I have a 69 396 Block that has about 15K on a rebuild. Everything appears clean after taking off the intake, valve covers, time chain cover, and oil pan. I was thinking about changing the cast iron heads to aluminum heads (original 69 aluminum heads are fairly expensive, but there appears to be some reasonable aftermarket ones). How big of a difference does it make ... is it worth it. Would it require me to rebuild the engine even though it had low miles. I'm sure it all depends on what you got and what else goes with it .. but take a 350HP 396 .. what would changing out the stock heads do?

Naturally it's going to depend on valve sizes and the specs of the heads you are looking at. One thing for sure is you'll loose a decent amount of weight off of the engine. If you post the specs to the heads you are considering, or just name the heads, then i'm sure someone could tell you the benefits compared to the stock heads. I'd say I lost at least 50lbs off of my small block by putting aluminum heads on it (not to mention a nice performance difference).....not that weight lose should be your reason for buying aluminum heads.....and i'm sure it's not. I wish I could help you more, but I'm not very familiar with big blocks.

Whats the casting number on the heads on the motor now? Aluminum heads let you run a little more compression,and they are easier to repair,but that doesnt mean they will perform better than good ole GM cast iron. graemlins/thumbsup.gif

If you have the stock pistons, you will lose a lot of compression with anything other than the Edelbrock Alum heads that are cut to 100CC. My own oppinion is the Alum Heads may save some weight, but it all depemds on what you are after. You could plan on spending close to $2000 for heads, gaskets, fluids, etc, etc. for a maybe a 40 - 50 hp gain (that's if you have headers and a good intake/carb to match). Expensive HP IMHO. If you don't have these, you won't gain that mutch. I would do a mild cam swap first before I would consider anything else.

What are you trying to do with this motor? What heads are on it now? What pistons does it have? What cam?

Weight reduction!

Eighty-two(82) lbs. right off the front end of my car. I bought a set of used GM BowTie aluminum heads(flow 385cfm)and they each weigh 41 lbs less then my cast iron 502 heads. I paid $1000 for the aluminum heads and sold my cast iron for $500.

Aluminum heads are almost like an investment, you
can always sell them and probably get most of your
money back. I have people all the time wanting
to buy mine...for MORE then I paid for them.

Emil Dusek
71 Chevelle-502SS
6.68@102mph 1/8 NA

If its a true 69 motor, you'll lose a point in compression, and no matter how good the heads are, chances are you won't gain the torque back.

Pick a good modern camshaft for it if you think it needs more grunt.

You can do alot with GM iron Oval port heads.

Most aluminum heads on the market are too large for a street 396.

What would much more bang for the buck, would be to have your iron oval port heads bowl blended, and have a competition valve job done.

Thanks everyone for the information. From your input and others "aluminum" heads need to be done in conjunction with serveral other things to get the cost benefit out of them (usage). I'll try and post some more specifics on the engine.