best for what?
short strokes fill cylinders better when in their rpm range. but, with shorter strokes, they loose leverage.
undersquare motors have a deffinate rpm range where the heads perform the best, but since the stroke is longer, they dont build up the vacuum to suck in the charge quite as much as the short strokes, but they have monster torque. torque moves things.
the pontiac 455, the buick 350, rocket olds 455 (same 4.25 stroke), were all undersquare engines.
can anyone disputer the power of these engines? with good components, they can easily tach 6500. you fit the 400 with good heads and a 434 stroker from tim meyers and you can match the power of these, or come very close to it.
the thing you really need to worry about is rod ratio. thats the measure of your rod length vs stroke.
the longer the rod, the more verticle the piston travels in the cylinder. lets say you have a 6" rod and 4" stroke. when the crank is perpendicular to the bore centerline, your rod is at a 45 degree angle. which means the piston digs into the block some. this wastes power by generating friction and wears the block out. the longer the rod, the further up the piston is making it have a better angle. think of it this way...a 3" stroke and a 4 foot rod. no matter where in the cycle the crank is, its always pushing the piston strait up. very low friction. thats why you can put longer strokes in tall deck blocks and still be golden. the 400 uses 6.580 rods from the factory. now, check that against a 4" stroke? 1.645 rod ration. it beats the 1.5 from the 351 stroker with the 4" stroke and 6" rods.
ok, use longer rods in the 400 and you get an even better ratio. the higher the ratio, the better you can rev it reguardless of the under/over square aspect.
longer rods, shorter pistons will help with the revs.
examples:
ford 289-1.756 rod ratio
302-1.718
5.4l mod-3.552 bore X 4.165 stroke 1.598 rod ratio.
351W-1.702
351c-1.653
from these numbers, the 289 has the highest rod ratio and has always been known as a screamer. the 302 next. the windsor has a higher ratio than the cleveland, but it had 3" bearings, which makes for more friction and loss of power over the cleveland...but still a great ratio.
now looks at the 5.4l mod motor in trucks. its WAY undersquare. it has a descent ratio tho so itll wind up and generate power. but over .5" difference..plus there are stroker kits for them to increase this to 4.415" thats almost an inch under bore...but has a descent ratio still. anything over a 1.5 is good. the higher, the better. 351's running boost should stick to the 3.75 or so stroke. good ratio for winding up and no real loss in power from friction. plus, power comes from the adder. if no adder, than the 427 isnt bad. the 434 is better tho..=)
the 434 stroker uses a 6.490 rod length= 1.53 rod ratio. still in the good zone.
http://cgi.ebay.com/ebaymotors/Ford...ptZMotorsQ5fCarQ5fTruckQ5fPartsQ5fAccessories
on a side note, using dynosim engine builder, CHI 208 heads, an 850 carb, dual plane max flow intake and open headers, i managed to squeeze out 600 ftlbs from 4000-5000 and 600 hp from 5500-6000. and those are moderate heads. i will run some sims on different build and post some numbers if you like. i can even cut and paste the graphs so you can see if you like them. lol..400 ft lbs at 1200 rpm.
