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.
Pull a couple of spark plugs and look for tiny flecks of silver on the white of the porcelain. Those specks are aluminum from the piston-a definite confirmation of a too lean condition. At that point, the driver probably felt the engine "popping" near the end of the straightaway. Raising the high-speed pop-off pressure will cure that. You can be lean without specks; they just tell you you're about to have some serious trouble.
I look for a plug that's just showing a light brown color on the porcelain and a heat, or color line, on the curve of the electrode. From the tip to the curve will be a lighter color than the base. If the lighter color runs around the curve and down toward the threads, you're too lean. If the color doesn't make it to the curve, you're too rich.
These are very basic techniques. I still take plugs to Nelson for an experienced "read." You should work with your engine builder to get a good, solid opinion.
Adjusting The MixI like to run my engine a bit on the rich side. A slightly rich engine makes more torque and lives. A lean engine makes more horsepower and, if you're not careful, dies an unpleasant death.
Let's say you plug the ADR number into Computech's computer. It tells you to install a #70 main bypass pill in place of your base, #64 pill. That'll bypass more fuel and lean the engine. You do it and the engine takes off fine, but gets lazy at the end of the straightaway and blubbers just as you roll into the turn. Or, if the opposite was the case, you change from a #70 to a #64, the car takes off fine again then, halfway down the straight, the engine begins popping and slowing down, but recovers once you burp the throttle or the resistance of turning lowers the engine rpm.
You forgot to change your high-speed to stay in tune with your main. Even though, in the first example, you leaned the main, the engine is still too rich on the top end. That's because by putting less restriction in the main line, (that bigger, #70 pill) you lowered the pressure in the entire fuel system by 6 to 9 pounds. The high-speed bypass you carefully set at, say, 65 pounds, never opened because the system pressure never got that high. What you needed to do was lower the high-speed's pop-off pressure accordingly.
In the second example you raised the system pressure by the same amount and caused the high-speed to open early, leaning the engine on the top end, even though you intended to richen things. I like Kinsler's diaphragm high-speed bypass, because you can simply loosen a lock nut and turn the adjusting screw 11/48 turn for every .002 inch of main pill size you change. When you went from that #64 pill to the #70, you needed to unscrew the Kinsler high speed 31/48 turn. If you go from a #70 down to a #64, tighten it 31/48 turn. If you use one of the can-type high speeds, take it out of the return line, open it up and subtract or add shims to lower or raise the pressure anywhere from 1 to 211/42 pounds for every .002 inch of pill size.
Waterman recommends changing the high-speed by 1 pound for every .002 inch of pill size. I've always used the 211/42 figure. You'll need to do some experimenting to find what works best for your engine. BR Motorsports carries a high-speed checker with a big, easy-to-read gauge that's awfully handy no matter what type of high speed you use.
High-Speed FlowIf the high speed is such a hassle, isn't there a way to get by without one? The answer is a simple, "no." Today's pumps, like the Waterman, put out so much fuel that you absolutely must bypass the excess. And the problem gets worse with every rpm the engine turns.
My Waterman 400 (a typical pump for a 360) puts out 2.9 gallons per minute at 6,000rpm. At 8,000rpm it is flowing 3.9 gallons per minute. A 360 might use around 2.1 gallons per minute in race conditions, at a wide-open place like Knoxville. The excess has to go somewhere. Without a high-speed bypass that opens somewhere in the second half of the straightaway, the fuel will simply force its way into the engine through the nozzles (refer back to the discussion on fuel bind).
Why not downsize the pump? Since fuel injectors don't have an accelerator pump to add extra fuel for the starts, according to Waterman, "You need a pump that will supply roughly double the amount of fuel required on the top end to have enough for the bottom end. At idle, the pump only puts out about 1 gallon per minute. That's barely enough to keep the engine running."
Another thing to consider is rpm. If you normally turn 7,500rpm with your high-speed set at, say, 65 pounds, and suddenly decide to gear the engine for 8,000rpm, you actually need to bypass more excess fuel. Remember, the problem gets worse with rpm. Again, we turn to Waterman for a tip: "Everything is based on percentages. If you go up 1 percent in rpm, you need to reduce the fuel by 1 percent, divided equally between the main and high-speed bypasses."
Never try to heat up an engine, or cool it down, with fuel. If you're only running 140 degrees on a cold night and the Computech tells you to richen the engine more, do it! Then, cover the radiator to build heat. I've seen blown engines caused by someone leaning them down to build heat. Check for head gasket problems, a worn water pump, a blocked radiator, a bad cap, or restricted lines if it runs too hot.
I certainly didn't develop these methods; I learned them from Dyer, Nelson and Waterman. You have access to experts at your track and your engine builder's shop, so use them! You'll save yourself some money and go a little faster, too.