Engine build advice 331 NA vs 306 with possible boost


New Member
Apr 4, 2019
I just tore down my original ‘90 5.0 block with 200k miles on the bottom end and she’s going to need new pistons. The cylinders look pretty good, but since I have to get new pistons, I would just get the block bored out 30 over and buy standard oversized pistons to match.

Here’s my issue...I’m in CA and I have to build this new engine to comply with all the smog laws.

One option is to rebuild it as a 306 with a possible smog legal small boost supercharger later should the NA build HP leave me unimpressed and looking for more. The bottom end would be built with the assumption a supercharger could be added. I would purchase a set of AFR 185 heads, use either an e303 cam or similar custom cam, Holley systemax 2 upper and lower intake.and 24lb injectors

The other option would be to use the same parts, but purchase a 331 stroker kit and keep the engine NA. I’m guessing the 24lb injectors would need an upgrade to something larger.

I’m pretty certain the stroker would need some type of tune to make it run properly whether it be a chip or on board computer replacement.

Do you think the NA 306 will need a tune also?
If I’m going to need a tune with either engine, then I’d be leaning towards doing a stroker.

Any suggestions or words of wisdom from those who walked the smog plank in CA?

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