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

In the continuing saga of the Scoggin-Dickey–supplied Goodwrench 350 that we’ve been beating on for five installments, the story is really starting to get interesting. Since we’ve already delivered the headline news, here are the details: 408 hp at 5,800 and a stunning 430 lb-ft of torque at 3,700 rpm with only minor changes to the engine! How did we do it? Just follow the bouncing ball.

Last time, we bolted on a set of GM Performance Parts’ iron Vortec heads that flow air like a wind tunnel. We achieved 384 hp by simply pocket-porting the heads and bolting them to our existing combination. As a quick overview, the engine is a stock bottom-end GM Goodwrench 350 supplied by Scoggin-Dickey with a Comp Cams 268 Xtreme Energy camshaft (224/230 degrees at 0.050-inch tappet lift and 0.477-/0.480-inch valve lift with 110-degree lobe separation angle), roller-tipped rockers, and the Vortec heads. The rest of the engine is outfitted with an Edelbrock Performer RPM intake, a Holley 750 double-pumper carburetor, Hooker 1-5/8-inch headers, and a pair of Hooker 2-¼-inch turbo mufflers. That’s it, except for the stock HEI distributor, MSD wires, and 92-octane pump gas.

Testing...Testing

After last installment's exercise, we really wanted to make 400 hp. While we could have added a bigger cam, a single-plane intake, or even nitrous, we wanted to see if we could hit four big ones without major changes. In all previous stories, we merely bolted parts on the engine and ran the tests. In virtually every case, we could have taken the time to fine-tune each change by running through the ignition timing and jetting exercise. We didn’t do that because we decided to perform these tests by just bolting the parts on. But now that we were so close, we felt that a few tune-ups might push us over the top.

Ed Taylor has ram-rodded this buildup from the beginning, including doing the parts-swapping and the dyno-testing. His first tune-up idea was the best. In the previous test, we had used a set of Fel-Pro composition head gaskets that put the engine at 9.1:1 compression (we got that wrong last month—math was never our strong suit). We knew we could get away with a little more compression, so Ed swapped the composition gaskets for thinner rubber-coated Fel-Pro gaskets. This bumped the compression to 9.4:1, which is a safe compression ratio for iron heads and 92-octane fuel. A point in our favor to defuse the detonation problem was the engine only wanted 34 degrees of total timing for the best power.

The first pull on the dyno with the added compression was encouraging when torque improved throughout the entire power curve, generating 6 to 13 lb-ft of additional torque between 3,500 and 5,100 rpm. Everything else remained the same from the previous installment's test—timing and jetting were also the same with 34 degrees of total timing and stock jetting in the 750 Holley.

The next couple of tests weren’t as successful, but they’re worth reporting if for no other reason than to save you the effort. We thought a 1-inch open spacer under the carburetor would help top-end power—it didn’t. We expected to lose a little torque below the 3,800-rpm peak but nothing like what happened. The motor fell flat on its face, losing not only a massive 57 lb-ft of torque at 4,100 but also an average of 28 lb-ft of torque across the entire powerband! We didn’t try adding fuel to improve the situation, even though fuel flow dropped. Basically, the response was so bad we felt that we were flogging a dead horse.

After retesting without the spacer to ensure nothing had broken on the engine, we next tried adding timing to the engine. This also resulted in a loss of power with no substantial gains even at the lower engine speed, where we thought this might help. This leads us to believe that the excellent Vortec combustion chamber design is responsible for the reduced timing.

After only limited success with compression and still 6 hp shy of our 400hp goal, it was time to try something else. Since the Vortec heads flow well in excess of 0.500-inch lift, we thought that more valve lift might help power. We bolted on a set of Comp Cams’ Magnum rail 1.6:1 roller-tipped rockers in search of more lift and were rewarded with more torque and horsepower. In fact, for the first time, the Goodwrench 350 exceeded the 400hp watermark with 402 hp at 5,800. More surprising was the torque increase, with a stunning peak torque of 416 lb-ft at 3,600 rpm and increases of well over 10 lb-ft at various points. Now we were really cookin’.

We could have stopped here, but we wanted more. Ed next wanted to try a set of 1-¾-inch headers to pump up the top-end power, along with a pair of Borla XR-1 stainless steel straight-through-style mufflers. The exhaust combo was worth 6 hp and as much as 13 lb-ft of torque, creating a peak horsepower of 408 at 5,800 and an amazing 430 lb-ft of torque at 3,700. This is outstanding power, especially when you consider that we’re working with a basic short-block with probably the worst cast piston design known to small-block Chevys.

When we started this engine test sequence, we harbored aspirations of making 350 to perhaps 375 hp and maybe the same amount of torque. We really didn’t think this engine could make over 400 hp and 430 lb-ft of torque. That’s truly awesome power from an engine that is docile enough to drive on a daily basis. While we used the Goodwrench engine as the test bed for this experiment, there are several different ways to get to this same place. The easiest step is to buy a set of Vortec heads, a Comp Cams cam, Edelbrock intake, and a set of headers and bolt them on your existing 350 short-block. Depending upon how serious you are about duplicating our combination, it’s certainly possible to equal 400 hp.

You could also use a rebuilt short-block with typical four-valve relief pistons (cast or forged) and use the same bolt-on parts we used while investing less time in building the whole engine. We’ve also bench-raced about substituting the next-step-smaller Comp Cams Xtreme Energy 262 cam to replace the 268. Comp’s own testing shows that with stock heads, the 262 cam will make the same power and slightly more torque. This would be a more docile street combination even with the Vortec heads, and it could make even more torque at the cost of perhaps 5 to 10 hp at the peak. This would be the combination we would go for if this was a daily-driven engine.

Conclusion

This Scoggin-Dickey Goodwrench 350 has flat amazed us. With only a few exceptions, virtually everything we’ve bolted on has improved power, and it’s been dead-on reliable. To put this entire project in perspective, we went back to the Part 1 story to see how far we’ve come.

Way back then, the out-of-the-box Goodwrench 350 with iron exhaust manifolds, a stock Chevy Q-jet aluminum intake, and a Q-jet carb made 239 hp and a respectable 324 lb-ft of torque at 3,700. Adding the Hooker 1-5/8-inch headers and an Edelbrock Performer but still using the Q-jet, the engine perked up to 265 hp and 350 lb-ft of torque. From the original baseline, we managed to crank this pedestrian Mouse motor with 169 hp while adding 106 lb-ft of torque. That’s not bad for a few bolt-on parts. This is especially exciting when you consider that anyone could duplicate our efforts with the Goodwrench 350 for an affordable price.

So have we completed our Goodwrench Quest? Not exactly. This motor has been so successful that now we want to see what it would do with a supercharger bolted on top. Weiand has a very affordable bolt-on supercharger that would look great sitting on top of our Goodwrench motor. This means we’ll have to go back to the stock iron heads, since the Weiand blower won’t bolt up to the Vortec intake pattern. Stay tuned to see what this rascal does with a blower.