We're sure you've read the benefits of the block on the Dart website. By now you have seen our story on the block in the May issue ("Minimal Assembly Required"). A few benefits really make the block superior to a production casting. First, running nitrous on a standard 350 four-bolt block is asking for the crank to move around. The Dart SHP starts by increasing the main web strength and installs deep-registered ductile iron main caps, which together keep the crank where it's supposed to be and out of the bearings. To keep the crankshaft happy, the oiling system was revised with priority oiling to the mains. This involved removing several 90-degree turns in the main galleys, increasing oil pressure and reducing oil temperature. Next, the Siamese cylinder walls have a minimum thickness of 0.230 inch at a maximum overbore of 4.165 inch. This will keep the rings sealed against the high cylinder pressures of nitrous loads. Also, reliefs were added at the bottom of the cylinder bores for hone over travel. This is very important in keeping the cylinder walls round in the honing process. The deck of the block is increased to a thickness of 0.625 inch with blind-head bolt holes. No more water running up your cylinder head studs! Finally, the water jacket are scalloped around the large bores to increase coolant flow and capacity.
Like we said, after dealing with block fillers and machine shops, we think the Dart SHP block is money well spent. If you keep the internal components where they are supposed to be, it will be the last block you need to buy for your Nova. Give Dart a call and order PN 31161211 for the large 4.125 inch semifinished bores ready to finish-hone. The rest of the machining is ready for assembly. Dart has really helped out the mid-performance racing engines with these blocks.Source: dartheads.com
Load 'Er Up
Q: I have a couple questions about a nagging problem I'm having with my daily driver project, rough cruise range operation, and fouled plugs on any long road trip. I have a GM H.O. 350 crate engine I put in an '84 C10 and have completely rebuilt/replaced just about everything in it. The engine has 330hp iron Vortec heads with the dual-lift cam, and I have replaced everything that came with the turnkey package. I have an Edelbrock 600-cfm competition carburetor and a Mallory HEI distributor with a high-output cap coil, and I run NGKs out of the box at a 0.060-inch gap. I've run on the dyno at least three times, and the best I came up with is 300 rwhp. What is the advantage of a dual-lift cam? Why isn't it used anymore? And did GM screw up when mating it to the Vortec heads? Oh, yes, the exhaust is a dual 21/2-inch with Spin Tech mufflers and high-flow cats. The thing flies at WOT and has a slight cam idle and plenty of acceleration out of the hole (2,200 stall), but I was hoping for a long-range cruiser. Should I just give up and repower it? It has a TH350 and a 10-bolt.
A: First of all, don't throw out the baby with the bathwater! You have a very strong-running package, since you've seen 300 hp at the rear tires. The GM Performance Parts H.O. 350 Vortec engine is rated at 330 hp at the crank. With standard losses through the drivetrain (18 percent) you should expect around 270 hp at the rear tires with your package. Let's go over your questions.
Dual-pattern camshafts have been around for many years and are still in use today from the aftermarket to OEM stock camshafts. The main reason for increasing the duration on the exhaust side of a camshaft profile is to make up for the imbalance in flow between the inlet and exhaust ports of a given cylinder head. When you have a cylinder head with strong exhaust port flow potential, you can back off on the amount of duration differential. GM is right on target with the camshaft selection in the 330hp crate engine. It has very decent idle quality and gives you strong top-end performance for the component package of the engine.