Pi x Radius Squared = Area of Circle

Pi is approx 3.1416

Bore Diam = 4.6"
Bore Rad = 2.3"

3.141 x 2.3" x 2.3" = 16.619 sq. inches

Area of Bore x Length of Stroke = volume of cylinder

16.619"" x 5.25" = 87.25 cubic inches

volume of cyl x #cyl = volume of motor

87.25""" x 8 = 698 cu. in.

mcollinstn,
Thanks for the math!
tomcat,
The block has a deck ht of 11.665". Merlin Super block. They claim I can go 4.625 x 5.600 = 750ci. If I want to change bore spacing and go to the max.. 4.680 x 5.850 = 805".
If the long rod thing doesnt pan out.. a 750ci with a couple of hair dryers or a 18-71 on it would make some torque.. Oh the possiblities..

My next question has anyone experienced less tendancy to detonate with a much longer rod? Dwell time at TDC is longer allowing to complete the burn. Would this make the combination octane insensitive? In other words can I get by with regular 89 octane fuel with 10 to 1 compression with alloy heads?

Next one? Has any one heard of using an 8" rod in a BBC for Marine use? I know Oliver sells quite a few 7.75" and 8" rods..

Thanks for any input on this.

Dick

So without all this math, basically there is less angle=less friction=less heat, more power, less wear?

HyperBaja,
That kinda sums it up. Although the dwell time at TDC is suppose to give you something also.. But some say with today's modern combustion chambers that advantage is negated. I figured I would give it a try and not sure as yet if I spent my money wisely. But then what are hobbies for??

Dick

Rod length and stroke-

The dwell time at TDC/BDC is increased. Overall average velocity stays the same at a given RPM and stroke, but there is more...

Another item of consideration is the point at which the piston reaches maximum velocity- this does not occur at 90 degrees down from TDC.

The piston reaches maximum velocity when the rod and the moment arm of the crankshaft are at a 90 degree angle (Not degrees from TDC). This could only occur with an infinitely long rod and an infinitely short stroke (remember this is a family web site). I am too lazy to calculate it, but 80 or so degrees sounds right in a stock BB chevy.

As the piston travels from TDC, it pulls vacuum and initiates airflow. This increases until the piston starts to slow down. The piston slows down after that 90 degree angle point is passed. Increasing the rod/stroke ratio moves that point further down the bore.

This then results in longer cylinder filling time which can be used to gain horsepower.

Bulldog aka Ronnie

So I could make more power with a +500 rod over a +400 rod but my CH would be too small?