Engine Tips - Biggest Engine-Building Mistakes

Marvin "Dr. McAfee" of MCE... 

   

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Marvin "Dr. McAfee" of MCE Engines with a new patient.

One of the most exhausting aspects of 25 years in automotive journalism has been watching some of the things people do during engine builds that lead to failure. There are lots of engine-building myths and urban legends that are just plain, old-fashioned wrong. And, people get just plain, old-fashioned careless, forgetting things that are crucial to a solid, dependable engine build.

Despite all the shoptalk we've heard through the years, there are many misconceptions about engine building. Enthusiasts make them, and so do magazines. We've made a few of them ourselves through the years-incorrect torque values, carb-selection misinformation, incorrect cam selection, seals installed backwards, flopped head gaskets (it's getting awful hot in here), port jobs that led to water jacket penetration, bad balance jobs, snapped poly locks from overtorquing, dropped valves (ouch!), valve-to-piston contact (ouch!), slightly out-of-the-hole piston deck height, and more.

Engine failure happens when we don't do the job properly, but sometimes it happens through no fault of our own-we become victims of material failure. This is why we hold our breath anytime we fire an engine for the first time.

Our goal here is to help minimize the risk of engine failure with time-proven tips from some of the most seasoned engine builders in Southern California, including Marvin McAfee and Benton Jackson of MCE Engines, John DaLuz of JMC Motorsports, Mark Jeffrey of Trans Am Racing, and Jim Grubbs of JGM (Jim Grubbs Motorsports).

Carburetor Sizing

We get this one wrong more times than we get it right because we tend to believe bigger is better, and that it means more power. But that's not always the case; sometimes it means less power. Carburetion that's too small will stifle an engine and won't allow high revs, where real horsepower is made. But a smaller carburetor can actually improve torque off-idle and at midrange where it's needed on the street. Low-end torque is what gets you away from a traffic light faster than the other guy. Horsepower is what keeps you roaring along at high rpm once you get going, and it's what happens at wide-open throttle when you're moving at speed. For exceptional street performance, you want a nice balance of low- to midrange torque and high-rpm horsepower, dictated by vehicle weight.

Overbuilding

Too many people build way more engine than necessary. This means you're spending more money and time than you need to. Rule of thumb-build for the kind of driving your engine will be exposed to most. If the car is your daily driver, be modest in your approach, with a good roller cam that will give you excellent low- to midrange torque, with less emphasis on horsepower. There's nothing wrong with a flat-tappet camshaft if you can't afford a roller. Fit your engine with a dual-plane intake manifold and conservatively sized carburetor. If you're going to do some Saturday night drag racing or weekend road racing, step up the power a bit with more cam duration, modification of lobe centers, more lift, and a pinch more carburetor. In most cases, use of single-plane manifolds for street use is not a good choice because they're designed for high-rpm horsepower, not good low-end street torque. Be honest with yourself during engine planning. How much engine do you really need?

MCE Engines Quick Tip:

Want a hot street machine? A good starting point is a power-to-weight ratio of 10:1-1 hp for every 10 pounds of vehicle weight.

Cylinder Head Selection

Again, bigger isn't always better, especially for street use. Large-port heads, like Edelbrock Victor Jrs. or Air Flow Research 225s, don't always make sense for street use unless you're building one heck of a stroker. If displacement is modest, such as 289 or 302ci, and you're building for the daily commute and occasional weekend fun, more conservative castings such as the Edelbrock Performer or AFR 185 are adequate. Lower-displacement small-blocks like the 289 or 302 get by nicely with 1.94/1.60-inch valve sizing. Larger engines, like the 351W, will do fine with 1.94/1.60 or 2.02/1.60-inch valve sizing. Stroke any of these engines to 347, 408, or 427ci and Victor Jrs. and such make more sense. It is always important to remember displacement, regardless of what engine it is based on. You may have a 302 or 351W-based block. But, if you've stroked 347 or 427 ci into the 302 or 351W, you have big-block displacement. It's no longer small-block sizing you are dealing with. Head selection has to go accordingly.

Choosing The Wrong Cam

Proper cam selection has never been easy for novices. Much of the time, they choose too much cam or too little, or they choose a cam with screwball valve timing events that don't have much to do with lift or duration. They wonder why the darned thing doesn't come on strong at 5,000 rpm-or, it goes like gangbusters at five grand and is a snore down low coming onto the freeway.

Proper cam selection for your application takes a lot of homework and a bunch more study hall. How will a particular cam work with your intake manifold and head combination? What carburetor do you intend to use, or will it be fuel injected? What about headers and the exhaust system? Pipe sizing? Will cam profile provide sufficient intake-manifold vacuum at idle to run vacuum accessories such as power brakes, air conditioning, and more? How do you intend to drive the vehicle most of the time?

