Quick Guide to Bore and Stroke

[304065]

Bore Stroke CC Disp
80 66 1991 2.0
84 66 2195 2.2
85 66 2247 2.2
86 66 2300 2.3
87.5 66 2381 2.4

80 70.4 2123 2.1
84 70.4 2341 2.3
85 70.4 2397 2.4
86 70.4 2454 2.5
87.5 70.4 2540 2.5

Well, the formula is Bore x Bore x Stroke X (3.1416 / 4) x 6.

I thought it would be convenient to have a simple table all in one place.

[jluetjen]

Let's see John, 85x66 yields 2247 cc's. To round to liters the 7 rounds up to 2250 dl's (deca-liters?), the 50 rounds up to 2.3 liters.

Or did I not remember my old math teacher's rounding rules correctly. It was soooo long ago!

[304065]

John,

LOL. 2249 and down is a 2.2, 2250 and up is a 2.3!

Anyway, it's always better, when bragging about one's lap times, to round down. Some racers, in the presence of scrutineers, round WAY down by a class or two!

Well, I posted this because I've been thinking about going to 2.2 when the '66 motor is rebuilt, but after talking with Charles Navarro at LN this past weekend at the Parade, I'm leaning in the direction of 87.5mm CNC-machined cylinders with a 66mm crank, for a nice 2.4 in the old girl! Obviously external oil cooling would be a must.

Someone has raised the question of the spigot diameter, and showed me a sample 80mm jug, which clearly had a smaller spigot diameter than the 2.2/2.4, which was clearly smaller than the 2.7. But according to my factory spec books, the cylinder base dimension is identical for the 2.0/2.2/2.4 jugs.