401-Inch Chevy Stroker

The arrows indicate where...        read full caption The arrows indicate where American Speed grinds the block to clear the rods and long-stroke crank. All eight cylinders generally require similar clearancing. Current Mr. Goodwrench “Mexican” blocks retain more material for grinding than production U.S.-cast blocks made in the last 20 years.

Generally rods 6 and 8 come...        read full caption Generally rods 6 and 8 come closest to hitting. The profiled ASE 6-inch rods and ARP 12-point 7/16-inch capscrews provide more clearance than stock forgings with their nut-and-bolt rods. Despite being 0.300-inch longer than typical 5.7-inch– long GM small-block rods, the ASE rods are also lighter.

Manley Platinum Series 10:1...        read full caption Manley Platinum Series 10:1 forged pistons are retained on lightweight tool-steel pins by double 0.042-inch–thick Spirolocks. Bushed and drilled for pin oiling, ASE’s 4340-steel rods measure 6 inches center-to-center. Federal Mogul high-perf bearings are used on both main and rod journals.

This engine uses lower-priced...        read full caption This engine uses lower-priced (yet durable) Speed Pro 1/16-1/16-3/16 “claimer-moly” rings (PN R8902-060). A groove-lock spacer (arrow) is also needed because the stroker crank and 6-inch rods yield a short piston compression height, forcing the oil-ring groove down into the pinhole area.

The heart of the package is...        read full caption The heart of the package is ASE’s carbon-nitrided, 4340 forged-steel, 3.875-inch–stroke crank. Thanks to enlarged counterweights and drilled crankpins, the custom forging accommodates long strokes with no need for externally weighted dampers and flywheels— or expensive Mallory metal.

American Speed welds the pickup...        read full caption American Speed welds the pickup to the Melling M55A high-volume oil pump. An all-steel oil pump driveshaft adds durability and helps fight spark scatter.

MSD’s PN 85551 billet...        read full caption MSD’s PN 85551 billet distributor is recurved with a quicker centrifugal advance. For this test it was triggered by American Speed’s standard dyno ignition system—an MSD Digital 7 box.

The Air Flow Research heads...        read full caption The Air Flow Research heads used on this engine feature 2.05-inch intake/ 1.60-inch exhaust valves, 74cc chambers, 195cc intake runners, and straight spark plugs. Angle plugs offer no power advantage with flat-top pistons, and the straight plugs clear most standard headers.

The Crane Energizer roller...        read full caption The Crane Energizer roller rockers’ split ratio—1.6:1 intake and 1.5:1 exhaust—broadens the torque band with the AFR heads’ efficient exhaust port. Installed by Air Flow, the hydraulic roller cam–compatible dual, 1.550-inch-od springs (with damper) develop 130 pounds on the seat.

One example of how American...        read full caption One example of how American Speed pays attention to the details: To ensure the 5/16-inch–od Comp Cams High Energy hydraulic roller cam–compatible pushrods (PN 7809-16) don’t bind against the guideplates, the rocker stud is torqued only after pushrod installation and alignment.

Canton’s 7-quart (with...        read full caption Canton’s 7-quart (with filter) oil pan fits Camaros, Chevelles, and similar chassis.

Fuel metering is handled by...        read full caption Fuel metering is handled by a Holley 750-cfm double-pumper carb (PN 0-80779) and Edelbrock RPM Air-Gap high-rise dual-plane intake (PN 7501). American Speed says the Air-Gap makes more power and torque under 5,900 than the Victor Series, while only giving away 7 hp on top.

A custom-ground Comp Cams...        read full caption A custom-ground Comp Cams hydraulic roller cam and lifters provide a low-maintenance, user-friendly solution for making the big power and torque numbers. It’s worth 20-25 hp over a flat-tappet hydraulic. The quick-opening ramps match up well with a good-flowing head like the AFR 195.

