Hi All,
I have a 1979 Mini LE that we have transplanted a 1275 Engine from a same year austin allegro. We have added twin HS2 carbs, Freeflow Extractors, the head has been ported and polished and also planed to give about a 10.1 compression ratio, have done a brake conversion on the front to 4-pot caliper vented disc brakes from an MG metro turbo and put 13" alloys on the car. whew! Mouthful!
The cam is whatever was standard with the allegro at the time.
The car seems to really get up and boogie all the way up to 120km/h (75MPH i think), then it starts to slowly rise to top speed of around 150-160km/h (90-95MPH)
my one beef with it is that at 100km/h (60MPH) the revs are around 4000rpm which is freakin loud on a long trip.
I believe the Diff is a 3.4
How do I calculate the Diff ratio i would require to make the car run at 100km/h at a lower rev count, dropping the engine noise and making the car a bit more cruisy, while keeping a decent amount off-the-line power?
Any advice from this forum is always appreciated.
Thanks!
Mini 1275 Differential / Final Gear Ratio Question
Started by
MordredNZ
, Apr 07 2011 09:42 PM
3 replies to this topic
#1
MordredNZ
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Posted 07 April 2011 - 09:42 PM
#2
mini13
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Up Into Fourth
Posted 07 April 2011 - 10:45 PM
Have a play with this,
http://www.guess-wor.../Tech/ratio.htm
IIRC the allegro final drive is a lot shorter than 3.44, more like 3.9 or 4.1,
I run a 3.1 and get about 4000@ 80mph, for me its a good balance between acceleration and top end, but I do have the power to pull a tall ratio easily.
http://www.guess-wor.../Tech/ratio.htm
IIRC the allegro final drive is a lot shorter than 3.44, more like 3.9 or 4.1,
I run a 3.1 and get about 4000@ 80mph, for me its a good balance between acceleration and top end, but I do have the power to pull a tall ratio easily.
Edited by mini13, 07 April 2011 - 10:45 PM.
#3
danrock101
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Posted 07 April 2011 - 11:24 PM
mine was a 3.1 too and I agree it's a nice balance, but I thought it was a 3.44 untill I stripped the gearbox lol
#4
Cooperman
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Uncle Cooperman, Voted Mr TMF 2011
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Posted 08 April 2011 - 11:04 AM
4000 rpm at 60 sounds more like a 3.9:1 as you are on 13" wheels which do give a slightly larger rolling radius than a 10" which gives about 14.4 mph/1000 rpm in top.
You want to trade acceleration for cruise at lower revs and need to decide how much 'trade-off' you can accept.
You will probably find a 3.2:1 would be ideal as that will give around 18 mph/1000 rpm in top, i.e. 4000 rpm would be 72 mph. It's only a guess, but expect your 0 -60 mph time to increase by around a couple of seconds.
You want to trade acceleration for cruise at lower revs and need to decide how much 'trade-off' you can accept.
You will probably find a 3.2:1 would be ideal as that will give around 18 mph/1000 rpm in top, i.e. 4000 rpm would be 72 mph. It's only a guess, but expect your 0 -60 mph time to increase by around a couple of seconds.
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