Lean it down, it'll run cooler," long-time sprint car owner/mechanic Bob Dyer said as I struggled to figure out why my engine kept overheating. He'd already asked me what fuel pump I was running and what pill was in the bypass, so he knew my system was way off.
But lean an engine to cool it? That was opposite of everything several "experts" had told me.
Since grasping at straws wasn't working, I did what he told me. When I pulled in from the "B" main with the temperature gauge at a perfect 200 degrees F, I became a believer. But, when Dyer told me I really needed a high-speed bypass too, my head almost exploded. I was having enough trouble with one, let alone two!
Between Dyer, Sid Waterman of Waterman fuel pump fame and Lee Nelson at Ostrich Racing Engines, they finally convinced me that a high speed was necessary. They know that learning about weather conditions and my fuel system is as critical to going fast as gear and tire selection. Plus, it could save me money. How? Well, since I learned to manage the fuel system, I've never had a melted piston or an engine failure caused by too much or too little fuel.
If you boil it down, getting the fuel as close to right every race, every night, is fairly simple. Learn and work on the following rules, and you can do it.1) Know when the air changes2) Establish baseline settings3) Adjust the fuel accordingly4)Always change the high-speed bypass when you change the main pill5) Never use the bypasses to control engine temperature
Change In The Air Dyer knew I was way too rich, not just because he's been around these cars since the '50s, but he knew that the air was terrible. I thought, hot and humid, give it more fuel to cool it. He knew, hot and humid, give it less fuel because there is "less" air. Hot, humid air is thin air.
That one night convinced me I needed to keep track of the air. What I was experiencing, Nelson refers to as "fuel bind." "Fuel bind happens when the engine gets so much fuel that it can't burn it all in the cylinder," he says. "It washes down the cylinder walls, increasing friction, and creates a hydraulic effect that's hard on wristpins and bearings, and it will fatigue pistons causing them to break. The extra fuel gets pushed out the exhaust valve and ends up burning in the port. Anytime an engine is fighting against itself like that, it will build heat."
After watching Ken Hesmer, owner and mechanic for his son, Dave Hesmer, multi-time Knoxville 360 champ, track the air on a Computech RaceAir Weather Analyzer, I choked hard and paid the price for one myself. This little electronic marvel will set you back most of $600, but that's far less than it costs to fix one melted piston.
The Computech "box" pulls in outside air, measures temperature, humidity, air density, and barometric pressure, then combines them all into two numbers that will tell you where you are. One is a number people can understand, Density Altitude. The other is a number the Computech computer can understand, Air Density Ratio (ADR).
The first tells you what altitude the engine "thinks" it is at. For instance, central Iowa is actually about 1,200 feet above sea level. But, on many of those hot, humid, summer nights, the Density Altitude will indicate we're at 4,000 feet. You need a lot less fuel to run at 4,000 feet than at 1,200. Think of the ADR number as a correction factor the computer uses to tell you how much to change the system from your baseline settings.
Baseline Settings You need to first establish a base setting. The Computech, or any other gauge, can't tell you how much fuel your engine wants. All it can do is tell you how much to change from your baseline to keep performance equal when the air changes.
To find your engine's baseline, start with your engine builder's recommendations on pill size, high-speed pop-off pressure and pill, and learn to read spark plugs. Assuming everything is right in the cooling system, the temperature gauge can help, too.