A vs. A+ Engine
Turbo Mini Forums

Hey y'all. I am pretty new here (and to the world of minis) and had a question on an A vs. A+ engine. I have looked around and see some of the differences between the two as such:

http://blog.simonbbc.com/classic-car-proje...e-classic-mini/
"Here are the A+ distinguishing features:
• Strengthening ribs on the back of the block at the clutch end
• Thicker block-gearbox flange
• Dizzy clamp is a forked plate with a single bolt into the block
• Dipstick sits directly in block, not in a tube, and is shorter
• Verto clutch, slave on plate slanting downwards, short arm. (NOTE: The very first A+ engines had a pre-verto clutch)
• Alternator bracket mounting holes are closer to the rad on the A block
• ‘A+’ stickers on rocker cover if a Metro!"

Now, I assume if there is nothing else listed, it hasn't changed. So that would mean the pistons, the connecting rods, the crank...etc are all the same since I do not see those listed....correct? However, I do know there is some difference between the A vs. A+ gearbox with the drop gears or the primary gear (something to that sort)...so that doesn't give me the confidence that these are the only differences.

The main reason I am asking is because I recently bought a 1975 Leyland Mini 1000 that has a pre-verto clutch and a 998cc A-series engine. I would like to upgrade some components and put a GT1752 on it, but am unsure about if these difference make enough of an impact that I need to seriously consider getting an A+ engine. With living in USA, A-series engines aren't as common as where y'all are located, so I am trying to see how much effort I need in order to try and find one.

I appreciate any help.

Hello.

You've certinally done your homework. And what you say above is correct. But the A+ 998 rods are different, and better (they have a hole to squirt oil under the pistons).

The drop gear issue you mention is to do with the idler gear. This runs in beraings in the gearbox casing and flywheel housing. The A+ varients used a larger bearing, and if turboing, I'd advise using the larger type.

The pistons are different to, but not on all engines. The later A+ had a short skirt slipper type piston.

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

www.twin-turbo.co.uk

Wil, i honestly didn't know that about the oil hole... So do you have any additional under crown cooling, or has this hole alone fine the job?

I've never added cooling jets, not really that much room on the 998 anyway.

As I'm currently building a bike engine turbo motor I'm wondering how I might add jets.

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

www.twin-turbo.co.uk

Thanks Will. I didn't know about the rods. That's helpful.

Regarding the gearbox, most A+ gearboxes have the verto clutch, which can handle up to a certain hp. From that I was going to use a pre-verto and upgrade the force plate. However, from your suggestion, the larger bearing would be better. Could I replace the bearing and the idler on the pre-verto? What would be the easiest to have the A+ bearing feature but still be pre-verto? BTW, I am assuming that I do not have the A+ gearbox since it is pre-verto.


I know Coopers have the domed pistons. Then there are flat top and dished pistons, which would give it about a 8.3 or a 9ish ratio. However, it doesn't seem like the pistons are a function of whether or not it is an A+ or not, right?

FYI...I am looking at putting around 10-15psi boost in this. However, not more than 15psi.

If I were in your position, I would probably source a complete running a+ 998 and work from there, with regards to the verto clutch it is worth looking up on the RTS clutch on here instead of preverto upgrades, as it's much less stress on the crank thrusts.

The flywheel type is not affected by what drop gars you have. All flywheels fit all cranks.

As for the idler, easiest way is to use an A+ gearbox and flywheel housing. I think the gearbox could be modified for the larger bearing (not 100% on this). So you may just need the later flywheel housing.

Dished pistons are all 5 or 6cc, so depending on your head chamber size that's the easiest way to get the CR you want.

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

www.twin-turbo.co.uk