25 replies to this topic

[dangreen]

Hey,
I have a 1979 mini 850 and would like a little more power out of my engine for motorway cruising. I don't want to do an engine swap but wondered if there was some way of increasing the power lower down the rev range? I don't want to build a "screamer" that just revvs higher. I don't do much motorway milage but there is a dual carriageway near my house I often use with a speed limit of 70mph where I often get overtaken by lorries. It would be nice to be able to cruise at a lower rpm but I'm not sure if this is more of a transmission thing. Any advice would be helpful. Cheers

[mab01uk]

This thread below may help.

 

850 Power Upgrades:-

http://www.theminifo...power-upgrades/

Edited by mab01uk, 16 November 2019 - 10:56 AM.

[dangreen]

This thread below may help.

850 Power Upgrades:-
http://www.theminifo...power-upgrades/

Yeah I saw that thread but it seems to generally talk about increasing the power and I get the idea this means the engine would have to rev harder

[unburntfuelinthemorning]

To cruise at a higher speed with lower revs you need a higher gear.  You can fit a higher ratio final drive but the little 850 would struggle to pull it.

 

Although you don't wish to change the engine, the best way to increase the low down power is with more cylinder capacity, or you could supercharge your current engine!

 

Lorries are limited to 56mph so you only need to do 60mph to not be overtaken.  A standard 850 in good condition should be able to do 70mph flat out. 

 

I'm guessing you have a 3.76:1 final drive.  If so 60mph is only 4000 rev/min in top gear, well within the capabilities of the engine.  They'll go on all day at that speed.

[dangreen]

To cruise at a higher speed with lower revs you need a higher gear. You can fit a higher ratio final drive but the little 850 would struggle to pull it.

Although you don't wish to change the engine, the best way to increase the low down power is with more cylinder capacity, or you could supercharge your current engine!

Lorries are limited to 56mph so you only need to do 60mph to not be overtaken. A standard 850 in good condition should be able to do 70mph flat out.

I'm guessing you have a 3.76:1 final drive. If so 60mph is only 4000 rev/min in top gear, well within the capabilities of the engine. They'll go on all day at that speed.

That's what I suspected. So basically I should bore it out and fit new pistons or supercharge it to cruise at a lower rpm?

I have been 70mph in it but the engine sounds loud and strained. I'm not sure if this is just normal for an 850 but it would be nice to be able to cruise with less noise in the car. I guess I'm just used to more modern cars.

The lorries overtaking me seem to do about 60mph so I'd have to do ~65mph to stay enough ahead of them to not get overtaken which requires more rpm but not a lot.

[DeadSquare]

50 years ago, I fitted a '2A 948' cam and S exhaust to a friends 2nd hand 850 Mini Van, no other mods, and it did over 250,000 miles at 80MPH, five days a week from Bromsgrove to Bristol and back.

Edited by DeadSquare, 16 November 2019 - 10:37 PM.

[Minigman]

As said, 70mph is pretty much flat out for a good condition standard 850. But they do respond well to the normal a series tuning without braking the engine apart, provided it’s in reasonable condition. A better cylinder head with a slightly higher compression ratio (not too high, the split skirt pistons won’t like it!), better exhaust, inlet and ex manifolds, and upgrade to a HS4 should see upper 40s bhp and makes a big difference over the standard 34bhp. Will also help you achieve higher cruising speed too albeit at higher revs., but 850s rev nicely up to 6000rpm. Anything more than what’s mentioned above needs a better cam , cam bearing install and a better crankshaft to allow higher revs.

Edited by Minigman, 16 November 2019 - 01:13 PM.

[unburntfuelinthemorning]

That's what I suspected. So basically I should bore it out and fit new pistons or supercharge it to cruise at a lower rpm?

I have been 70mph in it but the engine sounds loud and strained. I'm not sure if this is just normal for an 850 but it would be nice to be able to cruise with less noise in the car. I guess I'm just used to more modern cars.

The lorries overtaking me seem to do about 60mph so I'd have to do ~65mph to stay enough ahead of them to not get overtaken which requires more rpm but not a lot.

 

Fitting a larger engine's easier like a 998.  You'd still need a higher final drive ratio like a 3.44:1 to cruise at the same speed with the engine speed lower.

 

Older cars were louder, it's just the way they were.  Until the 1980s, most cars only had four gears to play with so there was more of a compromise between crusing and acceleration. 

 

It's worth checking the bulkhead is sealed properly as this makes a big difference.  The speedo binnacle should be sealed to the bulkhead but often isn't when it's removed and replaced.  You can add additional sound deadening too.

 

The lorries are doing less than 60 unless they're going down a steep hill.  Their tachometers are very accurate and checked regularly unlike car speedos which tend to over read and are never checked for accuracy.  Most cars speedos will read about 60 when following a lorry.  Old Smiths speedos in Minis can get wildly out of kilter.  I like to get mine recalibrated so I know my actual speed.

