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We Build Two Old-School Small-Blocks - One Blown and One Tri-Power

A Tale Of Two Chevys – Part 2: Topping our short-blocks

Ron Ceridono Jan 26, 2016
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As we said in “A Tale of Two Chevys – Part 1,” the plan to build a pair of Gen I Chevrolet small-blocks came into being during one of those “Wouldn’t it be cool to do” bench racing sessions with John Beck of Vintage Hot Rod Design. The conversation centered on building what would now be considered vintage engines, both destined to power hot rods that would be regular drivers with reliability and driveability more important than huge horsepower numbers.

As the discussion continued the elements of both engines went from fuzzy to focused. John wanted to build a blown 302-incher and we wanted to breathe life back into a 283 that was sitting in the corner of our shop and top it with three two-barrel carburetors. Thanks to Weiand and Holley that’s just what we did. Weiand had just come out with their nostalgic 6-71 supercharger kit and Holley introduced their new Tri-Power setup—what other choice did we have? It was time to build a pair of engines.

In Part 1 we covered the building of both short-blocks; but to recap, John’s blown engine is based on a large-journal 350 block overbored 0.030 inches to 4.030 inches coupled with a 3.00-inch stroke 302 crankshaft, resulting in 306 cubic inches. Our 283 block was sonic checked then overbored 0.060 inches to 3.935 inches and combined with a 3.25-inch stroke 327 crankshaft for a displacement of 316 cubic inches.

Heads

Sticking with the vintage theme, both engines use early cast-iron cylinder heads (pre-1969 style without accessory mounting holes). The naturally aspirated engine uses Power Pack heads (dated January 1961). John installed larger valves, but the proximity of the new 2.02-inch intake and 1.60-inch exhaust valves to the edges of the chambers prompted some concern about shrouding. In other words, flow could actually be restricted in those areas, and the advantages of bigger valves would be lost. The cure was to reduce the intake valves to 2.00 inches and widen the areas of the combustion chamber closest to the valves. Additional headwork was done to open up the bowls and smooth the intake and exhaust ports.

The heads for the blown engine are “camel hump” castings from 1967-’68 equipped with 2.02-inch intake and 1.60-inch exhaust valves. The bowls and ports were opened up and smoothed, but because these heads were so much better to begin with they required considerably less effort than the Power Pack heads.

As we said, some of the shared goals for both engines were reliability and longevity—to that end, compression ratios were kept on the conservative side. The combustion chamber size, piston design, and deck heights were coordinated to provide compression ratios of 7.1:1 for the blown engine and 9.6:1 for the naturally aspirated engine.

Ignition

For ignition systems we wanted distributors that looked like vintage points-controlled units but had all the latest electronics under a small-diameter cap. To give us what we needed, we turned to PerTronix for a pair of their Flame-Thrower plug-and-play distributors. The Ignitor III technology provides multiple sparks over the entire rpm range and there is what is called “adaptive dwell,” which maintains peak spark energy throughout the entire rpm range.

Induction

When it comes to induction systems, there are two distinct methods of making a statement: a trio of carburetors or a 6-71 blower.

Tri-Power is the stuff legends are made from. Not only do they look cool, but they’re really practical, too. Holley’s new system uses a Weiand 3x2 intake manifold with three Holley two-barrel carbs. The center carb is rated at 325 cfm and is equipped with a choke, whereas the outboard carburetors have no chokes and are rated at 350 cfm each. Thanks to the included progressive throttle linkage you can cruise around on the center carburetor for economy, but as the throttle pedal passes the two-thirds point, the outboard carburetors come online and all three reach wide open simultaneously.

Holley’s Tri-Power kits are available with dichromate or shiny finish carburetors. Fuel lines, progressive linkage, and reusable air filters with polished housings are included.

For a variety of reasons, vintage blowers were getting hard to come by—a situation that Weiand decided to address by introducing redesigned 6-71 cases. The vintage no-name look makes them appear right at home on a street engine or a cackelfest dragster.

