Thread: SBC 350 build

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Originally Posted by Bowtiepickups

Haha. That sounds like a solid way of thinking. I read little article and the boys at Hot Rod magazine used vortec heads and used a set of COMP Cam's beehive springs and ran .490 lift. (they say they are good for .560) If i understand correctly, I can put on the beehive springs and retainers and be good for a .560 lift cam. I was thinking I would do this since the heads are already on the motor it would be a decent way to make power and save some serious scratch. Of course, I would check the casting numbers on the heads before I did it.
Link to the article:
http://www.hotrod.com/techarticles/e...ild/index.html
Check page 2
Link to springs:
http://www.summitracing.com/parts/CCA-26915-16/
Link to retainers:
http://www.summitracing.com/parts/CCA-787-16/

That could be a plan. Parallel springs such as the Cranes I linked really need a spiral-wound damper spring to cancel harmonics in my opinion, whereas beehive springs do not, so my choice in what you have presented here would be the Comp springs.

Notice that the builders used a cam ground on a 108 degree lobe separation angle and had some horribly low intake manifold vacuum because of it. Generally speaking, the motor will make more power the tighter you go with the LSA, but vacuum stinks for operating power brakes and other vacuum-operated accessories. You'll also note that they mentioned a reserve vacuum can or an electric vacuum pump. If you need additional vacuum, don't waste your money on a reserve can. Either pop for the pump or install a hydroboost system like was used on some Cadillacs, trucks and such. Works great with the wildest cam because the brakes are not dependent on vacuum to operate. I don't care what anyone else says, you need a minimum of 16 in hg to operate power brakes.

You can still make good power for street/strip and make a little more vacuum by choosing a cam ground on a 112 degree LSA and keeping the duration reasonable. You keep the duration reasonable by using a reasonable static compression ratio. Understand this: YOU CANNOT INTELLIGENTLY CHOOSE ANY CAMSHAFT FOR ANY MOTOR UNTIL YOU ABSOLUTELY, POSITIVELY KNOW THE STATIC COMPRESSION RATIO BY MEASURING COMPONENTS YOURSELF OR HAVING SOMEONE ELSE MEASURE THEM FOR YOU.
You need 5 values:
1. Cylinder volume in cc's
2. Combustion chamber volume in cc's
3. Piston deck height volume in cc's (the volume between the piston crown and the deck of the block with the piston at top dead center)
4. Piston crown volume in cc's (a true flat top piston will have about 6-7 cc's in the eyebrows that are cut into the crown for valve clearance. Otherwise, for a dished or domed piston, the mfg will usually publish the volume). Most of the stock-type 350 pistons have a recess that isn't actually called a dish, but it is a depression across the crown, with a very thin ring of material sitting up a little higher around the bore. That little thin ring of material is insufficient for generating a good squish and you should be very careful with compression ratio and cam if you use that type of piston. The very best type to use in a street/strip build in my opinion is a D-cup dished piston. These provide a generous shelf of material that comes up against the underside of the cylinder head to generate a very good squish. If you build any kind of reasonable static compression ratio into the motor without using a good squish, there is a good possibility that the motor will detonate on pump gas.
5. Head gasket volume in cc's
If you want me to go through the entire routine and teach you how to find the exact SCR, just ask.
The camshaft will normally be the last component chosen, after everything else is nailed down for the build.

If you do end up using L31 heads, don't let anyone talk you into increasing the valve sizes. Stock, they are 1.94"/1.50" and will do a fine job on a 350. Any cutting done on an already thin-wall casting is just asking for trouble.