Do aluminum heads make a difference?
 

I have two stock 502 MAG MPI's with 220 hours. I have a chance to purchase two new sets of aluminum heads at a great price. But it sounds too good to be true that I can just bolt on aluminum heads and get more power. Do I have to change timing, cam, exhaust, etc... to get any hp gains. Thanks.

yes aluminum heads make a difference
but it is a combination of things that will make the hp
bottom end ,cam,heads and intake

Depending on the head, how it flows and what compression ratio it ends up. Yes it can increase power quite a bit. Also maybe a 200# weight saving on a twin application.

Remember you get what you pay for, if its sounds to good there is a reason.:drink:
If they are an off brand you could spend more in machine work than they are worth. You need to find out what kind of valves are in them, what springs, what CC are they.
IMO enjoy what you have, changing heads on a stock engine will get you small gains and minimal increase in speed.

It is not so much that the heads are aluminum, as much as the weight savings. Also depending on the heads what makes the power is the style of head, port style, chambers etc...

Cam, intake, compression ratio, exhaust type, fuel system & overall cid all also have an impact on hp & tq.. ;) Jamie / Lakeside

Merc did a lot of research before they used the heads that are on them now. If you are not changing everything you would be better of leaving it alone.

Agreed. Also, if you don't have closed cooling your asking for problems.

weight and ease of repair when there is a failure are the major advantages IMO.

What heads are you looking at? If you don't know what to look for, you may end up hurting your performance.

I thought Chevrolet did the R&D on the 502?

I don't think that anyone is suggesting that Merc developed or even helped to develop the 502. That was all GM. That said, you can order the 502 with different heads on them right from GM (iron ovals, iron rec. port, aluminum ovals).


I'm sure Merc did plenty of R&D before they choose what castings to have GM bolt on them.

By bolting on a set of aluminum heads with the same size CC chamber as the ones you take off, you can actually lose 1/2 a point of compression.

wjb, OK now I understand what was said. The reason I asked is because I was in the motor plant here in Western NY in the engine cells a couple of times during it's developement. I was told by the engineers at that time it was being developed for the truck and marine industry as an alternative to a diesel power plant.

When I was looking into heads for my project I learned a fair amount, I think... The 502 is going to use a large rec port head. In reality this is not a very good head for your engine. The flow is going to be poor until the upper rpm range, and acceleration from midrange up is going to be poor becuase of the port size and shape. A great head for your engine would be the AFR 290 oval ports. These have fantastic flow numbers across the board. I have the AFR 265 ovals on my boat and its unbelievable how great these heads are. Either way I wouldn't buy a set of heads just because there a good deal... There are a lot of variables to take into consideration.

Thanks for all the replies everyone. A few clarifications, the heads I believe are GM performance aluminum ZL1 heads (I could be wrong about this). The guy I know owns a machine shop and has bugging me for years to let him do some work to my motors. I have been hesitant because I want my motors to be reliable, but since I cannot sell my boat to buy a faster one, I thought maybe I could make mine a bit faster. He can do anything to the heads as far as porting and what not as well as crank and cam work. I really don't have a clue about this stuff, so I thought I would ask for some input before I commit to anything. Thanks.

I haven't seen this mentioned...I thought you could run a little more timing or compression on lower octane fuel because aluminum heads disapate heat better and are therefore less prone to detonation. Am I misinformed?