Inside these all-new blower cases are roots-type, two-lobe rotors. The heavy-duty rear plate uses sealed ball bearings to support the rotors; up front, the bearings and gears are lubricated by an oil bath. Weiand’s nostalgic supercharger kits include a polished or satin 6-71 supercharger with gears and bearing plates, supercharger intake manifold, 2-4V carburetor adapter, all the required gaskets, 3-inch Gilmer belt, pulleys, brackets, idler, and necessary fasteners.

All Weiand’s superchargers are boost-tested and engineered to produce 10-12 psi of boost on small-blocks and 5-7 psi on big-blocks, but as they say, these blowers are a simple pulley change away from pump gas or hard-core racing.

Testing

The blower on John’s small-block was topped with the same carburetor setup as our naturally aspirated engine, and it too used a progressive throttle linkage to operate them. The engine pulled willingly from idle, and after some jetting adjustments, the little 306 made 419 horsepower and 362 lb-ft of torque breathing through air cleaners, exhaling through mufflers and we discovered we weren’t getting full throttle—nonetheless we were happy. The engine idles smoothly and the throttle response is instantaneous.

Other than building something unique, we had modest horsepower and torque goals for our little naturally aspirated engine. We were shooting for 325 horsepower and as broad a torque curve as possible. Frankly, we just wanted it to be in the neighborhood of what a carbureted 5.3L LS would produce because that’s the engine we were originally going to use in our latest hot rod but couldn’t bring ourselves to go new school.

When the testing began we were concerned that with 1,025 cfm our little naturally aspirated engine would be way over-carbureted, but there was no indication that was the case. After changing the jets in the center carburetor from 65s to 62s, and going from 70s to 68s in the end mixers we saw 338 horsepower and 349-lb ft of torque (with a 338 lb-ft average from 2,500 to 5,700 rpm). For giggles, we tested a carbureted LS1 and it produced 360.15 lb-ft of torque, but because our engine looks so much cooler, it doesn’t bother us.

In the final analysis, both engines more than met our goals—good power; reasonable fuel consumption; and great, vintage visual appeal. Those are tales worth telling.

1 Blown Small Block Engine Build 2/55

John Beck’s old-school Weiand blown, Holley-carbureted 306-inch small-block is just about ready to be fired for the first time.

2 Tri Power Small Block Engine 3/55

Waiting its turn on the Vintage Hot Rod Design dyno is our naturally aspirated, Tri-Power-equipped 316. Water pumps on both engines are from Weiand, this engine uses a Rattler crank damper.

3 283 Small Block Engine Build 4/55

For the naturally aspirated engine, the 283 block was fitted with cast 307 replacement pistons, stock connecting rods, and a Comp Cams hydraulic roller camshaft.

4 Supercharged Small Block Engine Build Pistons 5/55

John’s 306 uses a 350 block, Arias forged pistons, I-beam rods, and a Comp flat tappet camshaft.

5 Small Block Engine Build 383 Heads 6/55

Heads for the 316 are 1961 Power Pack castings. They were updated with Comp Cams’ screw-in studs, guideplates, springs, locks, and retainers.

6 Small Block Engine Build Valve Bowls 7/55

John opened and reshaped the bowls above the valves and blended them into the ports. The valveguides were trimmed to reduce restriction.

7 Small Block Engine Build Intake Valves 8/55

Intake valves are 2.020-inch Federal-Mogul replacements that were cut down to 2.00 inches. Note that the chambers have been opened up around the valves to reduce shrouding.

8 Small Block Engine Build Exhaust Valves 9/55

The exhaust valves are 1.60-inch Federal-Mogul replacements. Again, the chambers have been opened to reduce shrouding.

9 Small Block Engine Build Valve Guides 10/55

The 316’s heads were freshened with new, bronze valveguides.

10 Small Block Engine Build Valvestem Seals 11/55

The Comp Cams valve stem seals prevent excessive oil from passing through the guides.

11 Small Block Engine Build Head Gasket 12/55

To provide reliable sealing, both engines were equipped with PermaTorque head gaskets from Fel-Pro.

