26 replies to this topic

[Fast Ivan]

if you want a engine that will be happy around the town and at 7k then have a look at the K head conversion

[lawrence]

or a micra engine ;)

[driftz]

Out of curiosity what (design wise) is the reason the a series doesn't like to rev? push rods? crank/rod ratio? 3 bearing crank? Obviously they are all deciding factors but is there any one inherent flaw in the design that doesn't allow it to happily rev 7+ thousand. I have a crx that will hit 7 grand all day and my old AE86 had 300K klm and would happily sit at 7600 everyday without skipping a beat. They are very different engine designs but still curious.

[Cooperman]

The A-series is a 3-main-bearing engine with a bore to stroke ratio which is less than 1. All modern 4-cylinder engines have 5 main bearings.

 

That means the crankshaft is not so well supported and the piston speed compared to rotational speed is high.

 

Most old engines were like this and remember the A-series was designed in the 1940's, so it is over 70 years old. Back then the tax on a car depended on the 'RAC Horsepower' which meant the long stroke engines with smaller bores were cheaper to tax.

 

When Ford did the 105E 997 engine in 1959 it had just 3 bearings, but the bore was 80 mm and the stroke was 40 mm (approx - don't have the exact figures) so it would rev well. When Ford enlarged this they eventually went to 5 bearings and that is what the Mk.1 Cortina GT, a big competitor to the Cooper 'S', had and at 1500 cc it still had 80 mm bore with a stroke less than that.

 

Then again, why do you want to rev it to 7000 rpm. You gain nothing, but increase engine wear for no advantage. If you want to cruise at lower revs, then decide what cruising speed you want, match that to a suitable cam and final drive ratio which puts the excellent torque at the right revs With an A-series engine, 7000 rpm is for out-and-out competition cars which won't run at low revs and which are unpleasant on normal roads. The same thing applies to the MGA, MGB, Healey 3000 and other BMC cars of that era. 

 

Modern engineering has given us small, all alloy, single or twin overhead cam engines, sometimes turbo- or super-charged, with superb fuel injection, capable of high revs and low engine wear rates. The power & torque bands are wide and 5 and 6-speed transmissions allow a lot of flexibility. But the classic Mini is not like that and is not what one buys a Mini for. In the 1930's, i.e. 20 years before the Mini, some under 1 litre engines only had 2 bearings

 

There is no point in trying to make a 60-year-old design perform like a modern 1.25 litre hatchback. It's an old classic car and 1960's icon - and it's fun.

[minimans]

 

There is no point in trying to make a 60-year-old design perform like a modern 1.25 litre hatchback. It's an old classic car and 1960's icon - and it's fun.

 

Ah! But it is fun trying...............................

[Dusky]

Mini's arent unable to rev though. Mine hits 8.5k on the rev limiter. But I cant see the point of hitting 7k in your case :)

[Spider]

Out of curiosity what (design wise) is the reason the a series doesn't like to rev? push rods? crank/rod ratio? 3 bearing crank? Obviously they are all deciding factors but is there any one inherent flaw in the design that doesn't allow it to happily rev 7+ thousand. I have a crx that will hit 7 grand all day and my old AE86 had 300K klm and would happily sit at 7600 everyday without skipping a beat. They are very different engine designs but still curious.

 

Bore wear at those sorts of speeds. Fit liners, forged pistons that use a thin ring and a chrome top ring.

 

The other items that will cop a hammering at those continuous speeds is valve stems, valve guides and rocker gear, the latter can be helped by the use of full roller rockers.

[driftz]

Very enlightening posts thanks for the info. My longing for a high revving A series isn't totally based on "engine needs" and maybe more so on my personal desire (for no other reason) than wanting a little buzz bomb engine. I also do like the idea of taking an antiquated design and showing that it can still be made into a screaming little package. 

 

From all the wisdom given here though I see that this is not the best way to head in the engine build. No point in having a high revving engine if its way past peak power and vibrating itself to bits!

[AeroNotix]

I have an EP3 Type R honda that revs to 8.2k. It's hilarious and I love it. The sound, the long pulls, the power. I would love if I could nicely get an A-Series up like that.

[nicklouse]

Very enlightening posts thanks for the info. My longing for a high revving A series isn't totally based on "engine needs" and maybe more so on my personal desire (for no other reason) than wanting a little buzz bomb engine. I also do like the idea of taking an antiquated design and showing that it can still be made into a screaming little package. 

 

From all the wisdom given here though I see that this is not the best way to head in the engine build. No point in having a high revving engine if its way past peak power and vibrating itself to bits!

if you want revs then short stroke it like the 970s  but even then it is the wrong engine unless you have lots of spare cash.

[grizzler73]

Who needs high speed/revs in a road Mini? Noisy and costly. It's the corners where the fun is to be had!

[Cooperman]

Who needs high speed/revs in a road Mini? Noisy and costly. It's the corners where the fun is to be had!

It's just driving a true classic which is where the fun is to be had. It's the same type of fun as can be had driving a standard E-Type, a Sunbeam Rapier, an MGB, a Cortina GT or a Mk.1/Mk.2 Escort.

 

Driving as it used to be before we had all the artificial aids like ABS, ASC, etc.; that's what classic car driving is all about.

 

If you want a drive at modern car performance, then buy a modern car. For example, my current BMW E65 is faster than an E-Type, but it is so easy to drive, so safe and has fantastic road-holding and good handling. It is nothing like a classic car and I wouldn't want it to be. Similarly, I wouldn't want any of my classics to drive like a modern car as that would defeat the object of having them and spoil my enjoyment of them.