Chevy Performance Q & A - Performance Q & A

Kevin McClelland Dec 1, 2009 0 Comment(s)

My primary problem has been camshaft selection. I plan to use a mechanical roller, but nobody seems to have much experience with motors of this size on the street, and the recommendations from camshaft companies range from under 250 to over 300 degrees duration (all at 0.050 inch). My own intuition leans toward net lift over 0.700 inch and a 108 or 110 intake centerline, but I must admit I'm stumped when it comes to duration. I'm leaning toward the 250 end of the scale (e.g., Comp Cams 286RX-8; 253/260 @ 0.050; 0.727/0.729; 108; 3,200-6,200 rpm), but I'd hate to restrict breathing in a monster that can rev like this-not to mention that one cam-company expert recommends over 310 duration!

I'd sure love to hear your take on any aspect of this build. Thank you.
Larry Browning
Wimberley, TX

A: With the current economic meltdown, and taxpayers' dollars going to everyone from Wall Street to automakers, this is the best use of taxpayer dollars we've heard of! Building a killer Tri-Five with a nasty big-block just as a toy gets our vote. Thanks for re-enlisting and keeping our country safe and free. Let's talk about your camshaft selection.

Since 1996 we've probably built eight different pump-gas big-blocks and have helped many other people with combinations including drag-only, mud bog truck, street, and marine use. All the engines have been very reliable and make great power for their compression and skunk-piss gas! One thing we were told early on by Tim Wusz of Rockett Brand Racing fuel (a fuel engineer at 76 at the time) is that pump gas doesn't like to run much above 7,000 rpm. We've focused on the torque-making potential of these engines and had a blast doing it.

If it was ours, we'd work around a camshaft that spec'd out at 270-275 duration at 0.050 inch tappet lift on the inlet side, and 280-285 on the exhaust side. Also, you don't want the separation angle so tight. We'd bring it in around 112 degrees, with 110 at an absolute minimum, and no wider than 114. Install the inlet centerline at 108-109 degrees. Your cylinder heads flow extremely well to 0.800 inch lift. Pushing the lift with regularity will kill the valvesprings. Low 0.700s will work well.

Finally, to the real problem. The roller tappets will be the issue with this engine's durability. Many years ago our old friend Cole Quinnell had a very nasty '57 Chevy that was built while he was a staff writer at Hot Rod magazine. It had a very similar big-block to yours, and we installed a Crane Street roller camshaft that spec'd out in the low 260s at 0.050 and mid-0.650 inch lift range. He drove it on the Hot Rod Power Tour, we think around 1997. It ran great, killer power, and about 1,800 miles in it lost a roller tappet right before the last stop on the tour. He adjusted the valves every night of the tour, making sure he wasn't losing a roller. Well, he ended up wiping out the roller, which put the tappet body right into the lobe of the camshaft

There has been quite a bit of roller tappet innovation, with Isky's new Red Zone lifters with their EZ-Roll solid-bearing, needle-free tappets. These replace the needle bearings with a solid bearing in the roller wheel that rides directly on the axle of the tappet. These proprietary solid-bearing raceways are pressure-fed by three separate passages in the tappet body from the oil gallery. The secret in using this solid-bearing design is to keep it well lubricated to remove the heat. You won't want to install any type of oil restrictors to the lifter galleries, which would reduce the oil to the tappets. They were tested in drag-race engines for over three years before being released for sale to the racing public. We may have an answer for racing engines and endurance engines. With conservative lobe designs and manageable valvespring pressures, we believe they will live on the street. Check with Isky for the proper application; three endurance grades are available to suit your exact requirements.

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