i have a stock 351 ho out of a 86 f250. what i was wondering how a stock engine will work with aftermarket heads with either 1.94 intake or 2.02. eventually want to rebuild the motor but for now want to upgrade the heads. also was wondering the pros and cons of cast versus aluminin heads thanks.

 

I havenoideaaboutthe aftermarket heads on stock components. Well as I understand it cast iron heads aside from wieght tend to conduct heat to the the manifold faster and stay hotter longer then aluminuim heads. But I have heard just heard mind you that cast iron are much stronger. But I dont think it would measure out as iron heats up it looses its strength. Aluminuim heads allow for a colder denser charger in your fuel, better combustion which translate into more power, and better gas mileage, cool down is quicker and it takes some real wieght off your front end but thats it my 2 cent hear say lol-Rev

 

https://www.ford-trucks.com/forums/5...08-breath.html

 

Aluminum heads don't run any cooler than iron. Once the engine reaches operating temp, the heads are as hot as the block. Iron heads are more forgiving when it comes to overheating the engine (towing) they don't blow head gaskets as readily as aluminums do. If you plan on towing and using the truck as it was intended, stick with smaller heads.

 

Stick with cast iron unless you're building a race engine. They're more forgiving when overheated, and more easily repaired if damaged. Aside from the obvious weight savings of aluminum, they allow you to run more compression without detonation, because they dissipate heat more quickly, and are less likely to have "hot spots" that cause detonation. A stock 351 HO would be fine with the 1.94/1.60 valves (RHS makes an excellent Windsor Jr. head with this combo), but when you step up in valve and/or runner volume, you must cam accordingly to take advantage of the increased flow. A mismatched intake, head, cam and exhaust will result in sluggish performance, and exhaust gas reversion, caused by failure to attain proper velocity. Think of it as a sink full of water. If you slowly pull the plug out only a little way, vs. pulling it out quickly all the way. Larger valves and intake runner volumes will also push your optimum operating rpm range higher, meaning higher spring pressures to control the valvetrain, lower gears, and lower fuel mileage. Lots to consider when choosing an aftermarket head, but unless your truck is going to see track time, stick with the cast iron, medium valved, smaller runner volume head.


Pete