Jim Smart
June 13, 2014

The true origins of Ford’s oddball 351 Cleveland 335-series engine family may never be completely known. Suffice it to say this was an engine born for racing that never realized its true potential as a factory high-performance engine. What makes the 351C an oddball is how out of synch it is with the rest of the vintage Ford V-8 engine bloodline. It was produced for just four years in the United States though there were the tall-deck 400 and de-stroked 351M through 1982. Ford Australia never lost its love of the 351C where production continued down there well into the 1980s before the Aussies concluded the 351C was too much of a good thing.

JGM Performance Engineering tipped us off about a 351C it was building in the suburban Los Angeles community of Valencia in conjunction with a CarTech Books project with author George Reid. Their Cleveland was going to make unheard power thanks to an Eagle stroker kit that would bring displacement to 408 ci and the all-new Trick Flow Specialties CNC225 cylinder heads and single-plane induction topped by Holley. Jim Grubbs and Jeff Latimer of JGM were confident this engine would make at least 650 horsepower. They never expected it to make more than 700. What’s more, they’re planning a return trip to the JGM dyno for a shot at 800 horsepower with a few in-house improvements Jim has up his sleeve.

JGM Performance Engineering didn’t make this much power with an aftermarket block or custom made speed parts. It did it with off-the-shelf parts from Summit Racing Equipment, Eagle Specialty Products, Trick Flow Specialties, Jesel, Holley, and Comp Cams. This is a four-bolt main 351C D2AE-CA block Jim had put away for safe keeping years back. He hauled it out for book author George Reid and suggested they build a monster Cleveland. You get real horsepower and torque from displacement and stroke. You also get it from compression and good cylinder head flow. This is where Trick Flow’s expertise shines handing us the unexpected horsepower bonus.

The Valvetrain

Because we are aiming for 7,500 rpm, everything inside must be ready to march with lockstep precision when the heat gets hot. We want valves slapping their seats in just the right synch with piston timing events, which means we need to fill the cylinder bores with the densest charge possible before ignition takes place and consumes the mix. This is why JGM went to Comp Cams for its PN 32-000-9 custom grind mechanical roller camshaft, thick-wall one-piece Comp pushrods, and Jesel Pro Series shaft-mounted precision 1.650 rocker arms. Jim Grubbs did a lot of computer time coming up with the Comp custom grind, which is available to anyone who wants aggressive 351C performance.

Cam Specs
Manufacturer Comp Cams
Custom Grind FC 3207 /1660 SR108.0
Lobe Separation 108 Degrees
Lobe Lift 0.441/0.420-inch Intake/Exhaust
Duration at 0.050-inch 260/275 Degrees Intake/Exhaust
Gross Valve Lift 0.762/0.726-inch Intake/Exhaust
Duration at 0.020-inch 296/307 Degrees Intake/Exhaust
Valve Timing at 0.050-inch
Intake Open 22 BTDC
Intake Close 58 ABDC
Exhaust Open 65 BBDC
Exhaust Close 29 ATDC
Valve Adjustment
Intake 0.020-inch
Exhaust 0.026-inch

Rocker Arms

JGM wasn’t about to leave anything to chance in the Cleveland’s valvetrain system, which is why it went with race-ready Jesel shaft-mounted Pro Series rocker arms for spot on valvetrain stability. Jesel achieves this kind of excellence with its own 7000 Series aluminum alloy, which yields a super lightweight rocker with unprecedented strength. Our Jesel rocker arm assemblies aren’t just off the shelf, but ordered and manufactured to JGM’s specifications on Trick Flow heads. Surfaces are shotpeened for strength, which also relieves stresses at the same time. Our Jesels are also needle bearing supported for friction reduction and stability. ARP shaft bolts are engineered for spring pressures exceeding 800 pounds.

Seal It Right

Although a lot of us struggle with oil leaks in fresh engines, it never has to be this way if you properly prepare all contact surfaces going in. Engines leak oil and coolant when we fail to prep. With all sealing surfaces, you must perfect the surface. All contact surfaces must be hospital clean, flat as the American prairie, and free from scoring.

One mistake we see is a lot of excessive use of gasket sealer. Remember, gaskets are there to seal all by themselves. The only reason you should ever use sealer is for gasket security and small imperfections. That means you need only the gasket and, at the most, a very thin layer of Permatex’s The Right Stuff available from Summit Racing Equipment.

Two-piece rear main seals need a thin film of The Right Stuff around the perimeter, then, seat the seal with the lip pointed toward the crankshaft. Apply a modest amount of The Right Stuff to the seal tips and stagger the gaps away from main cap parting lines for best results. Use The Right Stuff at gasket ends only where pan gaskets meet end gaskets. JGM is using a deep-sump Canton race pan from Mustangs Plus.

1. JGM Performance Engineering is using a stock standard bore D2AE-CA four-bolt main Cleveland block for this exercise massaging it in every way possible to ensure success. To keep the bottom end from peppering the concrete floor of a dyno cell, JGM gave the block a good line honing and installed ARP studs.

2. Block has been prepped and fitted with ARP studs and Speed Pro tri-metal H-series bearings that live happily with a steel crank and a whole lot of stroke. Cam bearings have been pressed in place and we’re ready for methodical assembly.

3. Eagle Specialty Products has provided JGM with a complete 408ci stroker kit including an ESP treated 4340 steel 4.000-inch stroke crank, 6.000-inch H-beam rods, and Mahle positive dish forged and coated pistons sized to achieve 13.0:1 compression. Our Eagle steel crank has been ESP Armor treated for extraordinary strength. ESP isn’t a coating, but instead a treatment that hardens and protects the surface. It also perfects the surface with a mirror surface designed to minimize any risk of scoring.

4. Eagle’s 4340 steel crank is checked for endplay before main caps are installed and torqued. Endplay for an engine like this needs to smack in the middle of 0.004- and 0.010-inch. As main caps are installed, endplay needs to be checked again.

5. ARP studs have been threaded deep, but not seated. You do not want to seat them, but instead get them within 1⁄8- to ¼-inch of the bottom of the hole. With caps properly seated and alignment, ARP locknuts are torqued in one-third values from the center outward, then, torqued again and marked as torqued with a felt tip.

6. During mock-up phase, JGM found the pistons needed to be fly cut to clear the CNC 225’s larger than anticipated 2.08-inch intake valves.

7. Though a lot of builders like to roll compression rings on, Jim Grubbs prefers to use a ring expander and strongly suggests its use to prevent ring distortion. Did you know only the top ring is considered a compression ring? The second ring is an oil ring. Bottom rings are considered oil wiper rings that thrust oil back into the crankcase.

8. With the short-block assembled, piston deck height is checked. These Mahle forged and thermal coated units are a pinch out of the hole at 0.002-inch on average. The Cometic MLS (multilayer steel) head gaskets will provide necessary clearance.

9. Because JGM is running 13.0:1 compression, it has been decided to stud the block with ARP fasteners for added security. Never bottom the studs out. Leave about 1⁄8- to ¼-inch of space beneath the stud.

10. An adjustable timing gear allows you to custom tune valve timing based on what you want from the engine. Advance valve timing and you gain low-end torque. Retard valve timing and you gain high-end horsepower. JGM decided to keep this cam straight up at zero.

11. Cometic multilayer steel (MLS) head gaskets are JGM’s choice from Summit Racing Equipment. These gaskets offer extraordinary sealing capability.