Vinnie Kung
March 1, 2001
Photos By: MM&FF Archives

When stroker engine kits first came out onto the scene, they were considered to be reserved only for the big-buck racers. The kits were expensive, as very few machinists were capable of producing them, and the labor involved appeared intense. As a result, stroker kits were unpopular compared to major bolt-ons such as superchargers and nitrous.

However, as aftermarket companies began to offer stroker kits at more affordable prices, the idea of tossing in a big-armed crankshaft seemed more feasible. No longer were stroker kits considered a luxury. Instead, they became so mainstream that most street enthusiasts today are out there running them in addition to their favorite power adder.

But with the desire to add cubic inches comes the need to address other issues. As the displacement increases, the engine moves more air, fuel and exhaust like never before, and does so at lower engine speeds. It also has more aggressive torque and horsepower characteristics. Therefore, it is imperative that you pay attention to the details to make sure that your next stroker installation is taken to the fullest. After all, what good would the addition of cubes be if its power-making potential was lost due to inadequate support systems?

When you purchase a stroker kit, make sure you ask the merchant or engine machine shop what the rotating assembly is balanced to. There is usually one of three responses you'll hear. Most 315/331/347 stroker kits for the 302 reuse your existing 50-ounce imbalance flywheel/flexplate and corresponding harmonic damper. The other popular OEM Ford imbalance is 28 ounces and is often found on most 351-based stroker kits. The 28 ounce imbalance is the better of the two because it requires less offset weight to be placed on the far ends of the crankshaft. Generally, the heavier the weight of imbalance, the more weight the crankshaft has to swing around to spin smoothly.

The last type of rotating imbalance, and by far, the most desirable, is called zero balanced. That means all of the weight that needs to be removed or added to balance the rotating crankshaft is located on the crankshaft itself. It not only makes for a stronger crank, but it allows for high-rpm operation. Unfortunately, it comes at a high price, typically adding $500-$1000 to modify an existing crank, or up to $3,000 for a billet crank that is designed from the ground up as zero-balanced. Whichever setup you use, make sure you acquire the correct flywheel and damper. Another thing to look for is proper tooth count on the flywheel or flexplate. It will be either 157 or 164 teeth.

The stock 5.0 intake manifold is much better than most think. Although it can work well on mild 302s, once the cubes are upped to 315 and above, the need for a larger intake manifold is required. The term "larger" is mainly in reference to the crossectional area of the intake runners, and the manifold's plenum volume. Both play major roles in how well the heads and bores accept the intake air charge and will dictate whether your engine will be a dud or a stud.

Generally, with a modest bump in displacement, you'd want to jump to a larger intake almost immediately. There are a lot out there to choose from, but don't let your wallet dictate what goes on top. The most important thing to have is a matched combination. If you want to build a good street motor, consider one of the long-runner intakes. The most popular one out there is ,without a doubt, the Cobra upper and lower. Closely based on the GT-40 intake setup, it offers a great compromise in price, adequate runner crossectional area, and plenum volume. This has been the intake of choice for those who keep their engine speeds at or around 5500 rpm with up to 347 cubic inches. Other excellent long-runner manifolds include the Holley SysteMax II, the TFS Track Heat, and the Edelbrock Performer and Performer RPM manifolds. All work well, and are priced relatively close to each other. For the ultimate in streetable torque and great high-end horsepower, get any of these intakes Extrude-Hone ported or hand ported and polished for best results.

For you high-rpm 331 or 347 guys or those of you with 351-408 cubic inches, you'd better get some serious manifolds up on top of that mill. Some of the EFI favorites include the Edelbrock Victor 5.0 intake, the Trick Flow Specialties "R" series upper and lower for 8.2-deck motors and the TFS 351 EFI for the 9.5-deck blocks. Box-style intakes also work quite well with strokers. Remember that your engine now requires a lot more airflow than a motor that is smaller. Consequently, your engine at 3500 rpm is probably drawing the same amount of air that your old, smaller motor used to at 6000 rpm. Once your big-rig mill wants to rev, better make sure you've got plenty of runner and plenum to feed it. It you don't, you'll wind up with a motor that falls right on its face thousands of rpm below its potential peak horsepower.

Carbureted setups are a bit more intricate. Low-rise dual-plane manifolds are pretty much done at 315 cubic inches. It is practically a necessity to run a high-rise dual-plane manifold on any stroker motor with a good cam. One intake manifold that we've seen work great on the street is Edelbrock's Performer RPM. There are others out there that are similar, and work just as well. High-rise dual planes fill the cylinders nicely at lower engine speeds, and offer great top-end charge.

When it comes to single-plane manifolds, the Ford Windsor is a difficult engine to feed, particularly the low-deck (8.2-inch) 289s and 302s. This is because the symmetrical intake ports require manifold runners to be of unequal length. The middle four cylinders suffer from very short runner lengths, and therefore, make cylinder-to-cylinder feeding more difficult, particularly with cylinders number 5 and 6 feeding off each other as they fire sequentially. It is very important to ensure a good distribution of fuel and air to the heads, but with varying runner lengths, you'll have to make some sacrifices (but don't worry, power isn't usually the biggest).

Most carbureted tuners, from personal experience, prefer to put a larger carb than what is considered normal on the small-block Fords. A perennial favorite is the Holley Double Pumper. Contrary to what you've read in magazines in the past, this carb works great on everything from high-winding 306s to stout 408s, and even on automatic applications. If you want to make good power, and don't want your street/strip 331-347 to be soggy, start with a 750. An 800 or 850 would be the natural leap upward, should you want to swing the tach into the far end of its dial or make your 408 happy on the street. Remember that booster signal is what makes a carburetor work.

