OT: Harry Ricardo
- Thread starter updraught
- Start date
nkaminar
Well-known member
The flathead design in the Model A is a Ricardo design. Although the flathead design does not allow for high speed efficient scavenging, the combustion is very efficient. The squish area above the piston produces good turbulence for rapid and through combustion. As the rpm increases the turbulence increases for more rapid combustion, reducing the need for more advanced ignition timing at higher rpm.
As anyone with an overhead conversion can tell you, significantly more advanced ignition timing is needed. It would be interesting to see what could be done to include a squish area in an overhead design, maybe by offsetting the combustion chamber from directly on top of the piston and a shelf over part of the piston. Offsetting the intake valve to introduce a swirl would be another possible way. The question of efficient scavenging would also have to be answered.
The early brass cars mostly had T head engines with intake and exhaust valves on opposite sides of the engine. Two spark plugs were commonly used because the lack of turbulence required them to complete the combustion in a reasonable time. An interesting thing to try would be a high top piston to provide a squish area at the center of the combustion chamber. The squish area would provide a puff of air to both the intake valve area and the exhaust valve area of the combustion chamber. Since there are already spark plugs in these separate areas combustion could proceed in both areas. The question of uniform air/fuel ratios in the separate areas would have to be answered.
As anyone with an overhead conversion can tell you, significantly more advanced ignition timing is needed. It would be interesting to see what could be done to include a squish area in an overhead design, maybe by offsetting the combustion chamber from directly on top of the piston and a shelf over part of the piston. Offsetting the intake valve to introduce a swirl would be another possible way. The question of efficient scavenging would also have to be answered.
The early brass cars mostly had T head engines with intake and exhaust valves on opposite sides of the engine. Two spark plugs were commonly used because the lack of turbulence required them to complete the combustion in a reasonable time. An interesting thing to try would be a high top piston to provide a squish area at the center of the combustion chamber. The squish area would provide a puff of air to both the intake valve area and the exhaust valve area of the combustion chamber. Since there are already spark plugs in these separate areas combustion could proceed in both areas. The question of uniform air/fuel ratios in the separate areas would have to be answered.
Last edited:
Fullraceflathead
Well-known member
I agree you can always tell how efficient a combustion chamber design is by the amount of ignition lead is needed the less lead that you need the more efficient the design is!!!