My '67 has a summit street kit w/ 450 Holley. How much HP increase can I expect from taking it from 289 to 331 if I don't replace the heads and then also if I do replace the heads?

 

well best guess would be that it would be a 14.5% increase in cubes. So if your making say 200hp now your would see a 29hp increase. But yes it does depend on the heads. that will be the choke point.

 

Agreed. The cubes alone won't matter that much unless you can flow enough air to make use of them. Cam selection will also make a big difference, and stock heads will severely limit that selection.

 

IMO, a bigger bang from the buck would be found by changing the heads alone if we are talking an either/or situation.

I think that even with the stock heads, going from 289 to 331 would probably help low end torque, but it wont offer much change in top end HP. (due to head flow limitations)

Changing to 331 AND going with a good aftermarket head and intake would make a huge difference.

That said, I think all 3 engines have the potential to run good, just not equally as good.

 

Agreed, just increasing the displacement will give a bump in HP roughly equal to the % increase in displacement.

No way to estimate how much of a gain in HP if you replace the heads too w/o knowing what heads you're planning to go with and all the other factors like cam, intake, etc...

 

You could easily build the 289 up to 320 hp without stroking it. What's your goal here?

 

This is a trick question. All we know is that you have a 289 and a carburetor too small to reach the max potential of either engine.

Save your money until you can do it all at once. The build is pointless without the corresponding parts to reach full potential, IE headers and a larger carb.

 

Not if the heads don't flow.

 

so many people make a new thread then never respond.

 

This may or may not be true, if the 289 was pushing the limits of the stock heads and intake at the top of it's HP run, it could be that the equally equipped 331 might make about the same HP as the 289.

In any case going back bone stock with as a 331 would almost certainly NOT create an engine that had a corresponding increase in HP. As I said earlier, I think the peak torque would increase, and be lower in the RPM range. HP? maybe yes maybe no.. I lean toward a little to some.