17 replies to this topic

[georgevile]

Hi my name is george sorry to be a pain but i have got a 12g295 head and i was just wondering if anyone could tell me what sort of bhp i could get if i put it on my 998 i do have a stage one kit and i just want to put the 12g295 head on if anyone could tell me that would get a big help thank you.

[nomininolife]

Without the addition of a cam, I would guess around 50ish bhp.


Regards

David

[blacktulip]

if everything is working fine with the right compression i would also say around 50bhp at the fly.

[jayare]

with the right compression

This is the important bit - the 295 head has a much bigger volume than the standard 998 head and was originally used with pistons which had a raised crown in the shape of a 'D' so are commonly known as D-tops. Standard 998 pistons have a dish. If you just put the 295 head on, you'll lose a load of power as you'll end up with a really low compression ratio.

JR

[Burnard]

Is it cheaper to get the domed pistons or to have the head skimmed to the right compression ratio?

I was told that the head needed to be skimmed to 24cc to get the right CR, but what exactly is the bit that makes it 24cc? because it sure as hell aint the cc per cylender once the head is fitted.

[mini.rich]

Is it cheaper to get the domed pistons or to have the head skimmed to the right compression ratio?

I was told that the head needed to be skimmed to 24cc to get the right CR, but what exactly is the bit that makes it 24cc? because it sure as hell aint the cc per cylender once the head is fitted.

It would be cheaper to have the head skimmed, as having to change the pistons means stripping the engine, also i believe D-tops are pretty rare. I don't think all 998's have dished pistons, some are flat topped- but its sooo long since i messed with 998's.

The 24cc refers to the size of the combustion chamber in the head itself, the cc being cubic capacity(volume). But as i said depending on the piston, will depend on how much will need skimming to get the desired CR.

[Ethel]

24cc's is about the volume in a standard 998/850 head. There'll be another 10ish cc's in the piston dish & gasket. You'd only need to skim the 295 by about the thickness of the head gasket, assuming it hasn't already been to the machine shop.

It's the economy spec A+ 998's (City E from 83-87 or Metro HLE) that had flat tops CR 10.3:1

[tedmcedd]

998's have flat tops... my 1098 has 58bhp with twin hs2's and the 295 head. i have no cam or anything... i didn't skim it either, well... got it leveled off, 1098's have dished pistons in too... goes like a rocket, tones of torque!

[georgevile]

hi i have the new head on and it will not start can anyone tell me if the timing would have changed or if i will ave to do it to make the car start thank you.

[Dan]

Did you get the chamber volume of the head measured and calculate what it should be to make a healthy compression ratio or did you just put it on as it was? If you put an unmodified 12G295 on a low compression 998 engine I very much doubt it would run, the ratio would probably be down somewhere about 6:1.

[blacktulip]

hi i have the new head on and it will not start can anyone tell me if the timing would have changed or if i will ave to do it to make the car start thank you.

did you reset the rocker clearances right?

[georgevile]

we had the head skimmed by half a mill to bring the cr up which we addvised to do and set the rockers at twelve thou as standard

[Burnard]

I would check the ignition system and make sure there is a spark, and make sure its getting fuel.

[yeti21586]

ive got a 12g295 (i think) on my 1100

[1977 Loud_Mini]

998's have flat tops... my 1098 has 58bhp with twin hs2's and the 295 head. i have no cam or anything... i didn't skim it either, well... got it leveled off, 1098's have dished pistons in too... goes like a rocket, tones of torque!

I have a 1977 british leyland mini 998cc and it has dished pistons, but they are size +20 though.