March 1, 2002
After months of planning, periods of intensive work, and borrowing from the knowledge of some of the top engine builders in the country, Mike Wilson and Tom Honsaker drop the Pure Street engine into position at Paul's Automotive Engineering. With a goal of 400-plus rwhp for a 3,300-pound race car, the limited rules set forth by the NMRA give you only so much you can work with. Here's the breakdown of parts, piece by piece.

Horse Sense: At the time of this writing, the NMRA Pure Street class is booming. Expect to be heavily contesting for the 16 available qualifying positions if you decide this is your next racing endeavor.

Brought into existence during the birth of the National Mustang Racers Association in 1999, Pure Street has attracted an impressive number of 5.0 Mustang racers and fans. One of the most limited, and therefore most strictly enforced, classes in our sport, Pure Street requires racers to confine their engine combinations to less than 311 ci with mostly stock internals. A hydraulic roller camshaft of no bigger than 0.500-inch lift and stock hydraulic lifters are also mandatory. P/S engine builders must select their heads and intake from a list of street-oriented pieces that the NMRA has deemed legal. Other rules mandated by the NMRA include a minimum combustion-chamber size (58 cc for aluminum heads) to limit the degree of head milling done to raise compression ratio in an attempt to find power.

Racers must also decide if they want to run cast-iron GT-40P or stock-style heads, which allow for a smaller combustion chamber (40 cc), and therefore more compression at the expense of a less efficient head design as compared to some of the more exotic aluminum street castings available. Delving deeper into the NMRA rule book, you will find other small intricacies that are designed to keep P/S an economical and level playing field for all interested parties.

Ed prefers Scorpion 1.6:1 roller rockers because they are light, strong, have excellent geometry under load, and they are economical. And, polished rockers look trick. New designs with lighter reciprocating weight are in the works from Scorpion.

The bottom line is that P/S is a wildly popular class that requires strict attention to the guidelines laid out by the sanctioning body. Not surprisingly, there are more than a few experts who have stepped forward to address the growing needs of P/S racers across the country. One of the foremost experts on Pure Street racing in general and builder of killer class combinations is Ed Curtis from Coventry, Rhode Island. Ed's FlowTech Induction speed shop has been kicking out some awesome setups for this class since its inception. His dragstrip education began as a hands-on partner for a successful NHRA Stock Eliminator team. From there, his home-brewed horsepower turned into a lucrative sideline that still feeds many a 5.0 enthusiast full of motivation (see Street Car Desire sidebar). We had long wanted to work with Ed on a Pure Street combination story, but location and timing never seemed to work in our favor-until recently.

Enter Mike Wilson, head technician at Paul's Automotive Engineering in Cincinnati, Ohio (your author's hometown). When Mike's not tuning on 10-second supercharged modular cars or putting together 180-mph road racers, he works on his '82 GT project car that is destined to run in NMRA's Pure Street class. While Paul Faessler's shop is more than capable of putting together a competitive P/S combination, we persuaded Mike to try out some of the goodies offered by Ed Curtis so we could see things up close ourselves. In addition, Paul was quite interested in testing some of the newest Airflow Research cylinder-head castings (Ed has a long-standing relationship with that firm, which offers him sometimes proprietary access to its products). And Ed was looking for feedback from others in this field as a way to showcase his talents. Two speed shop owners who are willing to share ideas with each other? How refreshing!

Don't look at these as just your stock-replacement lifters ($125) and pushrods ($160). They are trick, and they play a vital role in keeping this little engine alive up to 7,500 rpm with steel valves! Remember, titanium valves are not allowed in P/S as they are in Renegade. If you want all the details, you will have to call Ed.

What follows is a detailed parts examination of what it takes to make a killer Pure Street engine-almost 380 rwhp worth. If you follow what has been laid out in this story, there's no reason you can't be at the least competitive in NMRA Pure Street. As we watched the assembly of this 310, we couldn't help but be impressed with the thought that has gone into these class-legal motors. From the Faessler-built bottom-end components to the Curtis top end to Mike's "whole-car" attitude, we think you will be delighted with the results.