12 Small Block Engine Build Arp Head Bolts 13/55

For the 316, we opted for ARP head bolts rather than studs.

13 Small Block Engine Build 14/55

All the fasteners on both engines, including the 12-point head bolts, came from ARP. Note that the 316’s heads have been modified for screw-in rocker arm studs.

14 Small Block Engine Build 283 Heads 15/55

The 316 heads have the pointed indicator that first appeared in 1956 on dual-quad engines. However, casting numbers are still the most reliable method to identify heads.

15 Small Block Engine Build Comp Rocker Arms 16/55

Both engines were equipped with Comp Cams Ultra Pro roller rocker arms.

16 Small Block Engine Build Arp Head Studs 17/55

To cope with the pressure of supercharging, the 306 was equipped with ARP head studs.

17 Small Block Engine Build Valves 18/55

Valves for the blown engine were 2.02-inch intakes and 1.60-inch exhausts from Comp Cams.

18 Small Block Engine Build Camel Hump Heads 19/55

John used cast-iron “camel hump” heads on his blown engine. These were often referred to as “fuelie” heads as they were found on fuel-injected small-blocks, as well as others.

19 Small Block Engine Build Heads 20/55

Head modifications on the blown engine were limited to mild porting on the intake and exhaust sides and blending of the bowls.

20 Small Block Engine Build 21/55

To go along with the mild porting and bowl work, the heads for the blown engine were treated to screw-in studs, guideplates, and dual valvesprings with dampers, followed by lots of grinding and gloss-black paint to match the block.

21 Small Block Engine Build Valve Springs 22/55

As a solid lifter cam was used in the blown engine, lash caps were used on the valve stems to protect them.

22 Small Block Engine Build Valvetrain 23/55

Comp Cams tool-steel lifters, pushrods, and rocker arms make up the blown engine’s valvetrain.

23 Small Block Engine Build Rocker Arm Valvespring 24/55

Establishing proper rocker arm geometry is essential. The tip of the rocker should sweep back and forth across the center of the valve stem.

24 Small Block Engine Build Pushrods 25/55

Proper rocker arm geometry can be easily established with these adjustable pushrods from Comp Cams.

25 Small Block Engine Build Pushrod Measurement 26/55

John used an adjustable pushrod to establish the required pushrod length for both engines.

26 Small Block Engine Build Comp Valvetrain Lubricant 27/55

Comp Cams offers valvetrain assembly lubricant in a spray can.

27 Small Block Engine Weiand Nostalgia Supercharger Kit 28/55

Topping off John’s engine is Weiand’s new nostalgia supercharger kit. To keep the old vibe alive, the 1/2-inch toothed drivebelt and pulleys were used.

28 Small Block Engine Build Blower Manifild 29/55

A test-fit of the blower manifold was made to check port alignment and clearance at the block’s front and rear bulkheads.

29 Small Block Engine Build Silicone 30/55

To seal the gaps between the block and manifold, beads of silicone were applied to the bulkheads.

30 Small Block Engine Build Manifold 31/55

Several of the ARP bolts that secure the manifold to the heads are under the blower.

31 Small Block Engine Build Pop Off Valve 32/55

To prevent damage in case of a backfire, there is a pop-off valve in the rear of the Weiand manifold.

32 Small Block Engine Build Pop Off Valve 33/55

The release point of the pop-off valve is established by adjusting the height of the springs to specs.

33 Small Block Engine Build Pertronix Distributor 34/55

To maintain the nostalgic theme and have all the benefits of contemporary electronics, both engines were equipped with Flame-Thrower distributors from PerTronix.

34 Small Block Blown Engine Build 35/55

Weiand’s blower case, front snout, and swinging belt adjuster have the vintage look John was after. John fabricated the manifold holding a trio of Holley carburetors.

35 Small Block Engine Build Weiand Blower 36/55

The finned rear blower cover is another nostalgic touch.

36 Small Block Engine Build Blower Belt 37/55

Here, John is mocking up the drive components—the blower will be underdriven 29 percent.

