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Building a Period-Correct 1968 Vintage Chevy 327 Engine

Class of 1968: We turn the clock back 50 years and build a small-block Chevy with only what was available in 1968

Jim Smart Aug 27, 2018
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The Vietnam War was in full swing. It was an election year and a pivotal time for the nation. There were two world-changing political assassinations. The Earthrise image was shot from Apollo 8 on Christmas Eve above the surface of the moon. “Hey Jude” by the Beatles was the number one hit song. Hot Wheels was introduced by Mattel, launching a phenomenon that lives on today. The Green Bay Packers defeated the Oakland Raiders 33-14 in Super Bowl II. Rowan & Martin’s Laugh-In debuted on NBC.

Do you remember?

The year was 1968.

Summit Racing Equipment remembers 1968. That was the year it was founded.

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Jeff Latimer, who was just 3 at the time has had this project brewing in his imagination for years. What if you could turn the clock back to build a 327ci small-block Chevy based only on what was available decades ago? How much power could you make on the tiny budget you had in 1968?

Forget aftermarket aluminum heads, current-day dual-plane intake manifolds, electronic fuel injection, nitrous systems, roller cams, multi-spark ignitions, and the rest of it. These items weren’t available to the novice in 1968. The best you could hope for were double-hump iron heads or perhaps the classic 283 Power Pack castings everyone wanted.

Jeff found a standard-bore 1963 327 block (casting number 3782870) and brought it to JGM Performance Engineering in Valencia, California, for machine work to conceive a 1968-vintage 327. From here, the block could have been turned into anything from a radical roller stroker to the old-school flat tappet street beast we’re about to build.

While he was shopping, Jeff unearthed a pair of 3890462 casting heads, one of the two most popular “double-hump” castings out there in 1968. He took these heads and had custom port work performed by Chris Brintnell along with the larger 2.02/1.60-inch intake/exhaust valves. He limited his efforts to what you could do in 1968.

Jeff’s search for period parts included an Edelbrock Streetmaster single-plane intake manifold, which wasn’t available until 1973 but we’ll bite because he had it in his stash. Jeff also found a well-worn Edelbrock C3B dual-plane intake manifold on eBay, which is a close cousin to the popular vintage C4B dual-plane manifold also available in 1968. He did some repair work on the damaged C3B and pressed it into service.

We learned on the dyno the Streetmaster and C3B sport remarkably similar power curves considering one is a single-plane and the other a dual-plane, with peak torque and horsepower numbers arriving in the same rpm range. Both manifolds, though of different dynamics, have long intake runners. The Streetmaster, as its name implies, was conceived for street use. It is the darnedest combination of mid-range torque and horsepower from a single-plane manifold. The C3B, as designed, is a terrific street/strip manifold. Great low-end torque, yet it makes horsepower at 6,000-6,500 rpm. In dyno testing, we tried three different carburetor sizes: 600, 650, and 750 cfm. The greatest difference in power came from the 750-cfm Holley (PN 0-80783C).

You’re going to look at this retro 327 and catch the PerTronix Ignitor, which was not available in 1968. However, solid-state ignition was available. You’re also going to see three contemporary Holley atomizers. We decided to opt on the side of convenience of getting new carburetors from Holley. Taylor ignition wires like these weren’t available either, but they look sharp.

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1. We’re working with a 1963 327 Chevy block (casting #3782870) with 4.030-inch bores that has been machined and is ready for assembly. JGM Performance Engineering in Valencia, California, has align-honed the mains, honed the lifter bores, cut the decks, and power-honed the bores using a torque plate.

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2. Most of us who remember 1968 will admit we didn’t know how to choose a camshaft for ourselves at the time. Instead, we looked to the advice of speed shops and engine builders. We’ve opted for a typical high-performance flat tappet hydraulic camshaft you would have found on the shelf in 1968 with 228/228-degrees duration at 0.050-inch, 0.512/0.512-inch valve lift, and a 108-degree LSA that would make our engine go “rumpity-rump-rump” like in the good old days.

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3. Jeff found a small-journal forged steel 327 crankshaft for this early 327 block. The crank was balanced by Doug Treutelaar with the correct bob weight requiring two small pieces of Mallory metal due to the use of heavier forged pistons.

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4. The main caps are set in place and snugged to check crankshaft endplay and freedom of movement.

