mk1-forum.net

Evening all,

I don't often post on this forum but I have a few questions I hope people may be able to answer or offer advice on.

I'd like to rebuild a MK1 mini, paint it cooper colours, and pop in a tweaked 998 cooper engine. At the moment I only have funds to secure the engine, the car will come later. You may ask why not just buy a cooper in the first place, but the problem is (as you all know i'm sure) that they pop up fairly infrequently and a basic Mk1 project car would probably save enough to fund the engine rebuild. The reason for wanting the 998 cooper engine is that I'd really like a genuine cooper powered car, and S engines are way out of my price range.

So, if I can find a 998 cooper engine to rebuild I'd like to gain a bit of performance if possible whilst replacing bearings/pumps/gaskets etc. I don't have a target final BHP in mind, but i'd love to pop from 55 to 60 I guess.

Does anybody have any experience of how to improve on this engine given it already has one of the best small bore cylinder heads, a decent exhaust manifold and twin SU's?

I'm thinking of a rebore (obviously dependant on what the engine bore is already at), maybe an SW5 cam (have read this is almost identical to the 997 cooper cam and gives good gains?), a small head skim, single box RC40, and maybe improved carb needles/springs to match the above. If money permits I guess I could look at going up in valve size.

Any advice on this would be appreciated. All that said I'd be very happy with a rebuilt standard 998 cooper engine, but if funds permit I'd like to improve it.

Thanks,

Alex

how about a straight cut gearbox

wolseley 1000 wrote:how about a straight cut gearbox

More of the 55bhp to the wheels. Like the idea, but sounds expensive!

Rampipes or decent filters, polished head with a bit of a skim, maybe bore it +40, 1031cc and a 266 cam. Mine gave 71bhp at the crank and very driveable, good fun

Alexm,

Your plan sounds like my sort. You are being very conservative & will as a result be very pleased with the results obtained.

Firstly, don't look for a 998 Cooper engine, just look for a decent standard 998 engine, you will always pay a premium for an original Cooper unit & you will almost certainly still have to replace the pistons, which are the only "Cooper" bit in the short motor.

My suggestion would be something along the lines of this;

Standard 998 bottom end, but balanced, Plus 40 pistons, aim for 10:1 ish comp ratio, nicely ported & polished 12G295 cylinder head, SW5 or 997 Cooper cam, 3into1 exhaust manifold, connected to RC40 exhaust, twin HS2 SU carbs on a modified standard Cooper type inlet manifold or tubular steel one if you can stretch to it. And as Smoke suggests carb trumpets give a big improvement over filters.

This will give a really pleasant reliable unit that will be an improvement in drivability as well as outright power.

Good luck & have fun,

I am amazed at how much Ram pipes can reportedly change things. What kind of BHP improvements are you likely to see over Pancake K&N type filters and would you mind suggesting the best socks to fit?

I have no idea on specific benefit of JUST TRUMPETS I have only used them as part of a build. I never use socks, just open mouths, and suspect that any benefit of using a trumpet would be negated by using socks.

Having used them for 20 years plus, I am still waiting for one or more of the terrible things that should happen to happen.

mk1 wrote:I have no idea on specific benefit of JUST TRUMPETS I have only used them as part of a build. I never use socks, just open mouths, and suspect that any benefit of using a trumpet would be negated by using socks.

Having used them for 20 years plus, I am still waiting for one or more of the terrible things that should happen to happen.

Socks kill the benefit of trumpets. And don't use trumpets with the gauze on the end.

use short-medium trumpets with K&Ns. It kills two birds....etc and it can be done.

For road use, I'd use a 1098 block if you can find one, with a metro turbo cam (6648?). The 998 is fine though but not as torquey - when you've been driving diesel company cars for as long as I have, you get used to not changing gear!

Thank you all for your replies.

