OK guys over the last few weeks I have been umming and arring about if I should change my diff ratios. A couple of factors have fueled this.

1) The weak link in my car is gonna be the std front diff size. Even though I have a quaife thickwall caseing, with a shot peened and polished CWP and an ATB, we all saw what Kev Sharp did to his . The only other option is to go for the 7" R&D front diff that comes with the std ratio. But you all know how I feel about R&D and the fact that if the company was on fire, I wouldn't give them the steam off my piss.

2) With my R&D box, I never ever used 6th gear on track as it was just to long. The fastest straight I have been down is the back end of Bedford and I have pulled just over 160 down there and that was the top end of 5th with the R&D ratios. Martin is the same here as well.

Now don't get me wrong both Mine and Martins cars would absolutly bang through the gears with the R&D ratios and the cars both felt electric. But the compromise that we make just for a high top speed I feel is to much.

So I have knocked the top speed lark on the head.

I have now decided to go 4.44 diff ratios. As the choice of diffs is good and readily available.

Yesterday I bought a newly rebuilt (in fact it is still at Bernies) Ford Motorsport 9" rear diff with 4.44 ratio, and I also bought a 7 1/2" Ford motorsport front diff, complete with Magnesium sump and all the whistles and bells, this also has a 4.44 ratio. Obviously strength for both diffs should not be an issue and the now shorter final drive gearing is gonna make the car foooookin animal through the gears!!!!!

My OS Geiken ratio's aren't a million miles away from the R&D ratios, so below you can see the differences in speeds through the gears. These are with my OS Geiken ratios:

4.44 Gear 3.62

52 1 63
76 2 92
103 3 125
129 4 157
156 5 190
184 6 223

As you can see with the 3.62 ratio at Donno I would probably never need more than 4th, with the odd snick into 5th, and at bedford only 5th. My car is gonna be a bit more powerful so say my bedford speed goes up 10mph, I am nicely into 6th with the 4.44 and useing all the gears to there best, where as with the 3.62 I would still be in 5th.

Steve Scott has 4.44 diffs in his Escort and I don't think anyone would call that slow would they, and lets not forget he has a 1:1 top ratio so his top speed at Donno was only about 130mph, which he was reaching by the Dunlop bridge down the back straight. The fact that I have an over driven top gear and a few more revs, gives me a better top speed and i feel more driveability.

I was always building the car to be a track day warrior with qtr's and top speed being an after thought. And I guess if push comes to shove and I want to do a top speed run, I can just change the back diff and run it in Rear wheel drive mode for the top speed run.

Anyway, what does everyone else think???

Sean..

 

DO it 4.44

then as you say, change the rear diff for a top speed run



what u gonna get the beast on the black stuff????

 

I hope that's not my money you're spending sean!!!!

 

its sounds to me you have picked the right option in your diff ratios

there no point in having gears you cant use

 

I hope my new R&D plate diff will be ok.

Sean buy them all....seems like you have the money to.

 

Good move on the face of it Sean.
First (and most important) consideration is strength.
Mechanical losses are generally lower through the lower ratio final drives
Gearing for an impossible to achieve theoretical top speed is a waste of time, unless you plan to use a lower (direct) gear in the box.
The lower you gear the car, the quicker it will achieve top speed, which will make for a quicker lap time, just so long as you don't under gear it to such an extent as to compromise top speed.

So, were these purchases your birthday presents to yourself?

 

Sean,

My old Saph 4x4 with the Paul Bailey 400 BHP engine was used mainly as a road car, but I did few track days as well.

With the standard diff ratios it was "OK" on the track (17" wheels) but when I blew up centre diff (cracked the casing in half) I got Steve Scott to fit a 3.9 rear diff and centre diff step-off/chain (3.9) and also to fit a plated front diff.

For road and track use it TOTALLY transformed the car. It now had much sharper acceleration an ALL gears.........The car was perfect for Castle Coombe, just pulling 6.4 k RPM in fifth at the crest of Avon Rise (145 MPH indicated).

Another huge benifit was that on the road in fifth gear (in a race situation lol) it became a single gear car from 90 MPH onwards..........I.E. on fast A roads I just kept both hands on the steering wheel, enjoying punchy 5th gear acceleration all the way to the rev limiter...........That car surprised many a M3/Scooby/EVO 6 owner, even on motorways

 

God knows mate. Fingers crossed before I get my free bus pass.

Of course it is Kev, why the hell would I spend my own money, when I can spend yours instead.

Fingers crossed for you mate on buying there stuff. Just don't expect them to deliver it on time, give you any aftersales service at all. If you do have a problem, it will always be your fault and not theres. And for fucks sake don't let them build it into your box, as they couldn't put together a lego model, let alone a real diff.

Yeah, something like that Bernie. So anyway how is that 9" coming along. Steve reckoned it would be sorted and ready to go in about a week. I guess it may as well come straight frrom you to me instead of back to Steve and then to me. I'll have a chat to Steve about it if you like?


Yeah I reckon it will transform the car. It will make it easier to launch, and as I am pants at launching I need all the help I can get and I reckon 184mph will be enough for any track I am likely to go round. And if my terminals over the qtr are 184mph, then foook me I will be going fast enough I reckon.

Sean..

 

So you wont be needing that sump that's kicking around your workshop floor anymore then!!!!!???

 

Noooooooooooooooooooooooooooooooooooooooooooooo!!! !!

Your supposed to be buying my engine bits with it!!!!!

 

Actually Kev no I wont, and yes it would be ideal for your new engine. But being a propper Mountune Group A item, it obviously isn't gonna be cheap, these things are like rocking horse shit to get hold of!! blah blah blah, you no the score.!

We'll have to haggle over the price!! Maybe you should send your sister to negotiate on your behalf!!

Sean..

 

i did post a large essay type thing about ratios etc etc , but pf lost it for me on a n invalid session so fook it !

but well donr and about time !!

 

Put it on my bill Sean!! and there's no point me bringing my sister.... You'd only get her name wrong!!!!!!!!

 

I guess you had better send another couple of grand up then Kev me old china!!!

 

Sean, how often are you likely to do tops speed runs, once or twice a year? compared to how many track days...............

PAul

 

The disturbing word in that sentence is "another" !!!!!

 

go for the acceleration when do you do 200MPH on the road? (except when late for tea!)

whats the prob with R&D just out of interest? sounds like they fooked u about big time?

 

Sean

On a slightly different level i just chanmged my diff from a 3.54 to a 3.9 in the Mk2

and FOOOOK me its a superb mod from a standstill it just lights em up in 1st and 2nd in the dry and 3rd in the wet which is mucho fun

So in your car fffoookkk me its gonna be mental

Nige

 

PMSL do you really feel that strongly sean?

congratulations on having a 9 incher firmly planted in your rear end

you can join my 9"club now

 

kjc300, AROTFPMSL!!!!!!!!!!




Ohhh the memorys!!!!!!!

Pete..

P.S Kev,il call her the right name,so im with sean on the "bring her up" thing!!

Pete...