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

An Overview of Testing The Goodwrench 350

Mike Petralia Jul 1, 2000

Step By Step

Paying tribute to the typical bolt on street fare, the first parts we replaced on the Goodwrench Mule was the intake manifold and exhaust system. The Edelbrock Performer RPM manifold and Holley 750-cfm double-pumper carb shown here gave us the most power in later tests.

Cam swaps are always a great way to make power. The Comp Cams XE268H-10 hydraulic cam we used to replace the puny stock cam didn’t let us down (see test 3-1).

Aluminum heads have become commonplace on high-performance V-8s today. GM offers its L-98 aluminum head, originally fitted to the C4 Corvette’s tuned-port engine, for a paltry sum. The small 58cc chambers in the L-98 heads increased compression to 10.1:1 (see test 3-2).

The last heads the Goodwrench 350 would see were these killer, new TFS aluminum castings. They feature a 64cc chamber. The stock TFS heads out- performed the ported iron Vortec heads by 7 hp. The TFS’s lightweight castings and great flow potential definitely make them worth their $850 price tag.

We went back to iron for Part IV and tried the new Vortec heads. These heads slightly lowered compression compared to the L-98 58cc aluminum heads, thanks to the Vortec’s 64cc chambers. A new Edelbrock intake manifold was also required due to the Vortec’s unique bolt pattern.

Several tests in our series saw Ed Taylor install thin, rubber-coated steel shim gaskets from Fel-Pro to increase the Goodwrench 350’s compression ratio. This usually netted a little extra horsepower and torque.

In addition to the new Comp Cams camshaft, roller-tipped rocker arms with different ratios were tested to find more power. The 1.6:1 ratio rockers netted us the most power overall.

What started out as a bread-and-butter basic buildup and dyno-test of GM’s brand-new service replacement engine, the Scoggin-Dickey–supplied Goodwrench 350 snowballed into a full-blown street thumper spread throughout seven stories in Chevy High Performance. During our trials with this crate motor, we learned a thing or two about how to build a better Mouse for less. We’d also like to take this time to acknowledge Ed Taylor of Ventura Motorsports who did all the work on the engine and Ken Duttweiler for the use of his dyno cell.

Dyno-Flogging The Mouse

To determine if all the bolt-ons we intended to try were worth their pudding, we first flogged the 350 straight out of the box and were pleasantly surprised at how well this underrated rodent performed (see test No. 1-1 in the "Dyno Mule" sidebar). Our Goodwrench 350 cranked out 239 hp at 4,100 rpm and 324 lb-ft of torque at 3,700-rpm stone stock. This power level was acceptable considering we assumed it would only make 190 hp. Then we replaced the stock aluminum Q-jet intake manifold with an Edelbrock Performer and threw out the cast-iron exhaust manifolds in exchange for some healthy 15/8-inch Hooker headers. The Mouse liked this breath of fresh air and rewarded us with 26 more horsepower and 26 lb-ft of additional torque (see test No. 1-3).

Ported Heads And A New Cam

With the normal bolt-on fare tackled in Part I, we tore into the top end to swap camshafts and pocket port the stock iron heads. We also milled the cylinder heads to ensure that the deck surface was true, which reduced the combustion chamber volume by 3cc’s. To further bump the compression ratio up over the pansy 7.8:1 where we calculated this engine to be, we installed a thinner head gasket that raised the compression to 8.4:1. This increase in compression combined with the pocket-ported heads netted a fair increase in power (see test No. 2-2) but not quite enough to justify all the effort. What this engine needed was a bigger cam. A new Comp Cams XE268H-10 camshaft was slipped in next to further improve the 350’s breathing, and on the following dyno-pull the 350 responded with more power (see test No. 3-1). The new cam, intake manifold, and headers along with the pocket-ported heads were so far worth 97 hp and 57 lb-ft of torque over stock. Not bad for a few bolt-ons and some backyard wrenching.

The Aluminum World

Part III began with Taylor bolting on a set of L-98 aluminum Corvette heads from GM Performance Parts with Comp Cams 1.5:1 ratio roller-tip rocker arms. The L-98 heads feature a very small 58cc combustion chamber, which bumped the Goodwrench’s squeeze up to 10.1:1. We felt that the compression increase alone would net a power increase, although it now required 92-octane fuel. As soon as the engine fired up on the dyno, the idle lope made the increase in compression obvious. Power pulls with the L-98 heads and higher compression didn’t net the increase we expected, gaining only 12 peak horsepower and actually losing some midrange torque (see test No. 3-2). But since these figures compare the pocket-ported iron heads to the rock-stock L-98 heads, much can be said for the performance potential of these factory aluminum castings.