I too wasn't aware of the benefits of usings trumpets. I always thought they were typically for the track only. I'd be nervous not running any sort of filter/gauze but I bet they sound fantastic with lots of throttle!

mk1 - i've been offered an early 998 cooper engine (n/o 4972) with an unleaded conversion on the 12G295 head, duplex timing gear and a 4 syncro 12G1128 g/box (any body know what g/box this would normally be mounted on and what the final drive might be compared to the cooper?) The box jumps out of 2nd so needs looking at, but the gent selling it is a Cooper forum member and the engine was only removed due to a 1300gt upgrade. On offer to me at £350 plus my petrol to collect it, which I thought was pretty reasonable.

Alex

350 quid? That's about right. You may want to check it over before you fit it, though

65ish bhp could be achieved with a +40 thou rebore on a 998, with decent exhaust, 12G295 plus mod of even the basic cylinder head and 1 1/4 SU's and yes, mainly a 229 Cooper 997 profiled cam. That is the secret, the camshaft. A basic 998 engine would sing with that with the rest, and be a joy to drive.

And dished standard 998 non-cooper, cooper which are domed or flat top I think, work better, but you need to get the meat off the cylinder head to get 10:1 comp ratio, but it can take it usually. Dished pistons get better squish for firing, or something like that. Anyway, they work better for a road engine. Domed/flat tops are needed for 13:1 CR and race cams, 85bhp off a 998 engine race prepared.

£350 is pretty reasonable for a Cooper engine & box. But a similar normal 998 one would be around £150, but you would have to source a 12 G 295 head.

The Cooper one is probably a good deal.

i have,still building up my 998 cooper engine, and glad to here i have done the right things to get a nice little engine,

+0.040
ported , polished, larger valves 295 head
around 9.5:1 comp ratio
sw5 cam
swift tune venier timing gear
uprated, pushrods and cam followers
twin HS2, maniflow inlet,
roller 1.3 rockers
lightern flywheel and back plate
stainless steel freeflow manifold, and stainless steel, twin box RC40
using a standard gearbox with comp baulk rings, and X pin diff, 3.1 ratio

so should be a good little engine, i choose not to go the 1275 route as i wanted to keep it close to what was in the car,

did not want to go too crazy with the cam, as i want it drivable around town but still fun to go for a blast, its cost me a fair bit but well worth doing,

comp baulk rings

I hope you didn't gpo for the bronze competition ones they wear like nothing on earth.

Always best to use the Standard Rover ones in all applications including competition.

I think given the approx £200 price difference I'll try and grab the cooper engine. Especially if it was a decent runner and the unleaded conversion is OK.

So, assuming the head can be removed for me to inspect, i'm looking for the 12G295 casting on the top of the head, the pistons should have the raised D-crown. There should be a 1000 tag on the back of the block and twin HS2's attached. Engine number is 9FD-SAH which ties up.

Am I right in thinking that if a 998 cooper engine has the D-topped pistons that it's running the standard bore? Are over sized pistons available with the D-shaped crown on them?

Alex

I Got it a bit wrong. There MS performance baulk rings. So they should be good.


Yeap should have D top pistons unless it's been rebuilt and changed. But the engine number should tell you if it's a cooper block or not. It will be a good price if you also get the twin carbs

Dean wrote:i have,still building up my 998 cooper engine, and glad to here i have done the right things to get a nice little engine,

using a standard gearbox with comp baulk rings, and X pin diff, 3.1 ratio

so should be a good little engine, i choose not to go the 1275 route as i wanted to keep it close to what was in the car,

did not want to go too crazy with the cam, as i want it drivable around town but still fun to go for a blast, its cost me a fair bit but well worth doing,

Dean, I think a 3.44:1 diff would be better, but if you do not do much motorway/dual-carriageway driving, even a 3.647 or 3.765:1, if I remember the ratios right. I think the standard Cooper 998 then was fitted with a 3.765 as standard., if I remember right. A tuned 998 stroke engine is quite buzzy, and would be wasted with a 3.1 diff, truely honestly. And that is with ten inch wheels. If you are planning 12" wheels, even more so, with their less turns per rpm.

Many years ago I had a 998 with a 997 cam in it and it didn't really work that well.

Innocenti 998 Coopers had, I think, a standard S cam in them which gave more power - if you want to use a BMC item. Modern cams are almost certain to give better results if you select the correct one.