The TestFor testing, we bolted a complete GM Performance Parts 350 H.O. Deluxe engine up on Ken Duttweiler's dyno and let dyno whiz Ed Taylor run it through its paces. For a baseline, we decided to see how well this engine would do with cast-iron manifolds and a dual exhaust with generic 211/44-inch turbo mufflers. This is actually not the way GM baselined this engine (the company used 131/44-inch headers and the deluxe 600-cfm Holley carb for the 330hp rating). After some initial experimentation with ignition timing, we ended up with 37 degrees of total lead, and on 91-octane pump gas, the 350 pumped out 354 lb-ft of torque at 3,800 and an impressive 320 hp at 5,600 rpm. This is an 1,800-rpm powerband between peak torque and peak horsepower, and anytime you can crank out over 300 hp with iron exhaust manifolds, you're doing well.
The obvious next step was to toss on a set of headers, so Taylor bolted on Hedman 151/48-inch long-tube headers with no other changes. This delivered an amazing increase in both torque and horsepower, pumping the peak torque up to 383 lb-ft-a stout 29 lb-ft of torque increase at 4,000 rpm. The horsepower also jumped to 341 at 5,400, an increase of 21 hp over our stock exhaust baseline. But perhaps most importantly, the average torque increase with just the headers alone was a thumpin' 23 lb-ft of torque and 17 hp. If you do nothing else, headers are the best bang-for-the-buck-bolt-on for the 350 H.O.
We also decided to try a couple more things for this first episode of our street 350 H.O. Since the addition of the headers performed so well, we upgraded the exhaust system to a pair of Borla Pro X/S stainless steel mufflers and a true, mandrel-bent 211/42-inch exhaust system. Then, just for grins, we also bolted on a slightly larger Pro Vac 650-cfm vacuum-secondary carburetor from Quick Fuel Technology. The combination of the two elements created a slightly better power curve and added an average of 4 lb-ft and 4 hp across the board. This is not a huge increase, but it did push the 350 H.O. up to almost 390 lb-ft of torque at just under 350 hp.
ConclusionWith very simple bolt-ons, the 350 H.O. engine made some very impressive gains on the first dyno flog. When you consider this is a brand-new engine with 348 hp and a GM warranty, this is quite a bargain. Just to make this more enticing, we plugged the power numbers into the ProSim dragstrip simulator to estimate how well this engine would perform in a typical 3,500-pound street car with 3.54 gears, a TH350 trans, a 2,600-stall converter, and sticky tires. The program spit out an estimate of 12.98 at 104 mph. That's perhaps a bit quicker than we would expect, but low 13s at 102 mph is certainly achievable. Clearly, with a few more changes, it's possible to make more torque and horsepower without sacrificing this engine's very mild street manners. That's what we'll get to next month. As they say on TV, stay tuned.
Spec SheetEngine: 350ci small-block ChevyBore x stroke: 4.00x3.48HP & Torque: 330 hp @ 5,000, 380 lb-ft @ 3,800Compression: 9.1:1Block: Cast-iron four-bolt main, one-piece rear seal, PN 10105123Crank: Nodular cast iron, PN 14088527Connecting rods: Powdered metal forged steel, PN 10108688Pistons: Cast aluminum, dished, 51/464-inch rings, PN 12361371Camshaft: 212/222 degrees @ 0.050, 0.435/0.460-inch lift, PN 24502476Heads: Vortec iron, 1.94/1.50-inch valves, PN 12558060Rocker arms: Stamped steel, 1.5 rail type, PN 10089648Valve covers: Centerbolt, chrome, PN 12355350Intake: Dual-plane aluminum, PN 12366573*Carburetor: Holley 600 cfm, vacuum secondary, PN 12497147*Distributor: GM HEI, PN 1104067*Water Pump: Cast iron, PN 12529305*As part of the 350 H.O. Deluxe package