Grant, via CarCraft.com: I recall an early 2000s program warning me of excessive piston speed in my 427 Ford FE, which has nearly the same stroke as a Chevy 396/427. Nowadays, stroker kits are almost routine, with strokes of 4.25 to 4.5 inches being common. What gives with this program's warning? Fear of the unknown, or was it some early version?
Steve Magnante: Grant, your Ford 427 is a rare bird! Today when we speak of Ford 427s, most folks envision stealthy, poked-and-stroked Windsor small-blocks in Fox Mustangs wearing 5.0 fender badges. But in the mid-1960s, the FE 427 big-block was Ford's NASCAR wonder weapon. Thanks to the 7.0L displacement limit imposed by NASCAR in 1962, its dimensions are 4.232-inch bore and 3.784-inch stroke. For comparison, the bore-and-stroke measurements of the 396 and 427 big-block Chevy are 4.09×3.76- and 4.251×3.76-inch, respectively.
As you note, the internal measurements of the Ford and Chevy 427s are quite closely matched. About piston speed, when we remember that each piston moves from a complete stop to some maximum velocity and then to a complete stop again twice for every rotation of the crank, it becomes obvious there are extreme forces at work in every reciprocating engine.
Ignoring the factors associated with combustion pressure, exhaust gas purge cushioning, and other elements involved in the thermal side of things, it's obvious the rapid acceleration and deceleration of each piston stresses the moving parts. Clearly, when parts are sized according to the job at hand, everything works out. Back in WWI, the first high-performance, internal-combustion engines were created for use in military aircraft. Sure, auto racers were seeking added efficiency before that war, but with the industrial might of the warring nations fueling the charge, development work on gasoline-fueled engines for fighter planes, zeppelins, and other airborne warbirds hit overdrive on an unprecedented scale.
Since then, enough improvement and research work has gone into automotive engine development that virtually every existing scenario has a suitable set of available stock or aftermarket parts to get the job done-with a reserve of durability built in. Frankly, there's not much room left for backyard tinkerers to reinvent the wheel, so to speak. Still, refining existing engines in search of extra power, economy, and efficiency is what car crafting is all about.
I'm guessing your simulated engine-building program was being extra cautious in warning you a stock Ford 427 was in danger of excessive piston speed, while the similar Chevy 427 wasn't. Perhaps it's designers/programmers were under some misguided impression Ford pistons were heavier than their Chevy counterparts. You know the deal with computer programming: garbage in equals garbage out.
Then again, did you enter an exaggerated crankshaft speed prediction? That could shift the outcome and trigger the program's theoretical piston-speed warning. Though Ford openly advertised a “7,000 rpm kit” in the 1960s, Ford's public spokesperson, Ak Miller, frequently stated that 6,400 rpm was the safe redline with the stock forged crank, rods, and pistons. Did you get carried away and claim an 8,000-rpm redline? That might do it.
To calculate approximate maximum piston speed (without regard for rod angularity or its center-to-center length), we first have to calculate Mean Piston Speed (in feet traveled per minute) using the formula: stroke multiplied by rpm and divided by 6. For your stock-stroke Ford FE 427 (3.784-inch), you haven't described modifications, so I'll assume your mill is close to stock (low-riser heads, 2.08/1.64-inch valves, 11.1:1 compression, 0.524-inch lift/324-degree duration factory solid cam, dual Holleys, and 425 hp) and you're not exceeding Miller's realistic suggestion of 6,400 rpm.
So 3.784 x 6,400 rpm = 24,217.6. Dividing the outcome by 6 tells us your pistons travel at an average speed of 4,036 feet per minute. OK, we still need to calculate your 427 FE's maximum piston speed, which goes like this: stroke x pi (3.14) divided by 12 x rpm. So 3.784 x 3.14 = 11.88; 11.88 divided by 12 = 0.99. 0.99 x 6,400 = 6,336 feet per minute. That's like 70 mph. In a stock-dimension Chevy 427, the same formulas and 6,400-rpm redline (totally realistic with a solid-cam) yield 4,011 average feet per minute and a maximum piston speed of 6,297 feet per minute. The Ford's slightly higher velocity numbers-25.34 and 39.25 feet per minute-are of minimal consequence.
