543 Reasons to Stroke Your Small-Block

When walking down the aisles of trucks at a show, you can pretty well count on half of them housing Chevy small-blocks. There's about as many recipes for how to prep a mouse motor as there are for apple pie. When we heard that Westech Performance was about to try its own, we had to follow along. Westech's project was to build a very streetable and powerful small-block that needed to get decent gas mileage, and have at least 12 pounds of vacuum for power brakes.

So how do you get phenomenal horsepower while maintaining engine integrity and longevity? The correct answer is to stroke it. The basic difference of a stroked small-block, as opposed to a 350, is the travel length of the rods, or length of the overall combustion stroke. In essence, the crank has a longer throw and the piston connecting rods are slightly shorter. This gives high horsepower at a reasonably low rpm of around 5,000. We are speaking of performance here so it should be recognized that some small-blocks don't reach peak rpm until 6,800 rpm. No one wants to put an engine through that many wraps on a regular basis for street driving--it just isn't practical.

Westech started with a used small-block from a '71 'Vette and bored it 0.030 over. While at the machinist's bench the engine was balanced, blueprinted, decked, and line bored. The machine work will increase the life of the engine dramatically and give a slight horsepower increase. The theory is to ensure that every component is counterbalanced perfectly so that no vibrations occur while at full power. As the travel length of the rods is longer than stock, Westech had the block and connecting rods modified. Areas of concern for modification are at the No. 1, 2, and 6 cylinders. In the final 5 degrees of crank rotation during a combustion stroke, the connecting rod caps are within 0.010 inch of slamming into the cam. Add in heat expansion and it's a real tight fit. To prevent the cam from being chinked by a rod cap, Westech shaved off approximately 0.060 of an inch from the topside of the connecting rod cap. In addition to the removal of rod material, the caps must be secured using bolts as the traditional pressed stud has too much head protruding from the topside to clear the cam. The block is also ground away at the No. 1, 2, and 6 cylinders to accommodate the extra angle the connecting rods need when at top dead center.

A must for building this engine is quality parts matched to the application. Although the technical displacement of the engine is 383 ci, the components used are fairly universal for all small-blocks. Internal components such as bearings, seals, and rings are supplied by Sealed Power. Seated in the bearings lies a custom crank from Scat connected to the company's rods as well. The Scat crank is a forged steel model and has been balanced to match the rods. This will have the engine running with very little internal vibration and promote smooth acceleration.

The area of critical mass in power is the camshaft. Linked to the crank is a full Comp Cams valvetrain. A hydraulic Retro-Fit roller camshaft from Comp Cams Xtreme Marine line was chosen as the best bet for this application. In camshaft selection, performance comes from the length of time the camshaft allows the valves to be open. As the cam is turning, the length of valve duration is measured in degrees. This is known as duration. With an advertised duration of 270 intake/276 exhaust, 0.503 lift, and 112 degrees lobe separation it should suck some wind and provide excellent engine breathing. The valve gate, or opening, is determined by duration at 0.050 valve lash. Rather, the 0.050 duration indicates at which degree of crank rotation the valve begins to open, while the advertised duration indicates when, in crank rotation, it closes. So, with a 0.050 duration of 218 degrees intake/224 degrees exhaust, the intake and exhaust valves will be open for approximately 52 degrees of crank rotation. Tying all these together is the job of Comp's double roller timing chain, bearing cam button, and billet timing cover.

Next in line of importance are valves, springs, and rockers. Comp Cams supplied a full set of springs and rockers, while the heads and valves are from AirFlow Research. It's critical that valves are matched to springs, rockers, and the cam. Most manufacturers supply kits of components recommended for use with application-specific cams. A set of Comp Retro-Fit hydraulic roller rockers was attached along with triple-stepped valvesprings. To guide the valve pushrods to center, Airflow supplied guideplates that bolt beneath the rocker stud. Things will be moving very fast in the engine, so they have to be kept lined up. Guideplates are one solution to keep the roller rockers from walking off the valve stem.

The real gem of performance is the Airflow heads. Sporting a displacement of 64 cc's in the combustion chamber, the aluminum heads are CNC-machined and ported, then flow-tested at the factory. With forged pistons pressing 10.04 compression, the engine will need to breathe deeply. The Airflows will give better fuel delivery, prevent layering, and allow the engine to suck as much air as necessary.

Now that the long-block is assembled, the 383 has to be fueled and sparked. For most applications of aftermarket ignition, capacitive discharge ignition systems using a traditional rotor distributor are preferred. There's a myriad of systems like these available from all major ignition companies. Westech chose MSD's billet aluminum model. The distributor is assuredly overbuilt for this application, but the quality-versus-cost factor is significant enough to splurge. Precision in timing and fuel delivery is the second critical area of concern for power. MSD's model will accurately provide spark without jumping cylinders in the discharge cap.

For induction, Westech chose an Edelbrock dual-plenum manifold combined with a Demon 750-cfm carburetor. It is difficult to calibrate a carb without a dyno, so Westech threw the whole package on an engine dyno to see the results. After some tweaking with carburetor jets, fuel discharge, and ignition timing, results came out to be a pleasing 465 horses at 5,700 rpm. Similar results can be expected using an injection system that will deliver better gas mileage and about $2,000 to the total bill.

To push the engine a little more, Westech bolted on nitrous using Nitrous Works gear. The engine was tickled twice using different jettings for the nitrous. The results topped out at 543 horses while turning 5,600 rpm.

Westech's 383 Recipe
•Block: 350 Chevy, four-bolt main, bored 0.030 over
•Crank and rods: Scat, 383 kit
•Heads and valves: Airflow Research, CNC-ported, 195cc intake port valves
•Cam: Comp Cams No. 12-418-8 Extreme Marine Retro-Fit hydraulic roller
•Valvesprings: Comp Cams No. 986-16
•Rockers: Comp Cams No. 853-16 Retro-Fit roller rockers
•Timing chain and cover: Comp Cams double roller chain, CNC billet cover with bearing cam button
•Oil pan and pump: Stef's Pan and Pump
•Bearings and seals: Sealed power
•Intake Manifold: Edelbrock No. 7107
•Carb: Speed Demon 750 cfm
•Dampener: Summit No. 64266
•Gaskets: Fel-Pro Perma-torque
•Fasteners: ARP anodized steel
•Distributor: MSD No. PN8361
•Test Results
Baseline: 465.2 hp @ 5,700 rpm,
465.6 lb-ft @ 4,700 rpm
•Jets: 84 primary 92 secondary
•Nitrous 1
&bull Timing: 35 degrees total advance NOS Pull 1: 510 hp @ 5,600 rpm, 526.9 lb-ft @ 4,800 rpm
•Jets: 84 primary, 92 secondary
NOS Jets: 25 fuel, 35 NOS