Street Car Desire
If you've read this story and thought to yourself, Gee, I bet this combination would make a nice street car regardless of the Pure Street rules, you're not alone. Much of Ed Curtis' experience with these parts has come through extensive testing on street-driven (and, um, street-raced) 'Stangs in his home area. A typical combination would consist of the AFR 165 head custom ported and prepared by Ed, a simple Cobra intake with some minor clean-up work, and a custom cam as prescribed by Curtis. Ed reports that there are dozens of cars across the country set up with this simple recipe for speed that he has worked with during the last few years. The results of this combination with the typical bolt-on supporting equipment that you probably already have is a car that makes from 315 to 335 rwhp and can rip off 11.80-12.20s depending on vehicle weight and other variables. The best part, Ed tells us, is that these cars suffer absolutely no loss in driveability and street-worthiness. Besides awesome power and good street manners, Ed says owners often report more than 25 mpg in fuel consumption. Sounds like a nice little package to us.

The power is in the heads, they say, and our Pure Street engine wears a set of Airflow Research model 165 castings with prep work by Ed Curtis at FlowTech Induction. Simply put, cylinder heads are the number-one consideration when you're working up a serious class engine. Top P/S racers John McGowan ('01 NMRA champion), Will Buckworth, and Darren Hendricks (both NMRA and WFC record holders) use Ed's components exclusively. The 165s were actually designed with P/S in mind, with a general focus on good street power from a naturally aspirated 5.0 Mustang. They carry 1.90-inch intake and 1.60-inch exhaust valves, titanium retainers, custom valvesprings designed for operation at the 0.500-inch lift level, 71/416-inch studs, and a casting that exhibits excellent velocity numbers. Ed reshapes the entire runner with a focus on the low-lift numbers and quality airflow, not just port-volume peak flow numbers. According to Ed, the AFR combustion chamber has "perfect" swirl-and-tumble characteristics promoting a complete and even burn. The final product produces tremendous velocity and quality flow through a much smaller port and valve size than many heads.

The flow numbers from the AFR 165 heads after FlowTech Induction gets through with them are simply awesome for this application. As with Ed, Paul Faessler's flow bench is conservative, but we think you'll get the idea from the numbers. Ed says confidently of his work, "I know what I need to make these cars run 11.00s, and that's what I build into my heads." From FTI assembled, the basic Pure Street-legal heads retail for $1,500. With Ed's magic thrown through the runners, they go out the door for only $1,800.

Lift (inches)Intake (cfm)Exhaust (cfm)Efficiency (%)

Comp Cams' hydraulic roller carries top-secret, FlowTech Induction numbers. Ed has more than 75 different designs for P/S combinations kicking around in his head. He looks for a ramp design that will not "shock" the lifters or valvetrain into valve float. This is also key in keeping the valvetrain intact at P/S engine speeds of more than 7,500 rpm! Mike Wilson's cam measures right at 0.499-inch lift with secret duration numbers. However, Ed says his $325 camshafts are much smaller than what the competition runs. Ed also looks for specific timing events that create a tighter lobe separation, with some split between 2 and 6 degrees of duration on the AFR head. A quick point here: On iron-headed combinations, where the compression is higher, Ed ups the duration. On spec-fuel combinations with lower compression, Ed counts on the airflow and engine rpm for power. The camshaft has to balance these conditions in the valvetrain with hydraulic lifters.

An Edelbrock Performer RPM carbureted intake was used on Mike Wilson's P/S engine. With the Air Gap lifter valley pan and its raised runners, the incoming air stays cooler, and with the "notch" at the carb flange/plenum, the runners are balanced between the right and left halves of the manifold to gain more top-end power. This is the only NMRA-legal manifold that comes this way. The only legal modification is a 1-inch port into the cylinder head side of the manifold. Ed does have 11/44-inch carb gaskets in place of normal gaskets to add to the ram effect and runner volume. A venturi spacer is also in the works. The carb is a 650 H.P. unit from Marty Brown at Quick Fuel in Bowling Green, Kentucky. Marty has experience with Adam Cox's 122-mph P/S combination, so he knew what he was getting into. The features include revised emulsion holes, less restrictive boosters and throttle bores, and adjustable high-speed air bleeds for a more linear fuel curve and better fuel distribution.

Stock block, stock crank, ultra-lightweight rods, ultra-lightweight wrist pins, and Probe pistons (595 grams for pistons with wrist pins) combine into a Paul Faessler masterpiece of 310 ci. All assembly and machine work was done in-house under the watchful eye of head machinist Steve "Scuba" Barker. Precision machining, assembly, and attention to detail are hallmarks of Paul's Automotive Engineering machine shop services and demanded in any serious P/S engine. Minus the block and oil pan (because of optional pieces), this short-block goes out the door for around $4,000 including all the bearings, gaskets, oil pump, machine work, and ATI balancer. It's the light weight and free movement of the rotating assembly that really set this motor apart from a stock 5.0 with a bolt-on, top-end parts list.