IO-540-A1A5 - Lightweight angle valve engine?

[digidocs]

I was looking at the FAA TCDS for IO-540s today and spotted the IO-540-A1A5/B1A5. The interesting thing about them is that the TCDS claims they output 290HP at 2575 rpm, but only weight 414lbs (a standard -K1A5 weighs 438lbs).

If my reading is correct, the main difference between the -A and -K is the crankshaft.

Can any of the engine experts out there comment on the -A1A5 and similar engines? What are we giving up to shed those 24lbs?

Thanks,
-DC

[rocketbob]

Yes the difference is in the crank, the K-series has the big-journal crank. I've overhauled a K1G5, and I'd guess the crank weighs in the neighborhood of 75-100 lbs. Its one heavy dude to pick up by yourself! The 4-cyl cranks feel like toys in comparison.