351 Cleveland Open Chamber vs Closed Chamber heads

[cascade202]

I converted my '70 4bbl Cleveland to open chamber heads so that I don't have to buy Premium gasoline. I'm happy with the performance but wonder how much power did I give up. Anybody got any idea?

[Roy]

You went from 11:1 to around 9.5:1. You lost around 40 HP. Maybe even a little more. Is it just a 4V motor or a CJ, Boss?

[cascade202]

Thanks for the reply Roy.
The first one I was a '70 stock M code. The next is a stock '73 Q code CJ. Other than model-year and 4-bolt mains is there any difference?

[Thor]

I'm curious to know why you've chosen open chamber as opposed to closed chamber heads?

[cascade202]

The lower compression allows me to use regular gas.

[Roy]

Originally Posted by cascade202

Thanks for the reply Roy.
The first one I was a '70 stock M code. The next is a stock '73 Q code CJ. Other than model-year and 4-bolt mains is there any difference?

Im pretty sure the CJ had the big valves and runners like the 4V but had open chambers like the 2V. Some M codes were 4 bolt also. I used to be big into the 351 Cleveland and could tell you all the differences but its been a long time.

[Thor]

Originally Posted by cascade202

The lower compression allows me to use regular gas.

Okay, I thought it may have been another reason other than that...

[Unrealford]

Originally Posted by Roy

Im pretty sure the CJ had the big valves and runners like the 4V but had open chambers like the 2V. Some M codes were 4 bolt also. I used to be big into the 351 Cleveland and could tell you all the differences but its been a long time.

Yes, and hardened valve seats.

[cascade202]

Unrealford could you expand a bit on the hardened valve seats? Did the '73CJ have them?
I also posted a question on notching the shock towers.