18 replies to this topic

[stevemkeen]

Hi all,

 

I have a 1380 engine with a swiftune SW5 cam, I use12 inch wheels on the mini, I've recently had to do a rebuilt of the gearbox which turned out to be the layshaft bearing collapses, I got to it time before any damage to lay-gear or the casting.

The final drive I currently use is a crown wheel of 59 teeth with a 19 tooth pinion gear, ratio  3.1,  it has good acceleration in lower gears but I'm not happy with the top speed it achieves in fourth gear, hard to reach 70 mph.

I have another crown and pinion gear pair which is 58 teeth with a 20 tooth pinion gear, would this alter what I currently experience in acceleration and top speed if so in what way, or should I use another ratio setup to provide a better balance between acceleration and top cruising speed, I am aware what ever I use will be compromise, I would appreciate some advice advice.

 

Steve

[imack]

Final drive won't be the problem if you're struggling to reach 70mph, an 850 or 998 will do that easy enough. I'd look at engine set up first.

[viz139]

I agree your engine should be hitting 70 and beyond very easy, needs a tune up. When set up properly it should also easly pull the 2.9 .  3.1 is a great ratio if you like to nip around the place but 2.9 if you use motorways a lot.

[stevemkeen]

Ok thanks for reply's, the engine goes well and has really good acceleration 1st through to third, but in fourth I feel its holding back , I get to 70 but the engine sound like it being driven hard and I feel its the ratio I use that prevents me reaching a higher speed, but I will have the HIF 44 carb set up on a rolling road.

[nicklouse]

Ok thanks for reply's, the engine goes well and has really good acceleration 1st through to third, but in fourth I feel its holding back , I get to 70 but the engine sound like it being driven hard and I feel its the ratio I use that prevents me reaching a higher speed, but I will have the HIF 44 carb set up on a rolling road.

What does sounds mean? With a 3.1 in it you should be able   to easily exceed the national speed limit.

[kit352]

Do you have a tach set up in the car?

[stevemkeen]

Sorry I need to describe issues better than just saying "sounds like the engine is being driven hard" I've never measured the engine RPM at full acceleration, perhaps I'm not achieving the full RPM the engine is capable of with the setup I have, I know the timing is good and I have a BCE needle, I had it rolling road over a year ago, just hoped for more acceleration up to 70 and above if I push it very hard, which is why I asked about the best final drive ratio combination to use., thanks for all responses , Ill do more home work and get the carb set up again.

[nicklouse]

So what you want is better acceleration  over 70 rather than more speed? Two very different things.

[Homersimpson]

It may also be worth mentioning that minis and really old cars in general were designed to be rev'd and while a modern running at that speed might sound wrong its probably what the original designers expected the car to do.

 

I think nowerdays we are all used to modern cars which are just ticking over at 70, I had a Jaguar S-Type R and it was only doung 2200RPM at 90mph (not on public roads of course).

[nicklouse]

Put your info into this to see what is really going on.

 

http://www.guess-wor.../Tech/ratio.htm

[stevemkeen]

Again thanks for info,  will use that calculator and see what I can expect to see throughout the gears for my setup.

[Stevie W]

My 1293 Mini has a 3.1 final drive and pulls well through the gears. Its fitted with an SW5 cam, twin 11/4" SU's and a Minispares "fast road" head breathing through a centre exit RC40 exhaust system. She runs on 10" wheels with 165/70 tyres.

At 70mph in 4th gear, the car will accelerate readily up to 80mph and has plenty left in reserve.....if your ears can take the din!!! With the 3.1 diff the engine is spinning at around 3600rpm. For me this fd ratio is a good balance between acceleration and motorway speed comfort. A Mini will never be quiet at 70mph, but mine is bearable for short bursts.

So your 1380 should pull aswell if not better. As others have mentioned, it sounds like it's down on power for some reason in 4th around this speed.

Cheers, Steve.

Edited by Stevie W, 26 April 2020 - 04:43 PM.

[Cooperman]

I run a 3.44:1 in my 1990 Cooper and at 4000 rpm in top it is doing just under 70 mph.
I'm happy to cruise at up to 4500 rpm which is about 75 to 78 mph. It will pull to 6000+ rpm with its MG Metro cam. With a Swiftune cam peak power is probably at around 5800 rpm, so it needs to be revved a bit to make it go. Ideally change into 4th at about 70 mph.

[area51]

Is your car doing 70 but your speedo states otherwise??

This might be a case of the speedo gear ratios in the gearbox being incorrect.

As suggested view Guessworks website,

 

http://www.guess-wor.../Tech/ratio.htm

 

As your gearbox is off, check what spindle and gear is fitted for the speedo drive.

Guess works sell these if you need to change them

[Magneto]

Yeah, it's unclear what the OP is really saying here....

 

I had a lady come in once to have her 78 Audi 5000 serviced and she complained that it wouldn't go over 55 mph. I took her for a test drive and it shifted out of 2nd (auto trans) at 80 mph and I looked at her quizzically - she said "Well, sure, if you push it all the way down!"

 

So, OP, are you saying you have to push it all the way down to get over 70? Or that it really won't go over 70? Or that you think it should do it more quickly?

 

My 1980 Clubman Estate running a 2:76 with a mildly built engine would easily pull 95 mph on a single Hif44 and was still pulling - that was using the GPS on my Garmin for a speedo, not the one in the car.

Edited by Magneto, 30 April 2020 - 12:43 AM.