High-rpm engines demand quality...
High-rpm engines demand quality parts, which is why we spec'd this engine with a good steel Scat crank and rods and Mahle forged pistons.
While car crafters are more into horsepower than math equations, the one formula most performance enthusiasts are intimate with is: horsepower = torque x rpm 5,252.
Big engines rely on lots of displacement to make torque and horsepower, but with smaller engines, the approach is to rev it high. Push the torque higher in the rpm band, and you'll make more horsepower. As an example, 400 lb-ft at 4,000 rpm equates to 304 hp. But that same 400 lb-ft at 6,500 rpm is a smokin' 495 hp.
Among the little V-8 engines, the most popular has to be the 302ci small-block Ford. While the rest of the world is building ever-larger engines, the little Blue Oval pushrod 5.0L continues to surge in popularity. Lately, Car Craft has been playing around with different 302 Ford combinations, so this time we decided to punch up the displacement a little while still relying on rpm to deliver a big horsepower number. While 347ci strokers are OK, we decided to go with the shorter 3.25-inch arm and build a 331ci screamer.
Our goal was aggressive yet simple: build a normally aspirated pump-gas 331ci small-block Ford that could make 1.5 hp per cubic inch that wouldn't explode all over the place. You've probably already skipped down to the dyno test, so you know we came really close 500 with 496 hp at 7,400 rpm that is dead reliable.
CC contributor Tim Moore built this engine, and it's currently scheduled as the motorvation for his Dan Gurney Trans-Am-tribute '67 Cougar. Just the thought of spinnin' this small-block up to 7,500 rpm and bangin' Fourth gear coming off Turn 6 at Willow Springs sounds like a great way to spend a Saturday afternoon.
Building Blocks
The 331ci small-block Ford is a classic stroker package that combines an excellent bore and stroke combination that can withstand the kind of rpm abuse Moore had planned. The stock 302 Ford small-block combines a 4.00-inch bore with a 3.00-inch stroke. To get to 331 inches, Scat offers a forged steel crank with a slightly longer 3.25-inch stroke that matches nicely with a 4.030-inch bore.
Heads And Cam
The one place "bigger is better" works is where the goal is lots of horsepower at high engine speeds. Since Moore is aiming for engine speeds in excess of 7,000 rpm, he was less concerned with low-speed torque. That's why he decided on a set of Air Flow Research 205cc runner wedge heads for his 331 spinner. AFR offers four different intake-port-volume cylinder heads, from the high-velocity 165cc and 185cc heads to the larger 205 and top-billing Outlaw 225cc monsters. Moore decided to go with the 205cc Outlaw castings that AFR claims will flow more than 300 cfm above 0.550 inch of valve lift on the intake. Packaged with 2.08/1.60-inch intake and exhaust valves, these heads can get with the program, especially with their much more efficient exhaust ports AFR says can generate 225-cfm-plus numbers above 0.500-inch lift. Taking nothing away from the impressive intake flow numbers, it's important to have good exhaust ports if you want to make serious horsepower. With strong exhaust port flow we can minimize the amount of additional camshaft exhaust duration necessary to make maximum horsepower.
 Even for stock engine rebuilds,...  Even for stock engine rebuilds, the smart move is to always use a stretch gauge when torquing rod bolts. These Scat rods use ARP capscrew bolts. |  This is the Scat forged-steel...  This is the Scat forged-steel crank and rod assembly, along with the Mahle forged pistons. The crank assembly is intended to be externally balanced using the early, external 28-ounce balancer and flexplate/flywheel. |  Mahle makes an excellent forged,...  Mahle makes an excellent forged, two-valve-relief flat-top piston for the stroker 331ci Ford that is also extremely light. In fact, Scat's balance shop had to take quite a bit of weight off the crank to equalize the rotator package with these flyweight pistons. |