Mk1 UK heads & Mk 2 Federal block, no go?

[darrellprice]

Ever the optimist …. I have an opportunity to get a pair of 1971 Mk 1 UK cylinder heads locally (long story!) and I have a 1973 Mk 2 Federal Stag. Now, I don’t think the heads will work, is this only due to the piston design on the Mk2 or are there other reasons that these Mk 1 heads are of no use to me? When you live a long way from anywhere you try all angles!

[flying farmer]

I thought all the heads were similar except that the mk1 had slightly smaller combustion chambers for use with the dished mk1 pistons. I believe the Federal stags were low compression anyway due to different pistons from UK types.

Neil

[Ian Durrant]

Hi Darrell,

I am with Neil. I don't think it will be a problem, especially as your pistons will be low compression ones anyway. There is a guy on here who has one mk1 head and one mk2 on and he has no issues.

if they are a good price and in good condition I wouldn't walk away from them.

Kind regards
Ian

[les M]

Darrell
The only difference that I know of between the MK1 and MK2 heads are the shape and volume of the combustion chamber the MK1 has a slightly smaller chamber than the MK2. I am presently running with one of each on my engine with MK2 pistons fitted the only mod that I did was to reshape the MK1 head to the size of the MK2. With you having a federal car it may be fitted with 7.75:1 pistons or even 8.8:1 , I would expect that there should be no problems at all in fitting the MK1 heads.

Les.

[darrellprice]

Thank you all for your encouragement! Yes, my car, in theory at least, will have the lowly 7.75:1 pistons and as a MK2 Federal car it did get the revised combustion chamber, as per the rest of the world. So the MK1 heads will have a different shaped combustion chamber only then; I wonder what that would do to the compression ratio with the 7.75:1 pistons? By the sound of it nothing is going to bump in to anything, pistons in to valves for example!

[Ian Durrant]

Hi Darell,

Most cars here will only have the low compression pistons because for some years that is all that has been available from the after market supplier, County. Add to that that quality head gaskets are only available in +0.020" and we are all doomed to the lowly compressions unfortunately.

[Westfaling]

Not all doom and gloom. Given how often most heads will have been skimmed it's pretty easy to get compression ratios back into the nines. I've got a Mk 1 Federal engine now with County flat top pistons. I'm at 9.3:1 CR with thick head gaskets (Compression test indicates 175 PSI - Not sure how that compares with others who know their actual CR). It would have been closer to 10:1 with standard gaskets.
There's been some debate on here about sub-optimal combustion chamber shape I.e. two cars with similar CRs but one with domed pistons and one with flat may not perform the same.

Nick

[flying farmer]

Thank you all for your encouragement! Yes, my car, in theory at least, will have the lowly 7.75:1 pistons and as a MK2 Federal car it did get the revised combustion chamber, as per the rest of the world. So the MK1 heads will have a different shaped combustion chamber only then; I wonder what that would do to the compression ratio with the 7.75:1 pistons? By the sound of it nothing is going to bump in to anything, pistons in to valves for example!

The depth of the combustion chambers is the same pre skimming, it is just that the bowl is cast smaller on the mk1, but only by about 1 - 1.5cc from memory.

Without doing the calculations I would guess it would raise a 7.75 compression to about 8.00. on higher compressions the same shift in cc produces a much bigger shift in compression ratio.

Neil

[Andy Rundell]

My old car ran a Mk1 and a mk2 head and domed +40 pistons, i fitted thick Payen gaskets as a matter of course.... no probs

....... Andy