by admin | Dec 21, 2012 | Clutches, Tech How-To |
By Sam Logan: It’s no secret that the modern day racing clutch has morphed into a pretty significant piece of engineering. Of course, all that became possible thanks to evolution. In short, constant increases in horsepower, ongoing trends in tire technology, nitrous oxide developments, better superchargers, and that all-important “need for speed” are responsible for wholesale changes in clutch design and application. Single-disc street-type clutches gave way to multiple-disc units, while at the same time clutch facing (or friction) materials went through a whole series of upgrades and changes over the years. You know the story – nothing stays the same in life. We thought it would be interesting to shed some light on just how these clutches operate in the intense arena of PDRA competition – namely, in the highly competitive world of Pro Nitrous and Extreme Pro Stock. In order to do that, we contacted the pros at Ram Clutches, based in Columbia, South Carolina., which seems to be the clutch of choice for many of today’s top racers. Intriguingly, most of these eighth-mile PDRA Pro Stock cars also compete in the MMPSA (Mountain Motor Pro Stock Association) championship, which run twice the distance with little or no changes to their specifications. Similarly eighth-mile PDRA Pro Nitrous cars regularly compete in quarter-mile NHRA Pro Mod events. Clutch Basics — Pro Nitrous and Extreme Pro Stock Looking at the numbers, there is no minimum weight requirement for Pro Nitrous cars, although they typically weigh in the 2,350 to 2,400 pound range. These cars can trip the 60-foot timers in .950 to .970-seconds and run from 2.55...
by admin | Dec 21, 2012 | Engine Builds, Tech How-To |
Kevin Stoa Engine Build part 1 of 3. Text & phots by Sam Logan: By the end of his first year in business Kevin Stoa had built 80 race engines. A twice Super Nationals winner in IMCA Modified, Stoa formed his company in January 2009, on his fortieth birthday, in his home town of Albert Lea, Minnesota. He renovated his shop and hired two trustworthy engine builders he’d known for decades, Preston and Jerry, and KS Engineering was in business. Located near the town’s water tower, the shop curiously displays no name. In fact, callers eager to visit the establishment can stand outside the building at 117 North Newton Avenue in confused silence while inside a dynamometer races at 7,300 rpm—a masterpiece in urban sound suppression. Acclaimed race engine shops usually succeed through the aspirations of one individual, and it’s unlikely there is a single shop of any consequence that is not the lengthened shadow of one man. And so it has been with the able young Stoa. Over the past two seasons KS Engineering’s race engines have demonstrated impressive pace and durability. In 2012, on Memorial Day weekend, four different customers prevailed in four different races. By mid-season the KS order book contained reservations two months ahead. Our interest aroused, we decided to pay a visit and try to document some of the secrets of Stoa’s race engine building techniques. On the dirt ovals Stoa is a much-admired man: quiet and understated he is uncomplicated, direct, and sincere. In the workshop, he has a thorough yet pragmatic approach to his craft, and his deftness around an engine cradle...
by admin | Dec 21, 2012 | Engine Builds, Tech How-To |
Kevin Stoa Engine Build part 2 of 3. Text & photos by Sam Logan: Probably the biggest fallacy about engine power output is the number that reveals its peak power. But it’s a deceit perpetuated by most of us. We run our finger down the page looking for it. The engine builder pursues it because often his job rests upon it, the car owner requires it, and the crew chief desires it—even magazine titles splash it across their covers, using it to entice greater magazine sales. The result is that the racer shopping for an engine almost always inquires of its peak power and the circle is complete: everyone engages in racing dynos. “In the eighties,” says Keith Wilson of Wilson Manifolds, “when I ported Childress race engines, their star Dale Earnhardt Sr. never cared about peak power. Instead he spoke of feeling it in the seat and dynamometer figures were of little account, he wanted to feel the car accelerate coming off the corner.” Kevin Stoa, the accomplished IMCA Modified racer and engine builder says, “The key in making the car accelerate is to determine its most effective RPM range. If the best oval track engine builder in the world made unrivalled peak horsepower from 8,500 to 9,500rpm, his engine would be beaten every time by another that’s producing its full power from 6,500 to 7,800rpm because it accelerates faster.” Bigger induction runners, for example, will often demonstrate impressive power on the dyno, but under racing conditions they often disappoint with lackluster throttle response. “Dirt track racers make most of their overtaking maneuvers when coming off the...
by admin | Dec 21, 2012 | Engine Builds, Tech How-To |
Kevin Stoa Engine Build part 3 of 3. Text & photos by Sam Logan: Let’s say your 400cu in race motor operates under water, like a fluid pump, and with every two revolutions of the crankshaft it would ingest and displace 400 cubic inches of water—receiving it through its intake and discharging it through its exhaust. But when the engine operates with air, especially at high engine speeds and equipped with a small cross-sectional area in the intake ports, it will consume more than its stated displacement. By pulses and resonant tuning and inertia and air speed and all kinds of trickery, the savvy race engine builder knows the more air he can persuade to enter his cylinder the more power he will generate. Carefully, using the cylinder bore as his beginning point, he’ll usually select the largest intake valve he can fit into the combustion chamber, making sure its head is positioned at an appropriate distance from the cylinder wall. Positioning it too close to the wall creates a shrouding effect and impedes the flow of the incoming air. He’ll probably use a valve with a concave head to save weight and he’ll surely consider the optimum compression ratio. The more astute will deliberate on exploiting the advantages of squish or “quench” which accelerates the combustion process. On the compression stroke the air-fuel mixture is squished out from the flat, narrow spaces between the piston and the cylinder head and forms fast-moving jets that agitate the mixture and boost combustion speeds. Intake port volume usually isn’t regarded with as much importance as the smallest cross-sectional area, which accelerates...
by admin | Dec 17, 2012 | Carburetors, Tech How-To |
By Sam Logan. Photos by Moore Good Ink. Download text and hi-res images 1 of 2. Download text and hi-res images 2 of 2. Before the new Street Demons were first released to the public on Friday, May 25, 2012, the carburetor company dispatched twenty to thirty pre-production units to discerning carburetor critics for testing and evaluating. For this purpose Street Demons were sent all over the country—even to Australia. Tests were conducted at sea level and in the mountains, in cold and in hot conditions, in stop-go traffic and in engines with unfathomable camshaft timing—profiles contrived for noise rather than power. Some even found their way onto towing vehicles, lugging heavy trailers up hills. All testers were invited to “Have at it,” as they say and were actively encouraged to present their findings—warts and all. One of these pre-production Street Demons appeared at Automotive Service and Performance (ASAP), a hot rod tuning shop in Gainesville, Georgia. Known as the poultry capital of the world, Gainesville nestles in the Appalachian foothills on the shores of Lake Lanier about 50 miles north of Atlanta. It has an elevation of 1250 feet. ASAP’s Bobby Tow had a 1972 Dodge Dart lined-up and awaiting the fitment of the new Street Demon. The Dart, now owned by Rick Ellis, President of the North Georgia Mopar Club, is one of around 250,000 produced in 1972 and was supplied originally with a Carter two-barrel carburetor, which was replaced by an Edelbrock 600 some years ago. Now the Edelbrock is being replaced by one of the first available Street Demons. Here in this sequence of photographs...
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