Horsepower Estimate?

I don't get why people think those calculators are more accurate then a dyno

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My thoughts are the opposite of that.
But I’ve been using the dyno since 1990.

When I want to know how much power an engine makes, I test it.

Built in 1987-
340+.030, Badger stock replacement pistons for 68-71……actual CR unknown.
587 heads with 2.02’s installed. Using the term “bowl ported” to describe the work done to the heads is very generous.
It was the 2nd set of heads I’d ever taken a grinder to(back in like 1987).
My guess would be 210-ish cfm.
Regular Performer, Holley 650, 1-5/8” headers, Comp 268H.

What did it make?

Back story on this 340……
When it was built originally in 87, it got a bigger cam.
A Crower 282-HDP.
The engine went into a LRE truck, and even with the 3.55’s and an 11” converter…….the cam was a bit too much for the application.

Fast forward into the 2000’s, and it’s been thru a couple owners……None of which are really “car people”.
It ends up ingesting the air cleaner stud…….which gets into a cylinder. Munches up the piston and puts a crack in the bore.
A friend of mine with a repair shop is working on the vehicle……..he brings me the engine.
I end up sleeving the block, and getting a “similar” piston(Badger is long gone and there aren’t any other cast pistons with the same specs).
Cam lobes are showing some wear by this time, and the heads need freshening.
So, heads get done, and the Comp 268H gets the nod as a more suitable replacement given the application and intended use.
I dyno tested it after the repairs.