GM 350 Crate Engine Build VI - The Goodwrench Quest, Part VI

The Goodwrench 350 small-block has proven to be so much fun and so responsive to improvements that we keep coming up with more ideas to test. If you are new to our now six-part series, these are the Cliffs Notes. We started with a brand-new Goodwrench 350 long-block from Scoggin-Dickey Chevrolet in Lubbock, Texas, and through dozens of variations on the cylinder head, camshaft, and intake and exhaust routine, we’ve managed to create a very stout, budget small-block.

In its last iteration, we created a thumpin’ small-block that made 408 hp and 430 lb-ft of torque, based on some carefully selected off-the-shelf parts. The key components were the iron Vortec heads, matched to a Comp Cams 268 Xtreme Energy camshaft, an Edelbrock Performer RPM intake, and a 750cfm Holley, list-number 4779, double-pumper carburetor. For ignition we used an HEI distributor and finished up with 1-5/8-inch Hooker headers and Borla 2-½-inch mufflers. Frankly, we were so surprised at how well the engine performed that we decided to keep going.

After a quick planning session with Chief Test Engineer Ed Taylor of Ventura Motorsports, we came up with yet another test of budget-based power. Initially we decided to run a Weiand miniblower across the engine, but since the Weiand blower manifold didn’t fit the Vortec bolt pattern, we would be hindering the blower’s potential to bolt it to the stock Goodwrench heads. Instead, since our Goodwrench engine has always been targeted as a cost-conscious performer, we decided to test the new TFS aluminum 23-degree cylinder heads. Based on our cylinder-head update story in the Dec. ’99 issue (“Flow To Go: Part III”), the numbers looked promising for a cylinder head that Summit sells for $800 a set completely assembled and ready to use. Since the rest of the combination had performed so well in previous testing, we decided to concentrate on testing the cylinder heads alone.

Head Games

The TFS 23-degree head is the latest of a new generation of cylinder heads that has surfaced out of Trick Flow Specialties (TFS). Chuck Jenckes is the engineering manager and head honcho at TFS, and the goal for this head was to create a simple, bolt-on cylinder head that offers great airflow at an affordable price.

Cylinder heads are the key to performance on any engine, and our Goodwrench 350 is a great testament to that fact. If you have kept track of the Goodwrench Quest series, we started out with stock heads, then pocket ported them, then stepped up to a set of over-the-counter Corvette TPI aluminum heads available through GM Performance Parts. After thoroughly flogging these castings, we then stepped up to a set of iron Vortec heads, also available through GM Performance Parts. In each case, power improved mainly based on increased cylinder-head airflow.

The TFS head features a midsized 195cc intake port, which is slightly larger than stock ports that generally measure around 165 to 170cc. But size is not everything. The key is how well both the intake and exhaust ports flow since the combination of the two establishes the head’s ultimate performance potential. The TFS head comes with a 65cc combustion chamber size and 2.02/1.60-inch intake and exhaust valves, and comparing the intake to exhaust flow at 0.400-inch valve lift reveals an acceptable 73 percent flow relationship. This means the TFS heads would probably benefit from Comp Cams’ Xtreme Energy 268 dual-pattern camshaft that offers increased duration and lift on the exhaust side.

If you compare these heads and their flow numbers, it’s clear these are not the best-flowing heads on the market for their size, but they do flow better than many cylinder heads with larger intake-port volumes. What this means is that combining excellent flow with a midsized port velocity yields plenty of potential for great power at an affordable price. It would be up to our Goodwrench 350 to see how well these heads would perform.

Before we could put this rascal back on the dyno, we again went through the compression-ratio drill to ensure that static compression would not be excessive with the 64cc combustion chamber. Normally, a small chamber like this with a flat-top piston would pump the compression way up over 10:1. But the Goodwrench engine is blessed (or cursed, if you prefer) with a cast piston well below the deck surface with a weird chamfer around the circumference of the piston. All this contributes to lowering the compression. The bottom line is the 64cc chamber works well with the Goodwrench engine’s piston and combined with a thin 0.015-inch thick, rubber-coated Fel-Pro head gasket, this generates 9.0:1 compression. The best way to improve this situation would be to pull the engine apart, deck the block, and use a true flat-top piston. This would create between 10 and 10.25:1 compression. This would still work with 92-octane pump gas without detonating, and we would see a power increase. While we could easily accomplish this task, it would pull us away from the basic premise of evaluating different heads on this off-the-shelf engine. So we decided to stick with the stock short-block, ugly cast pistons and all.

Power Per Dollar

Once Ed had reassembled the engine, he again bolted it to Ken Duttweiler’s Stuska dyno and began pulling levers. The rest of the engine remained just as it had been outfitted in the previous tests, including the 1-5/8-inch Hooker heads, Borla mufflers, Edelbrock Performer RPM intake, Holley 750cfm carburetor, Comp Cams 268 Xtreme Energy camshaft, and 1.6:1 Magnum rockers. Ed set the ignition at 37 degrees of total timing and after warming up the engine, he made the first of several dyno sweeps. Despite the low compression, the engine still made outstanding torque, pulling over 400 lb-ft from 3,200 all the way up to 5,000 rpm. Peak torque occurred at 4,000 rpm where it cranked out an impressive 423 lb-ft. Moving down the chart, peak horsepower occurred at 5,700 rpm where the aluminum heads flowed enough air to crank out 416 hp.

Ed experimented with rocker ratios, timing, and jetting, but the power numbers just moved around but never improved enough to warrant the effort. The logical step is to compare the 416 hp from these aluminum TFS heads to the iron Vortec heads that made 408 hp. The iron Vortec heads are certainly less expensive at only $400 for the pair versus the Summit heads at $800 per pair. But the Vortec heads also benefited from pocket porting. In the “Part IV” story (Dec. ’99), we tested the Vortec heads before and after porting and saw a 13hp gain with no substantial increase in torque.

If you were to take a set of the iron Vortec heads to a cylinder-head specialist such as McKenzie’s Cylinder Heads (which did the Vortec heads), minor pocket-porting work would cost roughly $250. Add this to the $400 initial cost, and now the TFS heads start to look more attractive, since for only slightly more money you can have the lighter aluminum heads that obviously show greater potential right out of the box. We really can’t compare the unported Vortec heads to the stock TFS heads because we changed the exhaust and a couple other minor items that make this an inaccurate comparison.

Regardless of which head you choose, it’s clear that just duplicating this combination guarantees you a solid 400hp 350 that will crank out well over 400 lb-ft of torque. We plugged this TFS head power curve into a theoretical 3,500-pound Chevelle with a TH350 trans, a 2,600-stall converter, 3.55 gear, and a 9-inch–wide sticky tire 26-inches tall (like a BFG Drag Radial). Using the Racing Systems Analysis Quarter Pro program, the simulation estimates the car would run 12.20s at around 112 mph. This is plenty quick for a street car, and yet is very conservative since the engine’s running through the lights at only 5,250 rpm. This is important since cast pistons don’t live very long at high rpm.

The bottom line is we’ve come up with yet another affordable power combination with the Goodwrench 350 engine. Frankly, we’re amazed this cast piston motor is still alive. We’ve beat on it for well over 100 dyno pulls, but we’re not done yet. There’s a Weiand miniblower sitting on the shelf that we’ll test next month. We plan to leave the TFS aluminum heads on the engine, but we will change to a smaller cam that may work better with the supercharger. We’ll give you a hint: This baby rocks! But you’ll have to wait ’til the next installment for all the lurid details. Hey, this is better than a soap opera.