SBC roller cam

[Roger]

Need a solid roller camshaft for a small block Chevy. At least 260* duration @ .050” and at least .600” lift. Will only be used to clearance a 383 Chevy build so the cam doesn’t have to be perfect (no wiped out lobes!). Trying to decide if I need to order a new reduced base circle cam or not.

[Frontenginedragsters]

Roger:
 One mans opinion: Don't use a small base circle camshaft. They are prone to twist and flex.
Find connecting rods that are 383 friendly.

Matt

[dreracecar]

Small base circle needed for alu rods. make sure its a tool steel billet and you will not have problems

 Roger, have you ever measured a small base circle cam to see how much it flexed or twisted???

[dusterdave173]

I agree --you use bigger cam cores to get a hundredth from a SS/ AA Hemi maybe and it is the answer if you want an A on the test but thousands of SBC's run with .900 base to clear rods and crazy stroker combos--no issues--we order all cams as .900 base so they will clear any combo any time even aluminum rods now and in the future  ther is usually std base, small base for street 383 cmnbos etc and then .900 base that makes life easy for all

[Roger]

Thanks for the input Matt, Bruce, and Dave. This is a gas burning engine using a set of SCAT stroker rods. SCAT told me they would clear the cam but that I really should check to be sure. I found a used cam on Ebay similar to what I need and will use it to check rod-to-cam clearance. My application will need a custom ground cam and I want it to be a regular base circle but before I sink $400 into the cam I want to be xxxx sure it will clear. $69 for the used cam and shipping is cheap insurance. Don’t know how much the difference in diameters would affect the resistance to torsional twist, but a larger diameter has got to resist twist better simply because of the additional mass. Also looking at the higher contact load between the cam lobe and lifter that occurs as the lobe gets a smaller radius with a reduced base circle and the resulting potential wear.

[dreracecar]

WAY over- thinking this

Roller speed is reduced by using a small base circle
Sky high spring pressure has more effect on twist then a slightly smaller shaft dia. and is why you go with the tool steel billet material.
 I broke 2  small base cams over the years and both at the same spot (#8 exhaust), just bad material for the cores, went to a tool steel and never another problem

[Roger]

Over-thinking? This is what happens when you’re retired and have time on your hands while you’re waiting for your turn in the chassis shop. Or maybe I’ve been hanging around some NHRA comp eliminator guys too much

I agree that roller speed is reduced with a small base circle cam but the reduced base circle increases the ramp acceleration rate of the lobe resulting in an increased unit load for cams as compared with a regular base circle with the same specs. For example, at some point during the intake cycle we find the lobe has raised the lifter 0.300”. If you have a regular base circle cam and move the cam 1 additional degree, we might find the lifter has now risen to 0.310”. If we take a reduced base circle cam and move it 1 additional degree we might find it has raised the lifter 0.320” along with an accompanying increase in spring pressure compared to the regular base circle. The same overall load exists on both cams but the reduced base circle has less area (rotations) to disperse that same load so the load per revolution will be higher. At least that’s my understanding.

[dreracecar]

I have lunch with Ed Iskedarian every day, I ask him

[Roger]

Great! I’m sure The Camfather will have some good input. And if you & he have time, ask him about the valve timing for a 383 SBC with 13.9-1 compression making 530# @ 5200rpm and 615hp @ 7200rpm. The fly in the ointment here is that this N/A gas burning engine will use zoomie headers. Can’t run collector headers, it’s against my religion. Not trying to make up all the horse power lost using zoomies with the valve timing, just trying to minimize the loss with proper valve timing for my application.

[ricardo1967]

Great! I’m sure The Camfather will have some good input. And if you & he have time, ask him about the valve timing for a 383 SBC with 13.9-1 compression making 530# @ 5200rpm and 615hp @ 7200rpm. The fly in the ointment here is that this N/A gas burning engine will use zoomie headers. Can’t run collector headers, it’s against my religion. Not trying to make up all the horse power lost using zoomies with the valve timing, just trying to minimize the loss with proper valve timing for my application.

We share religion . Of course I respect all denominations though.