I found one of my old posts. Since you've already got the 9.2:1 block then some doesn't apply. I got some of the stuff out of an old (circa 1985) Hod Rod magazine.
I've been researching this lately. I actually plan on rebuilding my old 305 and putting it in place of my 350. Then I'll rebuild my 350 and put it back in place of the 305. It's a good thing motor swaps only take 6 or 7 hours.
Anyway here's what I'd do and the order I'd do them. #5 has two parts because you can choose one or the other.
1. Tune your carburetor. Get some DR rods for the secondaries.
2. Edelbrock 2101 intake. Good for ten horses or so unless you've got a crappy equalized dual plane intake then it's worth more.
3. Headers. Good for just about ten horses. Find 1.5" primaries if you can because otherwise you'll sacrifice some low end torque.
4. 2" open spacer under the carburetor. This slowly generates horsepower but it doesn't break the 5hp mark until 3500 rpm. If you've got room, stick it in there. It's only $20. Worst case scenario is that you'll lose some bottom end torque and you'll have a $20 piece of phenolic plastic that would go great on that 400SBC powered Camaro you've been dreaming about.
5a. Find some 58cc heads if you don't already have them. Get them machined for 1.94 intake valves instead of stock 1.84. If you can, find a set that you can mill some material off so you can get the compression up a little higher yet.
5b. Camshaft. It seems that 108° works the best. I don't know anything more than that--I'm still researching.
6. Rebuild. Stick some higher compression pistons in it. Port the heads.
After both #5s and a rebuild you're supposed to be able to squeak [email protected]
,000rpm with a properly tuned carburetor.
Most 305s had between 7.5:1 and 8.0:1 compression ratios. If you take that up to 9.5:1 you'll see around a 5% horsepower increase. You figure 2-3% per point of compression increase.