The only wild card here that might trigger the computer program to issue warnings would be piston, pin, and rod weight. In an engine like the Chevy 348/409 or any Hemi-type design (Mopar, Ford 427 SOHC, Boss 429), much heavier pistons are needed to fill the chambers (hemi) or create the actual chamber volume (348/409). When heavier objects (like pistons) are asked to accelerate, stop, change direction, accelerate, and stop again, added weight becomes crucial. If the Ford 427 FE was like the Chevy 348/409-with super-thick, extra-heavy piston crowns-the computer program's piston-speed warning would make sense, but if anything, your Ford FE has a slight advantage over the Chevy 427 big-block. That's due to its 76cc, wedge-type combustion chambers and light, flat-top pistons. By contrast, the big-block 396-427-454-502-572 Chevy's “porcupine” heads have staggered valve trajectories and smaller semi-hemispherical-shaped chambers. The required pistons must have raised domes to create the increased compression. This all adds weight, but it is minimal compared to a Chevy 348/409. Again, by comparison, Ford 427 pistons are pretty light.
I'm guessing the programmers of your virtual-performance calculator were somehow misguided regarding their warning, or they accidentally based their parameters on the Ford 427 SOHC hemi-type engine of 1965–1967. If that's the case, as stated previously, the SOHC's hemispherical 120cc combustion chambers were teamed with domed pistons that certainly weigh more than your wedge's flat tops. Go and recheck the program. Is there any reference to its Ford 427 being of the SOHC variety? Then again, Ford engineers were/are among the best. They made sure to fit the Cammer with hefty, wide beam rods to keep the pistons secure. They also validated the combination with thousands of hours of dyno time.
In closing, did ya know that in 1962 Ford was working on a 482-inch doomsday version of the FE engine? It was developed right before NASCAR announced the 7.0L limit for stockers. It would have been based on a 427-type block with a 0.050-inch overbore and a jump in stroke from 3.78 to 4.250 inches. Plugging this 8.0L monster's vitals into our piston-speed calculations tells us the slugs would have shuttled up and down at 4,533 fps on average and a maximum speed of 7,117 fps. No doubt, this monster would send your misguided engine predictor into cardiac arrest!
Cam-Spec Quarrel
Kevin Richards; via email: I've got a buddy who loves to argue about cam specs. He says it's wrong to fixate on lift and gives me grief when I say stuff like how I'm planning on installing a 0.540-inch-lift cam in my next engine. He's always trying to correct me and says duration is the proper thing to fixate on when talking cams. Who's right here?
Steve Magnante: I hear you, Kevin! I was brought up to describe camshafts by their rated lift values, with duration being a secondary concern-and still do. It probably goes back to 1987 and how I saved up to buy the then-new Mopar Performance “509 hydraulic” cam for a 440 I was building. It was the hot setup, and because the MP catalog repeatedly used the “509” phrase to describe the cam, I took it as being the standard way of expressing cam specs in general. I was young and impressionable.
Then I looked at aftermarket cam catalogs. Isky, for example, didn't fixate on lift numbers, but instead on degrees of duration. They even went (and still go) so far as marketing many cam lines with the duration factor as part of the product name in the catalog and on the packaging. Examples are Isky's “Supercam” and “Mega Hydraulic” cam lines wherein the first half of the product name consists of the advertised duration number, resulting in offerings like the 292-Mega Hydraulic (one of which I currently have in my 512ci “Rampage” altered-wheelbase 1963 Dodge Dart). I've also gotten into heated bench-race discussions over camshaft semantics and stick to my guns that the lift factor tells us much more about the state of the engine's preparation than duration can. As such, lift should be the first detail discussed when buying a cam. I certainly agree that duration (the length of time a valve is opened, measured in degrees of crankshaft rotation) is important, but it is easily misrepresented and misunderstood.
