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View Full Version : Could you change the power split front to back eg 70% rear 30% front



Davezj
15-09-2013, 02:52 PM
Well as the title says, is it possible?
could it be done, if so, what would be involved.
what is the best power split to kill the massive understeer we have in the VR4, (50-50, 60-40, 70-30, 80-20, etc)
i know you could say just go into the corner at a slower entry speed, but that is not what i am asking.

this is another one of my what if, is it possible threads.

let the discussion comence, what are your thoughts.

Chris.W
15-09-2013, 03:08 PM
If I remember rightly the 8g VR4 although 4wd is biased towards the rear anyway. Somewhere between 60-40 & 70-30.

Nick Mann
15-09-2013, 04:01 PM
On rolling roads the rear wheels do see more power than the front. It seems to be a 50:50 split until the power levels climb, then the difference is more noticeable. The vr4 is too heavy to turn in fast, the 4wd lends itself to a slow in fast out approach and the ayc helps that too.

Davezj
15-09-2013, 04:02 PM
i was under the impression the split was something like front 48 and rear 52.

i am not sure but if someone knows for sure let it be known.

SGHOM
15-09-2013, 05:46 PM
The vr4 is too heavy to turn in fast, the 4wd lends itself to a slow in fast out approach and the ayc helps that too.

Hmm??

thinking about that, taking the perfect corner, what do you think should be your entry speed... apex speed... & exit speed?

Davezj
15-09-2013, 06:07 PM
entry speed is dependant on grip, and i would have thought the more power you put through the front wheels the less grip you have.
i would have thought once you have finished the turn in and have started to apply the throttle on the way out of the corner you could put more power through the front wheels to pull you out of the corner.

i understand the slow in fast out approch, but i was more talking about chaging the actual power split like the audi R8 20 front 80 rear, could it be done and with what. i presume it would be some other kind of center diff.

Nick Mann
15-09-2013, 06:30 PM
Hmm??

thinking about that, taking the perfect corner, what do you think should be your entry speed... apex speed... & exit speed?

That's a piece of string length question! Vicky had a 206 GTi for a long time, so it is easy for me to compare that and the VR4. The 206 would turn in and change direction at phenomenal rates, but you couldn't plant the throttle round the corner, you had to feather it. The 206 would turn in a lot better and at higher speed, but the VR4 would exit most corners faster I'd say. The VR4 slingshots out of a corner. I'm not known for being slow on track, so I'd say my approach is not a bad one.

scott.mohekey
15-09-2013, 07:35 PM
You can replace the center diff with a Cusco Tarmac which alters the bias towards the rear. Kenneth has one I believe.

Louis
15-09-2013, 07:39 PM
Hmm??

thinking about that, taking the perfect corner, what do you think should be your entry speed... apex speed... & exit speed?

It also depends on the car.
Rear wheel drive, front wheel drive, and 4 wheel drive are all slightly different approaches.

Also the answer to the question is:
S AYC
:)

Louis
15-09-2013, 07:44 PM
Also, personally I would not agree with VR4 's being prone to massive under steer!.
Any more than any other car!
If anything I would say they were a lot better than a lot of cars on the understeer.

What tyres are you using?

SGHOM
15-09-2013, 08:05 PM
Sorry for the slightly off topic comment, but I spoke extensively to Richard [physician] about this.
As a track day driver, as you know, he was superb. He also bought the book...studied the theory... & put it to good practice.

His thoughts & learnings were.... regardless of car, ie; fwd. rwd. or 4wd...... the entry speed, apex speed & exit speed should be exactly the same to take the 'perfect' corner. :)

So therefore, would changing the bias make any difference? It's surely the way you drive?




ok..... coats on :(

Louis
15-09-2013, 08:18 PM
entry speed, apex speed & exit speed
So: 50, 45, 50.
For every car and every corner, problem solved???!!!.

So a 4wd sports car has No advantage in a corner over a 1000cc front wheel drive Nissan???.


(Cat, pigeons) :)

Louis
15-09-2013, 08:25 PM
There are videos out there (and on here) that show the advantages of SAYC over other diffs. They also explain in basic terms how to make the most of the system when driving.
Have a look at them.

Doesn't matter what your driving, if you go in too fast for a particular car, you will get understeer.

SGHOM
15-09-2013, 08:40 PM
Doesn't matter what your driving, if you go in too fast for a particular car, you will get understeer.

Exactly my 'off topic' point ! every car has different characteristics. the point I'm trying to make is to take a corner perfectly, you need to know how the particular car will take it ! so going in too fast will cause understeer. slow in... fast out?? still not the right way !

