What's the "Diff"-erence?

[SELfor50]

HAha... yeah corny subject.

So.... will a 6.9 Diff go onto standard 450?  It'd be less work than turning the 450 into a limo right?

Cause a locker will be better for the track yeah? 

[13B]

You actually want more punch out of corners for the track and esp. needed for hillclimbing.  the 2.65:1 out of a 6.9 would be hopeless behind anything but a 6.9...

Aim to get your hands on one out of a 350SE, something around 3.3-3.7:1 would be ideal, then lock it up into a "CIG locker" (weld it). 

The easy way to remember is that numerically higher difs increase acceleration, at the expense of top speed.  And vice-versa.

I think the 450SE/SEL diff is 3.07, which is still a little on the low side, but worked alright in my 450SE for autocross duties... never got the car out of 2nd gear though...

Ian.

[oscar]

How about a 280 diff?  3.69:1 or 3.92:1.  I'll have to do a check again what I got, but that could be my contribution to teamw116.  If we blow one up, there's the other one to try.  I thought a 350 has a 3:07 too, but I'll check tomorrow.

[oscar]

Hi Ossie, best not to trust specs. listed in books. A far surer way is to remove the cover and count the number of teeth. Best regards, Styria

No books, just repeating some numbers I wrote down from sclass' thread on reading the stamped numbers.  So, tomorrow I'll get my back dirty and climb under a couple of cars to check. 

[s class]

Dirty back maybe, but easier than opening diffs.  True though if you want to be absolutely certain, you have to count the teeth

[500eguy]

I know very little about diffs for the record...so what is best diff to install if you want better go?

[s class]

Johnny B, 'best' depends on what you want.  A higher ratio (such as found in a 280SE or more so a 280S) will result in the engine revving higher for a particular given speed.  If you want to blast off the line, then a higher ratio diff such as the 280 units will do that for you.  But also realise that your diff and rear axle joints will be working harder, and so could have a limited lifespan.  With such a diff in a v8 car you could actually find that overtaking capacity (at highway speed) is diminished, because you will not be able to drop from 3rd to 2nd at as high a speed as with the standard diff (or else the motor will over-rev). 

At your American and Aus sad speed limits, maybe it will be OK as at 100km/h or so, the v8 will be running just a bit faster and will feel more lively.  Here where we have decent speed limits  I think I would run out of revs. 

[500eguy]

what diff would be good for a good combo of Accel. and top end? The American speed limits are crap... the Island speed limits are worse... Did you know if you go 30 over they will put in you in jail and take away your license!

[s class]

what diff would be good for a good combo of Accel. and top end?

THose two aspects are mutually exclusive.  Any diff is a tradeoff between the two.  Given your low speed limits, I think you would want to sway towards the acceleration aspect, so a 280SE diff might help you out.  I think a 280S diff is too extreme. 

280SE : approx 130km/h at 4000 rpm
280S : approx 110km/h at 4000rpm.

[SELfor50]

Fellas, this is great!!  I've been wondering what the hell will help the tank get off the line quicker and i guess this is it?
(Along with maybe some nitrous and a supercharger  )

So i'm guessing the verdict is stick with the current diff for the first few months / runs and see how she goes.
My mate who drives this hill-climb track reckons his celica never got past 100-110km's so i'd say the 280 diff would be ideal?!

When transferring to a 2km track like wakefield - would it still be wise to use a 280 diff or something in between the 280 / 350??

I'll give ASV parts a call this morning and find out how much a re-conditioned 280SE diff is, the 6.9 diff re-conditioned wasn't too bad at all on price.  So i'm guessing the 280SE will be a bit cheaper.

Anyone got the skill to "lock it up" and do the welding?  (I've never touched one in my life!)

[13B]

Cam,

Since you're looking for a diff for competition use, you might also want to look at your auto.  I know you've got your heart set on a 4 speed box from a 350SE (would be a good choice but finding one, and all the associated parts for an auto-to-manual conversion, in any reasonable timeframe would be a headache). 

No, talk to an auto place about turning the standard 3-speed auto into a 'reversed, manualised, competition box', they should know what that means, but if they don't it means it no longer selects the 3 gears automatically, but you need to do it with the selector, and have much greater control over your rev range, particularly at higher revs when the auto feels like it should be changing up.  You'll also lose kick down, but that can be achieved easily enough by flooring it and moving the selector to 2nd.  Reversed means they change the orientation of the PRNDSL to LSDNRP or more easily remembered 123NRP, 1st is forward and 2nd and 3rd you pull back on the selector in a more logical manner.  Its also a good idea to install a lockout on Neutral, so it can't be pulled from 2nd past 3rd into N at WOT. 

Oh and the now useless kickdown switch?  Connect it to your NOS system - put the switch to arm it on the dash, but make the activation from the foot at WOT.

Almost as good as changing your diff ratio is putting the car on a weight-loss program, and on a 116 that would mean ditching the interior, electric window motors, putting in hand-crank front winders and nothing in the rear windows.  Ditch the glass for perspex, replace the drivers seat with a lightweight one, lose the a/c, lose the interior heating and ducting... you get the idea.

