6 replies to this topic

[Leykor]

Good Day

I’ve got a 1000cc A series engine that has a 2A629 cylinder head. I want to change this head to something that will give me more performance.

I know the 12G295 is said to be the best replacement. I have found a 12G949 from a 1275 at a decent price, will this head work? I have not managed to find a lot of information on this Head.

Thanks

[Guess-Works.com]

you wont find much on a 12G949 because it's actually a 12G940 ( someone's missread the casting number )

They physically fit however, it is wise to pocket the small bore block when fitting a large bore head ( which the 940 is ), with a std or low profile cam you can sometimes get sway with it, but anything high lift then, you must pocket the block..

The 295's and 202's for that matter, will need to be skimmed to work with a 998, they had a larger chamber which without modification would give you very poor compression.

[Leykor]

Thanks Guess-works.com

Okay I have found a 12G295 slightly more expensive than the 12G940. How do I work out how much I need to skim the head? I do not want total performance Im just looking to make my mini a little more powerful for road use.

Thanks

[AndyMiniMad.]

The combustion chamber volume in cc's is where the gases get squashed into and as such the bigger the volume the less squash!! (compression). You will need to skim the head to bring the combustion chamber volume back down to the same or near the same as it was on your old head. I think the volume on a 1275 head is 21.4cc's, not sure on the 998.

Edited by AndyMiniMad., 22 October 2010 - 05:57 AM.

[PhilipGCaldwell]

i have gone down the 12g940 route. As i am rebuilding a 998 engine out of the car i have decided to pocket the block, you can howver get the exhaust valves recessed to stop them hitting the block. If you use the 12g940 then you need to use a 1275 head gasket. In my opinion 12g295s go for way too much money for what they are.

[Leykor]

Hi my engine is a 998cc with a 2A629 Head with Nominal cc of 24.9cc

The 12G295 has slightly higher nominal cc at 28.3cc.

Thats about as much as I know.

If I go to a machinist do I just say... "Please skim this head" Or must I give a value like 1mm?

Thanks people

[AndyMiniMad.]

If you take too much off the head the valves will come into contact with the top of the block!! Best to get a bit taken off the head and the block. It really depends on how far your pistons come up the bore. You dont want them smashing into a partially open valve... Very bad news.. You can use a compression ratio calculator (Google) to find the cc's that you require,