If, for example, redgate [donington] is a 60 mph corner max for a certain car.... that should be the max throughout the corner. 50 mph for some cars.... maybe 90 mph for some !!

do you get my point?

Kenneth
15-09-2013, 10:13 PM
Your maximum speed through every part of the corner is determined by grip. However with changes in force direction, weight transfer and all that other stuff the amount of grip you use for lateral adhesion (not running off the tarmac) vs acceleration can change dramatically.

Our cars suffer a asymmetric weight distribution. Because the back end is lighter, the lateral grip used to turn a corner at a certain speed is less in the back than in the front (force being a product of mass and acceleration). Therefore, you should be able apply more forward acceleration in the rear before exceeding traction.

Not only that, depending on your tyre budget, you can benefit from having more acceleration in the back than the front, using tyre slip to rotate the rear of the vehicle at a higher rate than the front to increase turning speed. Not good for rear tyre life though.

With 65/35 rear/front torque split (got to add that I have front helical, rear plate but no centre LSD), my Galant still has a lot of difficulty in breaking traction in the rear on a good surface.

I am quite a fan of Richards. I am pretty sure what he said is the best overall strategy in terms of smooth and consistent lap times (some would say perfect laps) however not sure that you could categorise it as the fastest way.
Personally I do it mostly his way because I don't like crashing, the "fastest" way always comes at greater risk and things like trail braking, rear rotation give me the runs :P

On topic, yes you can run asymmetric power distribution. To do so you need a planetary gear centre differential.
A planetary gear has essentially 3 rotating parts. If you turn any part, the other 2 will turn at various speeds determined by the gear sizes etc. The interesting thing with a planetary gear is that if you lock together any 2 of these, the whole assembly must (but can) run at the same speed. As a centre diff, the outer housing (the planetary carrier) is connected to the final drive and so rotates at the final drive speed.
The inner (sun) gear is connected to the front, the annulus attached to the rear wheels.

When grip is good, the sun and planet carrier are locked by the road surface, therefore gear speed is the same across the entire gear assembly. Any change in speed across the front and rear causes the planetary gear to move to accommodate.
However due to the annulus having gearing advantage over the sun gear, any force applied to the annulus is distributed at 65% to the annulus and 35% to the sun gear (at least in the case of the cusco tarmac gear diff)

Fairly simple arrangement. Expensive to buy :P


Sorry for the slightly off topic comment, but I spoke extensively to Richard [physician] about this.
As a track day driver, as you know, he was superb. He also bought the book...studied the theory... & put it to good practice.

His thoughts & learnings were.... regardless of car, ie; fwd. rwd. or 4wd...... the entry speed, apex speed & exit speed should be exactly the same to take the 'perfect' corner. :)

So therefore, would changing the bias make any difference? It's surely the way you drive?




ok..... coats on :(

Nick Mann
15-09-2013, 10:43 PM
So Derek, how come racing drivers on a circuit don't hold a constant speed round a corner? I know Richard was quick - I have had the pleasure of following him on track, as have you..... :D

In reality you are still braking as the turn starts and already accelerating before the turn ends. You need to use all the grip available at all points of this - you can turn tighter when you are not accelerating or braking, but getting on the power sooner gives you extra speed all the way down the next straight. I like this description:

The fastest approach to a corner will involve a little combined braking and steering at the entry to the corner, followed by acceleration combined with steering as the corner unwinds. While braking/accelerating the corner must have larger radius than when the tyres are providing cornering force alone, otherwise the total traction vector will exceed the traction limit

Adam.Findlay
15-09-2013, 11:43 PM
what is the best power split to kill the massive understeer we have in the VR4,



The torque split is purely 50/50 on our cars stock, any one saying otherwise is only measuring slip in the center lsd when on a rolling road / hub dyno due to different loading on the front and rear axles. as when our centre LSD is active it limits the slip between front are rear output trying to maintain 50/50 split. hence why some people report bias to the front and other say bias to the rear...

changing the power split via use of a epicyclic (planetary) gear set such as a cusco tarmac gear like Kenneths will mainly only help you when accelerating out of the corner. as when you enter a corner you wont be on the gas.
so understeer on turn in can more or less only be cured by the addition of a helical front lsd, suspension setups and tyre choice (ignoring driver capability)

increasing the the torque applied to the rear wheels will more likely induce oversteer on corner exit but again it comes down to more than just the torque split. a good rear lsd is drastically cheaper than a tarmac gear and dramatically combats under steer, well from my experience it does.

