Back in our January issue, we built our own version of the L89 big-block 427 using all aftermarket components. Our rev-happy Rat combo used a Dart Big M block, Dart 275cc Pro 1 heads, Eagle crank and rods, JE pistons, Weiand dual-plane intake, Holley 750 HP carb, and a Comp valvetrain, including a Big Mutha Thumpr cam. The recipe ended up producing 507 hp at 6,000 rpm and 471 lb-ft at 4,100 rpm.
Being the power junkies that we are, the engine wasn't even cooled down before we asked Jeff Strech (Speed-O-Motive's engine guru) "What can we do to make more?" Without hesitation he said, "Your combo is not using the heads to their full potential. We can swap in a bigger cam and a single-plane intake to wake that sucker right up."
While the Big Mutha Thumpr cam sounded very aggressive at idle, the 0.522/0.507 (intake/exhaust) lift was not using all the air flow capabilities the Pro 1 heads provided, just like Jeff had said. The heads flow (per Dart's flow sheet) 352cfm intake and 258cfm exhaust at 0.700-inches of lift at 28 inches of water.
Not needing any more convincing than that, we sat down with Jeff and picked his brain for a cam and intake selection. Jeff said, "The intake is easy-just pick up Dart's single-plane. For the cam, let's go with a custom grind I've had excellent results with." We let him know this better not be some secret grind because we were going to publish the specs.
He was cool with that so we grabbed the Comp Cams catalog and flipped to the BBC solid roller section. Jeff told us to have a solid roller ground with Hi-Tech 0.420 lobes, lobe number 4017 on the intake and lobe number 4024 on the exhaust, that have 0.715 lift specs, a 108 degree lobe separation, and a 4/7 firing order swap.
We will get into specifics of all this in the photo captions. We also picked up a Cloyes timing chain cover from Summit Racing with an integrated cam button to simplify setting the cam endplay. Plus, the stock stamped cover was too flimsy to keep this cam under control anyway.
We did all the work and dyno testing over at Speed-O-Motive in Covina, California, with Jeff doing most of the grunt work. We also have video of the engine making a pull so be sure to check out www.superchevy.com so you can hear it for yourself.