet not over

now I need help in understanding the AWD powertrain of CRV

what will exactly happen when I try to use the car with AWD turned on? does the lack of center differential cause damage ? how can I work around it

the thing is: is it safe to drive fast with awd locked on and take corners?
is there a chance that when turning difference in speed of axles may cause over/under steer

from my basic under standing: the avg radius that rear wheels follow when turning is shorter than front wheels
is that right?

so then I guess the rear wheels will try to make a burnout when taking a corner what will for sure cause problems in grip
Am I right?

what should I do to make it work
using the CRV AWD module is not possible because its integrated into the ECU
and im either going to keep my chipped ECU or go for SPEEDUINO
which neither one of them can control AWD

 

[BrianPetersen]

You need to find out what's inside the magic clutch that engages and disengages (more properly, modulates) the rear drivetrain, and probably develop your own control strategy for it.

Odds are, there's a pulse-width-modulated (PWM) control solenoid in there somewhere.

Or ... You transplant the entire vehicle electronics and powertrain module and wiring harness etc of the CRV into the Civic such that it has no knowledge that it's inside a bodyshell of a different shape.

 

[Rokita]

OK so i digged up a bit and there is a solution welding up the clutches in rear diff then installing a drive shaft from land rover with viscous clutch

there are no numbers but its assumed it splits torque 70% to front

 

[BrianPetersen]

So you want to have the rear wheels locked to each other even though they're not driving most of the time? That's sure to have some handling characteristics that are ... interesting.

What, exactly, do you propose to be doing with this vehicle?

 

[LionelHutz]

Going fast and turning corners????

Why not take the FWD drivetrain out of the front and install it in the rear? Adding weight to the front of a vehicle rarely helps it turn corners.

 

[BrianPetersen]

If the objective is to go fast and turn corners in something that has a Honda badge on it, the appropriate course of action is to sell the existing car (as-is) and buy a current-generation Civic Type R ... accepting that even this does not have all-wheel-drive.

If the objective is to get up a steep driveway in winter without having to shovel snow first and with something that has a Honda badge on it, the appropriate course of action is to sell the existing car (as-is) and buy a CRV or whatever the all-wheel-drive version of the Fit/Jazz is, which already has all-wheel-drive built in from the factory and comes complete with warranty.

If you can forgo the Honda badge, and you want to go fast and turn corners in something that has all-wheel-drive, buy a Subaru WRX. Or a VW Golf R.

 

[gruntguru]

If the objective is to get up a steep driveway in winter without having to shovel snow first and with something that has a Honda badge on it . . .

. . . reverse it up.

je suis charlie

 

[BrianPetersen]

True but the point is that I don't understand the point of doing a potentially failure-prone home-grown butcher job that is (to be brutally honest) unlikely to be successful, when you can buy something that does what you want it to do off the shelf with a warranty.

Original poster needs to explain this to me.

 

[SwinnyGG]

While my opinion is that OP is in way over his head here.. you guys don't sound like much fun. Never had a project car? Never tried to build something just to see if you could do it?

 

[GregLocock]

Grins, yes, here's one of mine.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[LionelHutz]

per OP this is a Honda Civic, not a unimog.

You've never seen a 4x4 Civic before?

 

[BrianPetersen]

I "get" project vehicles, I have one, a 1990 Yamaha FZR400 that I completely rebuilt and refreshed from ground up more than 8 years ago and spent more than the bike was worth doing so. But, I still have it, and I'm still riding it, and I've put 25,000 km on it since, and it runs well, and I get people asking about it whenever I am out and about with it. Works for me.

I am encouraging the original poster - who seems to have disappeared! - to set some objectives, targets, design criteria. Then evaluate feasibility and alternatives, and make sure to understand most of the hurdles that will need to be overcome ... with the understanding that you'll never predict all of them, so expect the unexpected. It is an engineering project.

 

[BrianPetersen]

You've never seen a 4x4 Civic before?

Remember the "Wagovan", a.k.a. Honda Civic Shuttle?

They actually had two generations corresponding to Civic generations 3 and 4. Both were primarily front-drive with (I think) a viscous-coupling drive to the rear. First generation used a live rear axle. Second one used IRS with the rear diff mounted to the rear subframe. I think the mechanical layout of the
second-generation one (Civic generation 4), is what eventually morphed into the first-generation CR-V.

Until very recently, the mainstream models of the Civic have never been designed to accommodate all-wheel-drive. I think the rear subframe of the new one will allow it, although they still haven't done it.

 

[LionelHutz]

Expecting to make the engine turn 11,000rpm makes me suspect it'll never get built, at least no how the OP is questioning here.

 

[SwinnyGG]

Honda K-series builds are hitting the 11k RPM mark without all that much drama. Ain't cheap though.