It’s been said that “Horsepower sells engines, but torque wins races.” There’s no question that a broad torque band makes for good street performance and driveability. An engine with more cubic inches has greater torque potential than a smaller displacement engine, and assuming similar overall displacement, a longer-stroke engine generally develops more torque than a short-stroke mill. That’s why for many years Chevy’s 400ci small-block—with its 4.125-inch bore and 3.75-inch stroke—was the choice for car crafters looking to maximize torque in a relatively compact, lightweight package. Unfortunately, used 400 cores are getting scarce. While the as-delivered 4-inch bore on GM Performance Parts’ Bow-Tie block can be overbored to 4.125-inches, the General charges premium prices for these premium blocks. What’s a torque-hungry small-block lover to do?

Enter American Speed Enterprises (ASE), specialists in building powerful but cost-effective Chevrolet engines for the masses. With the advent of affordable 3.875-inch forged stroker cranks and 6.0-inch rods, ASE owner Gail Trent has developed a 401ci small-block Chevy package built around a Mr. Goodwrench service replacement block (PN 10066034). Trent says these blocks have thicker cylinder walls than standard production blocks built in the last 25 years, so they readily accept a 0.060-inch overbore.

Even though a long stroke is good for torque production, traditionalists argue that a long-arm crank makes for a lazy engine upstairs. ASE fixes this with lightweight reciprocating components. Typical Chevy 350 bob-weights are in the 1,910-1,930–gram range, but on its 401, ASE holds bob-weights down to only 1,577 grams. The engine makes power past 6,000, and is internally balanced without Mallory metal.

Long-stroke engines also have earned a reputation for being hard on cylinder walls. Again, keeping the reciprocating weight down helps—as do the 6.0-inch rods. Although the 401’s stroke is 1/8-inch longer than a stock 400, the long rods still yield a 1.55:1 rod/stroke ratio—nearly the same as a 454 big-block’s 1.53:1, and quite a bit better than the stock 400’s 1.48:1. When used in conjunction with the proper camshaft and cylinder heads, longer rods can help broaden the powerband. They also reduce cylinder-wall thrust loading.

The cam in this case is a custom hydraulic roller that was ground for ASE by Comp Cams. Driven by Comp’s Hi-Tech double-roller timing chain (PN 3100), ASE’s grind utilizes a wide 112-degree lobe displacement angle (LDA). By contrast, typical Comp Cams street/strip sticks are ground with a 110-degree LDA. ASE says spreading the lobe centers is desirable on a street engine, which sees high loads at low rpm. The wide LDA makes for a smoother idle and higher manifold vacuum. Wider LDAs also yield increased piston-to-valve and cam-to-connecting-rod clearance than would an equivalent lift and duration cam with narrower lobe centers. That’s particularly critical on a long-stroke engine like this one—although the cam still must be ground with a rod-clearance-enhancing reduced-base circle.

Arguably the best all-around 23-degree valve-angle, conventional port location, small-block Chevy cylinder head, Air Flow Research’s 195cc Race-Port aluminum casting comes CNC-ported on both intakes and exhausts. The result is a more consistent casting that doesn’t require hand-finishing. The exhaust ports flowed so well that—with ASE’s dual-pattern cam—the best overall power and torque curve was obtained by installing 1.5:1 rockers on the exhaust side to complement the 1.6:1 rockers used to open the intake valves. The heads are fed by a Holley 750-cfm double-pumper carb atop an Edelbrock RPM Air-Gap intake, while an MSD distributor and Champion RC12YC plugs (gapped at 0.035-inch) ignite the spark.

You’re on your own for headers, but ASE recommends 1-¾-inch primaries with 3-inch collectors, which is what it used to dyno-test the prototype assembly. Installed on its Stuska water-brake dyno, ASE ran the prototype using a deceleration test regime (pulling it in “reverse” from the top down), which Trent feels more accurately simulates how a drag-race engine is loaded in the real world when you dump the clutch or load it up against the torque converter. Under these conditions, using 93-octane gas with 36-degrees of ignition lead, the engine churned out a whopping 538.5 lb-ft of torque at 4,500 rpm, and it developed a stout 554.2 hp at 5,900. The animal made over 500 lb-ft from 3,900 to 5,800 rpm, and it exceeded the 400 lb-ft mark through 6,300…definitely as advertised—and competitive with many a big-block! If you want to be the torque of the town, ASE’s complete 401 crate motor, assembled using all-new parts and carrying a 90-day warranty, goes out the door for $7,500 complete, less headers and a water pump.