Well, the next step in this calculation would be to find out the coefficient of friction of the ring material against the cylinder wall, and the tension of the rings (i.e., the force exerted by the rings on the cylinder walls).

Then the force needed to move the rings along the cylinder wall would be:

(coefficient of friction) * (force of ring on cylinder wall per unit of ring surface area) * (size of ring surface area)

For our purposes we can probably assume the coefficient of friction of the rings in a 300-six is the same as the 302. I don't know about the ring tension though, and that could make a real difference. We care about the force of the ring against the cylinder wall per unit of ring contact area. Since the rings in the 300-six are bigger, and assuming tension is equal to the 302, there will be more total ring friction per cylinder as compared to the 302.

Now we want to find out how much energy is consumed by overcoming this friction force. Work is (force)*(distance). The force in this equation is the friction force from the rings (shown above). Distance is the stroke. So total work done per engine revolution is something like (number of cylinders) * (number of strokes per revolution) * (stroke length) * (ring friction force).

Finally we can compute the horsepower (a unit of power, which is work divided by time) by multiplying the above work by engine rpm and dividing by 5,252.

So if we knew the following things:

o Force of rings on cylinder walls per unit of ring surface area
o Total ring surface area
o Coefficient of friction of rings against cylinder walls
o Stroke length

we could compute a real numerical answer.

Phew! (there are probably some mistakes in this post)

 

Funny you mentioned "work" it occured to me this morning that "work" would be a better measure than reistance, coming from someone like myself with basic education, thats an epiphany of the century.

If I've done this right...it proves my theory...so it must not be correct.


Example:

For the 300:

6 cylinders X 1 stroke X 3.98 stroke length X 10 (example lbs of force) = 238.8

For the 302:

8 X 1 X 3 X 10 = 240


No need to break it down, I would venture to say the extra 1.2 comes from the 2 extra CI.

Looks near identical once again. So with rings out of the equation we are left with two less connecting rods with the six but also left with more main bearing resistance with the six, as compared to the v-8. I could see less resistance with the six in that aspect, but overall minimal to be gained. The whole ring contact/resistance was throwing me for a loop. If silver streak were right and it were 60lbs vs 80lbs, then it would be very obvious the benefits but according to the formula given, they are the same.

Someone with patience would have to compute the bearing contact and relation to resistance or work....yep...theres that headache again.

 

The real question....dijera, have you received your clifford crate engine yet?

 

and does it have the same bellhousing as a '76? the six loved 2grand, hope the crate does. the 390 had finer jets available, but the fuel metering from fi is far superior, mileage and torque being programable on top of the inline application of torque. 4:10's, .62od, and 2K E-350 with a 351w was 70, and my guess is a properly massaged 50cix6 engine would be able to perform ably and be a tad more reliable. the six reminds me of vw engine adaptations, 3l 3k purpose built airplane power, generators, where the design inherently invited further refinement.

 

The concept of work may or may not be the proper way to look at this. Work is define as a force multiplied by the distance it is applied. It is easy to say that it moves the length of the stroke, but in a multi-cylinder engine the motion is for all practical purposes perpetual because the engine is never completely stopped. If we assume perpetual motion, the only thing that matters is the sum of the drag caused by the rings. If the rings of the 300 and the 302 are the same the 300 will have less drag because there are fewer rings.

If we use the concept of work, we have to make a few assumptions which I think we all agree on. The first is that each piston takes a certain force to move it down the bore. For ease of computation, lets assume it's 10 lbs per piston. The second, which we also agree on, is that the total distance travelled by all the pistons in the engine is the same for the 300 and 302 and is roughly equal to 24"(2 feet). In order to calculate the work done we need to multiply the total force by the total distance. The total force is 10lbs times the number of pistons. 60 lbs for a 300 and 80lbs for a 302. Then you multiply those numbers times the distance, 2'. You get 120 ft-lbs for the 300 and 160 ft-lbs for the 302.

 

The rings in the 300 are not the same as the rings in the 302. The 302 has smaller rings. There is less ring friction per cylinder in the 302.

Another way of saying this is that if you took all the rings from a 300 and bent them into a long straight line, and then did the same thing with the rings from a 302, the lines would be about the same length.

You first assumption (10 lbs per piston) is incorrect. Because of the smaller pistons and thus smaller rings in the 302, its pistons would take less force to move.

 

Even if perpetual, the rings must cover X area to draw in Y displacement, looking back, I think the formula mdmbkr first posted demonstrates drag or effort required, more so than work, no?

In my mind, the last part of your post is demonstrating effort of the engine as a whole over a given area/length, without taking into consideration the resistance/drag/work required of the engine itself.

Interesting stuff, thats for sure.

 

?????

Not hardly. They both have a 4" bore. Each ring is 12.56" long. The 302 rings would be considerably longer than the 300.

The pistons are the same size.

 

I'm sorry, you are right. A piston in either engine takes about the same force to move. However, the 300 moves each piston farther. So the total distance covered by the rings is about the same in both engines. "10 lbs per piston" is still wrong.

300:

6 cyl * 4 strokes * 3.98 stroke length = 95.52" piston travel per revolution

302:

8 * 4 * 3 = 96" piston travel per revolution

So the 302 does slightly more work to overcome ring friction, not nearly the 33% difference you described.

 

I NEVER said it took 10 lbs. I pulled that figure out of thin air to make the math easy and stated that previously.

You guys are modelling this from the point of view of a wrench on the crank bolt. You need to think of it from the other side. The pistons don't know what the stroke of the engine is, they just know a force is pushing them up and down.

No matter how you slice it, there will always be less force resisting the movement of 6 pistons than there will be with 8.

 

I'm not accusing you of making up the 10lbs figure, it's an assumption that we're both working with.

You are right that per unit of piston movement, there is less collective resistance in the six than in the V8. But the distance per revolution is an important factor. "Wrench on the crank bolt" is exactly how you want to look at it. In terms of applying power to the ground, "wrench on the crank bolt" is what matters.

The resistance to piston movement per engine revolution due to ring friction is almost equal between the 300 and the 302.

Imagine a V6 with the same bore and stroke as a 302. Open all the valves and put a wrench on the crank. It will be easier to spin than a 300 with open valves, because you don't have to push the pistons as far.

Conclusion: there is more ring resistance to overcome per cylinder in a 300 than a 302, so overall ring resistance is about the same in both engines.

 

Actually if you break the formula above, into piston travel per revolution per cubic inches or 95.52 divided by 300 and 96 divided by 96, they are near identical, if you round each up they are both .32 per cubic inch.


I will go back to my hole.


I will keep reading maybe I will make sense of this eventually.

 

I think we've made sense of it. The important factors are total ring travel in the engine per crank revolution, ring size, and ring tension.

Note: In all my earlier calculations I mentioned 4 strokes but there are only 2 strokes per crank revolution. So the 96" number is 2 crank revolutions.

 

Here you've overlooked the fact that your distance travelled (24") already accounts for the number of pistons. To arrive at 24" for the six, you multiplied its stroke by the number of cylinders (6 * 4"). Same for the V8.

So to again multiply by the number of cylinders when calculating force is incorrect.

 

No, failing to multiply by the number of cylinders is a mistake. Calculating the total distance moved and the total force are two different things.

I've said it before, and here it is again. It is easier to move 6 pistons than 8.