A 351w will not fit usually in small chassis cars (maverick,comet, early mustang, falcon, etc...without a lot more mods. In those cars, usually a 302 based engine is a lot less headache. Even the same can be said for a FOX mustang. 351w doesn't fit as well in a FOX as a 460 does, and since they came factory with 5.0's, a 347 is a natural and very cost-consicious way of increasing HP/torque..without having to buy new headers, pan, mounts, etc.
And...a 347 usually uses really light pistons and relatively short rods...less weight..and every one that I've driven (even the ones with 'heavy' parts) rev VERY quick. Cant' say the same for a windsor...the crank alone in a 351w is very heavy with the 3" mains and large counterweights.
"it is better to appear ignorant than to open your mouth and remove all doubt"--Mark Twain
<font size=-1>[ This Message was edited by: mavman on 5/24/06 12:06pm ]</font>
Another reason is that some people don't need torque, and as a matter of fact, for some people it's a negative. Smaller motors that rev higher meet those requirements, on top of being lighter. In particular cars that are raced on a limited tire and/or cars that are strictly street raced for money. Not running slicks or dot drag radials is worth big sleeper points for the street race crowd. In places like that, a smaller motor with lots of horsepower and minimal torque is a real killer...and will most always beat up on the bigger motored cars racing on similar tires...or even slightly better tires (PAST experience, I know). Aside from the fact of saying it's a flat out 289 rather than the 347 it is. Guys like that make big money lol.
mavman is right. a 347 rotating assembly is much lighter then a 351s. is does fit a little easier into the smaller cars.i think its kinda worth it to put in a 351 depending on your car.(i have a 69 mustang and it fit easily,only slight problem is for running huge headers.) i chose the 351,why. cause it has a stronger block and since a plan to build a stroker a figured why stroke the weaker block to 347ci when i can stroke my stronger block to 408. but everyone has there own opinion. either way ford engines will always put a smile on your face