21-01-2018, 09:13 PM
I was interested in Alans comment that larger valves make little difference. Seven valves are not small and with the extra masking with larger valves I have always been sceptical of benefit.
If valves have old wide seats, or a lot of metal above or below the seating, a larger valve with new narrow seats will likely be better.
An article which possibly has prompted interest in larger valves is that on page 101 of Wyatts “The Austin Seven “. A new Cup Seven had a top speed of just 45 mph. A significant c.r. increase barely improved this, but 1/16 oversize valves increased to 55mph. The article is a bit of a mystery ; it is strange that car was originally so slow, and the exact cause of the improvement unclear.
If valves have old wide seats, or a lot of metal above or below the seating, a larger valve with new narrow seats will likely be better.
An article which possibly has prompted interest in larger valves is that on page 101 of Wyatts “The Austin Seven “. A new Cup Seven had a top speed of just 45 mph. A significant c.r. increase barely improved this, but 1/16 oversize valves increased to 55mph. The article is a bit of a mystery ; it is strange that car was originally so slow, and the exact cause of the improvement unclear.