IHRA DRM - 2007 Issue #4
The last year of our racing activity was dominated by extensive study of the science behind engine operation. Writing about engines completely changed my view towards tuning. When you write a technical manual, you have to propose the question and the answer. The question had better be a good one. The answer had better be right.
CONFLICTS OFTEN AIRED BY SOME RACERS:
"That science and engineering stuff don’t work."
"I don’t pay attention to that engineering stuff, and my car runs fine."
"I tune only with spark plug readings, rod bearings, and the feel of the engine temperature."
And many other variations of these messages. I found more than ever the last year of my racing and all the years of my writing that science is science. Regardless of your view towards old or new sciences, your engine is designed based on scientific principles, and it runs based on scientific principle. It only runs because of the closeness of its design to science. It only runs well because of the closeness of its tune-up to science.
FUEL / SPARK ADVANCE: One of the common views of many tuners, especially in the high-powered ranks, is more fuel and ignition timing (spark advance) at launch. We had an interesting result with our blown alcohol racecar when were detuning it to run in a slower bracket class. Our ignition is a magneto with a locked spark advance. It does not have an advance curve such as street legal cars with a mechanical or electronic feature. In those cars, usually the faster the engine, the greater the spark-advance (although smog and mileage controls change the function a bit). Basically, the ignition system has to start the combustion sooner to make up for the reduced time for combustion. That reduced time occurs with faster engine speed. In our race engine, we have set as low as 22 degrees before top dead center and as high as 42 degrees before top dead center. Those settings were for various operating engine speed ranges and blower boost levels. We do not vary enrichment. That is, our fuel system is always the same enrichment for the amount of air from the blower. We vary the amount of fuel when the air is changed, but the air to fuel ratio is always set the same. We detuned it on this outing with a low engine speed launch and less timing with all else the same. Ironically, our 60 foot times were the fastest at the lower timing settings (least amount of advance). Keep in mind the key statements, “low engine speed launch and … all else the same.” Analysis of numerous technical references and a few good dyno test results revealed that a race engine has an appetite for spark timing that increases with engine speed just like the street engine (and decreases at lower speeds). A tuner can override the timing need with fuel enrichment or lean-out. More enrichment often needs more timing. Less enrichment (lean-out) often needs less timing. The engine can override its timing need with the temperature that it is at. A hotter temperature usually needs less timing. A cooler temperature usually can stand more timing. The conclusions are supported by numerous very accurate controlled experiments from reliable sources. You’ll notice that I said “usually.” That is one way a technical writer makes a conclusion that covers everyone just like the astrologists’ writing methods. Back to racing reality however.
YOU CAN BE WAY OFF: If, for example, you are running so lean that there is not enough “heat of combustion,” the engine can run cold. This is definitely the outcome with methanol fuel. The engine may be unresponsive to timing changes. The spark plugs have no heat in them, and the engine looks rich since there is no heat. It is starved of fuel. Flame speeds are slow because of low fuel density in the mixture.
THAT ANNOYING SCIENCE AGAIN: There is a three dimensional relationship between fuel enrichment, spark timing, and engine temperature. Tuners probe around that volume. Some operate in one domain. Others operate in another domain. I found that among the “one-off” engine builders, usually each one is different from the other as a result. That is an example of why crate engine builders are so successful. Each builder develops a tuning combination based on prior engine buildups and results. The crate engine builder moves the engine tune-up in the direction of more power, more reliability, and / or lower manufacturing cost. An individual such as myself, who builds a single engine, does his best to pick a fuel enrichment and spark advance combination that produces a reasonable engine temperature. That temperature determines the appetite for further enrichment or spark advance changes. We are stuck with an infant mortality rate that is a quantity of ONE. Everything that can go wrong, from our selection, goes wrong in our one engine. We have no previous identical engine that taught us a lot of tuning direction. Many of us have built previous engines; a Small Block, Big Block, carburetor, injection, supercharger or not. But more often each one was different. Just in the enrichment, spark timing, and engine temperature relationship alone, the choices of the combinations can vary for a single engine with an unimaginable variation among different engines. I saw one example in the late ‘60s. A wedge engine was converted from #86 carburetor jets and 36 degrees of timing to #100 jets and 52 degrees of timing. It screamed. The owner did the same change to a Hemi with about the same compression, intake, cam timing, and racecar weight. That car was a stone.
TWO MORE SUCCESSFUL METHANOL COMBINATIONS: The previous information applies to all fuels. However we will now feature my favorite, methanol. Two IHRA competitors are shown. They represent different combinations from other previous features. In addition to timing, enrichment, and engine temperature, additional engine design considerations are discussed for each engine. That discussion applies to other fuels as well. As you review these contributions, realize the complexity of a IHRA race engine program.
Alan Lee’s Hot Rod 8.9 second eMax Series, Accel Quick Rod 23 T bodied roadster with 468 Big Block running a stunning stack fuel injection. Stack length determines the tuning RPM for peak power. Stack volume with port volume should exceed cylinder volume for proper cylinder fill during intake valve opening. This combination of the Nostalgia T body with the open stack fuel injection and eight polished exhaust pipes makes one of the most vivid racecars for the public view. Could Alan let us know if the flames on the body ever go out!
Potent Small Block with Ron’s fuel injection throttle body on perfected single plane, tall manifold. One of the biggest evolutions in drag racing was cylinder head porting matched and coordination with optimum intake manifold development. Methanol works with combinations such as this fuel injection setup on a carburetor manifold, or with a methanol carburetor conversion on a carburetor manifold. Several highly competitive IHRA racers use either a carburetor (one or two) or fuel injection combinations. Methanol in both setups runs very well.
As a courtesy from IHRA to our readers, previous Tech Stop articles can be viewed or downloaded from our website www.racecarbook.com click on Articles.
About the Author
Bob Szabo is an owner / driver of a blown alcohol drag racecar and one of the few technical racing book authors. His new book: “5,000 Horsepower on Methanol, with Nitro, Racing Gas, Nitrous, & Ethanol Technology” covers fuel injection, carburetors, normally aspirated, supercharged, and turbocharged setups. His current book, “Fuel Injection Racing Secrets” provides added tuning info for methanol. Both are becoming popular gifts for birthday and anniversaries such as that first 9 or 8 or 7 second ET! Check the DRM Yellow Pages for Szabo Publishing or look on the Internet at http://www.racecarbook.com or call (916) 419 6649.