Davezj
16-09-2013, 09:00 PM
So if i fit an S-AYC rear diff (that i have spare in the shed) i will not gain any more power/torque to the rear, but as the S-AYC is supposed to shift about 30% more touque left and right than the standard diff, so it should feel likethe cars is smaller and more nimble in the corners

Nick Mann
16-09-2013, 10:30 PM
It does give a slightly more rear wheel drive feel, but I suspect that is due to the extra torque movement. It makes naff all difference on turn in though!

Davezj
16-09-2013, 10:40 PM
yes, i understand that that to fast in will induce understeer whatever car you are in.
but my initial thought was to do with, could you do something to allow you to enter the coner at a high speed without experiencing the understeer.
I supose one thing you could do is get stickier tyres, but is that the only thing.

scott.mohekey
16-09-2013, 10:46 PM
You could always invent a device that generates a localized field of altered physics.

Kenneth
16-09-2013, 10:56 PM
You should be able to tune the suspension to remove understeer. Understeer is considered safer and therefore cars from factory tend to be setup more that way, if popular wisdom is to be believed.

Also consider that your car is heavier in the front than in the rear. If you go into a corner at any speed, the force applied to the front is more force trying to push the front off the road than the rear. This will increase the prevalence of understeer.
So if you even up the weight distribution, you should suffer less understeer.

Davezj
16-09-2013, 11:07 PM
fair point, there is a lot of weight upfront in the car especially when i get into the drivers seat.

but it would be nice to gear box in the bac.

so if weight distribution is a factor, and you can't reduce the weight at the front, is it then benificial to increase the weight at the back.
so instead of pushing a 1700Kg car into a corner that is nose heavy, you push a car that has 50/50 weight distribution but weighs overall 2000kg.

is there any benefit to increasing the over all weight to achieve 50/50 distribution.

Kenneth
17-09-2013, 01:12 AM
Overall weight will affect things like acceleration and braking. Better to be light than heavy.

I have to ask what you want your car for though. If you want to race around, light and nimble. If you want a cruiser that can accelerate nicely and do the odd track day and corner OK, then by all means increase overall weight (and add sound deadening etc)

At least things like battery to the boot will get a few KG moved, then you can think about aluminium front subframes, floating disks with alloy hats and alloy calipers (these can save a surprising amount of weight). Bonnet can save some also.

After that, things start getting a bit harder, how far do you want to go?

Davezj
17-09-2013, 01:29 AM
As stated in the first post,
this is another one of my what if, is it possible threads.

it is just interest as to what is possible and what is not without spending tens of thousands pounds. i know anything is possible if you through enough money at it and give it to someone else to do, but that is not my style. i like to everthing for myself so i understand it properly.

adaxo
17-09-2013, 11:24 AM
I've got one question for you in known, is there any way that I can check how weight balance looks like on my car at home? or where to go to ??

I asking as this thread just turn in the way that I was thinking for long time, ie, shift the weight from front to the back to get better balance. In my case I take a quite few kg off the front (manual conv, cf bonnet, tiny battery, lightweight flywheel) and add at least 50-60kg at the back (LPG tank/valve, big heavy sub and amp).


Interesting thing i just read there is the subframe, is not FL have alloy sub frame and pfl steel ? or i got this mix up with n/a Galant?

chris g
17-09-2013, 09:08 PM
I've got one question for you in known, is there any way that I can check how weight balance looks like on my car at home? or where to go to ??

I asking as this thread just turn in the way that I was thinking for long time, ie, shift the weight from front to the back to get better balance. In my case I take a quite few kg off the front (manual conv, cf bonnet, tiny battery, lightweight flywheel) and add at least 50-60kg at the back (LPG tank/valve, big heavy sub and amp).


Interesting thing i just read there is the subframe, is not FL have alloy sub frame and pfl steel ? or i got this mix up with n/a Galant?

Find someone, a racer, with corner weight scales...

Nick Mann
17-09-2013, 09:45 PM
As far as I know, all 8th gen vr4s have a cast front subframe.
We did a dyno day years ago where the garage could offer corner weight setup. I can't currently remember who it was though. It was near the m25 if I remember correctly.

