Ring Gaps and Strokers
Really no connection, just want to bring up some "tips"!
Pertains specifically to "Percentage of Rod Overlap"!!
There's a formula for determining "connecting rod overlap"! This is an area of concern when "stroking" ANY unit, but moreso when using a "small-main" platform!
Anyway the formula is as follows:
[Main Journal Dia. (plus) Rod Journal Dia. (minus) Stroke] (divided by) 2 = the journal (rod) overlap percentage dimension!
For a stock Nailhead it would "read":
(2.498" + 2.249" - 3.640") / 2 = 55% Overlap. (This one is included for a member's question up here)
A 454" BB would be:
(2.749" + 2.199" - 4.000") / 2 = 47.4%
A 400" SB would be:
(2.649" + 2.100" - 3.750") / 2 = 49.9%
A 348" "W" using a 427" crank (3.766") with the 348" main journal would be:
(2.499" + 2.199" - 3.766") / 2 = 46.6% (Still acceptible limits)
A 409" "W" using a 454" crank (4.000") with the 409" mains would be:
(2.499" + 2.199" - 4.000") / 2 = 34.9% (Needs to be addressed at this point, this statement means you must pay careful attention to ALL the reciprocating weights being used on the "topside"! You would want some extremely "light" components on top such as the pistons, pins, rings, and pin locks.)
A 409" "W" using a 496" crank (4.250") with the 409" mains would be:
(2.499" + 2.199" - 4.250") / 2 = 22.4%! (Not acceptible in it's present state, you would most definitely have to "up" the main size to pull this one off!)
What these numbers show exactly is this: the further you take the rod journal from the main, the "percentage of overlap" (this is the lower numbers above) decreases and has a tendency to sacrifice much of the crank's and brg's integrity and begins to create issues with "cap-chatter", center-main brg. failure from severe vibrations, and finally, fatigue. The higher the HP and Torque numbers go the worse the results will become!
For all up here considering "upping" the stroke maybe along the lines of a 454" or more on these 348's/409's, let me give you a few things to keep in mind!
You are working with a 2.500" main journal AND a 2.200" rod journal. For a 3.250"/3.500" stroke this is still a reasonable "percentage of rod-overlap" area to be workable.
Take that equation and factor in a 4.000" stroke and some "heavy" pistons/rods and you have a recipe for a potential disaster for sure! Most aftermarket pistons are NOT "lightweights", this includes "Ross's", by today's standards! We spend add'l time "lightening" these up some while doing the build! Light wrist pins are also mandatory. Most forged pistons (aftermarkets) for the "W" must be
"lightened" under the dome area above the wrist pins!
Remember, these are NOT you're "standard" 348's and 409's, these are more "race" oriented even though they may be "streeters"!
When you step up to the 3.766" or the 4.000" stroke you begin to run into much
"lowering" of this "percentage" thereby decreasing dramatically the overall integrity of the build and this MUST be addressed when the initial plans are being laid out for the build. In other words, this factor must be incorporated into the platform/program.
Most shops simply "machine" the mains to fit the "W" block. Alone this is normally not an issue, but becomes one due to the amount of stock removal from the crank in conjunction with a stroke increase. You begin to "weaken" the crank before you start the project! A 396" crank in a "W" would be much safer than a 454" piece even though it's often done!
Finally, with respect to ring gaps, we recently delivered a "pump-gas" 396" BB with .026" top/.026" second, and made 510 HP with 93 octane. This was a not a "fancy" build, but an "old-school" Engle-cammed (solid-lifter) platform. Winter's heads and single 4 brl!
Thanks, Gary in N.Y.
P.S. One "major" tip here if you guy's go this route make certain you use a crank that has the "Center-counterweights" on the #3 main, I would NOT use just any old 454 crank, you need those 2 add'l c/weights in the middle These weights control the amount of "flex" the crank can tolerate! These weights also allow easier internally balncing to be accomplished WITHOUT any "heavy-metal" (Tungsten)! This goes back to the old days with the "Flatheads", if you could see these crank's they have center-weights also due to it only having 3 main bearings total! Ford engineering knew about this back then, it's called "crank stability"!!
Double P.S. "Happy Thanksgiving"!
: I am considering to 4 bolt the center main bearings if I have to line bore. Is this a good idea? It will get new cam, lifters, chain and gears, all bearings and oil pump, run hone in cylinders and rering as long as pistons are o.k. I already have crank studded. Would a main girdle be a good idea? What about head studs. Anything else I should consider? I will set the rev limiter at 6800 from now on. I will bet that will help some. I have in my notes that the oil clearance for the rods at .0018-.0022 mains at .0023-.0025 and the rear bearing acceptable up to .0035. I don't have piston to wall spec but I seem to remember .004 to .005. I can not find any spec on ring end gaps. What are you all running? Am I close on this stuff for an abused street driven 474 . Yes it will see the track, but that wil be a rest for the motor considering how it gets driven on the street!
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