i think that the 396's came in the 68 and 69 cars did they come in the 70 ??? and is it true after 1970 the engines didnt produce as much horsepower becasue of emissions and such?

At some point in the 69 production year, the 396 actually became the 402, although the SS396 name remained through 1970. In that year, Chevelle horsepower reached it's peak with the venerable LS6. From that point on however, published horsepower numbers declined, and by the end of the decade, all of the big inch, big horse engines had been factory castrated.

The power ratings didn't drop until `71 when they lowered compression ratios for unleaded fuel. An even bigger drop in hp ratings came in `72 when they went to net instead of gross and also got more smog stuff.

Basically, straight across the board (except the 71 HEMI), ALLLLLLLLLLLLLLLLLLLLLL American engines dropped in horse power (lower compression) in 71. The LAST hi-perf solid lifter BB was 1970 (except the 71 LS6 in the Vette, but it was lo-compression) and the last solid lifter SB was 72. The 71-72 LT-1 Vette and Z28 Camaro had solid lifters, BUT, they were lo-comp (9.5:1 vs 11.0:1 in 70-earlier).
In 73, exhaust gas recirculation valves were installed on all V-8s. That was the final blow. It really wasn't until the LATE 90s that GM (and other car builders finally pulled their head out of that hole where the sun don't shine. Toooooooooooooooooooooo late, Honda, Toyota, and many others were well entrenched by then.
I gotta quit now. I could get on this soap box and stay all night! :sad: