Rat
Well-known member
The bore x stroke you posted is theoretical displacement, not actual displacement. There is a difference due to the needed valve clearance at the top of the cylinder. Theoretical displacement is the mathematical formula of bore x stroke, actual displacement is the same minus the valve clearance.
Motors are rated for HP to alleviate these differences. HP ratings are an attempt to use a standard test to compare a 'system' (motor, linkage, prop etc). All else being equal, a lighter motor will go faster (top end) but a motor with more torque (lower gears) will have a better hole shot. What we are talking about is thrust to weight ratios.
Now talking about the difference of 20 pounds on two motors with the same HP rating is splitting hairs. You can be off that much with a cooler of sodas on the boat; and I doubt you will ever be able to tell by seat-of-the-pants, you would need to set up a test bench to verify this as the difference is too minimal for normal people to notice.
The big difference in these two motors will come from gearing. They are so close in HP/weight that selecting the correct prop will have a bigger influence on performance than whether on weighs 20 pounds more or not. Again, a compromise has to be made; are you looking for good hole shot or best top end performance? The answer to that question will determine the best prop, and they will be different props. TANSTAAFL!
Motor torque is another thing all together. Evenrude made two 25 years ago, one was a 2 cylinder and one was a 3 cylinder. The 3 cylinder made tons more torque and was a favorite of the shallow, tunnel-hull runners around here; they loved it because they could prop it to get out of the shallows in the blink of an eye. But now we aren't comparing apples to apples.
I think you are getting lost in the minutia. They are so close just pick the one you are most comfortable with (based on your own criteria) and go with it!
Motors are rated for HP to alleviate these differences. HP ratings are an attempt to use a standard test to compare a 'system' (motor, linkage, prop etc). All else being equal, a lighter motor will go faster (top end) but a motor with more torque (lower gears) will have a better hole shot. What we are talking about is thrust to weight ratios.
Now talking about the difference of 20 pounds on two motors with the same HP rating is splitting hairs. You can be off that much with a cooler of sodas on the boat; and I doubt you will ever be able to tell by seat-of-the-pants, you would need to set up a test bench to verify this as the difference is too minimal for normal people to notice.
The big difference in these two motors will come from gearing. They are so close in HP/weight that selecting the correct prop will have a bigger influence on performance than whether on weighs 20 pounds more or not. Again, a compromise has to be made; are you looking for good hole shot or best top end performance? The answer to that question will determine the best prop, and they will be different props. TANSTAAFL!
Motor torque is another thing all together. Evenrude made two 25 years ago, one was a 2 cylinder and one was a 3 cylinder. The 3 cylinder made tons more torque and was a favorite of the shallow, tunnel-hull runners around here; they loved it because they could prop it to get out of the shallows in the blink of an eye. But now we aren't comparing apples to apples.
I think you are getting lost in the minutia. They are so close just pick the one you are most comfortable with (based on your own criteria) and go with it!
