We've jonesed for a squeeze motor for sooo many years. Squeeze in the old-fashioned sense--compression, not nitrous--and a big, stanky roller cam to go with it. Trouble is, we had neither the need nor the short-block. We did have a trick Dart top-end and a juicy King Demon removable-sleeve carb. Meanwhile, our pal Jeff Jacobs at Dougan's Racing Engines has been scheming his own street-race unit for some time, and had scored some used odds and ends that added up to a stout small-Chevy short-block. You see where this is going.
Bore & Stroke
Jeff's combo was born more of happenstance than planning. First he got a 4.165-bore Chevy 400 block--a well-seasoned race unit with unidentified steel caps--then he found a similarly experienced 47-pound LA Enterprises billet crank swingin' a 3.500 stroke. Put 'em together and it's 381.5ci. The rods came next: a set of 6.250-inch-long Oliver billet units (again, used). Add up those components with the fact that the block had previously been milled to a height of 8.990 inches (9.000-9.025 is more typical for a small Chevy), and it was obvious that custom JE pistons were needed with a meager piston compression height of 0.976-inch, giving 'em an rpm-friendly weight of 414 grams with 128.5-gram pins. Light! The damper is one of Pioneer Performance Products' new SFI-approved, 61/8-inch units (PN 872021).
Compression
Jeff wants to be able to put this thing on the street and maybe even limp it on the occasional tank of 91-octane with some booster, so we ditched our 14:1 goal and ran 12.2:1. That number was largely dictated by the dome size and shape developed by JE Pistons after it digitally plotted one of the combustion chambers of the Dart 227 CNC cylinder heads so the domes would mate perfectly with the combustion chambers.
The domes ended up at 11cc, and piston-to-deck clearance was 0.004-0.006 inch. We selected Mr. Gasket products throughout this engine, and used the same type of Solicor head gaskets that have been in our heavily nitrous'd Anvil engine. The ones for a 400 block without steam holes are PN 5729, and have a gasket bore of 4.220 and compressed thickness of 0.042 inch.
Friction
Jeff did a few tricks to the bottom end to waylay frictional losses. First, the pistons used narrow JE rings: 0.043 wide for the compression rings (5/64 or 1/16 is more common in street engines) and 3mm on the oil ring. This was partially dictated by the very short height of the pistons, but it's a benefit for reducing ring drag; similarly, the short piston skirts reduce piston-to-wall drag. Also, Dougan's brushed the cylinders to a fine surface as is common for its circle-track customers. With a breaker bar on the crank snout, you can almost turn over this short-block with one finger.
Oil Control
Jeff designed the bearing clearances around 10W30 Royal Purple synthetic oil, setting the Sealed Power race main and rod bearings to 0.0024-inch clearance. The oil system included an off-the-shelf Milodon oil pump and PN 30908 pan with an integral louver-type windage tray. To promote piston-ring sealing, the second compression rings were set to a file-fit 0.024-inch gap, larger than the top ring at 0.020-inch. This is common in today's performance engines, with the secondary gap larger to help vent pressure between the two rings to prevent the unsettling of the top ring. A Moroso vacuum pump was used for the same reason; see the sidebar to see how it worked.
Top End
Jeff was not at all concerned about the low-rpm manners of this sucker and was happy to bolt up our Dart Machine Pro 1 227 CNC aluminum heads and Dart high-rise single-plane intake (PN 42421000) for a standard-height block, standard intake ports, and flanged for a 4500-series carb. Dart had totally ported the intake, including matching the port openings to the heads.
