Last month we went over the basic rules for building an affordable race car for the PRO racing series Cheap Street class sponsored by Car Craft magazine. This month, we'll dive into some ideas from some sharp engine builders on how to make the most power from this 365ci small-block.
Short-Block
The rules push for 365ci displacement, since anything larger is hit with a weight penalty of 10 pounds per cubic inch, and there is no weight incentive if you run a smaller engine. Displacement is power, so you will need to spend some time working out bore and stroke combinations that will get you close without spending a lot of money. For example, offset grind a 3.48-inch-stroke small-block Chevy crank to a 2.000-inch rod-journal size to create a 3.562-inch stroke with a 4.030-inch bore and you have a 364ci small-block! Always try to use the largest bore and shortest stroke possible. This will unshroud the valves and allow the heads to breathe.
A heavy crank, rod, and piston assembly requires more horsepower to accelerate than a lightweight package, but the light stuff isn't cheap. A used circle-track system might be a good place to look for these parts. Lightweight pistons and pins with wider clearances are always a good idea, but this may require costly custom balancing. Keep in mind that custom pistons are very expensive, so look for an off-the-shelf piston that will work. A 1/16-inch ring piston is probably the best compromise, but consult with your piston source on the details because nitrous means moving the top ring a little farther down the piston. Also consider opening up the top-ring endgap. Run as tight a piston-to-head clearance as you can--most pros will tell you that 0.037 to 0.039 inch is about as close as you can run. Minimizing the size of the valve reliefs will increase the compression.
Oil pressure requires more horsepower to create, so a stock-type pump at 50 psi will work along with lightweight oil. According to Joe Sherman, he's seen power increases of up to 25 hp on a 650hp engine using the Royal Purple 5W20 oil over a 20W50 mineral oil. Employ a 45-degree mini-scraper on the passenger side of the oil pan to pull oil off the crank at high rpm. Sherman also says that running a deep-sump oil pan and reducing the amount of oil in the pan will also help power. Sherman says these windage power losses rarely occur below 6,500 rpm.
Heads and Induction
Choosing the right head is critical for this class since there are so many restrictions. Compare the flow numbers of all the legal heads. Most of the flow numbers for the Chevy heads can be found at the www.chevyhiperformance .com Web site by clicking on "Tech Articles" on the far left side. Compare the flow numbers and look for a cylinder head that offers good flow in the 0.300- and 0.400-inch valve-lift areas. Don't bother to look at the flow numbers above 0.500 inch. Excellent mid-lift flow numbers will make your engine work.
The rules allow any valve job and any valve, so this is an area where you can really make a difference. Most professional engine builders will tell you that a single degree of difference in the seat or approach angle can make a huge difference in flow and power. Also pay attention to the exhaust flow numbers. The exhaust flow numbers in relationship to the intake will point you in the right direction when it comes time to choose a camshaft.
The best cylinder head will also benefit from a properly matched intake manifold. The rules dictate a cast-aluminum single-plane intake. It may be worthwhile to actually flow the intake manifold with the head to see which works best. You can angle-mill the heads to increase compression, but that will also require milling the intake to match. Working with a company that offers both heads and intakes, such as Edelbrock, Dart, or Brodix, may be beneficial. Look for an intake that has a generous radius directly underneath the carburetor mounting pad. This is important to enhance power and improved mixture distribution. Look carefully at the position of the port relative to the heads on both sides of the engine. Often a core shift will make one side fit better than the other side. This is important since the manifold cannot be ported or massaged. Carburetor height is limited to a 2-inch spacer; this might be an advantage, but be careful. Often a spacer will improve top-end power at the cost of midrange torque. When you add nitrous, especially at the launch, this really pumps the torque, so a small torque loss with the taller spacer may work out.
The claim rules exempt nitrous, so you could spend some money on a well-engineered nitrous system that works with your package. While the nitrous jet is limited to 0.63 inch, the way the nitrous and fuel are introduced into the manifold can have a big effect on power. The more evenly the fuel mixes with the nitrous, the less fuel you need, which can make a little more power. Be very careful here, because too lean a mixture will kill pistons in the blink of an eye. It happens all the time. Other nitrous tricks include running a full bottle with each pass to maintain system pressure throughout the run. Keep the nitrous pressures between 950 and 1,000 psi.
Cam Timing
We've left the voodoo subject for last. The rules state you must use a flat-tappet hydraulic or mechanical-lifter camshaft, and you can't run more than a 0.485-inch valve lift. We're assuming these engines will make peak power around 7,000 rpm, so this means you're limited to a camshaft lobe lift of no more than 0.323 inch for a 1.5:1 stock Chevy rocker ratio and 0.303 inch for a Ford with a 1.6:1 rocker. Assuming this higher engine speed for peak horsepower, our cam grinder and engine-builder sources like Joe Sherman and others suggest durations of between 250 and 270 degrees at 0.050-inch tappet lift for the intake side with 10 to 14 degrees more on the exhaust side to compensate for the nitrous. Lobe separation angles no tighter than 108 to 110 degrees and perhaps wider would be a good idea. Tighter lobe separation angles tend to make the engine peaky, while wider lobe separation angles produce a broader powerband that is usually beneficial.
Both Comp Cams and Crane offer specialty lobes in their master cam-lobe profile books that will produce lifts in the 0.485-inch range with durations at 0.050 from 240 degrees up through over 270 degrees of duration at 0.050. This is probably the area where you will do the most experimentation, since each engine combination (based on the cylinder head and induction flow) will desire very specific cam timing requirements.
Power to Run
The bottom line is that it's going to take 700 to 750 hp and a strong torque curve to run 10-flat or high 9s in decent air, along with an excellent chassis and suspension system to hook all this power to the ground. Low 10s and high 9s are a great ride in any car. If this sounds like fun, think about what it would take to build a Cheap Street car you could take to the track. If enough readers e-mail us with requests, we could probably be coerced into building a Cheap Street small-block to test some of these theories. It might be fun.
Cheap Street Engine Rules
If you want instant access to the Cheap Street rules, the easiest way is to log on to www.fasteststreetcar.com. Once on the home page, click on "Rules" and then scroll down to Cheap Street. There you will find all the current rules along with a list of all the cylinder heads that are legal for the class. Of course, it's still a good idea to get a rule book so you always have the information at your fingertips. The best way to do that is to join the PRO organization. You'll get a T-shirt, rule book, and a membership that includes a subscription to PRO's monthly magazine. Or you can call 866/694-3475.
