Originally Posted by stealthy1991
Ok I've posted some questions on my build before but have gone a different route since then. I had a newer truck block that ended up being a 2 bolt main so instead I bought a 1974 350 4 bolt main short block .020 over .010 square decked. The pistons are Servolite 1436-020 which are .031 in the hole. So the questions i have are... What kind of compression can I expect with these Vortec heads?
190cc Intake Runners, 64cc Chambers, 1 piece stainless valves; 2.02 Intake valves, 1.60 exhaust valves. Flow about 260/180 CFM.
The valve springs have a max lift of .600, open pressure is 325 lbs, closed pressure is 130 lbs.
Straight Plug. 3/8 studs, 5/16 guideplates. Standard accessory bolt holes.
Want to use either this: Howards Cams CL110245-12... Duration 280/292, Lift .501/.509
or Comp Cams SK12-422-8... Duration 270/276, Lift .495/.502.
Can I use the springs that came with the heads for these retrofit roller cams?
What kind of rocker arms should I buy? The screw in studs have a hex on them.
I plan On putting this in a 73 Corvette 4 speed 3:73 gears.
I'm sure I will have more questions.
You have chosen a piston that most of us hotrodders would not have chosen, a rebuilder special with a reduced compression height. Most 350 pistons have a CH of 1.560". Pistons such as you have chosen have a CH of 1.540". This is to allow the machine shop to cut the block decks 0.020" and still have the same piston deck height that the block had from the factory.
Your piston deck height is 0.031", so by the time you add a composition gasket of +/- 0.040", you are at 0.071" squish and have eliminated any chance of generating a good squish to create turbulence in the chamber.
What I would do at this point is to make certain that the block decks and heads are flat enough to use a shim gasket. An 0.016" gasket would yield a squish of 0.047", which would go a long way toward making a good motor out of it in my opinion. I generally shoot for 0.035" to 0.045" on a 350 build.
Silvolite says there are approximately 6cc's in the piston eyebrows...
My math tells me there are 6.44cc's in the piston deck height and 3.46cc's in the head gasket. Most all heads will pour a little bigger than advertised, so we'll call the heads 66cc's.
So, here are the values:
723.80 in the cylinder
66 in the chamber
6 in the piston
6.44 in the piston deck height
3.46 in the gasket
Added up, we get 805.7 cc's.
Dropping the cylinder out of the mix, we get 81.9 cc's.
Dividing the larger by the smaller, we get 9.83:1 static compression ratio. I would use a cam with somewhere between 212 and 224 degrees intake duration @0.050" tappet lift, ground on a 112 degree lobe separation angle for good manifold vacuum. A shorter LSA will yield a little more low end power, then peak early and peter out at the top. Counsel closely with the tech at the cam grinder that you choose, as to the suitability of the springs on the heads. The grinder is the guy who has to be satisfied, he's the only guy who will know for sure.
As far as valve to piston clearance, each and every build is unique unto itself and must be closely checked by the builder. Here is some excellent info from Isky for those readers who are unfamiliar with checking for clearances (valve to piston, coil bind, retainer to guide and rocker to stud).....
Bottom line, I like the Howards grind.