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Old 05-16-2018, 09:04 AM   #31
Jim/GA
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Join Date: May 2010
Location: Young Harris, GA
Posts: 1,808
Default Re: How Fast Will It Go?

I was told by my good friend and mentor, Bill Coleman (RIP), that a stock Model A engine is limited to about 3,000 RPM by it's air flow through the stock carb, intake manifold, valves, etc. In other words, the air flow. He never mentioned the babbitt. You can figure out road speed at this RPM for a stock car.

If you have modified the above, which is common, then this restriction is raised some.

I have concerns, on a stock engine, about rod lubrication in the dipper trays being able to keep up at higher RPM. You are slinging a lot of oil out of the tray at very high RPM and I'm not sure the oil pump and gravity feed to the tray can keep up. I have no evidence (hard to see in there while the engine is running at high RPM) so it's a concern, not a fact. I know that's why designers went to pressurized cranks in later engine designs.

I have driven a few original, low mileage, engine never been opened up or worked on, Model A's. They are amazingly smooth. They put modern rebuilders of the same engine to shame. Of course, you can't get away from the harmonics that are inherent to the engine design itself. But except for that, they are smooth. As Brent said, if you take the time to balance everything to the original specs (and I mean balance to be more than just weighing components... I mean balance everything, like combustion chamber volume, valves, proper cam specs, etc.) you should be able to reproduce it.
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Jim Cannon
Former MAFCA Technical Director
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