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The way I figure it, I've got 9.208 inches of block to work with that being the distance from the center of the crank to the top of the cylinder. The 401 starts with a stroke of 3.68 inches, a 5.85 inch connecting rod measured from center of rod journal to center of piston pin and a 1.508 (about) compression hieght on the piston measured from the center of the piston pin to the top of the piston. Take half the stroke, 1.84 + 5.85 + 1.508 and you get 9.198. This leaves .010 at the top of the stroke for rod and piston expansion. Also consider the thickness of the head gasket so there is a little more room before the piston hits the head). Given all of that, I think of the stroke as the diameter of the circle the center of the connecting rod journal makes as it rotates around the crank center. to make this circle bigger I'm going to off center grind the connecting rod journal, reducing the connecting rod journal diameter from 2.2474 to 2.1 inch (same size as sbc rod). This will move the center of the connecting rod journal .0737 (2.2474 - 2.1 = .1474 now divide this by 2 and you get .0737). The stroke will increas by .1474 because the diameter of the circle the center of the connecting rod journal makes as it rotates around the crank shaft center will increase from 3.68 to 3.8274 (3.68 + .1474 = 3.8274). The radius of circle increased by .0737 so diameter increases by 2 times that or .1474. That is how I intend to increase the stroke of my 401. It may not come out exactly 3.8274 because the connecting rod journals have to be turned to take out a few very minor scratches. Lets say we go .010 on the connecting rod journals, I'll end up with a 3.817 in stroke. Either way, this engine will stomp all over a sbc 383!! Any body see any flaws in my thinking? I'll deal with the compression ration next because if the stroke gets longer and nothing changes with piston or head, compression ratio goes up. I'm aiming for a 9.2 : 1.
Fella ran these 401 4x4 stroker #s for me on Dyno 2000, it's based on ICH's Bracket Master Moldex 4.15" stroke crank and std bores (I have not confirmed with ICH that this crank will stuff in a factory 401 block):
The Moldex crank used in the Indy "Bracket Master 500"
is 4.15" stroke,
probably safe to say that is probably the largest
stroke we will see for a
stock block (assuming the 401 block can be massaged to
clear those crank
throws). That nets 452.3 cubes with the 4.165 bore,
and 600 ft/lbs of
torque at 2000 RPM!!! (with Ultradyne's smallest
hydraulic (.517/.541 lift &
231/239 duration) AMC cam, stock big-valve dogleg
heads, stock intake,
600CFM 4bbl, small-tube headers w/mufflers, 10.2-1
compression). Not much
HP there, but loads of torque. I also tried adding
fully ported heads,
big-tube headers, big cam, big carb & Torker, the
rev-range is dictated by
the bore/stroke ratio, and 5500 RPM is peaked-out for
this one, no matter
how much cam, exhaust, or intake you throw at it.
WOW! Those are very impressive torque values. I'd be interested to know what rod piston combo a build like that requires. My goal is not so lofty. This truck gets drove everyday. I've opted to use a 6 in sbc rod and a standard 3 ring set on the piston. A chose the six in rod to maintain a good rod length to stroke ratio. (1.59 : 1 stock 401, 1.6 :1 for 383 sbc) I know there is debate regarding the use of longer rods and I believe a longer rod is the better option primarily for the following two reasons: With the piston pin set higher in piston (There is a limit, I don't want to have to contend with supported rings. I think 1.25 in comprssion hieght is about as short as I would want to go.) the side load pressure the piston exerts on the cylinder wall is reduced, The variance in connecting rod angle in relationship to the connecting rod journal is minimized with a longer rod thus reducing the ovalating stress placed on the connecting rod bearings. I believe these two factors will increase engine life and reliability. Any thoughts?
Posted a few pics, I think. Some may find value others may not. The cross section of the head shows there is plenty of material to remove at least 5 cc.
Working with Wisco for a piston. Here are a few of the things discussed: The block should be bored to a "standard" bore to make use of a "standard" ring pack. Example, 4.125 + .060 = 4.165 + .020. There are a few more examples that will work. This has a few advantages, cost being a big one. Wisco is happy that the combustion chamber can be expanded at least 5 cc. This allows a small enough dish to leave enough thickness between the bottom of the dish and the top of the connecting rod. The exact shape of combustion chamber and dish have yet to be determined. I think the compression height will come out very close to 1.2 in., close to the proven sbc 383 (1.120) with 6 in rod.
A couple of new tidbits. I called ARP (very helpful) asking about AMC main studs and why they were not listed. It so happens that the AMC 401 main bolt measures 3.5 inches from under the head to end and is 1/2 in, same as ch*vy big block. I'll use a set of ch*vy big block two bolt main studs without windage tray. Saved a few $$ by going this route. Also, ordered a set of hardened push rods, just so happens ch*vy small block push rods are identical, ask for ch*vy sb push rods, saved a few more $$. The Scorpian roller rockers arrived, they are beautiful, it will be a shame to cover them. Went with the ARP 7/16 thread diameter top and bottom rocker studs. Will have to re-drill/tap bolt holes and mill down for guide plate. Have not ordered guide plates. Piston design will go final late next week.
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