Hands On - Saturday Night Slayer - Car Craft Magazine

Hands On
Despite what the boo-birds on the Internet think, there are hundreds of small-block Chevy stories yet to be told. This is one of 'em. Car Craft staff meetings are great places for "what-if" musings. The question at one such meeting was whether we could make a survivable 500 hp from nothing more than a brand-new Goodwrench GM crate engine, a budget camshaft, and a single-plane intake--topped with a simple nitrous system. Right there on a yellow legal pad was born the Saturday Night Slayer.

For the benefit of the few car crafters who may not know about the Goodwrench GM Crate engine, it's only the most affordable crate-replacement 350ci small-block Chevy ever offered by GM. This GM crate engine comes with four-bolt mains, a two-piece rear main seal cast crank, cast pistons, a very low static compression, iron heads, and a very-short-duration, flat-tappet camshaft. It is the essence of the original small-block Chevy, and the best part is it's ridiculously affordable. We got GM crate engine from Scoggin-Dickey Parts Center in Lubbock, Texas, for $1,500 plus shipping. You could probably rebuild a small-block for that price, but who would give you a three-year, 100,000-mile warranty and all-new parts? GM does if you leave the engine stock. Our plan killed those warranty fantasies as soon as the engine cleared its crate.

Did we mention this GM Goodwrench engine has no compression? While GM Goodwrench claims 8.5:1 (Scoggin says 8:1), we measured 7.9:1. That's the reality, and it allows this motor to run on moose piss for fuel, but it's hardly conducive to excellent performance or mileage. We've had some experience with these engines, and each one we've beat on has survived to live a long, prosperous life. This latest effort plans to tax that longevity reputation to the max with a hefty whiff of nitrous.

The plan is to make 500 hp with minimal cash. That sounds simple enough, but it's a bit more challenging on the execution side. The easiest way to increase the GM Goodwrench compression is with cylinder heads, but that slaps the budget around a bit, so for this first effort we decided to retain the anemic 1.94/1.50-inch valve heads. A camshaft, however, was certainly within our modest means when we found a Summit flat-tappet hydraulic with appealing specs priced at barely more than $50. We didn't even need to buy lifters because we could use those that came with the engine. We're still smarting from the flat lobes used during a recent engine build, so we opted for 5 quarts of Comp's new Break-In 10W-30 that ironically cost almost as much as the camshaft. That's the price of ensuring cam survival these days, as 5 quarts of regular oil and a can of EOS is virtually the same price.

We also included a few other necessary pieces to complete the engine, such as a harmonic balancer, a carburetor, an ignition, and a set of headers. These invisible pieces can drive up the price of a complete engine and are often overlooked. In a second installment, we intend to bolt this motor into our Orange Peel '66 Chevelle to evaluate how quick we can make this entry-level power burner run while also revisiting some basic performance- tuning recommendations that anyone can do. But first, let's get into the game by loading up our Saturday Night Slayer and hitting the button.

Cam Specs
Camshaft Duration at 0.050 Valve Lift lobe-separation angle Stock cam, int. 195 0.390 114 Stock cam, exh. 202 0.410 Summit, int. 224 0.465 Summit exh. 234 0.485 GM Goodwrench Tuning Notes
NOS recently changed its tuning recommendations based on input from a recognized nitrous-tuning expert. Note also that there are different ignition timing specs depending on combustion efficiency. We took this to mean the combination of compression and quench. We used the low-efficiency number because of our engine's weak compression. We've listed only the two tune-ups we tried and changed the NGK spark plug recommendation to Autolite heat ranges for the plugs we used. Your actual plug part numbers will depend on the GM Goodwrench engine application.

Nitrous HP Combustion Efficiency Ignition Timing Spark Plug Fuel/Octane 150 Low 29 AR133 100+ 150 Medium 27 AR133 100+ 150 High 25 AR133 100+ 200 Low 24 AR132 110+ 200 Medium 22 AR132 110+ 200 High 20 AR132 110+

To make the most of our test day, we skipped the entry-level baseline but found an earlier test of this engine using the stock cam, Q-jet intake, a 750-cfm Q-jet carburetor, and a set of 1-5/8-inch headers that produced 348 lb-ft of torque and a wheezy 254 hp. After we added the new cam and intake, we were ready for our normally aspirated baseline. We expected the bottom end of the curve to be weak, as we were adding 29 degrees of intake duration and a single-plane intake manifold. Despite those changes, the Goodwrencher delivered nearly 50 lb-ft over the original package at 2,500 rpm and twisted 355 lb-ft of torque at 4,100 with 332 for horsepower at 5,500. We chose a single-plane because it promised to work well with nitrous, but a good dual-plane such as a Holley or an Edelbrock Performer RPM would pump the torque as much as 20 lb-ft with no significant loss of peak horsepower. This would be the best choice if nitrous were not part of the equation.

We were pleasantly surprised with the torque and horsepower numbers from the normally aspirated combination, but our goal was 500 hp, so it was time for the squeeze. Nitrous Oxide Systems has recently changed its tuning recommendations for all its nitrous kits by leaning the overall air/fuel ratio. For example, older NOS Cheater kits recommended an 0.063 nitrous jet with an 0.071 fuel jet for its 150hp combination. But the new kit uses 0.063 jets for both fuel and nitrous while maintaining the same 5- to 6-psi fuel pressure recommendation. NOS also offered new insight into how much timing should be retarded. The new tune offers timing retard recommendations based on three levels of combustion efficiency (low, medium, and high), with the highest timing allowed for low-efficiency combos. Since our Goodwrench engine barely pushed 8:1, the recommendation for a 150hp shot was to pull the timing back to 27 degrees.