If you've got a healthy cam with a good cylinder head and intake combination, you'll have some great under-carb low pressure that will make for a crisp and responsive setup. A good place to start with jetting on a 347 with heads and cam is 70s in the front and 80s in the back (stock 750 jets). Everyone talks about fuel pressure, but the most important thing to look for is volume and pressure drop. Maintain at least 6 psig in the lines and use at least a 3/8-inch or -6 AN hose for a feed. The most efficient setup uses a multi-port regulator with a return line.

Because a stroker engine's volumetric efficiency is unlike that of the smaller engine that it is replacing, it is important to tune an EFI system properly. Timing and fuel curves locked into your EEC-IV work great for a stock 302. But with a slew of new airflow and fuel consumption characteristics, it is important to tune your stroker motor accordingly. Of course, a mass-air conversion is necessary, as is a step up in injector size. Pro-M and C&L (Vortech) mass air meters work great on naturally-aspirated and forced-induction applications. Of course, it is necessary to have them calibrated to the injector that you will be using.

A set of 24 lb./hr. injectors is sufficient on 315s and 331s that are mild in nature. But to be safe, a set of 30 lb./hr. injectors with a matching mass air works better, and on most 347-377 naturally aspirated applications. An octet of 36 lb./hr. injectors will feed any hungry unassisted 408, and anything 347 or smaller that will use a small supercharger. Once you start getting into hairy combinations such as Thumpers with 427 strokers, you'd better look into stand-alone fuel management with 160 lb./hr. injectors. But for most of use street guys, the affordable and readily available line of fuel injectors from Ford Racing will suffice.

Believe it or not, the stock EEC-IV ignition system is strong and accurate enough to handle just about any Windsor-based stroker motor. A good set of wires combined with a quality coil can zap just about any air/fuel combination present in a small-block Ford. Of course, as with non-stroker applications, you'll want to look at some of the capacitive-discharge ignition systems for use with forced induction or nitrous. MSD, Crane, and Holley Annihilator all offer great boxes that will augment the firepower of your EEC-IV. Other ignition upgrades, such as the Davis Ignition Dyna-Mod will also work. Again, an ignition upgrade is nice, but not entirely necessary on naturally aspirated stroker applications.

Here's one of the most controversial engine-displacement-based conversations out there. As you've probably heard over the years, keeping the primary diameter in relation with the engine's displacement and intended usage is important. Although true to a certain extent, most of this folklore never took into consideration the Ford Windsor's need for a larger-than-usual exhaust system, or how well designed the aftermarket systems for the Mustang are.

In just about every instance we've seen or personally experienced, we find 1-5/8 shorty headers to work great. Although it cannot match the long-tube header's inherent ability to evacuate the cylinders with effective scavenging, the shorties perform admirably, fit easil, and are a lot simpler to deal with, especially if you enjoy R&R-ing your engine on a regular basis.

Once you've gone over the 6-liter area (around 383 cubic inches), consider a 1-5/8 long-tube header mandatory, and a 1-7/8 primary header as a very tight option. This is, of course, providing that you're building a healthy street/strip motor, and not some low-rpm torque monster for your tow vehicle. Another advantage of a long-tube header is that it allows you to maintain a consistent exhaust pipe diameter from the front of the car to the rear. This is because the ball flange that is used on most shorties necks down to around 2-1/4 inches, at most.

Muffler and tubing size should be at least 2.5 inches from front to back. Think about it. If you are going to continue building this car up, and are going to keep adding more hi-po parts to it, you might as well put in the best 2.5-inch exhaust system you can afford and leave it in there for the remainder of your car's life. There is no point in putting a smaller 2.25-inch system when you know that within a year, you're going to need 2.5-inch pipes. That would simply be a waste of money. Three-inch exhaust systems are cool but unnecessary for all but the most radical applications (435 inches with a blower). If you're a street guy and want to have fun with a simple stroker (like a 347 with a Vortech S-trim), 2.5-inch pipes will be more than you'll ever need. Besides, the 2.5-inch pipes fit under the car easier

Keeping Your Cool
Technically, a stroker engine shouldn't need any major cooling upgrades. If your existing radiator, water pump and hoses are in good shape, then you're ahead of the game and can spend some more money on making more horsepower. But if the car ran hot with a stock 302 in it, look into performing some cooling system mods.

Heat from an engine is directly related to the amount of friction and combustion energy it generates. An engine with a longer stroke will create more heat obviously because its pistons are traveling longer distances up and down the bores. This engine will also make more power (we hope at least) and that results in more thermal energy to press down on the piston, to heat the block and cylinder head with.

At a minimum, since the engine is out, replace the water pump with a new one, check the hoses and replace as necessary, toss in a new thermostat and pour in some fresh coolant. If you have a few hundred bucks lying around, step up to a high-capacity radiator that has more than the two cores.

If you still have extra spending money hiding in your cookie jar, go for a top-notch aluminum radiator like a Be Cool or Fluidyne unit. We've had some great result with these units in all sorts of supercharged, stroked, street-driven and even road-raced applications, and highly recommend them.

We love stroker kits and highly encourage that you build one sometime in your useful life. Although there are many things to take into consideration, the practicality and reliability of a stroked mill can bring ear-to-ear smiles. Again, we'd like to emphasize the importance of properly accessorizing your stroker motor.

What you'd want is to take full advantage of all the additional cubic inches in order to make more power. After all, isn't that the point of all this hard work?