I own an 84TA 4bbl HO. I'm going to switch out the tired L69 305 for a 350, but I'm not sure what block to get. I read in the Tech FAQ that all the 350's used from 86 to 92 were L98s. These blocks had, for one year, a 9.5:1 compression ratio, and the rest of the time had a 9.3:1 ratio. My question is, would this be the best block for me, and what compression would be best? I was looking for a ratio above 9:1, so which of the two should I go for? What kind of HP would be a good estimate? Just to keep in mind... I am keeping the 305's carb, computer, and emissions set up. I also plan to have emissions shorty headers insatlled on the 350 and a chip to make the mix more rich. Thanks for any replies.

 

The block doesn't determine compression ratio. The pistons and heads primarily do that, with a little help from the head gaskets.

The 87-up blocks will have the one-pice rear main seal design, which will necessitate changing your flywheel or flex plate. Of course, the newer ones, if you get one from a F car or Vette, will also be equipped with roller lifters, which is a definite plus. You would have an easier and cheaper build-up with an older block. Anything from 67 to 86 is all the same, except for the occasional 4-bolt one which won't matter in the slightest if you keep the CC Q-Jet.