Roush vs 427FE vs Keith Craft

[blykins]

Originally Posted by AL427SBF

I've always maintained my part of this debate in the context of a general rule of thumb. I also understand your premise Brent, but would ask when you say a lot of big blocks have lighter rotating assemblies than small blocks are you talking unmodified OEM to OEM motors? If not, are those BBs built with exotic light-weight components + whatever tricks you have up your sleeve to lighten the rotating assembly that beat the OEM SB? Seems to me if you use the same exotic light-weight components + tricks your SB build will have a rotating assembly correspondingly lighter which puts us back to square one.

When Max first posted that post, he mentioned a "stroked small block", so no, I didn't really think about the OEM side of things.

With the OEM, the difference in acceleration could be chalked up to the design of the engine and the parts used. For instance, a 427 S/O out of a Galaxie or Fairlane back in the 60's would be much more zippy than a smog-controlled 351W from the 70's. If you compared those two, you'd probably find the the FE would have really tall, heavy cast pistons, long 6.490" rods, heavy ring pack, etc, and the 351W would have heavy cast pistons (but much smaller when you look at a 4.000" bore and a 4.230" bore, plus the short deck block), shorter 5.956" rods, etc, etc. The SBF would easily have the lighter rotating assembly, but there are other variables.

When I do rebuild an OEM-style engine, I will use more modern parts: forged pistons, modern ring pack designs, modern connecting rods when available, etc. It makes a difference.

On a stroked FE or stroked SBF, I'll use high quality, modern parts, but nothing exotic. If you look back to the two pictures I posted of a stroked SBF piston and a stroked FE piston, you'll notice that they are both within 2g of each other, and those are not custom, exotic pieces.

The bottom line is that even though the rotating assembly is lighter, it doesn't necessarily mean that the engine will accelerate quicker. That's been my point all along.

Can you make a small block accelerate quicker than a big block? Yep. Can you make a big block accelerate quicker than a small block? Yep. But there can't be a blanket statement made that says the smaller engine is always going to be zippier.