Why different H.P. and C.R. in the same Engine

[Charger70]

A 1970 383 came in 290, 330 and 335 HP. It also came with 8.7 to 1 and 9.5 to 1 CR. This engine came with the same bore and stroke and I'm guessing the same heads. But why is there a difference in HP and CR?

[ehostler]

It was an options thing.

There was the 383 2bbl at 290 HP, the 383 4bbl at 330 and the 383 4bbl HP at 335 HP.

[PRO]

in fact the 330hp engine was overated,having owned 2 and known of 3 others they wouldnt even come close to matching the 335 HP motor,I did rebuild 1 and discovered no windage tray and no hp cam,Id say it was more like 300hp,I also believe the 290hp 383 2 bbl was grossly overated I think it was more like 250hp..........PRO............

[Jims451]

The Different HP ratings were because the engines had different cams, exhaust, compression, intakes (2-bbl and 4-bbl) and carburators.
They all had the same Bore, Stroke, Rods, and (usually "906" heads from 1968-1970.)
The HP engines also had a windage tray.

[Charger70]

So why did they have different Compression? They all had the same bore, stroke and heads. What made the compression different?

[ehostler]

The pistons make the different compression. The flat top gave the highest compression and then different depths of dishing give the lower compressions.