If you visit Comp Cams' Web site, you can get help selecting the right camshaft. Better yet, call Comp's tech line and chat with a pro about your Ford-what manifold, carburetor, and heads you intend to use-exhaust system, headers, and how you intend to drive your car most of the time. These folks can help because they are also performance enthusiasts. Aside from knowing cams inside and out, they can get you dialed into the right cam.

Another terrific source for information is Marvin McAfee at MCE Engines, known affectionately as "Dr. McAfee" for his keen ability to dial in just the right combination of parts to achieve spot-on results.

Gasket Selection

Gasket selection used to be simple because there weren't that many variations. Today, it's complex because there are so many types out there. Our advice here is simple-spend the money on better gaskets and save time (and money) in the long run. Buy the best gaskets you can get your hands on, such as Fel-Pro Print-O-Seal head and intake manifold gaskets. Invest in steel-reinforced urethane oil pan and valve-cover gaskets for exceptional sealing. They will cost more, but they're worth every penny invested for what they keep off your garage floor and driveway. What's more, you won't have to do the job over again.

Gasket Installation

We don't always treat today's high-tech gaskets the way they should be treated. We still throw all kinds of sealers and coatings on gaskets that don't call for anything outside of simple gasket installation and proper torque. For example, Fel-Pro Print-O-Seal gaskets don't require sealer-just a clean installation and recommended torque. Yet, too many of us apply silicone sealer just for extra measure. Don't do that. These gaskets already have help from the factory. One exception is intake-manifold-gasket cooling passages. If they are pitted at gasket contact surfaces, try a thin bead of high-temp RTV silicone sealer around cooling passages before gasket installation.

Cork gaskets require little sealer of any kind-just a super-thin film to close any gaps and maintain gasket positioning. If you torque valve covers, oil pans, and other engine components to the manufacturer's specified torque, you won't have to worry about leakage. Overtorque a valve cover or oil pan and you can count on leakage because it causes warpage, imperfections, and leakage.

Newer steel-reinforced urethane gaskets get the same treatment as cork and rubber gaskets except for the sealer part. Do not put sealer on these gaskets. Torque them to manufacturer's specifications.

Intake Manifold Selection

This has become cliche because we see it so often. Readers complain of no low- to midrange torque, and doggish performance coming out of a traffic light or onto the interstate. When we ask about their induction choice, we hear "Edelbrock Torker" or "Weiand X-terminator"-which clears up the mystery immediately. These are terrific race-only, high-rpm, single-plane manifolds. Single-plane manifolds do their best work when you're huffing a lot of air through them.

Proper manifold selection is simple. For the street, use a dual-plane manifold; for drag racing or road racing, use the single-plane. Why? Because each type of driving mandates a different kind of induction setup. Depending on the type of racing you intend to do, you may need a dual-plane if lots of low-end torque is needed coming out of a turn. You will just need larger runners like we find on the Edelbrock Performer RPM, Weiand Stealth, and even some of the older high-rise manifolds like the Edelbrock F4B or Buddy Bar Cobra manifolds.

Dual-plane intake manifolds have long intake runners, which help low- and midrange torque. Long runners contribute to increased air velocity at lower rpm, which gives torque down low. Making those runners larger helps velocity and volume at higher rpm.

Single-plane manifolds have shorter runners and a straight shot into the intake ports. This works best at high rpm because that's where we get velocity through these shorter runners. We have to spin the engine high to get air speed (velocity) through the ports.

Proper manifold selection is also a matter of choosing the right single- or dual-plane manifold because not all of them yield the same performance. Runner and plenum design directly affect performance on the street and on the track. Study runner and plenum design, port sizing, and port-alignment issues before selecting an intake manifold. Even though manifolds may look similar from one manufacturer to another, there are finite differences that make a difference in performance.

Block Overbore

In our quest for displacement, sometimes we take our blocks too far. Each engine family has its limits when it comes to bore sizing. All factory small-block Ford blocks (221, 260, 289, 302, 351W) should be bored no further than 0.040 inch over the standard 4.000-inch bore. If you are going racing, this maximum should be no more than 0.030 inch oversize. Although some builders take them to 0.060 inch oversize, it is foolish. Marvin McAfee tells us a 0.060-inch overbore is courting disaster. FE big-blocks can go to 0.060 inch oversize because they aren't thin-wall castings like the 289/302/351W and Cleveland small-blocks. For those of you with 385-series big-blocks, going to 0.060 inch oversize is risky because these are also thin-wall castings. At the very least, sonic-check your 429 or 460 before considering a 0.060-inch overbore. We stress this due to core-shift issues.

When you overbore, keep compression ratio in mind. Whenever chamber size and piston-deck height remain the same, overboring will drive compression higher because you are squeezing more volume into the same space. Pushing an overbore to the limits of a block's envelope is risky business because you risk cylinder-wall failure. Aftermarket blocks have their own overbore maximum measurement, too, so be sure to not exceed that if using an aftermarket block.