Thread: SBC 350 build

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Originally Posted by Bowtiepickups

Yep, I think the vortec heads with the COMP springs will be my best option. I will be sure to pull my rear-end cover and see what I have for gears. I'll be putting in new bearings all around in the bottom end of things and likely put in new pistons if the cylinder walls seem all good. You said not to run too much lift on my cam, what would you recommend for max lift I should run for a daily driver?
I was looking at the COMP XE274H
In lift-.490 lift
Ex. Lift-.490
In @.50-230
Ex. @.50-236
LS-110 degrees

Well, max lift will be determined by your valve springs and piston to valve clearance. I'm going to say it again. The camshaft is the LAST piece you buy for your build, after you have everything else lined out to work together.

One thing that I would not do, even if I were to use a flat tappet camshaft, is to use an extreme energy grind on a street motor build. The lift off the base circle of the cam on these grinds is the maximum rate of velocity that can be achieved with a flat tappet before the edge of the lifter digs into the side of the cam lobe. This is just stupid for a street motor. If you are in competition and an extreme energy grind will get you half a tenth, then the gamble might be worth it. Otherwise, use a cam with nice, easy ramps and let the valvetrain live in a kinder environment.

The following is my own approach to figuring out the relative work that a lobe is asked to do compared cam to cam. I don't know how scientific it is, but it makes sense to me in the context of how I use it. Math is black and white. There are no gray areas.
You can determine the relative tappet velocity of a grind by subtracting the 0.050" tappet lift duration from the advertised duration. I remember for years that Crane used a 56 degree difference on most of their cams. If you had a cam with 270 degrees advertised duration, then the 0.050" duration would be 214, for instance. Now, if we assume a symmetrical opening and closing lobe configuration for the sake of argument, that would mean that there would be 28 crankshaft degrees of tappet rise from the advertised point (usually about 0.006" up off the base circle of the lobe) to the 0.050" tappet lift point. So, we are lifting the tappet 0.044" in 28 crankshaft degrees. This would work out to a lift rate of 0.00157" per crankshaft degree.

Now, let's look at a cam with 270 advertised and 228 @0.050", a difference of 42 degrees. This would be a much more agressive camshaft lobe design. If we are using up the same 0.044" lift in only 21 degrees of crankshaft rotation, you can see that the rate of lift would be 0.00209" per crankshaft degree.

If you'll just think about it for a moment, you'll see that the cam lobe has to endure quite a lot more pressure to do more work in the same amount of time. If you plan to run one of these extreme energy grinds, then have the cam nitrided at the factory before they ship it and use the best lifters the grinder can offer. This is no job for "white box, no name lifters". Also, I would suggest backing up to the post where I listed all the things that can frag a flat tappet cam and pay attention there.

One other thing that I meant to address for you is the roller rocker. The value of a roller rocker is in the trunnion where it swivels on the rocker stud, not at the tip where is engages the valve stem tip. High speed filming of the valve action by a famous cam grinder, Racer Brown, showed that the roller tip is too small in diameter to generate a mechanical couple with the tip of the valve and that the roller just skids across the valve tip instead of rolling. As I said, the main advantage in a roller rocker is at the trunnion, not the tip. Do not be tempted to buy those fosdick Magnum rockers from Comp that use a conventional ball and socket at the trunnion and a roller tip. Comp got it bass-ackwards and those things should be against the law. They should have made a roller trunnion and a conventional tip if they really wanted to improve things. The other thing is, don't waste your money on 1.6 rockers for a small block Chevy. Use stock ratio 1.5's. In my opinion, the best value on the planet for roller rockers is the Scorpion units. You can get them in narrow body models to fit inside the L31 valve covers and they are made with the rail tip feature as well.

One other point. I made reference to using either the Edelbrock Performer RPM or the Weiand Stealth as the best manifolds for a street/strip motor. Tango has brought it to my attention that the Holley 300-36 is at least as good and after doing a little research on other forums, I understand it may even be better than the RPM or Stealth. Thanks Tango for the heads-up.