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5. Ryan Peart of JGM Performance Engineering checks crankshaft endplay before assembly continues. We want a range of 0.002-0.006-inch ideally, but no more than 0.010-inch.

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6. With the crank properly seated and the main bearings hit with engine assembly lube, Ryan torques the main caps to 65-70 ft-lb beginning with the inner main caps in one-third values, checking for crankshaft freedom of rotation as he goes. The crank should turn freely using two fingers with the mains torqued.

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7. Early small-block Chevys equipped with this oil/vapor separator made it impossible to run an aftermarket intake manifold due to clearance issues. Jeff modified this oil/vapor separator to clear the period Edelbrock Streetmaster and C3B intake manifolds.

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8. Jeff has opted for Speed Pro forged 4.030-inch pistons from Summit Racing Equipment with moly rings sporting a compression ratio of 9.5:1.

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9. The 327’s cylinder walls have been wiped with a tack cloth and lubed with 30-weight engine oil. The piston installation is smooth with everything going to plan.

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10. JGM has reconditioned these original 327 rods and fitted them with ARP bolts for strength. We’re running 11/32-inch ARP rod bolts, which get torqued to 40 ft-lb on this small-journal small-block.

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11. The pistons are 0.005-inch down in the bores because the block was machined to a 9.000-inch deck height. We’re checking true top-dead-center here.

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12. Jeff has opted for a conventional timing set you would have found at any speed shop in 1968. When we were teens building small-block Chevys we could not have afforded a nice double-roller chain setup.

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13. We’re checking the valve timing events from this period-style flat tappet camshaft from Summit Racing Equipment. It checks out at 228/228-degrees duration at 0.050-inch on 108-degree lobe centers with 0.512/0.512-inch valve lift with 1.6:1 stamped steel rockers.

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14. Because Jeff has been building small-block Chevys since he was in his teens, he knew he needed the best factory head available at the time, which were the 3890462 “double-hump” heads. Jeff is fitting these castings with 2.02/1.60-inch valves. What’s more, he had a custom port job performed by Chris Brintnell.

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15. The quickest way to identify these high-performance Chevy heads is this double hump at the end of each head.

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16. Back in the day, we weren’t thinking of unleaded fuels and hardened exhaust valve seats because leaded premium fuel was plentiful and cheap. This is a low-cost option you should consider today because it still applies. Jeff has fitted these heads with stainless steel valves, which eliminates the expense of installing hardened exhaust valve seats, and possibly cutting into the water jackets.

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17. Chris Brintnell’s port work shines here, demonstrating how nicely these heads cleaned up and ultimately performed on the dyno.

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18. Jeff dresses the flat tappet cam lobes and lifters with moly-lube to give us a safe startup. Moly-lube, along with a 30-minute engine run at 2,500 rpm with high-zinc 30-weight engine oil, will harden the cam lobes, giving us a good break-in. Those first 30 minutes of operation are crucial to cam break-in and durability.

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19. We’re running 1.6:1 ratio rocker arms to allow an aggressive vintage cam grind to make more power. Back in the day, Ford 289/302 1.6:1 rocker arms were used to get 1.6:1 ratio.

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20. Jeff has performed a complete oil pump blueprint, checking all the clearances and relief valve function. He completes the task with an ARP pump shaft (PN ARP-134-7901). Even if you’re building a dead stocker, the ARP shaft is a must.

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21. We’re going with a Moroso (PN MOR-20170) pan and pickup (PN MOR-24212) from Summit. Jeff has checked pan-to-pickup clearances and we’re good to go.

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22. Jeff has marked the harmonic damper with degree tape for accuracy. He is using an installation tool as most of us should. It is best never to use a hammer for installation. The timing cover has been installed (PN EDL-4860) and the crank seal generously lubricated for a wet startup.

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23. This classic Edelbrock Streetmaster (PN 3225) intake manifold was engineered for either the Quadrajet or a Holley square-base using this adapter.

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24. A borescope is used to check port alignment before the intake manifold is torqued. Any finite adjustments need to be made now.

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25. The intake manifold torque sequence must be followed with caution, especially with an aluminum intake manifold. Torque is 25 ft-lb beginning at the middle and working outward. Do this in one-third values and gently seat the manifold. Allow the manifold to settle in and check the torque again. Do not over-torque.

