The camshaft defines so many characteristics of the engine; its design is always critical. In wanting to maximize the performance of these 87-octane mills throughout a wide rpm band, we contacted Comp Cams and got the advice of their experts. We decided on a solid roller camshaft, since we liked the benefits of the design (rapid valve action, minimal friction) and we've got no problem checking our valve lash occasionally. While some may balk at the idea of a solid roller in a daily-driven street machine, we actually enjoy the fine-tuning and occasional lash requirements, and we want to take full advantage of the capabilities this engine can bring. A solid roller can bring us more, and we chose Comp's Xtreme Energy part number 12-772-8 (grind number XR286R). The specifications on this cam are aggressive, with 286/292 degrees of advertised duration, a quick 248/254 at .050-inch lift, and 110-degree lobe separation angle. Lift numbers check in at .576/.582-inch with a 1.5:1 roller rocker, and we'll experiment with different ratios (including the proven Comp Cams 1.6:1 Magnum rockers) to fine-tune the best-possible scenario with this particular cam.
The idea behind the aggressive lobe is to shed a bit of compression at the lower rpm ranges to further avoid detonation. It's honest inefficiency and overlap will shed some cylinder pressure below 2,000-2,500 rpm, and the lower pressures should be able to support the low octane gas. Once the engine picks up speed (2,500-plus rpm), the overlap will add to the efficiency instead of taking away from it, and the engines should be able to start supporting real power numbers all throughout the midrange to the 6,500 rpm (or so) redline. As you'll read, careful carb tuning and fine adjustment of the ignition curve will also be incorporated at the critical lower rpm levels to offset detonation at this most-susceptible rpm level. Careful tuning of our extremely adjustable components and parts selection focusing on precision-crafted performance hardware should become our best weapons against the curse of low-octane detonation.
Feeding this engine may seem like an easy task, but this is not so. We have a very efficient intake port in the AFR head, and feeding it becomes quite a task at low rpm. As we mentioned earlier, the properly sized port was the goal, and we were leaning toward a 190cc port to ensure good velocity. We chose the 210 for increased power potential upstairs and knew feeding it right off-idle may be a challenge. Also, knowing our cam of choice may be a bit choppy until it gets past 2,500 (or so) meant an efficient intake/carb combo was in order.
We looked over all our previous research and decided on Edelbrock's Performer RPM Air Gap intake (PN 7501). This super-efficient piece has all the features we want in a performance intake while maintaining streetable manners. We also like their new Perma Star finish, so we ordered PN 75012 (right). The "as-cast" finish is shown on the left; also a Performer RPM Air-Gap (which won't be used or tested, but it is shown for comparison to a standard, "as-cast" intake finish). The RPM Air Gap's tall dual-plane design delivers torque down low without losing anything in the higher rpm bands, and since our redline will be in the 6,500 rpm neighborhood, the RPM Air Gap is a good match with the rest of our performance package. We'll run it untouched, just like the heads. The as-manufactured ports on the RPM Air Gap are slightly smaller than the 210cc ports on the AFR heads, and we're hoping the smaller intake port will feed generously into the center of the AFR head port without losing much power (versus a port-matched example). The chrome-like Perma Star finish looks great without the maintenance required by polished intakes, and looking good never hurts, especially when you can back it up with serious performance.
We've chosen a BG Race Demon RS 675 carb with removable venturi sleeves (PN 3282010GC) so we can test different carb flow rates to find the best-possible scenario. Many tuners know how running the carb a bit rich can help keep detonation at bay, and should we encounter issues the Race Demon RS is flexible enough (through its wide range of fine-tuning adjustments in addition to the venturi sleeves) that we should be able to tune away any potentially damaging problems. We'll also test a series of carb spacers to see how they affect the results and if we can find more streetable power by using them. Both HVH Super Sucker and BG Fuel Systems spacers will be tested.
Spacer research is one of the hottest areas of innovation and development at this time, and hopefully our research results will help solidify which design is best for street enthusiasts using the popular Edelbrock Performer RPM Air Gap intake atop good-flowing cylinder heads like our AFRs. Dual-plane intake designs react differently to spacers than open single-plane intakes, and we're anxious to see how much can be gained, and which design is responsible for the greatest efficiency increase.
