Jenkins/Smeding 406 Crate Engine - Street-Friendly Small-Block Chevy

Jenkins Smeding 406Ci Small Block Chevy Crate Engine

Sometimes lightning does strike twice. The first bolt that struck was the 572 cubic-inch big-block Jenkins/Smeding Performance engine that we ran a story on in our December '08 issue. Ready for a second helping of horsepower, legendary racer Bill "Grumpy" Jenkins and Ben Smeding have teamed up once again to build a street-friendly 406 small-block.

As was the case with the 748-horse 572 build, the signature 406 will be produced in a limited quantity. Each of these engines is fully balanced, blueprinted, and dyno tested before it leaves the shop. And those results come only after a series of dyno tests and parts swaps. Only when both men are satisfied will the 406 be built and produced.

Once again, we spent a couple of days up at Smeding Performance documenting the build and test runs of this big small-block.

The bottom end of any engine build is just about the most important link in the chain. You can have the highest flowing heads, largest carburetor, and greatest manifold, but they will suffer if the bottom half of the engine is poorly built. The Jenkins/Smeding small-blocks all start life with a Dart Little M block. The bore size of each cylinder is opened up to 4.155 with a special cross-hatch honing that aids the rings in sealing and oil retention.
The bottom end of any engine build is just about the most important link in the chain. You
Ben Smeding (left) and Bill Jenkins discuss the various types of cranks and rotating assemblies.
Ben Smeding (left) and Bill Jenkins discuss the various types of cranks and rotating assem
The entire rotating assembly is private labeled and custom forged for Smeding Performance, excluding the pistons, which are from Keith Black. Notice on the Keith Black pistons the pivot point is higher up when compared to a stock SBC piston. The rings used on these pistons are Total Seal.
The entire rotating assembly is private labeled and custom forged for Smeding Performance,

In this photo, Smeding is working on the balancing of the 3.75-inch stroke crank.
He also tells us that this lightweight crank is lighter than most others out there and is gun drilled with undercut counter weights.
He also tells us that this lightweight crank is lighter than most others out there and is
The connecting rods are also of a better design than the standard SBC rod. The H-beam rod on the right is 6.125-inches in length compared to the stock 5.7 rod.
The connecting rods are also of a better design than the standard SBC rod. The H-beam rod

The wrist pin holes are honed to fit each individual free-floating pin.
The bearings that are used in this engine provide 240 degrees of oiling to the rod compared to the 180 degrees grooved bearings. That means that the rod receives oil during 66.6 percent of its rotation, compared to 50 percent of its rotation.
The bearings that are used in this engine provide 240 degrees of oiling to the rod compare
The cam that is used in this build is a Comp grind, but we don't have the specs on it. This part of the Jenkins/Smeding build is kept secret.
The cam that is used in this build is a Comp grind, but we don't have the specs on it. Thi

The cam is a full hydraulic roller, as evidenced by the cam thrust plate.
The tolerances are checked on each bearing. Since the build employs a sturdier aftermarket block with less flex, the tolerances can be tighter. Tighter tolerances can equal horsepower gains.
The tolerances are checked on each bearing. Since the build employs a sturdier aftermarket
Each piston finds its home in the designated cylinder.

Once the bottom end is done, which takes up most of the build time, things speed up.
The oil pump used in the 406 is a standard volume Melling oil pump.
The two-piece Comp Cams timing cover that is being installed in this photo is for the test build engine.
The two-piece Comp Cams timing cover that is being installed in this photo is for the test

The Canton oil pan has a seven-quart capacity.
Jenkins and Smeding talk shop as Ben works on a set of cylinder heads.
The top half of the engine consists of AFR 195 cylinder heads with 65cc combustion chambers.
The top half of the engine consists of AFR 195 cylinder heads with 65cc combustion chamber

The lightweight intake valves measure 2.050-inch and the exhausts are 1.600 with hardened ductile iron interlocking valve seats. The intake used is an Edelbrock Super Victor topped with a Quick Fuel 750 cfm double pumper.
The lightweight intake valves measure 2.050-inch and the exhausts are 1.600 with hardened
Once the engine was on the dyno and the rings were seated, a few different tests and parts swaps were conducted.
Once the engine was on the dyno and the rings were seated, a few different tests and parts
After we left Smeding Performance, they tried one last dyno run this time with a highly-tuned 850 cfm Quick Fuel carb with the Professional Products Hurricane intake. Ben informed us that the Quick Fuel carb was within 4 horsepower of the Mighty Demon. As for the final production version of this engine that hits the streets, well, that is up to Jenkins and Smeding.
After we left Smeding Performance, they tried one last dyno run this time with a highly-tu

Dyno Test 1
Maximum HP	Maximum Torque
526@5,800 RPM	519@4,800 RPM

Parts list: Edelbrock Super Victor single plane intake, Smeding rocker arms, AFR 195 cylinder heads Quick Fuel Technologies 750 cfm carb and MSD Pro Billet distributor. At lower range between 2500 and 3000 rpm, the engine torque starts between 431 and 458 ft-lbs and quickly accelerates from there until it hits its peak.

Dyno Test 2
Maximum HP	Maximum Torque
554@6,100 RPM	535@5,000 RPM

Parts list: This test consisted of the same exact parts as in the first dyno test with the exception of the carburetor. A highly-tuned Barry Grant 830 cfm Mighty Demon annular carb was swapped in place of the QFT 750. The torque gain was 28 ft-lbs and the horsepower gain was 16.

Dyno Test 3
Maximum HP	Maximum Torque
549@6,000 RPM	532@5,000 RPM

For this test, the Demon carb was kept and the Edelbrock Super Victor was swapped in exchange for a Professional Products Hurricane intake. The results were nearly the same, minus the 5 hp loss and 3 ft-lbs of torque lost at peak.

SOURCES
Air Flow Research 10490 Ilex Avenue, Dept. MMFF Pacoima CA 91331	Edelbrock Dept. 5.0 2700 California St. Torrance CA 90503 310-781-2222 www.edelbrock.com
Barry Grant Demon Carburetion	Quick Fuel Technology Bowling Green KY 2-70/-793-0900 quickfueltechnology.com
COMP Cams	Smeding Performance Dept. MMFF 3340 Sunrise Blvd. Rancho Cordova CA 95742
Dart 2-48/-362-1188 www.dartheads.com