"Block relief" - L.M. Williams book

[Alan]

But it isn’t about compression ratio, it’s about volumetric efficiency. What good is a high C.R. If you aren’t filling your cylinders.

[AustinWood]

Relieving the block is beneficial.
At the very least round it off to lose the sharp edge. It causes turbulence just where you don't want it.
For the same reason I round off the edge of the inlet valves. Improves the flow for the same reason.

[dickie65]

Hi, All.
The block relief is very common on flat heads (Side Valves to us )
It is beneficial for the faster sevens and higher reving engines.
Not so useful if you only do 40 Mph.
You can sleeve an engine with this mod, it just has to be redone after the sleeves are installed.
Bias towards the inlet valve.
Leave at least 1 mm above the top ring to protect against the flame front.
The Bill Williams mod is a good one which does not lose to much compression ratio but gains in better breathing.

[Parazine]

But it isn’t about compression ratio, it’s about volumetric efficiency. What good is a high C.R. If you aren’t filling your cylinders.

Absolutely right! With a side valve engine, if we improve the volumetric efficiency in the combustion chamber, we decrease the compression ratio, which has a detrimental effect on power output.
Hence, the side valve engine became obsolete in the 1950's as the volumetric efficiency of an OHV design is a magnitude better.
Of course, modern engines with 4 valves per cylinder are another magnitude better again......

[Terrytuned]

Modern engine 1924 Rudge motorcycle 4valve OHV engine and 4spd gearbox that was modern. Terry.

[Alan]

Bentley had 4 valves per cylinder in 1921.

[Rogerfrench]

Bentley had 4 valves per cylinder in 1921.

Peugeot in 1914.....

[Geoff Halstead]

What about on a sleeved engine, as mine is?

Geoff - Reluctant to relieve mine.

[Tom the Blacksmith]

Maudslay, SOHC, five mains all pressure fed by 05/06

[Chris KC]

Does the design of the Ricardo head not already optimise gas flow? I thought that's what they were good at...

"Harry Ricardo's contribution was to understand the combustion process and develop a cylinder head that retained the simplicity and the low cost of the side valve layout, but which rethought the shape of the combustion chamber to provide both the greater compression required for power, and the improved gas mixing that he realised was essential for stable combustion and the avoidance of damaging detonation. This he achieved with an asymmetric profile to the combustion chamber which used a squish effect to induce turbulence in the gases above the rising piston, compressing them into the chamber to one side, where they were ignited by the spark plug."

It's your call Jon. For me though the sentence which stands out in this thread is:
I've been resisting putting a new Ricardo on this engine as the engine is old and untested...
I have no hesitation in saying if you want to soup your motor up, first make sure you have a sound motor.