Discussion
Just a querie about gearbox ratios.
It feels like my car is revving an awful lot for what speed it is doing.
At 70mph, roughly - the speedo appears to be a mile out, its doing about 4200 rpm.
It feels like a 5 speed car whats being driven in fourth, like it should drop lower.
The engine is a 1275 from an '88 Austin Metro LX. 12HD12.
Is there something at fault? Is there actually a 5th but I've got the change rods misaligned?
Tom
>> Edited by Twelve_75 on Saturday 25th February 20:45
It feels like my car is revving an awful lot for what speed it is doing.
At 70mph, roughly - the speedo appears to be a mile out, its doing about 4200 rpm.
It feels like a 5 speed car whats being driven in fourth, like it should drop lower.
The engine is a 1275 from an '88 Austin Metro LX. 12HD12.
Is there something at fault? Is there actually a 5th but I've got the change rods misaligned?
Tom
>> Edited by Twelve_75 on Saturday 25th February 20:45
Look here- www.leedsyork.fsnet.co.uk/pages/ho
MiniGear. There is a chart on the site for working out your required ratio.
This bloke is very good, all he does is rebuild Mini gearboxes. Many of the those sold from well know establishments come from here. His prices are very reasonable.
Plank.
MiniGear. There is a chart on the site for working out your required ratio.
This bloke is very good, all he does is rebuild Mini gearboxes. Many of the those sold from well know establishments come from here. His prices are very reasonable.
Plank.
Twelve_75 said:
Just a querie about gearbox ratios.
It feels like my car is revving an awful lot for what speed it is doing.
At 70mph, roughly - the speedo appears to be a mile out, its doing about 4200 rpm.
It feels like a 5 speed car whats being driven in fourth, like it should drop lower.
The engine is a 1275 from an '88 Austin Metro LX. 12HD12.
Is there something at fault? Is there actually a 5th but I've got the change rods misaligned?
Tom
I was in a simlar boat. Took the box off and put a 2.7 in. Much much better now.
>> Edited by Twelve_75 on Saturday 25th February 20:45
No, I've got the same problem. I think they had a 3.7 final drive which is silly. Running 10" wheels, 1st gear is like a crawler gear, 2nd is like 1st and a bit, 3rd is like 1st and a bit more and 4th is like second and a bit. It's stupidly quick but slowed down by the fact that you have to change gear every 3 seconds.
Find a dead mini city e. They have 3.2 FD's which are more suited to road going than 3.44s. I'm using a 2.76 on my blower engine with spread ratio SC gears! 125mph? Yep, easy!
Edit, I'm after a 3.2 or 2.9 CWP if anyone has got some.
>> Edited by love machine on Sunday 26th February 23:57
Find a dead mini city e. They have 3.2 FD's which are more suited to road going than 3.44s. I'm using a 2.76 on my blower engine with spread ratio SC gears! 125mph? Yep, easy!
Edit, I'm after a 3.2 or 2.9 CWP if anyone has got some.
>> Edited by love machine on Sunday 26th February 23:57
70 at 4200, given the inaccuracies of speedos and tachos, seems to indicate that the diff is a 3.44 or 3.76. On 10" wheels it is almost definately a 3.44, assuming 165/70x10, whilst 165/60x12 would give around 4% higher speed for the same revs.
The 3.44 is a nice all-round ratio for a mix of acceleration and cruising speed.
With a s/c c/r box, first gear is much higher so you need a fairly low diff to avoid having to slip the clutch in traffic, especially if your engine is modified and the useable power band raised. In my 1310 rally car I can't really use higher than a 3.9 final drive (that's about 14.5 mph per 1000 rpm in top) and on the rally 1071 and 970 I have built the diff needed to be 4.1 (about 13.5 mph/1000 rpm).
With 4-speed box and the 'A-series' engine the final drive ratio is always going to be a compromise, especially with a normally aspirated modified unit. Unless being used for competions, where a 5-speed may not be allowed, then that is the ideal answer - expensive though it is.
The 3.44 is a nice all-round ratio for a mix of acceleration and cruising speed.
With a s/c c/r box, first gear is much higher so you need a fairly low diff to avoid having to slip the clutch in traffic, especially if your engine is modified and the useable power band raised. In my 1310 rally car I can't really use higher than a 3.9 final drive (that's about 14.5 mph per 1000 rpm in top) and on the rally 1071 and 970 I have built the diff needed to be 4.1 (about 13.5 mph/1000 rpm).
With 4-speed box and the 'A-series' engine the final drive ratio is always going to be a compromise, especially with a normally aspirated modified unit. Unless being used for competions, where a 5-speed may not be allowed, then that is the ideal answer - expensive though it is.
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