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26. Our dyno session begins with the old reliable 0-1850 Holley sporting 600 cfm atop the Streetmaster manifold. Although this is not a 1968 vintage 0-1850, this four-bore Holley was available in 1968. In fact, the 1850 design pretty much dates back to 1957.

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27. We’re running a period Delco distributor from the 1960s fitted with the PerTronix Ignitor module inside. The Ignitor wasn’t available in 1968 either. We found it more convenient than those original ignition points.

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28. Pull one of our dyno session begins with a flat tappet 327 Chevrolet with a period Edelbrock Streetmaster intake and 0-1850 Holley. We got nearly 400 horsepower and comparable torque from this combo. Jeff swapped out the 600-cfm 0-1850 for a more robust 750-cfm Holley and bumped horsepower to 402.6 at 5,800 rpm.

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29. We were convinced the Streetmaster would be disappointing due to its single-plane design. However, we would learn on the dyno the Streetmaster was an excellent choice thanks to its long intake runners. We swapped out the Streetmaster for this Edelbrock C3B dual-plane manifold and got 417.9 horsepower and 402.1 lb-ft of torque with the 750-cfm Holley. In 1968, this would have been one hot 327.

Dyno Room
Pull 1
Induction: Edelbrock Streetmaster
Carburetor: Holley 600 cfm (PN 1850)
Horsepower: 393.2 @ 5,600 rpm
Torque (lb-ft): 394.5 @ 4,500 rpm
Pull 2
Induction: Edelbrock Streetmaster
Carburetor: Holley 750 cfm (PN 0-82750)
Horsepower: 402.6 @ 5,800 rpm
Torque (lb-ft): 392.8 @ 4,900 rpm
Pull 3
Induction: Edelbrock C3B
Carburetor: Holley 600 cfm (PN 1850)
Horsepower: 398.0 @ 5,800 rpm
Torque (lb-ft): 394.0 @ 4,000 rpm
Pull 4
Induction: Edelbrock C3B
Carburetor: Holley 650 cfm (PN 0-80783C)
Horsepower: 405.5 @ 5,900 rpm
Torque (lb-ft): 402.7 @ 4,300 rpm
Pull 5
Induction: Edelbrock C3B
Carburetor: Holley 750 cfm (PN 0-82750)
Horsepower: 417.9 @ 5,900 rpm
Torque (lb-ft): 402.1 @ 4,300 rpm


Double-Hump—Second Wind

Trick Flow offers new “Double-Hump” DHC 175 head castings in aluminum for the small-block Chevy. Talk about having it all? Born out of an impulsive idea from Trick Flow’s Mike Downs, he envisioned re-creating the ultimate small-block Chevy factory iron head in aluminum. Mike said they started reworking an existing head then decided to begin with a new casting in an effort to make it an even better head in A356-T61 aluminum.

Retail is less than $800 per head, which is less than it would cost you to buy and refurbish an existing set of iron Double-Humps. What’s more, you get a better head in the process with ductile iron valve seats, new stainless steel valves, better flow, and petite 60cc chambers. Less weight. More compression. Greater heat transfer. A better head.

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Trick Flow announces new “Double-Hump” DHC 175 head castings in A356-T61 aluminum for the small-block Chevy. The legendary “Double-Hump” iron head has been reborn at Trick Flow with some nice refinements that make it a better head than those dated factory castings.

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Keeping with the original vintage casting, these heads are available with or without accessory bolt holes. Inside, you get 60cc CNC-profiled combustion chambers with blended bowl machining under the valves and small cross-section intake runners to promote low-rpm torque increases and boost high-rpm horsepower.

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Additional Sources

Treutelaar Equipment Sales (Balancing)
805.218.1375

Chris Brintnell (Head Porting)
661.309.3703

Photography by Jim Smart, Summit Racing Equipment

Sources

ARP (Automotive Racing Products)
Ventura , CA 93003
800-826-3045
www.arp-bolts.com
Trick Flow Specialties
Tallmadge, OH 44278
888-841-6556
www.trickflow.com
Summit Racing
800-230-3030
www.summitracing.com
JGM Performance Engineering
Valencia, CA 91355
661-257-0101
JGM Performance Engineering
PerTronix Performance Products
San Dimas, CA 91773
909-547-9058
pertronix.com
Holley
Bowling Green, KY 42101
866-388-5120
www.Holley.com

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