What should I consider when switching to a high compression head?

[Hurvinek]

Hi folks!

I am unsure... 
Can I just change the cylinder head without any problems, or are there other things that need to be done? 
Do I maybe need to change the ignition timing, adjust the valves, or something else? Or just screw the other head on... bam, done? Using the correct head gasket is obvious.

If someone could explain this to me, I would be happy.

Thank you very much!
Oliver

[Charles P]

You’ll need two longer studs for the ones shared with the water outlet.
Otherwise check the thickness of the head (1.5” is standard, unmachined).
Then I’d just bolt it on and see how it goes.

[Tony Press]

Good idea but from my experience if you have an original Austin 7 carburetor you need to consider changing to a different one- a 1 1/8" SU seems to work well on the standard later manifold.

[Howard Wright]

Hi Hurvinek

If you use a Ricardo aluminium head or possibly one of the other aftermarket heads there is no need to put longer studs in. Just swap heads see how it goes and maybe change the carb at a later date?

Cheers

Howard

[Andy Bennett]

When I thought about doing this a while ago I was advised by one of our cherished suppliers to pause and think about the possibility of the additional stress on the crankshaft etc as a possible problem. No idea if anyone has actually experienced a problem that might bear this out or has a calculation to show that the additional stress is negligible but I pass it on for consideration.
Andy

[Reckless Rat]

You will probably have to readjust the ignition timing to reduce crankshaft rumble; When I first fitted a 37 head to my RP it rumbled a lot, but it went like stink. In the interests of longevity I backed the timing off and the car is still running well several thousand miles later. I have also fitted an SU H1 carburettor. The standard manifold has had the venturi opened out in the inlet tract.

[Chris KC]

If you have standard valve gear there shouldn't be a problem, but otherwise you might want to check the valves don't foul the head.

As with any tuning mod, first make sure the bottom end is sound. Increased compression should give you better performance but will place more strain on your crank and bearings accordingly. I would also check the compression ratio as people sometimes get carried away and skim the faces more than I would consider wise.

[Charles P]

Chris KCs advice is good.
Do the absolute minimum when you actually fit the head.
Fiddle with things like breathing, mixture and timing afterwards in a methodical, one at a time manner.

[Malcolm Parker]

Whenever I have fitted a late Ruby head to an unknown engine the results have been disappointing, with rough running and fouling of spark plugs.   The head was soon removed and the earlier head reinstated.   If the engine is rebuilt with new pistons and crank etc a high compression head is a worthwhile addition.   I would personally opt for a Ricardo head with 18mm plugs, use the low compression gasket and you don't need to change any of the head studs.  Both my saloons are running on standard cranks and are fitted with Ricardo heads.   My experience is that the engines run more smoothly with the Ricardo head.  I have been lead to believe that this is due to the position of the spark plug.

[Ivor Hawkins]

I’m in full agreement with Malcolm, I’ve returned to a low compression head on three cars now and every time, the engine has lost its harshness, been much sweeter and the difference in performance has been almost undetectable!

The only cars I’ve left as high compression are the Rubies and the specials.