Since very little measurable airflow takes place at low lift, it isn't responsible-or fair to competing camshaft designs-to include this area in quoting the cam specifications. And since the lifter doesn't move the valve off its seat at all as the lifter slides (or rolls) through the clearance-ramp zone, the camshaft manufacturing community rightfully came up with a more accurate method of measuring duration. Starting around 20 years ago, this newer duration measurement method adopted an industry-standard “dead zone” located between the base circle of the camshaft and 0.050-inch tappet lift. This is at the core of why cam durations are given as “advertised” and “at 0.050-inch lift,” with the advertised spec always seeming more radical.
So remembering this discussion isn't about whether lift or duration makes more power (they must go hand in hand), let's discuss why I feel that lift is more significant and ought to be discussed first during bench racing and buying alike. Simply put, the higher the lobe lifts the valves off their seats, the greater the number of mechanical modifications will be required to keep pace. Adding duration doesn't have the same level of ripple effect on the rest of the engine. Hair-splitters will say that a load of duration can also collide valves and pistons-true, but it's still not as critical as added lift.
First up, many stock, muscle-car-era iron cylinder heads have tall, integrally cast, valve-stem guide bosses. In any situation where lift is increased beyond 0.450 inch, it's critical to check for retainer-to-stem boss clearance. If the mock up reveals contact, the bosses must be milled to reduce height or disaster awaits. To keep pace with the extended valve motion and inertia that goes with high-lift cams and elevated crankshaft speed, heavier valvesprings must be added to the mix. Often, a single spring just won't do, so double or even triple valvesprings must be used. Again, the outside diameter of the stock valve-guide bosses is often too large to accept the extra coils. Mopar iron heads are classic for this hassle, and nothing but a trip to the machine shop will remedy the problem.
The extra lift encourages breathing and, as a result, rpm. Here, the stock stamped-steel rocker arms found in most Detroit pushrod mills aren't up to the job and must be upgraded. In addition, a cam with added lift is much more likely to need piston notches than a cam with extra duration. Again, I feel that lift has the greater impact on the rest of the engine. This argument will never go away, and both sides have a point. But one thing we can all agree on is, the terms “three-quarter race” and “full race” have thankfully faded from the scene.
Cross-Bolt Conundrum
Steve Benoit, via email: I recently scored a 4.6L SOHC from a wrecked Town Car and want to perk it up with cams, intake, and maybe a stroker kit. I've heard there are several versions of the SOHC and each has a different way of mounting the cross-bolted main-bearing caps. Can you shed some light on the situation?
Steve Magnante: It's mind boggling to realize the Ford Modular V8 engine family has been with us for 25 years. That's a few more than the 1932–1953 flathead! It's also several years more than the Model T's 1909–1927 lifespan. Time flies when you're going fast. Builders of the SOHC need to remember they were produced by two factories-Romeo, Michigan, and Windsor, Ontario-and to your question, each has a unique way of setting the preload between the block skirt and main caps.
The Romeo caps are machined with threads that accept circular discs-called jack screws-through which the side bolts pass. It's a neat and simple way to ensure the correct main-cap tension. The factory spec calls for torqueing the Allen drive ends to 7 ft-lb. In the accompanying picture, the pen points to one of these jack screws. Next to it is an old-school Ford 427 FE-style cross bolt and spacer for comparison.
The other Mod motor plant was the Windsor, Ontario, Canada facility. For reasons unknown, Ford also blessed these blocks with cross-bolted main caps, but used a novel steel dowel to fill the gaps between the caps and the block skirts. These dowels are drilled so the side bolts can pass through them after they've been installed. Believe it or not, the pins are precision-machined and are hammered in place to deliver the required preload. It's an unusual layout, but it works and is no doubt cheaper to mass-produce than the many machine- and thread-cutting operations required on Romeo-sourced jack-screw blocks.
Generally speaking, it is easy to identify each block. Romeo blocks have easily viewed “R” letters cast into their forward ends (hidden behind the cam drivechain cover on an assembled engine) and/or cast into the oil pan rail near the cross bolts (easily seen on a complete engine). Likewise, Windsor blocks have a large “W” in these locations. There are hundreds of thousands of SOHC 4.6 engines in use (of both types). But remember, the main-cap fasteners are all one-time-use, torque-to-yield items. Never reuse them.
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