37 Small Block Engine Build Scta Bonneville Seal 38/55

Just for giggles, the new engine now has attached the Southern California Timing Association seal from John’s record-setting Bonneville engine of the same displacement.

38 Small Block Engine Build Tri Power Manifold 39/55

Weiand’s new Tri-Power manifold is a medium-rise, dual-plane design that looks right at home on the 316.

39 Tri Power Small Block Engine Build 40/55

Holley’s Tri-Power setup uses a 325-cfm carburetor in the center and a 350-cfm version at each end. The progressive throttle linkage allows cruising on the center carburetor only.

40 Tri Power Small Block Engine Build 41/55

At approximately two-thirds throttle, the outboard carburetors come into play, and all three reach wide open simultaneously.

41 Small Block Engine Build Tri Power Fuel Lines 42/55

Included in the Tri-Power kit are beautifully formed steel fuel lines. Note, only the center carburetor has a choke.

42 Small Block Engine Build Rocker Cover 43/55

The heavy aluminum Comp Cams rocker covers help prevent leaks, and the included internal baffles keep oil from leaking out the breathers.

43 Small Block Engine Build Pertroinix Flamethrower Distributor 44/55

A black PerTronix distributor cap fits right in with the nostalgia theme of the 316. The Flame-Thrower distributor features a vacuum advance to increase fuel economy under cruise conditions.

44 Small Block Engine Build Pertronix Igniter III 45/55

The PerTronix Ignitor III system includes an integral rev limiter that is easy to adjust. Note the screw slot and the plus and minus signs with an arrow.

45 Small Block Engine Build Pertronix Coil 46/55

For spark, both engines will rely on PerTronix Flame-Thrower III coils.

46 Small Block Engine Build Dyno Test 47/55

John’s engine was run on the dyno with 8 psi of boost on pump gas and through the mufflers that will be on his car.

47 Small Block Engine Build Inner Valve Spring Removal 48/55

So there’s no possibility of a cam failure during break-in, John removed the inner valvesprings.

48 Small Block Engine Build Inner And Outer Valve Springs 49/55

After breaking in the cam, the inner springs were put back in place before making any full dyno pulls.

49 Small Block Engine Build Dyno 50/55

Our Tri-Power engine was broken in, then several pulls were made. Indications were some jet changes were in order.

50 Small Block Engine Build Carburetor Drain Fuel 51/55

Here’s a cool little trick—John used a cut-off plastic oil bottle to catch the fuel after he removed the bottom screw from the float bowl before the bowl was removed.

51 Small Block Engine Build Carburetor Jets 52/55

The Tri-Power carbs have Holley’s non-stick gaskets and use standard jets and power valves.

52 Small Block Tri Power Dyno Sheet 53/55

After a jetting change, these are the results of the final dyno pull made with the naturally aspirated Tri-Power small-block. Peak output was 338.6 horsepower at 5,600 rpm and 349.7 lb-ft of torque at 3,800 rpm.

53 Blown Small Block 302 Dyno Sheet 54/55

The little 306 loved the top end of the tach. Hooked to a four-speed, this will be a fun engine in a lightweight hot rod. Peak output was 419.9 horsepower at 6,600 rpm and 362.1 lb-ft of torque at 5,500 rpm.

54 Dyno Sheet 55/55

Out of curiosity, we compared our Tri-Power engine (dotted line) to a carbureted 5.3L LS (solid line).

Sources

TCI Automotive
Ashland, MS 38603
888-776-9824
www.tciauto.com
Comp Cams
Memphis, TN 38118
800-999-0853
http://www.compcams.com
PerTronix Performance Products
San Dimas, CA 91773
909-599-5955
http://www.pertronix.com/
Holley
Bowling Green, KY 42101
270-781-9741
www.Holley.com
Vintage Hot Rod & Design
Chico, CA 95928
530-343-9228
http://www.vhrcustoms.com
Fel-Pro Gaskets / Federal-Mogul Motorparts Corporation
Southfield, MI 48034
www.felpro-only.com
ARP
Ventura, CA 93003
805-340-4807
www.ARP-BOLTS.COM

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