November 2011 Chevy High Performance Q&A

Kevin McClelland Sep 22, 2011 0 Comment(s)
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The 496 cid of your engine will help with a larger size camshaft. The EZ-EFI is also going to help by constantly learning the correct fuel curve needed by your engine and feeding it properly. The Thumpr camshaft series even surprised COMP Cams with the power they produce. These camshafts were first designed to satisfy the masses out there who wanted an aggressive idle to give their cars and truck personality. What COMP didn’t figure is that these camshafts made really good power on the dyno, to the point that they rivaled the best grinds out there for street use. If you equip your car with the proper converter, gears, and brakes, you can have one badass street car with your engine combination. As always, we’re going to stay conservative with the selection and not go “bottom of the page”. COMP offers three grinds in the hydraulic rollers for the big-block: the Thumpr, the Mutha Thumpr, and finally the Big Mutha Thumpr. Again, if you equip the car with the right parts, we’d recommend going with the Mutha Thumpr grind (PN 291THR7) that specs out at 235/249 degrees duration at 0.050-inch tappet lift, 0.558-/0.542-inch max lift, and ground on a tight 107-separation angle. With the right aluminum cylinder heads and 10:1 compression ratio, you will be pushing the limits of the EZ-EFI’s 600hp headroom! Sounds like fun to us!

Sources: compcams.com, fuelairspark.com

Stripped gears

I rebuilt a 350 small-block a while back for an early Chevy pickup. I put in a COMP flat-tappet hydraulic cam and used an Edelbrock RPM manifold and an MSD distributor. Recently, it stopped running while driving down the road. The problem turned out to be the distributor gear: The teeth wore off. I have talked to both COMP Cams and MSD about this. COMP said that with a flat-tappet cam and a double roller chaindrive, I shouldn’t have that much trouble with cam movement. MSD said it might be an alignment problem. Is there some measurement I can take that would help me solve this issue? Thank you for any help you can give, and I enjoy the magazine.

Dale Heck
Via email

Usually our Chevy engines don’t have issues with distributor gear wear when using standard cast-iron camshafts. We see issues when we run billet steel shafts and have to run special gears. We agree with the tech at COMP Cams. The camshaft lobes are ground with taper into them to force the camshaft to the rear of the block when it’s running. If you didn’t have any issues with the engine except for the gear wear, we doubt it’s an alignment issue. If the camshaft was offset too far forward or rearward to tear up the distributor gear, you’d have had lifters running into adjacent cylinder lobes. When this happens, everything gets really ugly!

Other issues that can accelerate distributor gear wear are using a high-volume/pressure oil pump with heavyweight engine oil. We’ve seen where people use high-volume pumps when not necessary and 20W-50 weight oil and have wear. This usually happens when they run the engine too hard before it has come up to operating temperature and the oil isn’t close to temp.

To check for the proper alignment, climb up into the engine bay and, with the distributor out of the engine, look down the distributor hole in the manifold with a flashlight. The gear of the camshaft should be somewhat in the center of the distributor hole, down in the block. It can be slightly forward or rearward without causing an issue. If you’re running the above high-volume pump with thick oil, try lowering the viscosity of your oil.

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