[olddog]

To make more power you have to burn more gasoline, per unit of time, at the correct air fuel ratio. Putting fuel in is easy. Putting more air into an engine, is not. Talking normally aspirated, more cubic inches is king. More cid moves more air, until you reach a size that the valves and ports become the bottle neck.

For any given bore, there is a limit on how big of valves you can fit into that space. A long time ago people, quit thinking 2 dimensional, and realized that if you change the angle of the valves you can fit bigger valves into the same bore size. The hemi is the ultimate canted valve design. The 3 and 4 valve per cylinder heads have proven to be better, when considering emissions, but now I have digressed.

In my opinion, the heads make the engine. When I was a puppy, there were very few head options and the cost was more than a pup could afford. Access to a mil to port factory cast iron heads was hard to come by. Therefore we were forced to go down the road of ridiculous cams. You do not have to do this today.

Your only problem is to pick the right heads for what you want your engine to do. Now for the bad news. The biggest, baddest, highest flowing, Hp making heads, are not the best heads for every engine and its intended use. What! A mid range head may be a better head, for a desired engine personality.

You may have already thought all this out and just have not shared it with us. Picture a dyno chart. Now remove the Hp trend line, and forget about Hp. Now what you have left is the Torque trend line. What shape do you want that line to look like? Are you willing to give up tons of torque on the low end to get more torque high up the rpm scale? How many rpm are you willing to turn?

An engine that has a torque curve that looks like a mountain (peak torque at a very narrow rpm range and falling off rapidly on either side) is absolutely no fun to drive on the street. They can make huge power, but only in that rpm band, at very high rpm.

On the other hand, a flat toque curve (same torque at every rpm used) is the easiest most friendly engine to drive anywhere. You get the exact same pedal response at any rpm. The problem is this engine has yet to be designed. You have to give up something somewhere to get more where you want it. Picking the right heads with the right cam is how you balance this out.

The other two factors you have to consider are rpm and idle quality. Idle quality goes hand in hand with street manors. There is that nice rumpty rump idle that is music to the ears, but too much and you have an ill mannered engine that bucks and hops when you try to drive slow.

RPM goes directly to longevity and cost to build. The more rpm you want to turn the stronger the bottom end has to be and harder it is to control the valves. Where do you want the Hp to peak (at what rpm do you want the torque to start dropping off faster than the rpm is increasing)?

Once you lay this out, a builder will know what heads are best, but I do like the AFR heads.