I have a 71 340 demon with a 75 mm turbo. It currently has stock x heads and was wondering if there is an afternarket head that would be worth switching to for the money? I like the idea of an aluminum head for the weight savings but some people are telling me its not worth the expense because it wont make much power difference on a boosted engine.

If the aluminum heads flow better than your X heads then it will make more power. So to answer the question you need to know how well your current heads flow and then compare that to the aluminum heads. Unless your X heads are really well prepped I'd think that you would pick up power. You'll also drop 30 or 40 lbs of weight depending on the head.

My x heads are totally stock

It will help.

Yes it will definitely help.The spinning impeller can only add so much energy to the air it's pumping. The more energy gets burned up along the way, the less there is to be velocity when it passes the valve. Velocity times area = flow.

Another nicety is that the Edelbrock head exhaust port flows better too. This means more energy gets to the turbine so it spins the impeller faster, creating more flow. Flow is proportional to horsepower.

With no other changes I think you're looking at 55hp minimum. Your mileage may vary.

R.

Exactly. I've had people tell me that porting doesn't matter with boost but that obviously isn't correct. Compressed air doesn't flow as well in a tiny hose as it does in a bigger hose. Turning up the boost to get flow with restricted ports works, but it also requires energy (power) to build the boost. That extra power turns into heat which then causes other problems.

Boost pressure is also a measure of restriction. We did nothing to a 5.9 Cummins engine but port the cylinder head. Lost boost and gained horsepower. Then cranked the boost back up. Ah-Hah!

Hard to answer your question without a little more detail. What 75mm turbo is it, how hard are you pushing it, and on what fuel/intercooler?

But really unless the heads you have are damaged, usually adding boost makes a lot more sense, and is WAY cheaper to gain power then adding head flow.

My 3700lb pig went 10.08@136mph with a 75mm and home cleaned up iron heads. That was at 20psi of non-intercooled boost. I don't know how close you are to that kind of power level, but it shows you can do pretty good without much head flow.

I now have CNC ported eddy's, better intake, bigger cam, billet 76mm wheel, and 23psi of boost, and it's been 9.55@142mph. Now the thing is 2 full tenths of that was in 60ft. So it's really only about 3 tenths quicker and 6mph. Some of that HAS to be the added 3psi of boost too. So I can't say that the heads were really worth much of anything at all honestly.

Adding boost is usually around 20-25hp per PSI. My car went 123mph on 10psi, and then 136mph on 20psi with the exact same combo. That's about 20hp per PSI almost right on the money. As long as you're not knocking on the door of detonation with the fuel you're running, it'd be foolish not to just add 4-5psi for 100hp. I can almost guarantee you won't get that from cylinder heads.

People are afraid of boost numbers for some reason. It's really just a number. If the motor will take the power, and the fuel octane and/or intercooler keeps detonation in check... you can add a LOT of power basically by just turning the knob for free.

X2 - how much boost now, what A/R? Where is your ignition?
At your knock limit, there are many combinations of boost + A/F + spark and they may be 100 hp apart.
A smaller turbine housing might add 50 hp for $200.