Yes, you should change the purge valve out, but this isn’t a likely reason for the leak. When you stated that the sender has been modified for the return line, you didn’t mention if the return extended down into the tank. The fuel is returning at a high rate at idle and no load operation. The fuel pressure regulator must bypass most of the fuel volume that the pump produces to control the fuel pressure to the correct amount. There should be no restrictions in the return system or the fuel pressure regulator can’t control the fuel pressure. Let’s get back to your return line in the tank. If you just put a fitting into the sender lid, the fuel is coming out of that fitting at a very high rate and can spray all over the tank. The tank is baffled across the top of the tank to prevent fuel from escaping from the vent lines. Without a line extending down from your return line fitting below the level of the fuel in the tank, you’re creating a heavy mist of fuel in the upper part of the tank. This could be causing most of your headache. We’d drop your tank down and check for any cracks in the top of the tank, and double-check all the connections for your vent lines at your tank. We hope that not installing a tube down into the tank below the fuel level is the answer. When installing this line, make it long enough that you have to get below a quarter tank before it becomes exposed to open air.
Now that’s what we call a “bottom of the page” camshaft selection. Your Xtreme Energy camshaft is the largest COMP offers. Your engine combination should easily produce 550 hp. We can see where you must have a vacuum pump to operate your power brakes. We’d recommend reducing the camshaft duration by a good 20 degrees. Going with either a XE268H or a larger XE274H would be a much better choice for a 100 percent street car. The increased torque will completely outweigh the loss in top end horsepower in the performance feel of your Chevelle.
For an engine of this power, 21/2-inch exhaust is the bare minimum. This will be a restriction at high engine speeds, but again, like your smaller camshaft, the power loss will be minimal compared to the noise of 3-inch exhaust. Replace your full exhaust system with a quality 21/2-inch system from Flowmaster. The American Thunder PN 17119 true dual exhaust features Super 40 mufflers for a great deep tone with very low backpressure. The full 21/2-inch mandrel-bent head pipes and tailpipes come complete with all the factory hangers to bolt right into your Chevelle.
Finally, the recommended Pennzoil SAE 25W-50; this is a race-only oil recommended for its antiwear properties for the flat-tappet camshaft in your engine. Yes, it’s tough to come by, but replacing your flattened camshaft because you didn’t use the correct oil is much worse. Other oils on the market have the correct levels of zinc and phosphorus to protect the sliding surfaces in your big-block. COMP Cams offers a specific break-in oil to protect its camshafts from failure. You can pick up these oils from any of your mail-order outlets. The 15W-50 break-in oil is sold under PN 1591. We would use this oil to break in the camshaft for the first 500 miles. Then you can switch to a quality grade of diesel motor oil as they still have some of the zinc and phosphorus that the government required removed from motor oil. We have had great luck with Chevron Delo 400 15W-40 oil in all our flat-tappet–equipped engines. COMP also offers a 12-ounce bottle of break-in additive (PN 159) that we’d use as an oil supplement to the Delo 400. This will give you great protection and is easy to locate.