17 replies to this topic

[systemshock]

I'm currently rebuilding an old 998 mini 30 engine and was looking at getting a bit more out of it.

Looking at the stage 2 and 3 cylinder heads, they seem to give a nice enough power / torque increase, but I wasn't sure about the reliability, and also what gasket to use?

As the head has been filled in to increase the compression, can I still use the standard head gasket? or do I have to buy one specific for the head?

Thanks

[jaydee]

Standard copper gasket will be fine.
If the head is a good biult, you wont have any issue.
Go for a stg3, for me its not worth buying a stg2 head as you can do yourself one head with some chepo instruments and a good old vizard's book.

[systemshock]

Thanks, It just seemed strange to have a gasket overlapping the cylinder.

If you know as well, I was playing with the idea of boring the engine. Can i use the standard 998 cooper gasket, or have to use an oversized one?

[bmcecosse]

Head 'filled in' to increase compression ?? I doubt it! The gasket won't overlap the bores - unles you have overbored considerably ? the 'best' head to fit in my view is a 12G940 - from a 1275 engine - the normal standard valve size head will be fine. Can sometimes be picked up for as little as £10/15 ! Just check if the exhaust valve will hit the block - if so - recess the valves by 40 thou into the head - and use with 1275 head gasket and rockers. It's about 'stage 4' for a 998 engine ! Best value mod by far!!

[systemshock]

Excellent.

Thanks a lot, I've been trying to think of what exactly to do to the project. This helps a great deal

[liirge]

the 940 head is only really needed if your building a screaming 998, The BEST option is to find a 12g295 head, old Cooper head.

[systemshock]

Is it just an eBay job to get hold of one? or is there somewhere particular you can get one?

[jaydee]

its an ebay thing, if you want to pay it a few quids.
Surely it will need a rebuild and valve springs, and probably the valves too..

[bmcecosse]

Stage 2 would be a 12G202 head - fom an 1100 engine - it would need skimming by ~ 60 thou. Stage 3 would be a 12G 295 head - from an MG 1100 or 998 Cooper - it too would need skimming by ~ 60 thou. Stage 4 is the 12G940 head - plenty about - and it works really really well - I have one on my 1098 engine - and it pulls well all through the range. You won't be disappointed! It's ideal for a 998 - needs no skimming - but 'may' need the exhaust valves recessed by 40 thou - you need to measure to find out - or just do it anyway and then you know it's safe! If you can find an MG Metro camshaft at the right price - that's ideal too -and complements that head very nicely. Go the 295 route if you wish - it's certainly quite a good head - but it does need skimming (but check to see if it's already been skimmed first!) and they tend to be 'over valued' on ebay.

[liirge]

the thing with the 940 compared to the 295 is, that if you are after a more drivable car the 295 is a better route, due to valve sizes. The valve sizes in the 940 are bigger, and due to this in the low revs the port velocity is less (slower) meaning that compared to a 295, at that lower road usage rev range you aren't able to fill your cylinder as much as a 295 and will loose power. The 940 comes into its own when the revs are alot higher, (so putting one on a slow revving, long stroke 1098 isn't going to get the most from the 940).
The 940 requires more work than the 295, the 295 is more expensive than the 940, but still cheaper than a new "Stg 2 or 3 head" - whatever that is meant to be...

[valve bounce]

best mod for the 998 is a 12g295 head, as for the person saying to fit a 12g940 i wouldnt its harder to do for not that much more. aslo if you skim a 940 head up to gain compresion then your going and cutting a lump out of the bore witch then loses some of the compression youve gained.
just my thoughts

[bmcecosse]

I did a direct swap from a 295 to a 940 on my engine - and the difference was quite amazing! The 940 doesn't need skimming - it has relatively small chambers and gives a good CR anyway.

[Turbo Phil]

I'd fit a 295. Putting a 940 on and recessing the exhaust valves is a bodge imo. Sinking the exhaust valves will reduce flow so it's possible it might not even flow as well as the smaller valved 295.

[bmcecosse]

The valves are sunk by only 40 thou (some heads don't need anything doing - but you MUST measure) - and then the floor of the chamber is chamferred away with a small grind stone (takes all of 5 mins to do all 4). I can ASSURE you - my 1098 runs excellently at ALL revs with 940 head, MG Metro inlet and HIF38 carb with AAA needle. I would never go back to the 295 I removed ! The valve sizes and ports are SO much better on the 940 - although a little work down the throats of the exhaust ports in particular does help considerably - the head is very restrictive just where it turns the corner at the guide boss.

Edited by bmcecosse, 14 August 2009 - 06:26 PM.

[liirge]

It could be because the 940 head raised your compression ratio, rather than it actually being anything to do with the head itself