New 5.5:1 Cylinder Head Availability

[Jim/GA]

Originally Posted by alexiskai

The idea that Babbitt bearings can’t handle higher compression is a myth.

It's not that babbit can't handle it. It can.

The problem I have experienced over and over is that the average Model A driver with the average original engine advances the spark too much on the 6.0 head and the engine knocks. The driver can't hear it knocking (for various reasons, including old age loss of hearing) and they pound the babbitt out in a short time.

Many drivers start the engine, then pull the timing lever down all the way and leave it there all the time. You can explain to them all you want about what they need to do with the timing, but they just pull it all the way down. The stock cylinder head is low enough compression that it is very forgiving to this sort of behaviour. With the 6.0 head and an engine that is timed to TDC like Henry called for, that engine won't last long.

So I mainly recommend the 5.5 head to save the driver from themselves. You get a little performance boost but less risk of hurting the engine.