Originally Posted by zildjian4life218
Hey I was wondering if someone could give me a couple pointers on what to look for when picking out a cam to best suite a given set of cylinder heads and power goals. I know cylinder pressure, head flow, converter stall, gearing, and weight all matter a lot when choosing a camshaft. I was hoping you guys could give me some insight on what determining factors will effect my power goals.
I currently have a 355ci late model sbc with hypeurtectic pistons and eagle rods. It also has vortec heads that i ported a little. On top of that is a performer rpm vortec intake with a 650cfm edelbrock carb. The current cam is a performer rpm hyd flat tappet has gone flat. multiple lifters are scored and lost their convex shape. So I would like to take the winter months here and pull the cam out and replace it with a hydraulic roller. I have a complete setup from a vortec engine, wishbone, hardware, and lifters that I could use but I heard that too much lift will cause the lifter to rotate in the bore which would not be good. I have also heard of people buying GMPP lifters because they handle rpm better or something? http://www.summitracing.com/parts/NA...5&autoview=sku
Is there any fix to the lift issue? I imagine not running a small base circle cam would be the first and obvious answer but idk if cams grinders do take the base circle down even a little to cause the lifter issue.
One thing I noticed about the vortec heads is the intake flows best at .5 and the exhaust flows better at .6 so should i get a cam where the intake lift is close to .500" and the exhaust lift will be close to .600 or maybe run 1.6 rocker arms on the exhaust? I also plan on buying a set of full roller self aligning rocker arms for this motor over the winter so I can go with whatever ratio will best suite my needs.
My end goals are I would like to get my car in the 12s for sure....... faster is always better. Drive train will hold. The title says it weights 3200ish with the original v6. So at least 320whp will get me there but the more the better right? lol Please any and all input is appreciated. I am still learning from all you guys on here so like i said any input is well appreciated. Thanks!
320 hp out of a 350 is not difficult and with Vortec heads is a no brainer. It certainlya cam over a half inch of lift isn't required. These kind of lifts get you into a parade of engineering problems to where valve to piston clearance, rocker to stud, pushrods to guide, springs to coil bind, spring rate and strength, and retainer to upper guide clearance all become additional problems to be worked out; often not inexpensively.
Lets talk ports and their relationship to the cam as it seems a lot of non-sense is out there. A port, any and all ports, has a maximum flow potential. Once that's hit adding lift at the valve is of no further help. What will help a maxed port is more duration because that adds time. But excess duration adds a lot of overlap and offers a late closing intake. At RPMs in the off idle to the torque peak range this causes the mixture velocity in the port to slow and even reverse at some lift points, this drops bottom end power and pushes the torque limit higher in the RPM range. A partial solution lies in raising the compression ratio, but in the end you are limited by the fuel's detonation limit. Gearing can help some reducing the load on the crankshaft either through stiffer gears, high stall converter, or a lighter vehicle all reduce the detonation sensitivity.
The issue of lifter's is not rotation in their bore, for Chevy, Chrysler, or Ford engines this is a non issue, the dog bone and spider is fine. Where very high lifts are used the aftermarket provides other solutions. The problem is the rate of lift that can be applied to a roller lifter, sudden lifts, especially in the ramp transition to the lobe flank if done to suddenly pushes the lifter sideways in its bore causing it to bind, this is one thing a flat tappet especially a large diameter flat tappet does better, it is the reason why, where the rules allow it, Chevy engines use Ford or Chrysler tappets which are larger and muy larger in diameter.
The SBC has been known to need more exhaust help compared to the intake, that's not to say the exhaust is poor compared to other engines, it just isn't as good as the intake on a ratio of flow for the port and valve sizes for this engine. The aftermarket has long used a little more timing and or lift on the exhaust side of the SBC.
But all of these issues are not a concern for a 320 hp 350, they're not even an issue at getting 380 to 400 horses out of a 350. A 350 with Vortec heads having a compression ratio from 9 to 9.5 with a cam that has about 225 degrees of duration and about .48 inch lift. With a good intake like the Edlebrock Performer RPM and a carb with about 700 to 750 CFM capacity, a decent ignition and long tube headers will pull 400 horses on an engine dyno without sweating and do it under 6000 RPM with a fat and flat torque curve.
I'd expect 380 with circular dish pistons where the squish/quench clearance is rather deep and as a result insufficient. With a D dish or flat top piston, a deck and head gasket combo that nets out about .040 to .055 inch of crown to deck clearance which with a 12 cc D cup will deliver an SCR of 9.6 or 9.3 respectively. You can diddle a few more ponies by using 1.6 rockers, back cutting the exhaust valves at 30 degrees and polishing the back side of the intakes with your home ported Vortecs.
That's all it takes to get some impressive numbers out of a 350, no crazy involved, just attention to the details and careful parts selection which sounds like something you've already done much of.