28 replies to this topic

[JackMINI]

Hi everyone,

As I'm getting my 1973 Mini soon, and intend to do a couple of reversible modifications, such as a Stage one kit, and possibly a camshaft, this got me wondering, what kind of RPM will a A-Series internals take? If I were to stick a camshaft and maybe double valve springs in it, what would be a safe maximum RPM?

I know that most A-Series will get valve float at around 5500-6000RPM, but what will the crankshaft and 'rods take?

Just because if that will increase the maximum RPM it might be worth doing, as it will increase it's flexibility when hustling along backroads, and will mean in gear speeds are better.

So, what I'm basically asking for here is a safe maximum RPM stock, with a cam, and with double valve springs and a cam.

He'll not be thrashed, but it's nice knowing it's there occasionally, and letting that rorty old 5 port sing!

Thanks in advance.

Jack

[Ethel]

I think you'd be hard pressed to damage a road going A series in gear - too asthmatic. Maybe 5500 to 6000rpm as usable limit, another 500 between gears. A centre main strap is the mod if you want more.

[Dave33]

In standard form i would guess around 7000rpm max,if it was built for higher rpm use(like the old mini7's) it would be fine up to 8500rpm.
The thing is you need quite a well sorted head/intake and exhaust for it to be making any power at them revs,just putting a cam on that works at higher rpm is a waste as you will lose low rpm and not gain much up top with everything else stock.
dave

[clambert81]

If you modify it to rev higher, and it can be done, you'll lose driveability, ie low down torque and power won't come in till about 3,000 so you'll have to rev it all the time to make it "Go". The stage one kit will give you most BHP for the least money, and you will notice a difference

[JackMINI]

Hi,

Thanks for the advice, so by a well sorted head, would something like a ported 12G295 head be suitable?

The overall spec would be, HS4 SU, suitable needle, K&N element air filter, Torque-master inlet, Maniflow Cooper freeflow exhaust manifold, Fast or Mild-road cam, Double valve springs and then, if suitable, the 12G295 head.

Would that be a good set-up?

Thanks.

[clambert81]

I used a stage 3 head with twin carbs and fast road cam in my daughter's 998. Power really comes in after 3,000 and goes like hell after that. they got 107 MPH on the rolling road with it at only 5,800

[benb12]

Looking at your Mini I'm assuming you mean a 998 not a 1098. A 998 is safer at high RPM than a 1098. I'm fitting a centre main strap to my 1098, they're cheap to buy and all you need to do is machine the mains bearing flat. But if you have no plans to take apart your engine and gearbox then I wouldn't worry on a 998 - they're tough enough for road use really. If you're changing the cam then the engine will have to come out (some people say you can change it by cutting out the inner wing, but I'm sure you don't want to do that to yours!)

[HARBER07]

Standard crank is good for 7k i believe.

[Wil_h]

A totally standard engine will happily rev to 7k with no issues at all, infact it will hold together at 8k, but you'll be really pushing it a little bit. Any reasonably sorted 998 should be capable of 7k.

[Calum_Ward]

Hi I've got a 1974 dished piston 38hp mini 998cc engine

I was just wondering for it's age what would be it's max rpm? The engine hasn't had a rebuild or had any parts changed on it since it was built. I'm hoping to rebuild it and tune it for a rally car but would that old engine still be worth it?

It can go to 5k rpm fine just i don't trust it beyond that since it hasn't had any bearings changed and it's been in an accident with the oil pipe burst and a loss of compression before i got it.

 

This is a pic of all that carbon and crap in the engine....

 

 1454606597167.jpg   42.52K   27 downloads

 

 

Edited by Calum_Ward, 08 April 2016 - 05:59 PM.

[carbon]

Calum,

 

From the picture it looks a lot more like an A+ (post 1980) engine than a 1974 unit. The rockers are definitely A+, and the head studs also look like A+ but need a clearer picture to be sure. What's the prefix on the engine number?

[Cooperman]

It is impossible to give a figure for maximum revs without stripping and inspecting the engine. If it is old and worn even 5000 rpm could be too much.
A 998 in top condition can use over 6500 rpm.
You can either guess and hope or strip and rebuild as required.

[MRA]

Looking at your Mini I'm assuming you mean a 998 not a 1098. A 998 is safer at high RPM than a 1098. I'm fitting a centre main strap to my 1098, they're cheap to buy and all you need to do is machine the mains bearing flat. But if you have no plans to take apart your engine and gearbox then I wouldn't worry on a 998 - they're tough enough for road use really. If you're changing the cam then the engine will have to come out (some people say you can change it by cutting out the inner wing, but I'm sure you don't want to do that to yours!)

 

That is correct all you need to do with a centre main strap is machine the cap...... especially if you want your engine to fall to pieces at speed !  CMS is not such a good idea, firstly the machining needs to be dead flat, not milled but at the very least surface ground, then fitted, torqued up and then line bored and honed to compensate fro the distortion you will get.

 

Not a cheap option as the line boring can cost you £200+ ! 

 

Fitting a camshaft really needs to be part of a full strip down to get the best benefits and service life.

[MRA]

A fully worked 998 race engine will reach 9500 and in some cases possibly higher, however this is as high as it goes and "detuning" will reduce this according to what mods you actually end up with.

 

A decent 998 doing 7000 rpm will need a fair amount of head work and the associated costs that go with that.

[MRA]

Hi I've got a 1974 dished piston 38hp mini 998cc engine

I was just wondering for it's age what would be it's max rpm? The engine hasn't had a rebuild or had any parts changed on it since it was built. I'm hoping to rebuild it and tune it for a rally car but would that old engine still be worth it?

It can go to 5k rpm fine just i don't trust it beyond that since it hasn't had any bearings changed and it's been in an accident with the oil pipe burst and a loss of compression before i got it.

 

This is a pic of all that carbon and crap in the engine....

 

1454606597167.jpg

 

 

 

Oh yeah, that is one unloved engine....  what you will find is more often than not it is burnt valves that cause the reliability issues at speed, as the bearings will cope with it quite well.