A Stroke of Genius PART III

Engine dynos make very good polygraphs. So many times, the latest engine-building vato will brag to his friends or foes about the mighty power beneath his hood without any true dyno figures to back him up. So who's going to dispute his claims?

This month we dyno test the "stroker from a different point of view" built by Sod Bogosian at Hye Tech Performance (in La Puente, California) and find out if it can muster the power to run with the big dogs. (For the engine build up see Part I and Part II in May '04 and June '04 LRM.)

Sod's customer wanted a unique small-block with a great torque curve, and he wasn't at all concerned with peak power numbers. He planned to drive this beast all over the place and liked the idea of having torque to spare at any rpm. So Bogosian designed and built a 391-c.i.d. Mouse that, in the end, made more than 400 lb-ft of torque from 3,000 to 5,900 rpm and lost only 4 lb-ft at 6,000. This little pack mule eventually had no trouble cranking out more than 450 lb-ft of torque at a relatively low 4,200 rpm. That's enough to make any lowrider's tires squeal with delight.

STROKED TO PERFECTION: A RECAP
For just a few extra machine-shop dollars Bogosian offset-ground a 3.75-inch stroke 4340 C.A.T. Power Engine Parts crank by turning the rod journals down to the small 2-inch diameter of the old 327-c.i.d. small-block. This added an extra 41 cubic inches to the combination, making the little 350 think that it's a big-block (with 391 cubic inches). Then Bogosian hung a set of full-floating 10.25:1 JE forged pistons on 5.7-inch 4340 H-beam C.A.T. rods and produced a stroker bottom end strong enough to haul the Queen Mary from Long Beach to Long Island without a trailer.

BREATHING SCIENCE
The top end of Bogosian's big Mouse motor was designed to optimize fuel efficiency and power, while still being a smooth-running street engine with great throttle response. For his top end, he choose to go the dyno-matched route and selected Holley's new Street Avenger package, which included aluminum heads, intake manifold, cam, carb, and all of the needed accessories to go with. That way he knew that he wouldn't have to waste days on the dyno figuring out which combination would work best.

While not huge by anyone's standards, we learned that the Street Avenger heads included in the Holley package did flow a respectable number and were designed mainly to make power in real street rpm ranges. That meant that a 6,500-rpm power peak was not in our future, and the 223-cfm that these heads flowed at 0.500-inch lift on the intake side meant that a huge cam would not be needed to optimize the package.

Bogosian chose a Lunati hydraulic camshaft with slightly more duration than the recommended Street Avenger cam because he felt that the 41 extra cubic inches this engine displaced would need a bit more breathing room. He also asked for the cam to be ground with a 112-degree lobe-separation angle to better accept the shot of nitrous that was in this engine's future. He combined the big cam with Lunati's 1.6:1 roller rockers and a double-row timing chain to be sure that the valvetrain would be up to the long-term use that it would see.

POLYGRAPH TEST
With the top end finished off and a set of March Performance serpentine pulleys bolted on the damper and the Weiand water pump, Bogosian hauled the motor to Vrbancic Brother's Racing Engines and Dyno shop (in Ontario, California) for a full-day's dyno bashing. Brothers George and Bob had no trouble tuning this street combination to deliver every last ounce of useable power.

The first dyno pull with the 770-cfm vacuum secondary Holley carb, taken right out of its box, was promising. The Mouse belted out 430 hp and peaked with almost 440 lb-ft of torque. Twenty-nine dyno pulls and a few carb spacers later, Bob and George squeezed out 453 ponies and, coincidentally, exactly 453 lb-ft of torque. But the real performance story with this engine was its ability to produce consistent torque figures above 400 lb-ft no matter what was changed on it. Only when they made a few pulls up to 6,500 rpm, did the engine really fall off in power, indicating that it was definitely over after 6,000 rpm. Average power figures were terrific for an engine that will spend most of its life on the street and would work great with tall rearend gears or an overdrive transmission for long-distance cruising.

