My apologies first up, I am a complete idiot when it comes to searching threads. It just don't work for me.
I want to dig up any discussions on diff ratios, particularly the 3.1 versus the 3.4.
I would appreciate any help for this village idiot
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| Diff ratios https://www.ausmini.com/forums/viewtopic.php?f=2&t=70201 |
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| Author: | bamnfi [ Mon Apr 18, 2011 6:29 pm ] |
| Post subject: | Diff ratios |
My apologies first up, I am a complete idiot when it comes to searching threads. It just don't work for me. I want to dig up any discussions on diff ratios, particularly the 3.1 versus the 3.4. I would appreciate any help for this village idiot
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| Author: | GT mowog [ Mon Apr 18, 2011 6:56 pm ] |
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There is a bit to take in to consideration when playing around with diff ratios;- What size engine / power curve? Wheel Size? Driving conditions / style? Gearbox ratios? What is it your actually looking for / hoping to achieve? |
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| Author: | bamnfi [ Mon Apr 18, 2011 8:09 pm ] |
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GT, it's 1970 Cooper S. 60 thou pistons. Head not done yet. 1.5 lifters KAD 5 speed box. Twin 1.5 SU's 10 inch wheels (of course) What am I missing
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| Author: | rehab1964 [ Mon Apr 18, 2011 8:49 pm ] |
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we put a 3.1 in Ms Plum, running a Morris 1100S engine and gearbox - both standard and 10 inch wheels I'm loving the new diff, amazing high speed crusing and no obvious loss of flexibility around town The only downside so far...... no more wheel sping in first...... second....... third |
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| Author: | VulcanBB18 [ Mon Apr 18, 2011 9:41 pm ] |
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All you're missing is driving "needs" as rehab put, 3.1 will be great on the highway, good around town. 3.44 will be great around town & good on the highway 
cheers Jacob |
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| Author: | drmini in aust [ Mon Apr 18, 2011 10:00 pm ] |
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I put a 3.647 in my 1360, as I was doing a few track days back then Trouble is when it hits 5000 rpm in 1st gear, the A008s just spin on the road! Next time it's out, I'll put the 3.44 back in it. Or buy some A032Rs... 
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| Author: | GT mowog [ Mon Apr 18, 2011 10:15 pm ] |
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bamnfi wrote: GT,
it's 1970 Cooper S. 60 thou pistons. Head not done yet. 1.5 lifters KAD 5 speed box. Twin 1.5 SU's 10 inch wheels (of course) What am I missing OK. What Cam will you be running? Do you have the KAD Ratio's to hand? (Glad on the 10" wheels )
Are you sure about the twin 1 1/2" SUs? |
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| Author: | bamnfi [ Mon Apr 18, 2011 10:22 pm ] |
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GT mowog wrote: bamnfi wrote: GT, it's 1970 Cooper S. 60 thou pistons. Head not done yet. 1.5 lifters KAD 5 speed box. Twin 1.5 SU's 10 inch wheels (of course) What am I missing OK. What Cam will you be running? Do you have the KAD Ratio's to hand? (Glad on the 10" wheels )Are you sure about the twin 1 1/2" SUs? KAD 5 speed specs. * Face dog type, straight cut gears. * Compact gear train fits into a standard rod change casing * 1:1 direct top gear, lower torque loss in fifth gear compared to an overdriven 5 speed unit. * Dog leg first; 2nd, 3rd, 4th and 5th gears in 'H' pattern. * Gears manufactured from S156, an Aerospace VAR steel, selector forks from AB2 aluminium bronze. * Ratios: 1st 2.616:1, 2nd 1.989:1, 3rd 1.671:1, 4th 1.294:1, 5th 1:1 * Input and output spline as standard Mini * Supplied with extra bearing support for pinion end of main shaft and centre oil pickup pipe Am employing some help re cam. The Kent 266 is gonna go and am looking at an RE to suit. SU's? Why not? Will either go that way or injection. Prefer the grubby SU's; that's what I grew up with. Webers? no thanks. Just my taste, no technical basis. cheers, bam |
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| Author: | GT mowog [ Tue Apr 19, 2011 7:44 am ] |
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bamnfi wrote: Am employing some help re cam. The Kent 266 is gonna go and am looking at an RE to suit. SU's? Why not? Will either go that way or injection. Prefer the grubby SU's; that's what I grew up with. Webers? no thanks. Just my taste, no technical basis.
cheers, bam Until we sort out what cam your running, it's a bit difficult to advise properly. SU's are fine, I like them a lot and use them most of the time. Q. Is this to be a street car? Your gearbox, while being a 5 speeder, is not what I'd call 'streetable'. |
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| Author: | Lillee [ Tue Apr 19, 2011 9:43 am ] |
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If you have a fair amount of power (80hp or more) then 3.44 diff is the best IMO. It gives good accelleration and with the amount of power you can maintain a good cruising speed on the freeway without much trouble. I think it's the best all round ratio. If you have loads of power (120bhp+) then a lower ratio will still do OK like 3.105 which is probably the tallest you should go. It will still give pretty good acceleration, won't spin the wheels too much in low gears and because you have loads of power and your final drive will be good for the freeway. If you have anything under 70-80bhp then 3.647 is probably the better ratio for good acceleration but sacrificing top speed. If you run any taller a ratio then you'll have trouble climbing hills... 
All these are for road cars of course, and if you don't do any freeway miles, then go for the shortest possible such as 3.647 for best 0-80km acceleration |
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| Author: | Irish Yobbo [ Tue Apr 19, 2011 11:09 am ] |
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Everybody has their own opinion on this, I guess. I have a stage 1 998, and have a 3.4 diff. And I love it. Most of my driving is country roads, so bends around the 60-80km/h mark, and I don't need to rev the guts out of it on the highway. But yes, hills murder it. I still prefer it as it is, though. |
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| Author: | sgc [ Tue Apr 19, 2011 12:07 pm ] |
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With the 5-speeder, I'd be tempted to run a slightly taller diff ratio (3.1 or maybe higher) if you have the power, which I think you will. This will give you plenty of around-town flexibility in the lower gears, and a taller final-drive in the 1:1 5th gear for highway cruising. |
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| Author: | Convertible Mini [ Tue Apr 19, 2011 12:28 pm ] |
| Post subject: | 3.1 Final Drive |
I have 2 cars (Minis) both have 3.1 diffs in them. But they are both big capacity engines being a 1408 stroker and a 1380 std stroke. On that sort of capacity There is no need for the engine to be doing a million revs to get the torque needed for cruising. They sit at around 3100 RPM at a 100K. Both cars are on 12inch wheels. One word of advice though do not combine a tall diff with a big cam. I had a 649 in one of them and I could not drive it below 80KPH in 4th gear. It was a pig to drive and I ended up taking that Cam and twin 1 1/2 SUs out and replacing it with a 104 Cam and a HIF44. It is a much more drivable car now and a pleasure to drive. Even fuel consumption is great I think I worked it out on the 1380 to get 15.5Km per ltr. |
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| Author: | paul_ewins [ Tue Apr 19, 2011 2:51 pm ] |
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I used to run a 2.9 diff with a mildly modified 1100 engine and that was just fine. The only times that hills were a problem were very long climbs at highway speeds (like the Pentland Hills on the way to Ballarat). Getting to top speed was a long process but up to 100kmh was fine. It all depends on whether you want to race or cruise. |
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