What's a 2.76 final drive like?
Turbo Mini Forums

I am currently running a relatively tuned N/A 1293 with 10" wheels and a 3.44 final drive. Boring stuff. First gear is a bit of a joke and just involves lots of torque steer, weaving and noise.

My blower engine for development is based on an MG lump, I am planning on running about 6PSI for starters and then upping it to about 10 or so, seeing how it goes. I am running 19.5" dia tyres and need something a bit more long legged, not too long legged though. Want it to be as fast as I can without excess tyre smoke.

Any relevant suggestions?

stu

Bugger off, I'm getting there.

3.1:1

2.7 is looooong!

alex

AlexF

standard helical box?
then find a 2.76FD

CR box? Forget it...

TD

Do you say that because of the CR box having a higher first, so the combination of that with the tall diff makes setting off slow?

Just a bit concerned now as I have built a box with a 2.9 diff in it and have 13"'s......want it to be able to cruise comfortably at speed......

if a std 1275 mpi can pull a 2.7 you should be fine on a 2.9!

alex

AlexF

Yeah thats a good comment I suppose.....the MPi's on 13"s are a bit sluggish but I suppose I will have the advantage of approx double the horsepower and a good dollop more torque when the T3 is doing its thing......and less transmission losses as well due to the s/c box....

OK, I will stop panicking now!!!

1st gear overall ratio on an A+ box with the 2.7FD is virtually the same as the 1st gear overall on a SC gearset (2.54 1st ratio) with a 3.44 FD - ie 40ish mph in 1st at 6500 rpm.

From my investigations into MEMS MPi a few years ago (when trying to get injection to work on my a-series) I discovered the MPi has a very flat torque curve - it also has more low down torque than previous models - giving more evidence to the rumour that the camshaft timing was also tweaked for the MPi....

Watch an MPi set off - they are far from brisk... Change it to a 3.2 however, and they're flying machines!

I have been looking at this....

http://www.csgnetwork.com/automotiveconverters.html

Which has a handy "ring gear calculator".

I have been trying to work back from a desired cruising speed.. The 2.76 looks great but a 2.95 looks better.

I can go down to the scrapyard and have loads of 2.76 CWP's but I'm not sure what 2.95's were fitted to. According to Haynes, they are not Mini or Metro. I would have thought a bigger Leggy 1100, etc had something with short legs......

So far, I think I will whack a 2.76 on the A+ box, just to give me a good load to fight against. In my final build, I will probably have a better idea.

Bugger off, I'm getting there.

city e's had the 2.95 diff iircc, prolly the same in metro e's. the 'e' stood for economy, hence the long diff.

And on the 7th day........... God created turbochargers!

2.95:1 Diffs were fitted to the economy 998cc Minis with 10" wheels. When the move to disc brakes came about, the ecomony diff ratio was changed (to take account of the larger wheels I think) to 3.105:1.

The metro turbo used 3.2:1, whereas all the 1275cc Metros used 3.444:1 as I remember. I do not know what the 998cc Metros used but think it was 3.444:1.

Allegros used a 3.9:1 diff ratio as they had much larger wheels. Also there is a 3.7:1 ratio available that was fitted to early 1275GT's and I think some of the CooperS's.

The 2.76:1 ratio was fitted only to the TPi cars from MY97 onwards. This was done to get the cars to pass driveby noise tests as it dropped the engine revs.
But I severly doubt you will find many 2.76:1 crown wheel and pinions in any scrapyards, that is for sure.

For what you want I would lean towards a 3.105:1 or a 3.2:1.

The 2.76 was fitted to Auto Metros which are 3 deep in my local scrapyard.
I also have a 1000 city e engine sat in a corner. I will whip the CWP out of it and see. Thanks Tom!

I will put all the info I have found on a thread in Technical.

Cheers, stu.

Bugger off, I'm getting there.

2,95:1 diff were fitted to the minis from 1983 year- 10"wheels.
TurboHarry was the first one who gave me a drive with his turbo mini with that diff (2,95 FD). i was positive surprised. that is why i put 2,95 in to my turbo mini too.
i found it is great for the cruising on the highways and my mini is much more quiet (i drive quite offen long distances) but it is not ideal for the town driving which i do every day too.
perhaps i will try 3.105:1 next year.

Ahhh, shit.....I have just whipped the CWP off the old city engine and the pinion teeth have been really badly topped for about 3/5 the width. The crownwheel is OK though. I am assuming this is wear, not some oiling curiosity.

Very odd, having a closer look, the teeth which have been topped have also been worn considerably. The pinion is an ornament. Looks like I might have to find another one.

Bugger off, I'm getting there.

Stu, How sure are you about the auto metro FD. Have you actually taken one out of a metro auto and checked it?
Not saying it aint - just that i've never heard it mentioned before!!!

Besides, if the Metro auto box is the same as Mini box the FD is way bigger than manual FD. Forget it !

I have 2,95 diff with helical box and 12" wheels (165/60 tyres). I am seeing about 3300 rpm at 100 km/ (62 mph). Very nice both on long journeys and city traffic.

2,76 may be a bit too long although in theory with enough torque it should run quite nice.

Jukka

Dave, it is in the Metro Haynes manual, (the good one with all models, no 718, page 218, which is the supplement.) I can't remember where I heard of it but there was some thread about late minis (which I know nothing about) having 2.76 FD's and the Auto Metro (1300) was the cheap mans choice. When the weather backs off a bit, I am going to the scrapyard to whip one out.

Bugger off, I'm getting there.

I have broken quite a few Minis and never found a 2.9 FD,but plenty of 3.44's and the odd 3.1. Mind you i have never broken anything from around 1986 ish. I know the later Mpi models had tall FD's to pass all the drive by noise regulations i do believe.

Pretty sure the auto crown wheel and pinion are a totally different design the the manual box.

3.44 works for me!!

Edited by giallofly on 26th Oct, 2004.

Looking at my best Metro manual, in the world....ever, I can not see anything resembling a stripdown/photos. Anyone got a proper workshop manual. From what I remember, the selectors have different markings and I think the Metro autobox is a bit bigger. I will go down the scrapper and see what I can find in due course. I expect they would have used the same CWP for economic reasons.

Bugger off, I'm getting there.

I need a 3,44 Pre A+ pinion.. Jon?? :)

Why not just get a complete one off Mark???

I thought it was good practise to always keep used crown wheel and pinions in a matched pair??

So if you need one really better to change both together.

It's good practice to do that with all meshed gears. Only time it seems unneccesary is with the 'mangle' gears that our SC transmissions and drops are based on... These are so crude it wouldn't make any difference!

Looking at the few I have had off, it seems to be the pinions which wear more?!?!?! The pinion I just whipped off, I wouldn't use, but the crownwheel is fine.

Bugger off, I'm getting there.

Why is it surprising they wear more? That's a given surely...

i run a 2.9 on 13's with sccr box and drops and runs realey well, but yes pulling away is a bit of choir but you soon get use to it, crusing is supurb and also the econamy is as well, with the added torque you will get from the turbo once moving she will fly, also i find traction in the wet is a lot better as well, eg alot less whell spinning than you would get from running 3.1 or lower wnen under power.

but the end of the day is always your choice in what you want the motopr for.

just drove my mates 1380 with a 3.1 and after a while it was charring me of when went for a cruise down the motorway,

always looking for them bigger bunches of bannanas