Regardless if you're a Chevy, Ford, or Mopar fan, almost anyone can acknowledge that the Ford 5.0-liter Coyote packs a lot of punch with its 302 cubic inches. Add a small amount of boost and you're guaranteed to make over 600 horsepower at the wheels. While being gigantic in size, the cylinder heads flow extremely well and the Ti-VCT-controlled quad cams optimize the power band. All the way down to the short-block, the six-bolt main caps and factory 4340 forged crank are virtually indestructible. But every engine has its weak point, right?
The piston and rod combination in the Coyote isn't ideal and the oil pump gears become an issue when turning a lot of RPM, launching hard at the track, or running a supercharger. Once you start crossing the 1,000 horsepower mark, the next major issue is the block. The factory thin-wall, gray-iron sleeves are only about .062-inches thick. Combine that with a minimal amount of material separating the bores from the water jackets. The result? The piston begins to create stress on the thrust side of the bore, cracking through the thin sleeve and into the water jacket.
A stopgap was to weld in a support brace on the thrust side and deck the block, then Ford Performance came out with the Sportsman (and now the GT350) block that shored up the water jackets during the casting stage. This helps, but the factory sleeves still have their limitations. If you want to make north of 1,000 horsepower to the wheels reliably, thicker and much stronger ductile iron sleeves, like ones sold by Darton International, are a must.
Steve Demirjian owns Race Engine Development and develops all the new engine applications for Darton. He's been sleeving blocks since the '70s, working with Darton since 2000, and has sleeved just about every conceivable block out there he even builds custom sleeves for one-off applications.
Rolling Up Your Sleeves
Darton's Coyote sleeves are .098-inches thick at stock bore size and the ductile iron material is more than three times stronger than the stock gray iron sleeve. These dry sleeves are very similar to the sleeves found in most Top Fuel engines that produce over 10,000 horsepower.
According to Darton, Ductile iron is a cast, ferrous alloy that contains carbon in excess of 1.5 percent. It also contains silicon, usually from 1.0 to 4.0 percent, and manganese up to 1.0 percent. To obtain the needed properties, both phosphorus and sulfur contents must be low. Phosphorus content is usually less than 0.1 percent, preferably less than 0.05 percent. Sulfur content must be less than 0.02 percent. One more element, magnesium, is always present in ductile irons. Its concentration normally ranges from 0.02 to 0.08 percent.
Darton's claim to fame is a minimum tensile strength over 100,000 psi and that the sleeve's surface is more abrasion resistant than any of their competitors. Also important is the specific honing techniques that Darton provides on their website that ensures the best possible ring seal.
There's no easy way to get the old sleeves out than to just cut them out. To find the true bore center, Demirjian uses a Blake Co-Ax indicator and manually adjusts the axis to get the bore centerline for the CNC work offset table. The new bore is corrected to be precisely over the crankshaft axis.
The first pass is a clearance bore up to 3.710-inches at 5.800-inches length. This reduces the possibility of the stones hitting the bottom of the block during the final hone with the new sleeves. Demirjian douses the cutter with coolant to keep the heat and expansion down to a minimum. If the heat isn't controlled, the bore could take a reverse bell mouth shape and not end up straight. The block would also expand length wise during machining making it impossible to hold tolerance, which Demirjian keeps to a half-thou bore center-to-center of the 3.937-inch/100 mm factory spec.
At 3.750 the sleeves are gone and we are getting into the aluminum. Here you can see how thin the un-bored portion of the Coyote sleeve is.
It's critical to check the machine's work with a bore gauge after each machining operation. Demirjian checks the top and bottom of the bore to make sure the bores are machining straight.
Demirjian checks all the sleeves for outside diameter and length using a micrometer and caliper.
A 3.826- by 5.295-inch length bore is the final number. The sleeves have an outer diameter of 3.825, allowing for a clearance of a mere one thousandth of an inch.
A .200-inch deep counter bore is milled for the flange at the top of the bores to hold the sleeves in place. The stock Coyote sleeves seat at the bottom and are flangeless.
The finished bores on one bank are ready to be cleaned and sleeved. Now it's time to do the other four cylinders.
Here you can see the difference between the clearance bore and the final 3.826 bore in terms of the amount of material removed from the block. Demirjian only takes out what he needs to keep the stiffness in the block as high as possible.
Loctite 515 (purple) on the bottom of the bores keeps oil from coming up while Loctite 620 (green) is the sleeve retainer that holds everything in place and acts as a heat transfer agent between the bore and block. Aluminum and iron expand at different rates and both of Loctite's sealants provide up to a 40 thousandths buffer between the two.
Per Demirjian, the sleeves should be installed at room temperature and not require any heat. They slid perfectly down and with a little persuasion from a hammer, seated fully into the block.
It's extremely important to clamp the sleeves firmly in place for about an hour while the Loctite cures. Failure to do so can result in the sleeves dropping when the engine is started resulting in a blown head gasket.
Any time you cast, forge, cut, bore, or weld a piece of metal, stress is formed in the part. Demirjian uses his Formula 62 Vibratory Stress Relief machine to reduce this residual stress in engine block castings after the sleeve are installed. This process eliminates warpage of the block when put into service. The larger the casting, the greater the warpage and that can cause out-of-round cylinder bores as well as crank and cam bores to move around and no longer being in line.
Demirjian decks the block flat. On high-horsepower builds (1,500+ V8 applications) he will step deck the block where the sleeves will provide additional sealing power and act like a large o-ring.
The final step is to bore the sleeves. Demirjian stops 20 thousandths under the final bore size unless specified by the shop conducting the assembly. This gives enough left-over material to perform the honing.
Race Engine Development
760 630 0450