Destroked 351c into a 331CI

Two thoughts Mark

(1) All other things being equal, less displacement doesn't mean any less horsepower, it just means the power band is moved to a bit higher rpm (in this case about 300 rpm higher). That would normally mean a bit more gear is needed.

(2) However, the second consideration, especially in street cars, is "crank arm leverage". I've always felt the 351C had a bit too much crank arm leverage for the Pantera. With a 3.30" stroke crankshaft you will be able to come out of a slow/tight corner and punch the accelerator to the floor "harder" without the rear tires breaking loose and the car spinning off the road. The bottom line is the ability to negotiate curvy roads faster and/or easier.

If you use a 5.7" chevy rod (r/s ratio = 1.727:1) that would indicate the need for a piston with a compression height of about 1.855" (or less depending upon deck height). With a shorter stroke you'll need less deck clearance and/or less combustion chamber volume to attain a compression ratio of 10:1.

Bechtloff (Hank the Crank) is from my neck of the woods, he made good parts.

Questions: Is this an off-set ground factory crank, or a steel forging/billet? Is it fully counter weighted?

Rock and Roll

If the crank you have has standard size journals, ie: it is not a stock crank that has been turned down to destroke it you could use the 302 Cleveland's 6.040" rods (which make Chev rods look like they are out of a lawnmower) and use short pistons. This combination is sometimes used in the 351c when a longer dwell period at TDC and BDC is desired.

I feel the longer rods do make the engine a bit smoother, but you have to watch the relationship between the piston pin and ring grooves and also overall piston design. Short pistons can rock unacceptably. A round skirt piston is best.

Or you could build a 302c using totally stock off the shelf parts with 4v heads.

302c's rev like mad and i've never heard of a bottom end failing on one.

What are your intentions for this motor? 347 SBFs are quite popular, cheap and around 80 lbs lighter than a destroked Cleveland. There are a few running around in Panteras and they are not slow! The block itself is more compact, too. But one needs a good block- maybe Aussie blocks are stronger? Factory 302 blocks from the U.S & Mexico tend to split vertically at around 450 bhp and 7000 rpms, while Clevelands (mostly) have thin cylinder walls. Pick your poison...

Boss, One could always go with the Ford Racing Boss 302 block. Very stout.

Mark, I think you are likely to reduce your engine's power output approximately 6% with the stroke decrease. Unless you change gearing and increase your peak rpm limit your car will be slower accelerating. Destroking engines may sound "racey" but is typically done to get under a displacement limit set by race rules-- rules imposed to limit performance.

You would be better served having a high-reving stroker engine. An aftermarket lower end assembly should be able to withstand 4500 ft/min mean piston speeds reliably.

-Matt