Davezj
17-09-2013, 10:12 PM
i think it is the ST and ST-R that have the alloy front subframe, or it could be the n/a V6 as well. i can't remember.
but i was under the same impression as nick that all vr4 had the steel subframe.
i never found out why it was though, i had assumed it was due to the alloy one not being strong enough to handle the power/torque of the 6a13TT engine.
but this was just a guess.

the n/a V6 subframe is MR223582

the vr4 subframe is MR297541

i don't know if these are interchangable or not
it does not look like it, as the one in the VR4 has a large cut out for the transmission tunnel for the prop shaft/transfer case which the n/a V6 does not have and so the subframe for that does not have the big cut out in it.

but the 4wd ST-R will need to have a subframe of the same shape as the VR4 due to the space required for the transfer case and prop shaft.

but i can't check this as i don't have a chassis number for an ST-R.
if some has one i will check it.

scott.mohekey
17-09-2013, 11:15 PM
The ST-R/ST25 front subframe is an alloy casting of the same shape as the VR4 one. I have a couple lying around.

Davezj
17-09-2013, 11:33 PM
nice to know, Thanks
do you have a chassis number of an ST-R so i can do comparision in the future.

i think ST-R's are few and far between in the UK due to the fact you can import a VR4 easily, so i don't think many would go to the both of import an ST-R. plus the N/A V6 is plentiful as well.
so the chances of getting an ST-R over here is unlikely.

scott.mohekey
17-09-2013, 11:36 PM
I have an ST-25 chassis number at home. Largely the same except for 4 stud hubs and 4 speed auto.

Davezj
17-09-2013, 11:38 PM
if you could post it up or pm the chassis number it would much appreciated but there is no rush.

c0xxy
18-09-2013, 01:29 AM
dave, if you just type in a model code, it'll list every thing.
for ec5w you get subframes

64351

Kenneth
18-09-2013, 02:15 AM
Same mounting points, same basic shape but actually there is a fair difference in the subframes. The alloy one has more meat in a number of places, all necessary to maintain the strength with an otherwise weaker material.

I don't do masses of miles in my car, but I have been running an alloy subframe for roughly 3 years now.

The ST-R/ST25 front subframe is an alloy casting of the same shape as the VR4 one. I have a couple lying around.

scott.mohekey
18-09-2013, 02:28 AM
Same mounting points, same basic shape but actually there is a fair difference in the subframes. The alloy one has more meat in a number of places, all necessary to maintain the strength with an otherwise weaker material.

I don't do masses of miles in my car, but I have been running an alloy subframe for roughly 3 years now.

Yeah, sorry. I was being a bit too general there.

Davezj
18-09-2013, 11:15 AM
dave, if you just type in a model code, it'll list every thing.
for ec5w you get subframes

64351

good point i had forgotten that methed of checking the part numbers

rajvr497
18-09-2013, 09:25 PM
what about using a different gear ratio in the ear end,for e.g 4.0 rear diff from the skyline....

Nick Mann
18-09-2013, 10:10 PM
You would destroy the transfer boxes viscous coupling and possibly the centre diff in the gearbox too.

Adam.Findlay
19-09-2013, 11:36 AM
what about using a different gear ratio in the ear end,for e.g 4.0 rear diff from the skyline....

1- using a lower 4.0 instead of the stock 3.3 ratio diff in the rear will mean that the rear wheels will want to spin SLOWER than the fronts. in effect having the opposite effect
2- having different ratio diffs does not change the torque split given by the centre diff, the center lsd will always try and maintain 50:50. all you will acheive by having 2 different diff ratios will be the front wheels fighting the back wheels via the center lsd causing the centre lsd to fail. and once the center lsd has failed (if it does not completly destroy the transfer case) the speed difference between front and rear outputs will put excessive load onto the center diff which will most likely cause that to fail.

Z-Kev
29-11-2013, 07:43 PM
Has anyone tried a slight widening of front track to aid turn in on these?

Davezj
29-11-2013, 09:28 PM
i don't thinks so intentionally, but i am sure there are people who have fitted wheel spacers if that is what you mean, not sure how wide you can go without modifying the front arches.

Kenneth
29-11-2013, 10:40 PM
Heh, thread revival reminded me... I have some pictures for those who like to see things visually.

Actual unit beside standard centre diff.
65526
A couple of pictures from the web of what it looks like when taken apart. A work of art almost, just look at the size of the gears! 4 planet gears of that length should hold some serious torque.
As you can see from the pictures, the outer housing (connected to the final drive inside the gearbox) is connected to the planet carrier, the annulus is connected to the rear drive and the sun gear is the front drive.
In this manner, when there is a speed difference between the front and rear wheels, effectively the annulus and sun rotate in opposite directions (or at least different speeds) and the planet carrier continues to freely turn at whatever speed.
65525
65527