The SituationIn our May 2006 issue, we built a 383 stroker motor using a 413 crankshaft and rods from 440Source, and pistons from Diamond Racing. This little 432-inch stroker-motor cranked out 500 hp using cast-iron 906 heads, and then stepped up to 545 hp when topped with some Edelbrock aluminum heads. While that was a nice amount of power for a fairly simple combination, we got a little greedy and decided to see how much power our simple 3.75-stroke short-block would make when we topped it off with a pair of Indy EZ heads. Not only did we step up to these brand-new Indy heads, we treated the heads to a CNC porting job at Modern Cylinder Head, and we called Competition Cams for a bigger bumpstick.
The Short-block CombinationThose of you who read part one in our May issue will recall we were using the new flat-top pistons from Diamond Racing hung on 6.760-inch-long I-beam rods from 440Source. This combination gave us a compression ratio of 10:1 with the 84cc Edelbrock heads, but with the smaller 75cc chambers in the Indy heads the compression ratio increased to 11:1.
We did not make any changes to the short-block for this next round of testing other than changing the oil and sliding in the bigger camshaft. The camshaft we ordered from Comp Cams was a custom grind using what Comp calls their SQ lobes. The SQ family of lobes are an aggressive design when used with an .0875-inch diameter solid lifter (Ford diameter), but work well with the slightly larger .904-inch diameter lifters. This particular camshaft used number 7265 lobe on both intake and exhaust. The 7265 lobe has 270 degrees of duration at .050-inch lift and has a lobe lift of .400. The lobe center angle was 106 degrees, and the cam was installed straight up on a 106-degree centerline. We were able to reuse our existing lifters since we are using Schubecks with the super hard face material. The Schubeck lifters can be cleaned up and dropped back in on the new cam without any break-in period required.
Indy EZ headsThese new heads from Indy Cylinder Head are the answer for engine builders who need to keep the exhaust ports in the factory location. While other Indy heads have the exhaust ports raised for better flow, the guys at Indy figured out how to get a decent exhaust port into a fairly stock location on these heads. These EZ heads can be ordered in four different configurations, including an unported version and three different versions of CNC porting. The CNC porting available from Indy includes their 275cc EZ-1 version, as well as their 295cc and 325cc version. The Indy EZ head with the 295cc port is called the Little Easy; the 325cc version is called the Big Easy. The EZ-1 head uses stock-type rocker arms and provides oil to the valvetrain through the block-like stock heads. The 295cc and 325cc heads from Indy have to use external oiling since the porting makes the wall thickness too thin in that area. In addition to the external oiling, the Indy 325cc head has to use offset rocker arms on the intake valves since the pushrods have been moved to accommodate the larger runner size.
The size of the runner is important to consider when building an engine since there is a direct relationship between the size of the motor, the size of the intake runner, and the rpm where the torque peak occurs. A subject such as this can start to get a little complex, so your best bet is to call the guys at Indy Cylinder Head and have them help you pick the correct version for your application.