After turkey was consumed, I got to thinking about Gary's formula. Another tool for engine building. Spent an hour trying to figure out how best to use the formula. Nothing. Could not come up with one example of how this formula would aid in parts selection. The wider an arm swings, the more pressures exerted on the crank spine and block main bores. Didn't need a formula to know that. A bigger main journal is stronger than a smaller journal. Didn't need a formula for that. Pick a block, pick the size of engine you want and put it together. Where does the formula come in?? No, I don't get it. Lighter pistons? Everyone uses the lightest piston-rod combo they can for any performance engine. Stroker or non-stroker. Gary uses the word "must" instead of "in my opinion , you should"....... There are many 4 inch stroke 409s across the country that have been running for years very well with 409 size mains. Ross pistons and steel rods. Since I have experience only with GM cranks, I would like to know which aftermarket cranks have the center courterweights. Maybe all?? That would be a big asset. Well, thanks anyway Gary for the formula. It is interesting to play with, I just dont see how it translates into a benefit for picking w-head stroker parts.
Ronnie, I don't put this info here to "scare" anyone but to make you aware of certain conditions that need to be addressed on every build from a "builder's" standpoint. By having this formula AND the dyno results to reflect back on, we can determine ahead of time whether or not we will have any issues. That's all this is about, I cannot have "comebacks" for any reason, I barely have time to do these things once, let alone twice!
When you start upping the stroke you should be paying close attention to the details. Most especially the details that cover the all the reciprocating pieces. You want these to be as lightweight as possible but NOT sacrifice the integrity of the part. Light pins, pistons, rings, etc. should all be used if possible! The newer 2618 material for the pistons was a move in the right direction, as the material became stronger, the weight was able to come down some! It's only slight, but it helps.
You really need a piston in these strokers around 650 grams. Remember, this is a fairly large bore to support that weight piston when you factor in the "dome". We are using 600/650 grams, with medium domes, in the BB 540" platform.
With these "W" units you are battling a heavy piston in most part due to the inherent design of the unit itself. You cannot redesign that area, or are very limited!
The "rod overlap percentage" number to us is only used to make us aware of a reasonable expectation of how much stress/power the unit can withstand. If you stay around the 40% area you should be comfortable. Installing "steel" main caps is a "plus", but should be tied into the pan rail area (splayed) to "tie" the block together.
It all comes down to how much power will be made before the 'lower" percentages come into play and cause damage.
Chevrolet became aware of this when they drew up the plans for the BB as we know it today. They needed larger mains to support the "numbers". We have found through extensive testing that the really long strokes (4.750") in these "standard BB" blocks need the center counterweights, we've had some units without them that would not even get past the dyno tests. If you keep the stroke "reasonable", at/under 4.000", you can get by without them, but as I said, you really do need light pieces on top.
I would go one note more here and state this: these should NOT be externally balanced, they should be "internal" only, even with the 4.000" stroke and also with NO "tungsten" (heavy-metal). This is easy to accomplish with "aftermarket" cranks. The 454" (4.000") shafts we use here, not G.M.'s, will "zero-balance" with a "target" bobweight of 2350 grams. No "external" damper/flywheel!! This allows the use of the "standard" 409" components if required.
(Add) One other VERY important item to remember here with respect to "RPM limits", just as a general "rule-of-thumb", as you do go up on the stroke you tend to actually lower the power band that peak power occurs. I have some 540" BB's (4.250" strokes) coming off the dyno with 740+ HP occuring at 6200/6300 RPM. This is an extremely reasonable range for almost any BB, "W" or otherwise.
Thanks, Gary in N.Y.
P.S. When laying out the platform with the 348"/409", we try to "prefigure" if you will, the "bobweight" that we will be using on the build. If the numbers don't "look" good on paper we try to alter/adjust them to make it happen. For arguments sake here, if you said you wanted a 4.000" stroker I would try my best to come in with a 2250 (nominal) gram weight, staying with the "steel" rods. Going back through years of dynoing different combos we can draw a parallel drawing on previous "rod overlap percentages" that have NOT presented an issue.