On our first pull, the 150hp tune netted exactly that with a 482hp peak. This left us only 18 shy of our 500hp goal, and after a discussion with Westech's Steve BrulÚ we felt brave enough to hit it with a full 200 shot. This required a simple swap to 0.082 fuel and nitrous jets with the timing yanked back to 24 degrees. All that paid off with a very successful 520hp number. You'll note that we didn't hit the nitrous until over 5,000 rpm, as we were only interested in a peak horsepower number. The advantage with nitrous flowing through a fixed orifice is that the same amount of nitrous at a lower rpm generates a tremendous increase in torque. That doesn't show up in this test, but if you look at the torque increase at 5,200 rpm, you'll see there's an additional 200 lb-ft that generate the additional horsepower. That same torque gain at 3,500 rpm would kick it up to almost 550 lb-ft. We felt those cast ring lands might fail with this much torque at a lower engine speed, so we elected to delay the nitrous until 5,000 rpm. Pulsed controllers or staged nitrous systems offer the same kind of protection.

Brule also noted how badly the engine fell off after peak horsepower with the 200 shot. This indicates the engine is maxed out in terms of what we could expect if we tried to feed this engine even more nitrous. Effectively, we have arrived at the point at which the stock exhaust ports are not capable of pushing more spent gas out, especially at high engine speed when there is less time for that to occur. This leaves a greater percentage of the exhaust gas in the chamber during the intake session, thereby reducing power. Effectively, the nitrous horsepower limit for most street engines is roughly 75 to 100 percent of normally aspirated horsepower.

We've got some further plans for our Saturday Night Slayer, including a set of forged pistons to give us some detonation durability and a better set of iron Vortec heads. This engine has far more potential with a set of better heads and the iron GM Vortec heads are both affordable and offer dramatically better flow potential. The smaller 64cc chamber will also jack the compression a little and with a good dual plane, we could be very close to 400 hp normally aspirated.

By The Numbers
Test 1:
This is the Goodwrench engine baseline using a factory Q-jet manifold and Q-jet 750-cfm carburetor with 1-5/8-inch Hedman headers and a pair of 2-1/2-inch Flowmaster mufflers. Test 2:
The change for this test was the Summit camshaft, a new Weiand single-plane intake, and a previously owned 750-cfm Holley mechanical-secondary carburetor. Total timing was 37 degrees with 72 primary and 76 secondary jetting in the carburetor. Test 3:
Now we get serious, bolting on the NOS Cheater system with 200hp jetting and 24 degrees of total ignition timing. The retarded timing explains why the power is down below 5,100 rpm where the nitrous was introduced. RPM Test 1 Test 2 Test 3 TQ HP TQ HP TQ HP 2,500 265 126 318 151 310 147 2,700 269 138 317 163 311 160 2,900 310 171 317 175 313 173 3,100 299 176 330 195 316 186 3,300 294 185 334 210 320 201 3,500 307 204 341 227 324 216 3,700 348 245 348 245 331 233 3,900 336 249 353 262 333 248 4,100 325 254 355 277 334 261 4,300 310 254 354 290 335 274 4,500 296 253 350 300 332 285 4,700 276 247 345 309 330 296 4,900 259 241 341 318 338 315 5,100 239 232 335 325 379 368 5,300 218 221 326 329 520 525 5,500 -- -- 317 332 482 505 5,700 -- -- 305 331 450 488 5,900 -- -- -- -- 420 472 Peak 348 254 355 332 520 525 Avg. 290 213.1 337.6 281.5 N/A N/A

Parts list
Description PN Source Price Goodwrench long-block, pre-'86 10067353 Scoggin-Dickey $1,499.99 NOS Cheater nitrous system 02001NOS Summit Racing 539.95 10-pound bottle fill N/A Orme Brothers 50.00 Summit budget cam SUM-1105 Summit Racing 54.95 Weiand X-celerator manifold 7547 Summit Racing 159.95 Holley 750 mech. sec. carburetor 0-4779 Swap Meet 150.00 Hedman 1-5/8-inch header, painted 68299 Summit Racing 169.95 Summit header gasket, copper 111406 Summit Racing 22.95 Summit intake gasket G2410 Summit Racing 12.95 Summit carb gasket G1418 Summit Racing 1.95 Fel-Pro head gasket 1094 Summit Racing 34.99 GMPP water neck 10108470 Summit Racing 6.95 Mr. Gasket thermostat, 180 4364 Summit Racing 13.95 HEI distributor used Boneyard 15.00 MSD HEI cap, rotor 8416 Summit Racing 26.95 Summit spark plug wire set 868836 Summit Racing 29.95 Autolite spark plugs AR132 Summit Racing 28.00 Wix oil filter 495-51060 Summit Racing 4.95 Comp Break-In oil, 10W-30, 5 qts 1590 Summit Racing 29.75 Harmonic balancer 594-012 Summit Racing 31.95 Summit balancer bolt G1677 Summit Racing 5.95 Gates water pump 43101 Boneyard 24.79 Total Rock Auto $2,915.82