how much to skim off a 12g 295 head?

[Chalkie]

You could Zero deck the Cylinder block.

[Pandora]

So, I went shopping at Carbon's garage.....

I now have the makings of an in-line 998, (well, actually a 1014 as the pistons are +20) and will be fitting a Piper 270 cam. (The pistons are flat-tops)

I have 2 12G295 heads, one of which is a bare casting with guides, the other complete. One has been skimmed, the other hasn't.

One measures 69.8mm thick, the other 68.3, so a 1.5mm skim

I think with the overbore and the skim, that one is going to be too high a compression, so might sell it to re-coupe the funds to put back into the project, but want to be sure before I flog something I may have use of in the future.

I actually haven't ruled out using a 940, if I could get away with that without hitting the block when using the 270?

Anyone got any thoughts on my likely CR with the 69.8mm / 2.75" one? I'm aiming for about 10:1 - 10.5:1, or the viability of a 940?

I tried the calculator linked to earlier in the thread, but can't seem to get it to work - I have MS office and it doesn't seem to like it*

I like carving pretty shapes and hate engines!!

Al

* seems I sorted it (I think...). the unskimmed head, it appears will give a CR of 9.07:1
So, my question is, what effect would the 1.5mm skim have on the CR?

[CooperTune]

Thanks for posting the above info. I'm currently building a 997 for a project. It took a couple of years to locate NOS .030 pistons for it. It currently has a Speedwell alloy 5 port cyl. head fitted. Between Christmas and New Year I recieved a NOS 998 Cooper 295 cyl. head still in the box. The plan is to offer the Speedwell head for sale and strip the 295 clean, lap valves, and surface to reach 9.5/10 CR. I realize it's not the correct head but should do eveything we need it to do. Always fun to open a box for the first time in years and find a 30 year old bill of sale. Steve (CTR)

[mini63]

an interesting thread as it reminded me of the same quandry about 25-30 odd years ago trying to sort out my 997 block. I had a new set of 0.030 'D' Mahle pistons, a brand new wax papered 12G295 head/valves/guides, NOS standard rockers, a standard silver frost head gasket and a BP270 cam. my concern then was leaded fuel was being phased out in Oz at the time and pinging would be a problem....
The engine has always been a bit cammy but never overheats, copes with a 3.44 diff nicely and sings over 4500rpm........

[Spider]

Throughout this thread, I have seen various values quoted for the 998 Cooper D being mentioned;-

The D alone is worth 2cc, an overbore will increase the CR marginally. M.

The raised D has a volume of 4.5cc (according to Vizard) not that it matters if you are using flat top pistons.

I've actually tried to measured the D, and found it to be approx 2,5-3,5 cc. It's NOT 4,5.

Recently I have had cause to find out exactly what the CC's were. Just now found in ST Documentation that they quote it as being 2.16 cc (based on stock bore size). Hope this is of help.