Smaller engines like this 327 small-block Chevy (now bored out to 337 ci) are more economi
Orlando, Florida, is home to one of the most iconic and recognized destinations on the planet: Disneyworld. But not all travelers venture south in the dead of winter to visit Tomorrowland or the Epcot Center. Just after Thanksgiving each year, those of us fortunate enough head to Orlando for a different E-ticket ride. We go there for the Performance Racing Industry trade show, or PRI for short. It was at this convention in December 2007 that our small-cube small-block project was born. In a side room, a group of interested parties, myself included, joined together to hear our friend, Ed Zinke, announce that the rules for the 2008 Engine Masters Challenge had been finalized. We immediately tore into the rulebook, eagerly looking at changes and building mental images of the combinations that we thought would rule the world. Me and my crew from Revolutionary Performance and Machine spent countless hours contemplating how we could make big power and torque with a 10.5:1 flat-tappet engine. We had to break it down to the basics, and go from there.
The trick to going fast and performing well at the EMC is to make tons of torque, and spread it out over a wide rpm range. As horsepower is literally just a mathematical function of torque and rpm, and cannot be measured, it should make sense that we focus on torque here. So then the keys to making that torque were to induce as much air/fuel mixture into the combustion chamber as possible-across the whole rpm range-trap and Compress that mixture, and light it off just in time to take full advantage of the expanding flame front. It sounds like a very basic explanation, and it is. Sure, there are other factors, like reducing friction and thermal efficiency, etc., but in the end, it all boils down to the induction system.
At the previously noted PRI show, we ran into Rick Sperling of Air Flow Research (AFR), and spoke with him at length about his cylinder heads. Having decided to build a .060-over 327 (actually 337 cubic inches), we thought it might be easier to start with a relatively large runner cylinder head, and shrink it down to a usable size, rather than porting a small head. AFR's ace head designer, Tony Mamo, recently redesigned the 210 Eliminator heads, and included a swirl-inducing wing on the back side of the intake guide. I had seen these designs on several race heads, but had yet to see whether it would help or hinder the performance of the engine, so I ordered a set of the Competition-ported heads, and we had our first seed part.
The business end of the intake runner for our 327 small-block is reduced to just under the
We dissected the heads as soon as they arrived at our doorstep, and were quite pleased with the new design features. Lightweight 8mm-stem valves were a clear break from the previous tradition of using 11/32-inch stems in small-block heads. The reduced reciprocating mass of the valves allowed us to use a lower spring pressure than we would normally have to. This would keep the valves in control with the extremely aggressive cam lobes we had in our plans. Naturally, we put the heads on the flow bench to see how they performed in out-of-the-box condition. They put up good numbers on our Superflow SF600 flow bench, peaking at 287 cfm on the intake, and 225 cfm on the exhaust (without a pipe) at .700 lift. Knowing that the advertised numbers were slightly higher than what we saw, we did a quick cartridge roll cleanup of the runners, and saw an immediate increase to 307-cfm intake, and 227-cfm exhaust. This increase is more than likely due to the removal of a small parting line on the short-side radius commonly created on CNC-ported heads where the cutting tool changes from cutting down through the valve side of the head, over to the runner entry side of the head. Newer versions of the heads are said to have greatly reduced these transition lines. The intake runners actually measured a hair less than the 210cc advertised volume, but with a mere 337 cubic inches to feed, we felt that making the runners smaller would aid in increasing the port velocity and getting the runners working sooner in the rpm range. Globs of Splash Zone marine epoxy (aka green death-wear a respirator when porting!), properly shaped and finished, reduced the runner volume to 203 cc without dropping a single cfm below our target .650 lift. The legendary Edelbrock Performer RPM intake manifold was given the same treatment in a mirror image with the runners gradually tapering to the as-cast sizing at the runner entries.
To take full advantage of the large airflow potential when running this small-cube engine, we consulted with Chris Mays at Comp Cams, who ground us a couple of small-duration solid flat-tappet cams to try with the most aggressive opening rates possible for a Chevy lifter. We were initially pleased with the first cam, a 236/242-at-.050 grind; however, I spent some time with a degree wheel and a dial indicator and realized that I could get the same intake valve seat-to-seat time, but with more duration everywhere else if I ran a 242/242-at-.050 cam, but opened up the lash on the intake. Dyno testing confirmed my theory, and we were rewarded with a 7-12 ft-lb gain in torque across the board. Opening the exhaust lash increased power as well, indicating either the exhaust lobe had too much duration, not an aggressive enough ramp rate, or both.
In situations where we are building an engine with an extremely aggressive cam, it is imperative to make sure the lifters are properly positioned, and will survive the punishment given to them, so we had the block Lifter-Trued by our friends at Shacklett Machine in Nashville, Tennessee, and Comp Cams was able to use their recently added nitriding process to treat our cam and lifters. Even with those precautionary steps, we broke the cams in without the inner valvesprings before switching to the Royal Purple racing oil, and testing on the dyno at full load.