How does cid make power?

33IMP said
So, If you don't adjust the combo for the increased stroke/displacement, you get "disappointing" results. What if you do? What if you improve the cam and heads and exhaust?
Take your 273, exchange it for a 408 shortblock with the same compression, and use your 273 heads, a two barrel intake, .398 lift cam, tiny exhaust manifolds, and sure, you'll be disappointed.
Match the combo to the displacement, and a 408 WILL be better than a 340/360 for STREET use. (Disregarding race use of a 340 with rpm to the moon, and 5.something gear)
When I build a 400 into a 512, I'm not gonna keep the 7 1/2 to one, .420 lift cam, 906 heads, and log exhaust. I'm gonna use parts to match the 512 displacement, and expect a LOT more than 2%. I would expect more than a horse per inch of increase.

Once again, you need to make a different comparison. Why a 273 and a 408? Why not look at a 360 verses a 408? Or a 340 verses a 408? Then you are looking at engines with similar bore sizing.

I could do the same as you and compare your 408 to a say, 520 inch engine. The 408 has a .400 larger bore than the 273 and that 520 has a .400 bigger bore than the 408.

That 408 would get shredded simply because the 520 has a bigger bore and wider bore centers. That means you can use bigger valves, which means you can use bigger ports. And THAT makes more horsepower.

That’s why all the paper tiger arguments set up like you did skew the results to the favor of everyone who thinks displacement rules. It does IF the rules are set up in its favor.

If you are talking which platform has a higher horsepower density (I don’t like that phrase but it’s what everyone uses so I’ll stay with common vernacular here) the smaller engine would win. In other words, if the 408 made 550 hp, and the 520 made 718 hp, they would have the same horsepower density. I say it horsepower per cubic inch. In the above case, both engines made 1.38 hp/cid. It would be unlikely that the 520 would make that hp/cid if both engines were built for the same purpose.

I won’t even get into BMEP but it’s an important number that should be carefully considered.