By Richard Holdener
Some call them life lessons, some call it experience, but the truth is we all make mistakes, We are, after all, only human. Some mistakes are less costly than others, like forgetting to tie your shoe. Others, like not looking both ways before you cross the street, can be considerably more so. The same goes for mistakes in the automotive kingdom. Forget to tighten a nut on your carburetor, and you might develop a small vacuum leak. Forget to tighten a rod cap, and you’re talking about a vacuum leak of epic proportions.
Somewhere between the two extremes are what we call necessary upgrades. Things that fall into this category include a valve spring upgrade required by a cam swap. The cam will make the power, but only if you have sufficient spring pressure and coil-bind clearance. The same goes for injectors and fuel pump, as the larger injectors will only work if they have sufficient fuel flow from the pump. The components in any performance motor are interrelated and work best when they work together.
One area often overlooked by enthusiasts is intercooling. By now, most of us know intercooling exists and that it is necessary, but sticking just any old intercooler on your supercharged performance motor isn’t going to optimize the combination. This is especially true when looking for big power. The problem comes from the notion that adding power is as easy as adding boost. You want more power? Just crank up the boost with a pulley change, right? Well, yes and no, as more boost can increase power, but higher boost levels also bring their own set of problems.
With boost comes higher temperatures, as inlet air temps increase in direct proportion to pressure (why we employ intercooling in the first place). The higher temperatures and flow rates that accompany pulley changes can tax your intercooler. Like the supercharger and nearly every other sub system on the motor, the intercooler was designed with a specific power level in mind. Kept in the designed range, the system works well, but exceeding the capacity of the system will cause problems, not the least of which is a reduction in power.
Before we get to the test, we need to understand that intercooling is a balancing act of sorts. The job of any intercooler is to counteract the increase in air temperature. To do this, airflow through the intercooler must do several things, including coming in contact with a cooling medium that is cooler than the inlet air itself. Since nature seeks stasis, heat will be drawn away from the air and into the cooling fins of the intercooler. Ambient air (or water) can then be used to remove the transferred heat from the core. The greater the surface area and length of time this transfer has to take place, the more effective the heat rejection will be.
The problem is that adding internal surface area restricts air flow, which causes an increase in boost before the core, but a drop in boost (and flow) after the core. Thus, a core design must balance the need for flow and cooling with the available size (fitment) constraints, to say nothing of cost. The take away for this is intercoolers should be sized properly for the given application, and one size here does not fit all.
To illustrate this fact, we set up a test with our Magnificent LS7 test motor. The 427 featured a GM LSX block from Gandrud Chevrolet stuffed to the gills with a Lunati crank, Carrillo rods, and CP Pistons. The power producers included TFS Gen X 260 LS7 heads, an MSD Atomic intake, and BTR Stage IV LS7 cam. Included in the build-up was an ATI 8-rib Super Damper, Moroso oiling system, and FAST 75-pound injectors.
The Magnificent LS7 was the perfect test mule for taxing the limits of the intercooled D1SC from Procharger. The idea was to run the D1SC first with the standard intercooler, then with the intercooler upgrade designed for the larger F1A supercharger. Both air-to-air units, the intercooler upgrade featured 4.40-inch thick core (3.1-inch for the standard) that allowed room for 3.5-inch inlet and outlets (3.0-inch for the standard core). For our test, the standard core was run with 3.0-inch intercooler tubing (supplied with the kit), which we upgraded to 3.5-inch tubing for the larger intercooler. The pulley size, air/fuel, and timing were all kept constant during the testing.
First up was the standard core. Run in anger on the dyno with the self-contained D1SC supercharger, the 427 LSX produced peak numbers of 944 hp at 6,600 rpm and 794 lb-ft of torque at 5,700 rpm. These were pretty impressive numbers given the fact that Procharger rated the D1SC at just 925 hp. Boost supplied to the motor (measured in the manifold) started at 3.5 psi and rose to a peak of 9.9 psi. We figured making 944 hp at just 9.9 psi was nothing short of magnificent, that is until we installed the new cooler.
After installation of the intercooler upgrade, things got serious. How serious? How does 1,003 hp and 864 lb-ft of torque sound? The extra flow offered by the larger core allowed more of that lovely boost into the motor, with a peak of 10.7 psi. This test clearly showed the importance of intercooler sizing and what happens when humans err with air.
A couple of things should be immediately evident from these power curves. First and foremost is the fact that adding the Procharger to the Magnificent LS7 LSX motor made for one powerful combination. Even with the smaller of the two intercoolers, the supercharged 427 exceeded 940 hp. The second obvious observation is the intercooler upgrade offered substantial power gains. Gains of this magnitude show the combination was nearing the flow limit of the smaller intercooler, making the upgrade a necessity. Installation of the larger intercooler core and plumbing increased the power output through the entire rev range, with the peak numbers jumping from 944 hp and 794 lb-ft of torque to 1,003 hp and 864 lb-ft.
Naturally, we data-logged the boost curves during the test. These curves represent the boost present in the manifold, as opposed to the boost present before the intercooler. Run with the smaller intercooler, boost from the D1SC started at 3.5 psi and rose to a peak of 9.9 psi. After installation of the larger intercooler (with no change in blower or crank pulley), the boost curve started at 4.2 psi and rose to 10.7 psi. The larger core offered less restriction and allowed more boost to the motor. The result was a sizable increase in power.
Sources: ATI, Atiracing.com; ARP, Arp-bolts.com; Brian Tooley Racing, Briantooleyracing.com; COMP Cams, compcams.com; CP Pistons/Carillo Rods, cp-carrillo.com; FAST, fuelairspark.com; Gandrud Chevrolet, parts@gandrud.com; Holley/Hooker/NOS, holley.com; Lunati, Lunatipower.com; Moroso, Moroso.com; MSD, Msdignition.com; Procharger, procharger.com; Speedmaster, Speedmaster79.com; Trick Flow Specialties, trickflow.com