Performance Tech Questions - Performance Q & A

Kevin McClelland Aug 1, 2009 0 Comment(s)

The 1.6 ratio roller rockers will increase the max lift around 0.030 inch. This would put the exhaust valve max lift on your engine at 0.490 inch. The factory dish pistons with valve reliefs in your engine will accept this with plenty of room to spare. Max lift isn't where the problem lies with increased lift. It's right around top dead center (about 12 degrees either side), when the engine is in overlap. This is between the exhaust stroke and the intake stroke. When you increase the duration or tighten the lobe separation angle, this is when the valves get closer to the pistons. Increasing the duration opens the valves earlier relative to the piston location. Using the stock 330hp camshaft with its 212/222 degrees of duration at 0.050 inch lift is very mild, and you have a ton of piston-to-valve clearance.

We really like the GM Performance Parts 1.6 ratio rockers (PN 12370839 for the kit). The rocker body is the same design that GM used on the one-year LT4 Corvette engine. This is the only production small-block that came with aluminum roller rockers. The body was a proprietary extrusion, and the machining of the slot in the body for the rocker stud was kept to a minimum to reduce flexing. These rockers will only accept a max lift of 0.570 inches before the rocker body will crash into the rocker stud. They are perfect for mild street camshafts. It's important to note that they are a self-aligning design, which works perfectly with the Vortec cylinder heads. Also, they have a special posi-lock that is very short and will clear the stock valve covers. This rocker swap will give your 330hp engine an extra 10 ponies easily.

As for the extra 5 or 10 hp, the 330hp deluxe engine comes with a GM Performance Parts inlet manifold that is great for low- and midrange torque. If you swapped to an Air Gap-style, high-rise dual-plane you'll find your other 10 hp. Both Edelbrock and Weiand have great manifolds to choose from. Either the Edelbrock RPM Air Gap Vortec PN 7516 or the Weiand Stealth Air Strike PN 8502 will give you the extra power you're looking for as an easy bolt-on.

Both these modifications will help the power without killing the great gas mileage you knocked down on the Power Tour. Simple bolt-ons are always a great addition to any crate engine. Have fun with your Camaro.Sources:,

Double Trouble
Q: Over the years you have spoken of the good luck you've had with a 502, and it prompted me to write. I have purchased a 502 H.O. for use in my motorhome. Previously I had a 496 with very good results, until an intake valve broke and trashed the engine.

What kind of oil do you prefer? Petroleum or synthetic? Straight weight or multi? Ask 10 people and get 10 different answers! I want the best for my new engine! The motorhome is 18,000 pounds and I tow a 4,000-pound Jeep. The engine lives at 3,200 rpm at 65 mph, and I only use it in the summer, no cold weather. Also, the engine is being broken in and tuned on a dyno, and my guys says Joe Gibbs break-in oil is the best for break-in. What do you think?

Finally, what causes a valve to break? The stem is still in the head with spring and keeper in the same place? My mechanic says valves sometime break. Never heard of this before! Thanking you in advance.

Oh, and a word from my wife. Prior to rebuilding the stock 454, which lasted 120,000 miles with little trouble, we spent $5,000 for the 496ci. With good components, including valves, rings, sparkplug wires, heads, and manifold, the 496 lasted less than 10,000 miles. Talk about modifications! Can all that hurt reliability?
Kitty and Will Grosse
Ingleside, IL


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