I am always surprised with the "you can't block fill" crowd responses. I can only give my limited personal experience, but it has worked fine for me. On top of it I went against a LOT of the mainstream information that pops up from time to time.

1) I did not use hardblock... I used Embecco 885. It's a metallic based grout, and a 50lb bag is only about 1/3 of the cost of a hard block bucket. It's shrink rates are very good (Only 0.8% after 28 days). It also has the same thermal expansion rate as cast nodular iron (6.5 in/in). Meaning it's properties allow it to maintain it's shape long term, and it will grow/shrink with the block well.

2) I filled the block AFTER it was honed. The motor showed zero signs of blowby at idle cruise. It does show some oil out the breathers under high boost, but NEVER in the exhaust.

3) I have no oil cooler. I had previously never even come CLOSE to having an oil temp problem until I put the engine diaper on the car. The diaper holds a LOT of heat. But previous with standard pan out in the air, the car would idle/cruise/WOT just fine with nowhere near an oil temp issue.

I probably have 100 total runs on my stock block, anywhere from 600~800hp level (depending on boost). Obviously boost is a completely different animal, so it's hard to judge just how much better it made the block, but I certainly think it helped it.

Just my