which diff ratio

[Miniböttcher]

right. i have a 1275 engine bored out 0.20" to 1293.
stage 3 head fast road cam and a 4 syncro sc gearbox. not sure if the gear set is close ratio. and it has 10" wheels

i was running a 3.44 diff with a standard gearbox ( not my new 4 syncro sc )
and i found that it was so fast up the gears and reved really quick. but was doing 4000-4500rpm at 70-80 mph

i want to bring the revs down ,as i want to travel to shows and do not want do 50mph on the motorways so i will not blow the head gasket or the engine.

which diff is best? i have been told a 3.11 or a 2.??
i still want good excleration but good motorway crusing

please help.

thanks dean

[minimole]

the 2.9 provides quite tall gearing for a more comfy motorway ride. personally out of the 2 i would go for the 3.1 the 2.9 imho is to tall for a mini. i think the mpi's had a 2.9 so you could always try and have a go in a friends mpi see if you like it. i know it probally wont be a 1293 but it would give you a feel for it.

I myself will be sticking with the 3.4 but i dont have to take my mini on motorways very often only for shows. tbh at 4000 rpm i still will have another 1500rpm to go which suits me as i am not going for massive top end etc. i just wanna get there fairly quick. i have 3.4 in my 1330 btw

[Simon1275mpi]

Classic question, I'm running my MPI with a standard 2.7. I love it. It pulls away okay and just keeps going, crusies at 70 at 3000-3200rpm , oh so quiet at 60mph ;D

But I'm guessing with your 1293 you want that acceleration still... 3.1 fits the bill.

Speedometer driveunit may need changing if you want to see what speed your doing.

Si

[Miniböttcher]

thanks for your help. i had a felling that a 3.1 would be good . but you know whats it like when lots of different people say hundred of different diff ratio . you just get confused

i try the 3.1 if its not good enought i will have to swap it over

thanks again

[annon]

if you knew which straight cut set it would help, m/spares? all 4th gears are the same 1,2,&3rd are the only ones that are different reverse is 1:1 a 3:1 diff is a good one if you have a good engine with mods i allways use 2:9, just note the ones above are running 12s you say you are running 10s, still made your mind up?

[Miniböttcher]

i have found out what gear set it is . a
4 syncro the from mini spares for a pre A+ gearbox
it is not a cross ratio like the cooper s , so a 3.44 diff will be to quick

i need to drive or find out what rpm it does in each gear.

so if anyone has a 3.11 or a 2.9 ratio could they tell me what rpm it does a different speeds and gears.

thanks

[monkeyjim]

I asked AC Dodd the same question a few months ago .

I wanted to know the correct diff ratio when using 10 inch wheels to give the same characteristics regarding revs per mph as you get on a factory standard 12 inch wheeled Mini .
Think we can all agree they give the best all round performance .

Regardless of engine capacity his answer was 3.1

Obvoiusly if you spend loads of time on a Motorway a lower number diff can be used and if you up and down the B roads a 3.4 or higher could be used .

The 1275 MG Metro I used to have fitted and the 998 Metro currently fitted in my MK1 both use the 3.4 . Great around town and the B roads but to much of a screamer for me up the dual carriageways . Remember the higher the revs the more pressure it puts on the engine .
Remember AC Dodd will be at next Mondays meet so speak to him again about it then . He will also tell you that ideally a higher powered engine (100 hp plus ) is needed to make straight cut gears work properly .

Check out the ML Motorsports Forum and leave a message . Excellent questions and answers section for technical stuff.
See www.mlmotorsports.ckto.co.uk and click on the forum prompt.

Dave

[annon]

i would disagree when i raced a 1070cc s and 970cc cooper s i used 4 snc s/c box , then moved on to dog box on a 4.6 dif 108;1 drops, but i didn't have 100bhp, there were several reasons for using s/c. longer 1,2,3, and strength

[monkeyjim]

what a surprise , you disagree . Why does every post u put up end up being confrontational and finally results in deletion . I am not the only one who wants to know this .
Anyone mention race cars ?
Argue with AC Dodd on the ML forum. Should keep you off this one for a bit or better still do it in person with him next Monday.

Dave

[Simon1275mpi]

Lads, at the Dodd meet we'll set up a mini boxing ring and you can sort it out there... No spanners below the belt ;D

Dr - Think Dean is after an all round diff than a perfect race diff, would be nice for the weekends thought

[MiniGT5]

I Dont think we have ever had to delet any posts have we???
N :-)

[Deleted]

i have but cant be bothered any more.

[Simon1275mpi]

Free speach!!

[MiniGT5]

Well I dident know that...

N :-)

[noisymini]

calm down boys.

anyway

this is pretty usefull

www.ime.org.uk/ime/f/final_drive.html

I have used 3.44 and 3.15 on RSP and turbo. Not really a massive difference if you ask me and if it were me i'd use a 2.7 as will prob be just as quick as a 3.15 just not neccesarily feel as quick as not crashing through the gears. Always wanted to fit a 2.7 to my turbo as 1'st gear was pointless with the 3.15.

www.vtec-mini.co.uk