318 build advise
Page 1
60779 heads are advertised at 63cc..... of alloy.
With FLAT-TOP pistons down .057, in the 3.91 holes, that would be 11.2cc, add 8.77cc for your gaskets, and 63cc for the heads,; and your 318 gets a new Scr of (652+83)/83= about 8.8 .....This is a huge improvement from the nominal 8.0 of the factory.
>However, the alloy heads have the somewhat un-enviable characteristic of being able to transfer heat OUT of the chambers much more efficiently than iron. Heat is power. We have heard it said, that at WOT, this is worth 1/2 point in compression. If that is true than your 8.8 is gonna operate like 8.3@WOT.
>However, at Part throttle, the loss will translate to be more. And this is why with alloys, on the street, we need to run more Scr/ higher pressures. That extra .8 Scr will not translate to much of a power increase if at all. And even if it did, the increase of WOT power is said to be less than 4% per point of compression increase, so on a 200hp engine, that translates to .8x4%x200=6.4hp, at say 4400rpm! with the stock cam; which with 3.55s will be at around 34mph, in first gear............. For what cost, again?
>But if alloy heads suck heat at PT, then you lose torque/power in that mode..
This is irrespective of the better flowing ports, and valves.
Now if you combine that with a later closing intake valve, you get a double-whammy of low-rpm torque loss.
SO;
>With 3.55s, 3200rpm with 26.5 tires comes to 29mph at zero slip. Dial in some throttle and say 26 @10% slip. To compensate for that torque loss, you would need a higher stall TC. At WOT, thru the power curve, you might break even in power-production, due to the better ports and bigger valves. Is it worth the buy-in? Not to me and not by a longshot.
>If you cannot budget for; an after-cam FINAL Dcr around 9.0,and a pressure up or over 180psi, with alloy heads, then I recommend to stick with an iron head. You'll be bucks ahead and end up with more PT torque.