The heads are the same casting as Dart's 215cc Pro 1 aluminum heads, but with an in-house CNC porting program that brings the intake port to a 227cc volume and the exhaust to 85cc (PN 11970040). Advertised flow numbers are included in the sidebar, peaking at 314 cfm at 28 inches of water at 0.0800-inch valve lift. The valves are 2.08/1.625 and the guides are set to position the valves at 0.030 inch wider apart than stock. The chambers are designed for a 4.155-inch-or-larger bore, and one of the things we were most impressed with was the way every chamber lined up perfectly with the circumference of the bore beneath it. Similarly, while the intake manifold had to be milled by Dougan's to line up with the heads on Jeff's severely decked block, the intake-to-head port match was phenomenal. The intake gaskets need to be medium-port race type, and we used Mr. Gasket PN 5822 (1.31x2.19 port opening).
Another fitment item we liked was the alignment of the intake runners in the plenum directly below the throttle-bores of the 4500-series carb. Ours was a King Demon race carb with the removable-sleeve option for altering the cfm with interchangeable venturi sizes. This one was set to 995 cfm, which seemed happy.
Cam & Valvetrain
We chose Erson Cams for the bumpstick and paraphernalia. Erson was known for Super Shops cams for years, but for even longer than that the company has made custom grinds for race shops nationwide. It sells cams direct and has guys on the phones to help with your combo. When faced with our desire for peak power between 7,500 and 8,000 rpm, here's what Erson recommended: 276/284 degrees of duration at 0.050 tappet lift, 0.675/0.675 lift (net 0.0682/0.655 observed with 0.030 lash and 1.6 intake/1.55 exhaust rockers), 108 degrees of lobe separation, and installed at a 108 intake centerline. That's big. And, naturally, a solid roller design. Erson is most respected these days for its new valvespring material, said to have fantastic fatigue resistance. The recommended PN 915150 springs had a massive 1.630 diameter and pressures of 235 pounds on the seat and 700 open at an installed height of 1.900. They were used with Erson 10-degree titanium retainers.
With that kind of valvespring pressure, Jeff opted for a Milodon geardrive rather than a conventional timing chain. Also, he used Yella Terra shaft-mounted rockers (PN YT6341), an Australian brand carried by Dougan's. The shaft rockers eliminate the stock rocker studs as well as the need for stud girdles and pushrod guideplates. The Dart Pro 1 heads can use conventional stud-mounted rockers, but when using shaft-type, require those made for stock (1.770-inch) stud spacing and an 0.070-inch-offset intake rocker (to accommodate the spread, 1.890-inch valve centers). Manton custom 11/32-diameter pushrods were also used, with 5/16-diameter, 270-degree balls on each end.
Ignition
Keeping with the Mr. Gasket theme, we had a Mallory ignition, including a billet Comp 9000 distributor (PN 8448204H) and crank trigger kit (PN 621) with a 7.25-inch pickup wheel. We really liked the ease of adjustability with the Mallory crank trigger. We wrapped it up with Mallory pro Sidewinder 8mm spiral-metal-core wires and Autolite AR3923 race plugs.
On the Dyno
Bolted to the SuperFlow pump at Westech Performance, the 381ci small-block was dressed with 13/4-inch Sprint Car headers with 3-1/2-inch collectors and no mufflers. We also used the Meziere electric water pump borrowed from the Anvil. The engine was broken in with the Moroso vacuum pump disconnected and with dinosaur oil in the pan, then we switched to the 10W30 Royal Purple. The King Demon carb was set with annular boosters and a 6.5 power valve that seemed to be opening at idle, so we swapped it for a 3.5 valve. Jetting wound up optimal at 79/84, and timing seemed to be best at 36 degrees total (rock solid at any rpm thanks to the Mallory crank trigger).
This thing is way rumpity. It idles uncomfortably near 1,500 rpm. Vacuum? Don't know, don't care. The tone doesn't really take a set until about 3,500 rpm, then it's wicked snappy and screams smooth all the way through 8,000 rpm. You oughta hear it! With the tune up done and the vacuum pump on full suck, It peaked at 682 hp at 7,500 rpm and 532 lb-ft at 6,000; we didn't pull it lower than 6,000, so it probably made a bit more torque at 5,700 rpm or so. Driveable, no. Set for full dragstrip thrash, yesss.