As far as engine mods, don't let that hold to back from starting competition - I've seen many upstarts who have delayed starting their club competition career, sometimes by years, because they felt they didn't have enough power to have a go.  Not so, and you have to start somewhere.  I've always said, with the w116 in particular, the greater handling and braking will somewhat offset lower power and heavyish design, compared with other 1970s cars. 

Ian.

[SELfor50]

Cam,

Since you're looking for a diff for competition use, you might also want to look at your auto.  I know you've got your heart set on a 4 speed box from a 350SE (would be a good choice but finding one, and all the associated parts for an auto-to-manual conversion, in any reasonable timeframe would be a headache). 

No, talk to an auto place about turning the standard 3-speed auto into a 'reversed, manualised, competition box', they should know what that means, but if they don't it means it no longer selects the 3 gears automatically, but you need to do it with the selector, and have much greater control over your rev range, particularly at higher revs when the auto feels like it should be changing up.  You'll also lose kick down, but that can be achieved easily enough by flooring it and moving the selector to 2nd.  Reversed means they change the orientation of the PRNDSL to LSDNRP or more easily remembered 123NRP, 1st is forward and 2nd and 3rd you pull back on the selector in a more logical manner.  Its also a good idea to install a lockout on Neutral, so it can't be pulled from 2nd past 3rd into N at WOT. 

Oh and the now useless kickdown switch?  Connect it to your NOS system - put the switch to arm it on the dash, but make the activation from the foot at WOT.

Almost as good as changing your diff ratio is putting the car on a weight-loss program, and on a 116 that would mean ditching the interior, electric window motors, putting in hand-crank front winders and nothing in the rear windows.  Ditch the glass for perspex, replace the drivers seat with a lightweight one, lose the a/c, lose the interior heating and ducting... you get the idea.

As far as engine mods, don't let that hold to back from starting competition - I've seen many upstarts who have delayed starting their club competition career, sometimes by years, because they felt they didn't have enough power to have a go.  Not so, and you have to start somewhere.  I've always said, with the w116 in particular, the greater handling and braking will somewhat offset lower power and heavyish design, compared with other 1970s cars. 

Ian.

Yeah, the manual would be nice - but realistically the auto is the way to go.  Will definately be looking at doing the gearbox thing you suggested...is this the same as a 'shift kit'?

280SE diff it is - been quoted $750 for a re-conditioned one.  All new guts..  would this bolt straight up to ol' silver or would it need a new tailshaft??

The NOS thing is a definite goer - a mate has NOS (and a supercharger) on his Torana and when i asked him what a 50shot would be like and if the engine could handle it, he said 50SHOT?? It would love it, he reckoned i could go a 100 shot and it wouldn't strain too much.  But this is coming from a bloke who put a 200Shot through his torana and blew the sh!t out of it!  He said no matter how good it is, you just want more.. 

But yeah, with the diff and gearbox done i'm sure it will add a LOT more up and go.
The weight loss thing has already begun.  with the front & rear bumpers removed and headlight wiper motors, lower horns (under the front grill) etc.
She has a noticeable improvement in the pick up area. 

As for the handling, i'm already well accustomed to how good they are for their size..... let's just say - i'm glad it could swerve and pull up at the same time..otherwise this conversation wouldn't be happening. 

So repeat question - after the purchase of the 280 Re-conditioned diff, anyone able to "lock" it up for me?   

[13B]

Save your $750, take up Oscar's offer on the free 3.69 diff - get the local diff place to turn it into a "CIG locker" (they will know what you mean, and it will cost you about $50) and chuck it in.   

One thing I didn't mention about the manualised box, it needs to be driven as a manual, if you put it in D, it will attempt to take off in 3rd, even though you have no clutch.  So you have to drive it 1-2-3 like a manual.

I suppose you'd call the reversal a shift kit, but there's no way B&M or anyone else would make one for a MB, so it'd be a custom job done by the auto place.

Ian.

[SELfor50]

Save your $750, take up Oscar's offer on the free 3.69 diff - get the local diff place to turn it into a "CIG locker" (they will know what you mean, and it will cost you about $50) and chuck it in.   

One thing I didn't mention about the manualised box, it needs to be driven as a manual, if you put it in D, it will attempt to take off in 3rd, even though you have no clutch.  So you have to drive it 1-2-3 like a manual.

I suppose you'd call the reversal a shift kit, but there's no way B&M or anyone else would make one for a MB, so it'd be a custom job done by the auto place.

Ian.

Word...   

You down with that shizzle Oscar? 

Will try find a tranny place in canberra that can take care of this - would it be best to purchase the re-conditioned 450 Gear box from ASV for $950 with a 12 month warranty and get them to chuck that in at the same time as doing the reversed / manualised thing?
And yeah, i'm sweet with driving it like a manual - i pretty much do that now anyway with the stock setup and it luuuuurvs it!

[13B]

Shouldn't be too hard to find a place in canberra who'll do the mods I mention.  Some of them are internal mods to the auto, but that shouldn't be a big problem since the design of the MB box is similar to the TH 400 used in GM vehicles.  While you're at it, ask them what their recommendations about the "stally" (torque converter stall speed) should be matched to the maximum torque point of the engine.