47 replies to this topic

[minimk1]

Hi brought a 998 cooper engine with an early 997 head a 185 and d top pistons however this one has had work. So far I have stripped the engine to the block and box and have painted it bmc green I will be refurbishing and renewing parts etc.

The spec I was thinking of would be a
12g940 head
Pocketed block ^
276 cam
Lightened flywheel
Mainiflow exhaust system
Twin 1.25 carbs with sub stacs

Can anyone give me and idea on the bhp I will be getting and any other things I should consider doing I would hope to get about 70-75 bhp

Will have pictures soon

[Cooperman]

My guess would be 60 to 65 bhp. That is not a much higher spec than a standard 998 with a 295 head and they gave 55 bhp. The 1071 Cooper 'S' gave 70 bhp with the bigger valve head and a 510 cam. I got 66 bhp at 6000 rpm from a 998 bored to 1060 cc with flat-top pistons, a 510 cam, HIF38 on a Howley inlet manifold, re-curved distributor, lightened flywheel, fully flowed 295 head with bigger inlet valves. However, it was very smooth to drive and fely 'nippy' enough for a classic car in modern traffic.

[minimk1]

Yeah maybe an optimistic 10bhp over. I want to keep it a 998 just want it revy and quite camy on idle but with usable power I think I would be happy with 65 bhp is the 276 the right cam to use ?

Edited by minimk1, 22 April 2013 - 07:46 PM.

[minimk1]

Any specs better than mine welcome

[Cooperman]

I once used a 286 in a 998, but it was a pretty 'full-on' rally engine and it gave 72 bhp at 6500 rpm and needed a special close ratio gearbox and a very low final drive ratio to keep it on the cam and the revs above about 5500 ropm all the time.
I would think a 266 would be about ideal, unless it is a serious competition car.
You can overbore it to +0.080" which gives 1060 cc.
Maybe consider a 12G295 head which avoids having to pocket the block.
Make sure you set the compression ratio to around 10.3:1.
Build the engine very accurately.

[minimk1]

Would a 12g295 give the same power as a 12g940

[Cooperman]

I think so, others may disagree. The 295 head was designed for the 998 Cooper and can be fitted with larger inlet valves and fully gas-flowed. With a 295 you don't have to worry about valve clearance to block deck. The 940 head can & will work well, but it is a lot of messing about for little real gain and unless it's for real competition a few bhp won't make any difference to the way it goes on the road.

[Spitz]

Can you use "d top" pistons with a 1275 head?

[minimk1]

What do you mean by a re curved distributer

[minimk1]

And I probably will go for a 12g295 as it means less hassle and is made for the engine

[Cooperman]

When an engine is 'improved' to give more power the rate at which the distributor advances from its idle setting of, say, 10 degrees BTDC to it maximum of, maybe, 32 degrees BTDC at over 4000 rpm will need to alter to cater for the new engine specification. With a higher compression ratio and a greater fuel/air volume in each cylinder, it may well be that the engine needs to 'fire' slightly later than when standard to avoid pre-ignition (also called 'pinking') which can damage the pistons. In such cases the distributor is 're-curved' to give optimum advance at all revs right through the rev range. Specialist companies such as Aldon Automotive can advise on this and do the necessary modifications to a distributor.

[jonny95]

I want to keep it a 998 just want it revy and quite camy on idle but with usable power

i have 998 with flat top pistons, 266 cam and 12g295 head with bigger inlet vlaves

It is good low down as it happily sits at 30 in 4th (3.44 fd), but it is still pulling hard up to 6 - 6.5k rpm

I think it would be a better spec than yours for a road car as it works well all round

i have a single hs4 but with twin hs2's like you plan to use i would imagine a small increase in power of the hs4

you say you want 70-75bhp from a 998 but i would imagine that to get this kind of power you will be losing a lot of low down pull

i hope this is helpful

Jonny

[minimk1]

Yeah I though so ill stick to aiming for 65 :)

[Vipernoir]

The difficult bit about builiding a Cooper engine is finding the D-crown pistons.
If yours are in resueable condition and the bores are good enough, I'd re-ring the pistons, hone the block and go from there - this would allow the use of an unskimmed 12G295.
As the std Cooper angine gave 55bhp, a cam change for something like an MG Metro (KC500), an SW5 or a Piper 255 would make a very nice engine that didn't need a million revs.

I'm not convinced that a 12G940 shows any advantage of a 295 at normal speeds and revs.

[minimk1]

Yeah the d top pistons are in very good condition and the rings look recently replaced how hard is doing an engine rebuild as I would only be changing the head and cam. I would obviously be getting the head done with bigger valves and get it polished and ported by a professional but is cam fitting and timing hard ? As I would be up for doing it myself to save money ;)