If you are serious about installing Alloy heads, it behooves you to study it out.
Smarter men than me have said that with a straight swap to alloy heads with no other changes, your engine is likely to lose power. They say that this is because the alloy heads suck heat out of the combustion chambers, and heat is power.
Most sources will say that the engine needs a compression ratio boost of at least a half a point, to compensate.
IMO,
it's more like a full point for a street machine.
I'm not telling you what to do, BUT
For alloy heads, I have boosted my cylinder pressure up to 195 psi, on my alloy-headed 360, and the engine ran gangbusters, and even ran on 87E10 at WOT at full ignition timing. At my elevation of 900ft, and with my cam, this required a static compression ratio of 11.3:1
My engine is definitely not lazy, and will pull any gear I ask it to. I installed a 4-speed behind it.
I suppose, this 11.3, would be considered the equivalent of 10.3 Scr, if the engine had iron heads. But you cannot compare them directly that way, because at 10.3 the pressure is likely to be close to or greater than 170psi which with open chamber iron heads would very likely self-destruct in detonation.
The point is this; If you truly are gonna use closed chamber alloy heads, and you are installing new pistons anyway, it behooves you to set the Quench up right and crank the pressure up; to take the most advantage of the swap. Else you will spend a lotta money on a mediocre build.
As a newbie, I highly recommend you just get a crate engine from a builder right here on FABO. I think they all know what they are doing, and they'll give you the right engine the first time.
If you make it a 360, you'll get the benefit of extra bottom end torque, allowing you to run a more hiway friendly rear gear, and/or less stall; and then you can sell your 340, or save it for later.
If you make it a Magnum, you'll get the benefit of the roller lifters.
These are my opinions.
Happy Hotrodding
