Discussion
Check the CR. The 12G295 had the hargest combustion chamber of any A series heads, and the engines they were original fitted to had pistons with a raised section on the crown to get the CR up. With flat topped pistons you have to skim a lot of metal off the head.
As for the cam, the humble MG Metro item works well, and can be had free or very cheap secondhand. Personaly for a road going 998 I'd consider a Kent 266, better idle quality than the Metro cam and a healthy power increase.
My brothers first engine was a 998 with a nicely ported 12G295 with Powermax flat top pistons and an MG Metro cam and it was surprisingly quick, enough to upset a few 1275 engined minis!
As for the cam, the humble MG Metro item works well, and can be had free or very cheap secondhand. Personaly for a road going 998 I'd consider a Kent 266, better idle quality than the Metro cam and a healthy power increase.
My brothers first engine was a 998 with a nicely ported 12G295 with Powermax flat top pistons and an MG Metro cam and it was surprisingly quick, enough to upset a few 1275 engined minis!
Entirely agree with Mr2.
The 266 will be lovely in the 998. The 12G295 is a really great head, but it does suffer from large volume chambers. Be very careful when skimming this head as it's easy to go through an oilway. If you have a vernier caliper you can measure the depth of the critical oilway from the top (i.e. valve spring side) of the head and subtract the depth of this hole from the total head thickness. Don't skim to give less than about 0.070" remaining thickness from base of oil way hole to lower head face - be very, very careful with this. What you can do is to allow the pistons to project a couple of thou proud of the block face, skimming the block to permit this. You can actually allow the pistons to project a bit more, say up to 0.007" above the block deck level, but you must check the valve clearances to do this safely. If you do a trial build as you should using linished down gudgeon pins, you can measure everything before final machining. It does mean two trips to the machine shop, the first for the re-bore/crank grind, and the second for the block to be 'decked' and the head skimmed.
With the set-up you describe I would think you'll get around 65 to 68 bhp at the flywheel and it will be nice and driveable.
Good luck. Email me if you want any more help with the measuring or critical dimensions.
The 266 will be lovely in the 998. The 12G295 is a really great head, but it does suffer from large volume chambers. Be very careful when skimming this head as it's easy to go through an oilway. If you have a vernier caliper you can measure the depth of the critical oilway from the top (i.e. valve spring side) of the head and subtract the depth of this hole from the total head thickness. Don't skim to give less than about 0.070" remaining thickness from base of oil way hole to lower head face - be very, very careful with this. What you can do is to allow the pistons to project a couple of thou proud of the block face, skimming the block to permit this. You can actually allow the pistons to project a bit more, say up to 0.007" above the block deck level, but you must check the valve clearances to do this safely. If you do a trial build as you should using linished down gudgeon pins, you can measure everything before final machining. It does mean two trips to the machine shop, the first for the re-bore/crank grind, and the second for the block to be 'decked' and the head skimmed.
With the set-up you describe I would think you'll get around 65 to 68 bhp at the flywheel and it will be nice and driveable.
Good luck. Email me if you want any more help with the measuring or critical dimensions.
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