Differentials For Landspeed racing.

Moderator: DLRA

User avatar
Dr Goggles
Posts: 1310
Joined: Tue Jul 05, 2005 11:23 pm
Location: Right behind you Chief !

Differentials For Landspeed racing.

Post by Dr Goggles » Tue May 19, 2009 6:25 pm

Hi everyone. This is a thread for people to wax lyrical about diffs. The 9 inch does not rule in LSR so tell us everything you know ....what make ,what ratio, what centre, what axles what have you broken?...put it here.

..........and while we're here ......I'm looking for a 7&1/2 inch 10 bolt Diff. It has to be series 2.They have 28spline axles.

The numerically highest ratio for this is a 3.08.

We intend to get a torsen carrier and will be getting the Ring and Pinion set from the States but I want to pick some brains here to see if there was an Aussie car( rumour has it WB six cylinders and VB/VC Commodores ran them).

My source of info in the States reckons late sixties Camaros had them there were also T/A's and some front wheel drives..Caddys maybe , I'm not sure there....However,I don't want to have to freight a housing from the States if we can help it.

If you're really really nice to me I'll tell you why we want one... :?
...few understand what I'm trying to do , but they vastly outnumber those who understand why..

ben james
Posts: 279
Joined: Mon Dec 12, 2005 6:45 pm
Location: melbourne

Post by ben james » Tue May 19, 2009 8:24 pm

is that the what grumms monaro has in it
ben james dlra#389
moriwaki monster.

User avatar
Dr Goggles
Posts: 1310
Joined: Tue Jul 05, 2005 11:23 pm
Location: Right behind you Chief !

answers not questions

Post by Dr Goggles » Tue May 19, 2009 9:44 pm

ben james wrote:is that the what grumms monaro has in it

I thiiiiiiiiiiiiiink he has a 10 bolt , he'll pipe up and tell us no doubt.
there are 8.2 and 8.5 inch versions, then there is the 12 bolt I am not an expert on either ....but it's the 10 bolt 7&1/2 I'm interested in.....for now, here......
can't credit this image because I can't remember where I got it from, thanks whoever you are......

Image
...few understand what I'm trying to do , but they vastly outnumber those who understand why..

User avatar
Lynchy
Posts: 1099
Joined: Mon Mar 07, 2005 6:12 pm
Location: Brisneyland

Post by Lynchy » Wed May 20, 2009 1:10 am

I saw the toughest looking diff just the other day. It was out of a 1920's Vauxhall. It looked like it was out of a tank!

grumm441
Posts: 522
Joined: Mon Nov 14, 2005 5:43 pm
Location: Buggery, a tidy town
Contact:

Post by grumm441 » Wed May 20, 2009 10:41 am

No my Monaro has a nine inch and a quad cam v6
Actually my Monaro has some wierd limited slip , the likes of which i have not seen before. I know that I can't buy a rear cover gasket for it
They make it
I make it work

Rob
Posts: 1092
Joined: Wed Jul 06, 2005 5:30 pm
Location: Richmond, NSW. DLRA #888

Post by Rob » Wed May 20, 2009 1:19 pm

Telephone book covers Grumm,

Used 'em for years :lol:

Cheers,
Rob
I owe, I owe, so off to work I go.

grumm441
Posts: 522
Joined: Mon Nov 14, 2005 5:43 pm
Location: Buggery, a tidy town
Contact:

Post by grumm441 » Wed May 20, 2009 2:03 pm

Rob wrote:Telephone book covers Grumm,

Used 'em for years :lol:

Cheers,
Rob


White or yellow?
They make it
I make it work

nitro-nige
Posts: 73
Joined: Fri Jan 19, 2007 3:38 pm
Location: Melbourne

Re: Differentials For Landspeed racing.

Post by nitro-nige » Wed May 20, 2009 8:34 pm

Dr Goggles wrote:If you're really really nice to me I'll tell you why we want one... :?

It's obvious... the tank is going 4 wheel drive!

Have you considered asking over at ozerodders or one of the old holden websites?

Great talking point though. Ford (8" & 9") have better bearings, GM (10 & 12 bolt) have better tooth profiles. Why not turn the motor east west and use a chain drive :shock:

User avatar
Dr Goggles
Posts: 1310
Joined: Tue Jul 05, 2005 11:23 pm
Location: Right behind you Chief !

this blokes up for it

Post by Dr Goggles » Wed May 20, 2009 9:32 pm

nitro-nige wrote: Why not turn the motor east west and use a chain drive :shock:


When we run with a "wee" motor that may well be the way we go, in the mean time we've spent a stupid amount of time building what we've got.Our options for increased speed are , well, two. We build a motor that will rev, 7500 or 8000 is what we'd need, you all know how much that can cost, and , it might break. Or , secondly,gearing, we have a Borg-Warner LSD at 2.77.....if we had a 2.4 we'd be doing about 8%faster in each gear....and there are lower ratios in the 7.5 10 bolt. It seems , going on the rev v speed from our runs this year at Gairdner that we weren't wheel spinning( I'm drawing the conclusion that we have a low resistance shape), we don't have much power(!!!!) so it would indicate that the motor, as it is, could pull over some steeper gearing, that's why we're after the 10 bolt. :shock:
...few understand what I'm trying to do , but they vastly outnumber those who understand why..

nitro-nige
Posts: 73
Joined: Fri Jan 19, 2007 3:38 pm
Location: Melbourne

Post by nitro-nige » Thu May 21, 2009 1:36 pm

Doc

I'd be careful about your assumptions. When Chris was running his roadster at Bonneville they were have trouble getting over 200 mph with the tall gearing. They actually dropped the diff ratio and have now run the record up to 229 mph. The problem they were facing was that the step between gears with the tall diff gears was pushing the engine revs too low. The motor was struggling to pull the revs back up to where it made big power.
Obviously what happens in an 800hp gas roadster won't be the same for a more slippery car like yours.
Wouldn't it be nice to have the budget for multiple diffs or one of them fan dangle quickchanges?

hawkwind racing
Posts: 593
Joined: Sun May 04, 2003 7:59 pm
Location: Captains Flat
Contact:

Post by hawkwind racing » Thu May 21, 2009 7:07 pm

Ive read that differential calculus works rather well :D
fastest busa in Captains flat pop. 200

User avatar
Dr Goggles
Posts: 1310
Joined: Tue Jul 05, 2005 11:23 pm
Location: Right behind you Chief !

ON IT

Post by Dr Goggles » Thu May 21, 2009 9:19 pm

nitro-nige wrote:Doc

I'd be careful about your assumptions. When Chris was running his roadster at Bonneville they were have trouble getting over 200 mph with the tall gearing. They actually dropped the diff ratio and have now run the record up to 229 mph. The problem they were facing was that the step between gears with the tall diff gears was pushing the engine revs too low. The motor was struggling to pull the revs back up to where it made big power.
Obviously what happens in an 800hp gas roadster won't be the same for a more slippery car like yours.


Absolutely,

ideally we all want a close ratio box, a push to 80mph and 800hp......not gonna happen for us. With a dyno sheet and a little calculation we could plot the shift points against speed , it would give us the step between each gear then the power curve would show us what power we have available at those points, the unknown would be the exact Cd so that's when the guesswork would start. We can't even afford that.

The roadster has a larger frontal area and a vastly different rear end treatment and so we can safely assume ( there's that word again) that they're going to have something like twice the drag.On basic terms that means half the (useable)power, but more importantly it means the shift time becomes more critical( the car slows more quickly when rolling) , AND the "powerband" crisis is more severe( higher wind-resistance when the motor is under the cam and bogging down).

This is yet another reminder that aero is the key to going faster, the adage " double the speed by cubing the power" is for a given shape, the better that shape the lower the starting price is for power.
In a perfect world we would have a motor that had a torque peak at the point where the revs drop to AFTER a shift, and a power curve that kept going up, then after carefully estimating the total drag we would calculate the force applied to the front of the vehicle at the speed we need to run to break the record, we then find the area on the dyno chart ABOVE that power rating and then choose a diff ratio that puts the revs there AT THAT SPEED.

Seems dead simple doesn't it.

The reality is that we can't afford any of that .

What we can afford to do is buy ring and pinion sets, change our rear bulkhead so we can use a different housing AND have an intermediate step by subbing smaller rear tyres.......between that and the range of ratios available for the series 2 7.5 inch 10 bolt we just MIGHT be able to make the car go as fast as possible and avoid the ratio "hump" of which you speak......

there'll be more.........
...few understand what I'm trying to do , but they vastly outnumber those who understand why..

David Leikvold
Posts: 977
Joined: Mon Apr 16, 2007 11:57 pm
Location: Brisbane

tars

Post by David Leikvold » Fri May 22, 2009 8:27 am

Don't forget Doc that up to 200mph you can run V or Z rated road tyres, so you could experiment with different diameters (and widths) without having to spend a fortune on the Goodyear LSR tyres.
Good, Fast, Cheap, pick any two!

User avatar
Cookey
Member
Posts: 443
Joined: Mon Oct 03, 2005 7:36 pm
Location: South Australia

Post by Cookey » Fri May 22, 2009 8:58 am

I now have 2 of these rear ends for my project and can't see what all of the fuss is about :roll: :roll: :roll:
Image
Image
Cheers,
Tony Cooke
DLRA # 363

nitro-nige
Posts: 73
Joined: Fri Jan 19, 2007 3:38 pm
Location: Melbourne

Post by nitro-nige » Fri May 22, 2009 9:54 am

2!! now that;s just being greedy.
Doc I'll distract him, you nick off with one.

Post Reply