 

Don't be the person doing 55mph in a car as every lorry driver will overtake you at 56mph, half of them will get far too close to your rear bumper, and every car driver will hate you because the lorries are getting in their way whilst taking ages overtaking you.

[mab01uk]

Driving an 850 Mini in modern traffic and on motorways requires skills that most modern car drivers don't really need or have long forgotten. Such as reading the road ahead.....anticipating what is happening to traffic way ahead to minimise the need for any braking.....

eg:-

A start from standstill at traffic lights in a low power car is much slower than slowing down well in advance and keeping the car moving until the moment the lights change, even a little forward momentum will mean you can accelerate away far more quickly.

Hills and inclines are hardly noticed even in modern small cars but in an 850 Mini you will gradually slow and eventually struggle unless you are in the right gear early or have seen the incline ahead in good time and so got a good run up coming down the previous descent !

It can be fun when you get it right but can also be stressful when you get it wrong and can't make it past a lorry on the motorway with your foot flat to the floor, while losing speed and unable to drop back due to a queue of impatient modern cars sitting on your rear bumper !!

Edited by mab01uk, 16 November 2019 - 04:31 PM.

[bpirie1000]

The 850 engine is awesome.. accept it and respect it...

Still gets you there....

Eventually.

[Magneto]

I think the easiest and least expensive way to get more power out of your 850 car is to remove the engine and put in a late model 998 with a 3:44. It will still be loud on the motorway tho…..

[dangreen]

50 years ago, I fitted a '2A 948' cam and S exhaust to a friends 2nd hand 850 Mini Van, no other mods, and it did over 250,00 miles at 80MPH, five days a week from Bromsgrove to Bristol and back.

Right, so basically it's fine to drive fast a lot and I shouldn't really worry about it

[dangreen]

As said, 70mph is pretty much flat out for a good condition standard 850. But they do respond well to the normal a series tuning without braking the engine apart, provided it’s in reasonable condition. A better cylinder head with a slightly higher compression ratio (not too high, the split skirt pistons won’t like it!), better exhaust, inlet and ex manifolds, and upgrade to a HS4 should see upper 40s bhp and makes a big difference over the standard 34bhp. Will also help you achieve higher cruising speed too albeit at higher revs., but 850s rev nicely up to 6000rpm. Anything more than what’s mentioned above needs a better cam , cam bearing install and a better crankshaft to allow higher revs.

Right. I think I'll probably stick with some fairly basic engine upgrades that don't need a new crankshaft

[bpirie1000]

If your going to change cams, valves, cranks and pistons just change the engine...

[dangreen]

That's what I suspected. So basically I should bore it out and fit new pistons or supercharge it to cruise at a lower rpm?

I have been 70mph in it but the engine sounds loud and strained. I'm not sure if this is just normal for an 850 but it would be nice to be able to cruise with less noise in the car. I guess I'm just used to more modern cars.

The lorries overtaking me seem to do about 60mph so I'd have to do ~65mph to stay enough ahead of them to not get overtaken which requires more rpm but not a lot.

Fitting a larger engine's easier like a 998. You'd still need a higher final drive ratio like a 3.44:1 to cruise at the same speed with the engine speed lower.

Older cars were louder, it's just the way they were. Until the 1980s, most cars only had four gears to play with so there was more of a compromise between crusing and acceleration.

It's worth checking the bulkhead is sealed properly as this makes a big difference. The speedo binnacle should be sealed to the bulkhead but often isn't when it's removed and replaced. You can add additional sound deadening too.

The lorries are doing less than 60 unless they're going down a steep hill. Their tachometers are very accurate and checked regularly unlike car speedos which tend to over read and are never checked for accuracy. Most cars speedos will read about 60 when following a lorry. Old Smiths speedos in Minis can get wildly out of kilter. I like to get mine recalibrated so I know my actual speed.

Don't be the person doing 55mph in a car as every lorry driver will overtake you at 56mph, half of them will get far too close to your rear bumper, and every car driver will hate you because the lorries are getting in their way whilst taking ages overtaking you.

I don't much feel like fitting a new engine to be honest.
Right. I'm not old enough to have driven these cars when they came out but I do enjoy driving cars of that era (my dad also has a 70s mgb I've been able to drive). I'm happy to put up with it but it would've been cool to make it a little quieter when cruising. I'll check the sound deadening as I had a little poke around the bulkhead and remember it was a little "disintegraty".
I have been meaning to check the Speedo actually. That's pretty good advice, I hate being overtaken by lorries but I don't want to stress my engine. I guess it should be fine to go at 65ish. I can always find ways to avoid the dual carriageway it just takes longer. Although makes the drive a lot nicer so kinda worth it if I'm not in a hurry