31 replies to this topic

[Luke Denver]

Hi everyone I’m currently building my 1293 the planned spec is as follows.
1293 bore
AC Dodd rs road cam
MED duplex timing gear
Ported polished big valve mg head 35.6mm by 29mm might have more done to it havent looked in detail yet.
Single 44 carb
Lightened flywheel or weight taken out of the clutch/flywheel
Maniflow exhaust system
Aldon yellow dizzy or recurved to suit spec
Balancing of engine and clutch
I plan on fitting larger rockers but this may have to wait and be something I add in the future
The car has 13” wheels which I understand affects acceleration
Aiming for around 80-90bhp


Now I’m not sure what to do with the gearbox i plan on getting an oil pickup for it and stronger diff pin as well as having it taken apart and all worn items replaced by my local machine shop. Now I’m unsure what to do with the gear ratio/final drive I’m unsure what is in the car at the moment will find that out tomorrow when I visit the machine shop but I can only assume it’s a 3.44. So I don’t know what to do I’m thinking about changing it to a 3.1 so that I can have a higher top speed I’m aware the acceleration will suffer but I’m sure it won’t be slow off the line with a lightened flywheel and the rest of the spec. I’ve looked on guesswork’s and seen that with the 3.1 I will have a higher top speed and be able to cruise at higher speeds with a lower rpm which I like the sound of as there’s nothing worse than being at 70 with the engine screaming at 4K like my 998 does now I’d much rather be able to go 70 at 3.5k and be able to pull right up to 90. I saw another post on here with someone asking a similair question but he was putting a 276 cam in his and most reccomended not to as he was wouldnt be on the cam most of the time so I wondered what a 3.1 would mean for my spec any disadvantages or advantages. I’ve also never driven a 1275 with a 3.44 so what I’m saying could be completely wrong which is why I’m seeking advice as I’m out of depth here. I’m also open to other suggestions other than a 3.44 and 3.1 but won’t be able to buy anything too expensive as I’m only 19 and this is my first fairly quick engine build thank you for your time and I look forward to your responses.

[nicklouse]

Personally I would stick with a 3.44

[Ethel]

Any of them. It'll go best on the 3.44. The taller ones will save a little bit of mpg & be quieter cruising A roads. Any will beat any of the others between gears in favourable conditions, but the 3.44 will hang on to top gear for longer.

 

 ....to be clear, the 3.44 will have the highest top speed, unless you're going down a big hill with a tail wind. All will go too fast for public roads.

[Midas Mk1]

3.1 3.2 all day every day for me.

[nicklouse]

Any of them. It'll go best on the 3.44. The taller ones will save a little bit of mpg & be quieter cruising A roads. Any will beat any of the others between gears in favourable conditions, but the 3.44 will hang on to top gear for longer.

 

 ....to be clear, the 3.44 will have the highest top speed, unless you're going down a big hill with a tail wind. All will go too fast for public roads.

Wrong way round. 3.1 will give a higher top speed.

[Luke Denver]

Personally I would stick with a 3.44

What’s your reasoning

[Luke Denver]

3.1 3.2 all day every day for me.

What’s your reasoning mate any clear differences advantages the more you can tell me about your experience the better

[Gaz66]

A bit of an aside but this reminds me of the time I fitted an "emergency" gearbox and ended up with the fastest accelerating mini Ive ever had.
Id built a quick 1380, slark head, 649 etc and also built a standard remote box with 3.7 diff.
After fitting it at my mates garage I went to reverse the mini out and found that I couldnt get any gears as something had locked up in the box.
He had just taken an engine and box out of an allegro and said I could have the gearbox so as to get me out of the garage.
The box was robbed from the allegro and slapped on the 1380 and away I went......
Very quickly..the allegro was an 1100 and fitted with a 4.1 diff which was interesting on 10" wheels.
After getting over the shock of the short gears I decided to keep the 4.1 as it was mentally quick to about 90mph.

[Ethel]

 

Any of them. It'll go best on the 3.44. The taller ones will save a little bit of mpg & be quieter cruising A roads. Any will beat any of the others between gears in favourable conditions, but the 3.44 will hang on to top gear for longer.

 

 ....to be clear, the 3.44 will have the highest top speed, unless you're going down a big hill with a tail wind. All will go too fast for public roads.

Wrong way round. 3.1 will give a higher top speed.

 

It  won't if it hasn't got the power at the rpm  it's turning to overcome the drag.

[Spider]

Road use on 10's or 12's - 3.44 all day, every day.

[floormanager]

I've got a 3.44 in a S and for me it's perfect but, you'll be driving at 3.5 to 4K along the motorways.  It was what used to happen back in the day, with modern cars we are not used to it any more.

Edited by floormanager, 22 April 2022 - 06:22 AM.

[Cheeser]

Why don’t you get ACDodd to give an opinion, the cam very much governs how the engine will perform.

A bit of a rant…WHY, WHY don’t people talk about mph/ 1000 in top, then you can get a better comparison with different size wheels AND tyres!

[Ethel]

It used to be easy for manufacturers: they'd look at the maximum power they got from the engine and how fast that could make the car go, then pick a final drive that matched the peak power rpm with that road speed. That was 3.44 for a lot of Minis. 3.1 & 3.2 are from the era where noise & economy were more important & most of the competition had 5 speed boxes.

 

If your tuning efforts create more power by increasing the usable engine speed to consume more air then, conveniently, it's likely the optimum final drive is unchanged.

[ac427]

I think having a gearset where you get a taller first gear or at least a closer set of ratios generally would be more beneficial.

Edited by ac427, 22 April 2022 - 11:03 AM.

[jeffster06]

When I was rebuilding my gearbox for my 1310 I went from a 3.44 to 3.2 I was trying to find a good compromise as cruising on the highways at 80mph had me sitting around 5k rpm. I was hopeful going to the 3.2 the rpms would be reduced enough to make highway driving more enjoyable. In hindsight I wish I just kept the 3.44 as the 3.2 was noticeably sluggish off the line initially (kind of got used to it now/ forget how the 3.44 felt) Highway driving really didn't give me the improvement I was hoping for I cruise maybe around 500rpm less. If I ever have a reason to split the box again I might consider putting the 3.44 back in while I have it off. *edit* forgot to mention I run 10" wheels as well. 

Edited by jeffster06, 22 April 2022 - 12:12 PM.