An MSD ignition system (distributor PN 85551) will be utilized so we can fine-tune our timing curve to achieve the best-possible results. It's possible to add a few degrees of timing and add to the detonation avoidance in some cases, especially when a well-designed combustion chamber is part of the program. Having a surefire spark is an absolute necessity to try and burn as much of the 87 as possible, and having the multiple firings MSD is named for will assist in this further, especially at the critical lower rpm levels we expect the worst fighting to occur at. Having a tried-and-true MSD 6AL box (PN 6240) and coil attached will give us plenty of ignition power and the accuracy to fire it when we want, instead of when it feels like it.
Many enthusiasts run this basic MSD ignition system, and rather than choosing a more expensive digital or programmable setup, we felt it would be in the best interest of our readership to base our research on an ignition system many of our readers already know well.
Keeping temps down is a huge part of fighting detonation. We've added a Weiand high performance water pump (PN 8223, "short" version) to the engine to work in concert with the many other aluminum components we've got, and the teaming of these aluminum components will act as an efficient heat sink. It's also an "adjustable" design; with height adjustment possible through the twin bolts mounted over the upper mount bolts. In case you're racing with a single belt (no alternator for tension adjustment), this is how belt tension would be dialed in.We'll plug in a 160-degree thermostat and we'll be cooling through an aluminum high-flow radiator on the street, but for the dyno test-and-tune sessions we'll keep temps in the 160-170 range, like we hope the engines will maintain on the road. We will experiment with temperature ranges, but we're confident cooler will be better here.
THE OILING SYSTEM
The lubrication system is also being treated like a cooling system, since in many ways, it is. Adding additional oil to the system (by using a deep-sump Milodon pan) is a big part of that, but also paying careful attention to windage control is a big part of our oil system design. While not directly cooling-related, it is still a power tip. An effective windage tray serves to pull oil off the spinning reciprocating assembly (which is also smoothed to encourage this action) and not force the crank to carry this additional weight around every turn. A lighter crank means more power to the flywheel, and that is precisely our goal. We kept a stock-type pickup and pump, and trimmed the integral louvered windage tray to fit around it.
Like the crank/rods/pistons, we chose to run a "system" of parts designed to work perfectly in concert. The Milodon oil pan is engineered to provide outstanding performance in applications like ours, and we've chosen a Melling small-block HV pump and stock-type pickup. The pan is deceptively stock appearing, which means fitting in our street-based chassis will be no problem. Engineered inside is a louvered windage tray, which requires some minor clearancing to fit the stock-type pickup. We checked for clearance with clay between the pan and pickup and found approximately 5/8 inch, which should be fine for our street engines.
We topped the engines off with some Comp Cams valve covers, routed our MSD plug wires, and were ready to fire up. The power charts show we're on the right track, and know that if you're planning to build a new engine for your street machine, some careful planning and parts choices will make it possible to get very good usable power on 87-octane gas. For those special times when you'll be pushing it hard at the dragstrip, running nitrous, or spending a day on the road course for an Open Track event, filling up with higher-octane gas will only add to the insurance you've already built into your car.
We can also see the power variations between identically built 355 and 383 Chevy engines, so the additional stroke of the 383 can be seen in the numbers. Many have wondered exactly how much more a 383 would be worth when compared to an identically built 355, and we were curious too. Now we know.These engines idle well, run cool, and make good power. They should serve as a good blueprint for small-block Chevy fans, and we hope the ideas behind their design will help all enthusiasts looking toward the future with an eye on saving some cash at the pump and not sacrificing the brutal power American V-8s are legendary for. Enjoy!
We've done plenty of homework and have come up with a battle plan to fight for true street performance using the least-expensive fuel possible. We want to be able to rely on this engine to get us around town, and we've built in plenty of durability for weekends at the drags or on the road course. Should we encounter heat and/or detonation issues in the depths of the hottest summer heat or during heavy towing or racing, adding a mix of the pricier pump premium or relying on tuning information gleaned from our time on the dyno should clear everything right up. This has got to be a better daily driver option than a lifetime commitment to always pricey 92-octane. We have done our best to design a pair of detonation-fighting powerplants capable of serious performance on bottom-dollar gasoline. We think this is the kind of story readers want to see, and hopefully the tips and tricks we've shared will help make 87-octane performance less of a misnomer and more of an honest goal for the future. Unless gasoline prices begin to drop dramatically, we genuinely feel this route will be our future, and we're preparing for it now. Let us know how you feel about it.
The engines were both run on pump 87-octane gasoline. We are showing the power figures with the 1.5-inch HVH spacer in place, and the 1.6:1 Comp Cams Magnum rockers installed. Both engines were built as identically as possible, and these pulls were done at normal operating temperatures (coolant over 160-degrees; oil over 180-degrees) to best duplicate a street effort.