A When GM combined a pile of off-the-shelf parts to create the 290hp crate engine, it picked the L46/L82 small-block hydraulic camshaft, developed back in '69. The L46 was released for Corvette use at 350 gross horsepower. This engine was equipped with very good (for the time) 186 casting heads and 11:1 compression. Then GM used the camshaft in the Corvette again in the L82 smog-era 350s. They also had decent cylinder heads and a true 9:1 compression. The L82 was rated at a whopping 250 net horses before the catalytic converter years. Now, let's talk about the 290hp crate engine on the market today.
The base long-block is derived from the solid foundation of the GM Goodwrench replacement 350 engine. In its stock form (with stock inlet and exhaust manifolds), the engine produces 230 hp and 330 lb-ft of torque. The engine is a replacement for the GM LM1 small-block and is rated at 8.5:1 compression; however, every one I've disassembled and cc'd came in around 8:1 compression. The 290hp GM Performance Parts crate engine starts with this base Goodwrench engine with the L46/L82 camshaft. As I said above, this camshaft was designed back in the '60s to run with much more compression. The camshaft specs out at 222/222 degrees duration at 0.050-inch tappet lift, 0.450-/0.460-inch max lift, ground on 114 centers. Why your engine likes so much timing is because it has very low cylinder pressure at low engine speeds. These engines are great for stick shift, lightweight vehicles and for light street rods that want a cool cruiser engine.
If you swapped in a Crane Powermax 260 or a Comp Cams Xtreme Energy EX256, you would have a much happier engine. This engine, with either of those camshafts, will still make 290 hp with a street-performance inlet manifold and a set of 15/8-inch headers. This is the gain of current technology in camshaft lobes. Is there something wrong with your engine to make GM warranty the engines? Absolutely not. It's just a case of misapplication. Good luck.
Sources: compcams.com. cranecams.com
Water Shaft
Q I am going to put a '90 Corvette L98 engine in my '87 Chevy pickup. I read in your Jan. '07 column about a marine roller camshaft. Being a marine technician, I have a couple of these cams. Will this cam work well with a TPI engine? Also, would a Fel-Pro head gasket (PN 1003) at 0.041 inch compressed thickness work well on this engine? Thanks.
Charlie AndersonVia e-mail
A The Mercury Marine hydraulic roller is a very mild performance camshaft. This cam will produce tons of midrange torque and run out of air at about 5,000 rpm. GM uses this camshaft in its Ram Jet 350 and HT383 crate engines. The torque curves of these engines are just about flat from 2,200 to 4,700 rpm. This is right where the Tuned Port Injection (TPI) inlet track is tuned to run on the 350. If you wish to step up the runners or inlet base, it will only boost the upper-rpm power potential. This, in conjunction with 1.6 roller rockers, will give you a very nice, mild 350. The camshaft you're looking for is sold under PN 14097395. It specs out at 196/206 duration at 0.050-inch tappet lift, 0.431-/0.451-inch max lift, and is ground on a tight 109-degree LSA. The tight centers work out because of the small duration lobes and low overlap area. Cross-reference the camshaft to make sure you have the small Mercury Marine camshaft. GM builds several power levels of the marine engines for Mercury. The camshaft listed above is the mildest engine package offered.