We applaud Bogosian and the Vrbancic Brothers for working so hard to create such a great street package. If your dreams include having the next engine under your hood be something truly unique and ultimately reliable, try this stroker from a different point of view for a new twist on some old performance know-how.

STROKER PARTS BREAKDOWN
The following is list of all the essentials used to assemble this 391-c.i.d. stroker small-block.

BLOCK
GM four-bolt main, over-bored to 4.030-inch diameter, surfaced to "zero" deck height, clearanced for extra stroke, brass freeze plugs.

CRANK
C.A.T. 4340 forging, 3.75-inch stroke, rod journals offset-ground to 2-inch diameter providing 3.832-inch final stroke.

RODS
C.A.T. 4340 small journal H-beam, 5.7-inch long, bushed pin end.

PISTONS and RINGS
JE (PN 183119) forged flat-top pistons with two valve reliefs, Moly-coated ductile iron rings from JE.

BEARINGS
Clevite H-series rod bearings, 77-series mains.

CAMSHAFT
Lunati custom-grind hydraulic flat tappet with 245/255 degrees at 0.050 lift, 0.569-inch valve lift intake and 0.576 exhaust, ground on 112-degree lobe separation angle.

OIL SYSTEM
Milodon low-profile stroker pan (PN 30908), high-volume pump (PN 18750), pickup (PN 18050), Diamond Stripper windage tray (PN 32255).

HEADS/INTAKE/CARB
Holley Street Avenger package.

IGNITION
Holley HP Annihilator, Laser Shot 9mm wires, billet distributor, Laser Shot coil

DYNO FIGURES
It's important to remember that the owner of this engine was not looking for the ultimate fire-breathing monster under his hood. Rather, he wanted a street engine that would pull like a team of oxen and never let him down on the long haul. Sometimes, in our quest for superior power, we lose sight of what's really needed to get down the road. Sure, belting out 550 hp at 7,500 rpm is a kick in the pants, but that same engine may have trouble keeping up stoplight to stoplight with this little torque monster.

This particular dyno pull represents one of the best and was made using two plastic spacers stacked under the carb. The spacer closest to the carb was a 1-inch thick, four-hole spacer, and the one closest to the manifold was a 1-inch thick, open spacer.

The proof of the pudding was...        read full caption The proof of the pudding was in the dyno pulls.

1. The new Holley Street Avenger...        read full caption 1.The new Holley Street Avenger 770-cfm vacuum secondary carb worked well right out of the box. Bob Vrbancic had to swap a 2.5 power valve for the stock 6.5 power valve because the engine made only 8 inches of vacuum at its 800-rpm idle.

2. Jet changes are usually...        read full caption 2. Jet changes are usually worth some power when fine-tuning on the dyno, and Vrbancic came up with the best jetting combination of 70 primary/75 secondary which was only two jet sizes smaller than stock on the primary side. Holley has really done its homework on this line of carbs.

3. We first ran the engine...        read full caption 3. We first ran the engine with 37 degrees total advance, but in the end it liked a little more and ran best with 39 degrees.

4. An engine will often respond...        read full caption 4. An engine will often respond well to different carb spacers and this Mouse was no different. We stacked two carb spacers (a four-hole and an open spacer) under the Holley, and the engine picked up power all around.

5. With 2 inches of carb...        read full caption 5. With 2 inches of carb spacers under it, the Holley four-barrel sat sky high. This setup might prove difficult to fit under some stock hoods but it made great power on the dyno.

6. Since this engine was...        read full caption 6. Since this engine was going to see tons of street duty, it was outfitted with a set of March Performance pulleys to drive the Weiand mechanical water pump. The alternator and power steering pulleys and belts will be added later.

7. The Holley HP Annihilator...        read full caption 7. The Holley HP Annihilator ignition system and billet distributor with 9mm Laser Shot plug wires provided enough spark to light up Manhattan on Christmas Eve.