14 replies to this topic

[liam-ds]

hi all was just wondering if i was to put a 12g202 cylinder head on a 998 mini would i see any real difference in performance? its got a stage one and a little more on at the moment but it has a little blue smoke and this is the second cam4810 head ive had on one i killed my self haha and this one a valve stem has a little wear. i know the 12g295 is the best but this is only a out on engine until i decide what my next engine will be either a mg metro or a mad 998 as i have both sat in the garage

many thanks Liam

[twrminisport]

Theoretically, yes due to slightly bigger valves and ports
In practice the difference may be noticeable but minimal without a cam change

If you decide to sell the 998 let me know won't you

Jesus

[liam-ds]

Theoretically, yes due to slightly bigger valves and ports
In practice the difference may be noticeable but minimal without a cam change

If you decide to sell the 998 let me know won't you

Jesus

OK thanks, ill keep a eye on that 12g295 then of it goes cheap ill have a go at it the mad 998 will be a mg metro head pocketed block etc with a kent 276 cam in may go for 286 yet but depends on funds the cam is the only thing i need for the 998 ive got everything else. but if i decide to sell ill drop you a PM

again thanks Liam

[twrminisport]

Yeah a 286 could work well with a nice carb and the appropriate bottom end mods

Jesus

[liam-ds]

Yeah a 286 could work well with a nice carb and the appropriate bottom end mods

Jesus

ok great thanks for clearing that up wasn't 100% sure what carb would be best suited twin hs4's or a hif 38 or 44?

Liam

Edited by liam-ds, 28 October 2011 - 06:51 PM.

[Shifty]

286 is way to heavy for a 998!!

I think a 276 is about as high as you want to go really, unless you plan on revving the knackers off it all the time

12g202 is a nice cheap upgrade, probably better than some 'performance heads' that are sold.

Light flywheel as well and let her rev!!

[liam-ds]

286 is way to heavy for a 998!!

I think a 276 is about as high as you want to go really, unless you plan on revving the knackers off it all the time

12g202 is a nice cheap upgrade, probably better than some 'performance heads' that are sold.

Light flywheel as well and let her rev!!

OK thanks shifty think 276 may be better the head in question has been snapped up was on ebay for £25 should have got it when i had chance but ive got my eye on a 12g295 if it goes cheap ish . ill be getting the flywheel lightened and all the bottom end lightened and balance not be cheap but worth it

Liam

[li mick]

if a 12g 295 was fitted to a 998 what else would need to fitted, not wanting to make it fly just better without breaking the bank 

[bpirie1000]

Water pump possibly 12g mostly do not have the little bypass hose that the 998 has...but the 12g can have the pipe added....

[Icey]

Holy 13 year old thread revival, Batman!

An original 12g295 will need heavy skimming to work on a 998 with flattop pistons.

Edited by Icey, 03 January 2024 - 05:41 PM.

[li mick]

thats the joy of old minis, new owners of old minis need to know the answers to those questions that some knowledgeable people take for granted.as i thought the 12g295 would go straight on without skimming.but you live and learn.

thanks for the reply

[timmy850]

It will bolt straight on without skimming

 

However, the 295 has much bigger combustion chambers, so the compression ratio will be very low. Ideally you'd want an increase in the compression ratio plus the additional flow of the bigger head to make more power.

 

Or put a 295 head in the place it was designed for - an 1100cc engine

[li mick]

thanks, i get the picture.

[Cooperman]

The original 295 head was fitted to the 998 Cooper which had pistons with a raised D-shaped piston. This was to reduce the combustion chamber volume when compared the the 1098 MG 1100 engine which used the same head.

If you have a 998 with flat top pistons you will need to skim the head to remove around 4 cc, but of course you need to carefully measure and calculate how much actually needs to be skimmed to give your required compression ratio.

If your 998 has dishes pistons it will need a lot removed and the maximum which can be safely skimmed from standard 295 is around 80 thou.

Before skimming you need to measure the total thickness of the head, the combustion chamber size and the distance from the bottom of the critical oil feed hole to the current deck level. The distance from the base of the oil feed hole to the head surface should never be below 50 thou. Measure accurately and carefully!

[li mick]

many thanks Cooperman very interesting information.