Test No. 3-3 replaced the Edelbrock Performer intake and factory Q-jet carb with a Performer RPM intake and 750-cfm Holley double-pumper. The new carb and intake combo pushed the torque to 402 lb-ft and also produced a slight horsepower gain. Then to mine a little more power out of the Corvette heads, we pulled them off and gave them the same pocket-port treatment that the iron heads received. With our relatively long-duration cam and good-breathing intake and exhaust system, pocket porting the L-98 heads didn’t net anything notable in this case (compare test No. 3-3 to 3-4). It was clear by then that the best overall package so far had been the stock L-98 heads with the RPM intake, XE268H cam, and Holley 750 carb.

Back In The Iron World

The L-98 heads proved worthy, but there’s a new iron head in Chevy’s arsenal that we wanted to try out. The new Vortec iron head borrows its port designs from the very successful LT1 aluminum head. A complete set of heads sell for $400 and may be the best deal on the planet for mild small-blocks.

Taylor bolted the Vortec heads on our Mouse, and their 64cc combustion chamber instantly lowered compression to 9.1:1. We felt this might not present much of a challenge to the Corvette heads’ 10.1:1, but we forged ahead regardless. The first pull netted a peak power increase of 16 hp, but low-rpm torque fell off slightly (see test No. 4-2). The torque loss calculated out to only a 4 percent average over the entire rpm band, which would hardly be noticeable in a car, but it couldn’t be ignored for our test. Then for test No. 4-3, Taylor had Todd McKenzie of McKenzie’s Cylinder Heads perform some grinding magic on the Vortec heads. The pocket-ported Vortec heads still suffered in low-end torque compared to the Corvette heads but gained an additional 13 top-end horsepower.

Fine-tuning was next on our list to see if we could push this bad boy over the 400hp mark. Taylor swapped out the thicker composition Fel-Pro head gaskets used in the last tests for an identical set of the thin, rubber-coated Fel-Pro gaskets used to make power in test No. 2-2. This increased compression from 9.1:1 to 9.4:1. This time the added compression did us a favor by bumping torque up 13 lb-ft (see test No. 5-2). The engine was now only 5 hp shy of 400, and we thought more valve lift may be the answer. Taylor bolted on a set of 1.6:1 ratio rocker arms from Comp Cams, and for the first time the Goodwrench 350 saw the other side of the 400hp fence, making 402 hp and 416 lb-ft of torque (see test No. 5-3). Taylor now had a gut feeling that the exhaust was backing up and wanted to try some 1¾-inch Hooker headers and better-flowing Borla XR-1 race mufflers. Those parts netted another 7 hp and 14 lb-ft of torque (see test No. 5-4). We were really smokin’ now.

Back To Aluminum

There’s a new aluminum head for 23-degree small-blocks available from TFS that we were aching to try on this engine. The TFS heads share a 64cc chamber volume with the Vortec heads, so compression didn’t change from its 9.4:1 state. The TFS heads right out of the box were not worth much improvement when compared to the ported Vortec heads, gaining only 7 top-end horsepower and losing some torque (see test No. 6-1). But when you consider the lightweight benefits of aluminum casting and compare the overall costs of both sets of heads ($850 for the TFS heads complete and $650 [$400 stock + $250 for porting] for Vortec’s heads), the TFS heads shine as the better choice.

After effectively testing seven sets of cylinder heads, three camshafts, three sets of rocker arms, three intake manifolds, two carburetors, and two exhaust systems, we learned what worked and what was wasted effort. In reality, almost any small-block would see similar results to these parts and modifications. By far the biggest improvement came from the cylinder heads, intake, exhaust, and cam installations. One thing’s for sure: The Goodwrench 350 crate engine is definitely a deal worth its weight in horsepower.


Hooker Headers
Aberdeen, MS 39730
Comp Cams
Memphis, TN 38118
Chevrolet Performance Parts
Detroit, MI 48232
Holley Performance Products
Bowling Green, KY 42101
Borla Performance Industries
Oxnard, CA 93033
Trick Flow Specialties (TFS)
Tallmadge, OH 44278
Ventura Motorsports
Ventura, CA 93002

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