5 replies to this topic

[Mini Mad Drakeley]

hi everyone,

after reading this months mini magazine article on the engine strip down and rebuild, ive found i have got an A+ series cylinder head and my main engine is pre a+. do these come running on unleaded as standard or slight more power output?

on another note im considering putting an 1100 cylinder head on my engine for the slight extra power and so it runs better (im assuming i read the magazine right lol) i can easily get an 1100 head but am i right in saying it can just bolt straight on the 998 block and no one will be any the wiser?

i know pretty much nothing about engines which is why im learning lol

many thanks, Adam

[Wright&Wright]

The 1100 engines are the same as a 998 engine in bore size but have a longer stroke, hence the slightly larger displacement. I think the compression ratios are different and the 1100 heads have larger combustion chambers which would need to be skimmed in order to give the correct compression. A simpler move would be to buy a 12G295 cylinder head from a Cooper S 998 or a Sprite. These give an affordable increase in usable power for road going applications. Once again though, this would need to be skimmed in order to give the correct compression for a standard 998.
To get the most of a cylinder head it usually requires a change in the camshaft. A metro camshaft combined with the head I mentioned would give a reasonable boost to your power output.
Buy Vizards book on tuning the A-Series also, learn how to do the basics in cylinder head modifications, apply them to your new head and you should be more than happy with the results.
As for unleaded heads, the simplest way to check (if the head is already off the block) is to look for hardened valve seats.

Edited by Wright&Wright, 14 January 2011 - 02:28 PM.

[bmcecosse]

The 1098 head is 12G202 and ha slightly bigger inlet valves and ports - ie it's effectively stage 1. It needs 40 thou skimmed off for use on a flat top piston 998. The 12G295 head has slightly bigger again inlet valves and much better porting and chamber shape = stage 3. It needs 60 thou removed to use on a 998 engine. Best of all is the 12G940 head which needs nothing removed, has bigger again inlets and bigger exhausts and much better ports and chambers = stage 5 - but does need checking to make sure the exhaust valves won't hit the block.

[Turbo Phil]

buy a 12G295 cylinder head from a Cooper S 998 or a Sprite.
Buy Vizards book on tuning the A-Series also, learn how to do the basics in cylinder head modifications, apply them to your new head and you should be more than happy with the results.
As for unleaded heads, the simplest way to check (if the head is already off the block) is to look for hardened valve seats.

There's no such thing as a 998 Cooper S. The 12G295 head was fitted to the 998 Cooper & the MG 1100.
Sound advice on the Vizard book though !

[bmcecosse]

I ran a 998 with a Cooper S head - surely it was a 998 S ?????? I'll get my coat.

[Mini Mad Drakeley]

all right, thanks everyone, il get a vizard book ordered and im sure with haynes, vizard and mini magazine i can make a pretty good engine that will work and not break down and also the extra power to keep up with more powerful cars and embarrass chavs

again, thanks