"You've got to get more fuel in there," Bradham says of running oxygenated fuel versus standard race gas, "so the first thing a lot of guys will think of is just to go up on the jet sizes until you get what you need. You can do that, but as you go up on the jet sizes you start losing a little bit of driveability--the carburetor won't operate as cleanly. That's because the bigger the jet, the 'dirtier' the car drives, so to speak. When you start rolling onto the throttle on turn exit, the jets start moving more fuel, and the fuel isn't atomized as well because of the bigger holes in the jets.
"You can increase fuel in more ways than just increasing the jet size," he continues. "One way that you can keep the drivability nicer is by increasing the power valve size. That's a delayed fuel enrichment circuit that doesn't initially come in as soon as you roll on the throttle but adds fuel a bit later depending on the power valve you have in the carburetor. That way you can adjust it to add fuel when you are at wide-open-throttle but no part throttle. So that's one way to help the carburetor give the engine more fuel while still maintaining a good, crisp throttle response."
As a professional carb tuner, Bradham knows all the tricks, and he says that Willy's applies several to its carbs built for racing oxygenated fuels, but he was willing to share one more example. "Sometimes you may also need to richen the idle circuit up too," he says. "The idle circuit isn't just for idling around in the pits. It also affects the car when you roll off the throttle on turn entry and through the turns. When you go into the corner and get off the gas, those throttle plates shut and the only thing fueling your motor is the idle circuit. Remember, when those throttle plates are shut, that cuts off the fuel from the main circuit that you've worked so hard to tune. So if you have had to richen up the main circuit for the oxygenated fuel, then you probably will have to richen up the idle circuit too. If you don't, you will heat up the motor on deceleration because it's running too lean. And then because it is too lean, when you get back on the throttle it's going to stumble and fall on its face. And it's going to struggle to pull until you get over that delay when the carburetor is able to get fuel back into the engine through the main circuit."
Besides your carburetor, making the switch to an oxygenated fuel means you may also have to take a close look at the rest of your fuel system. Typically, an oxygenated fuel means 4 to 5 percent more fuel consumption. Typically, that's not enough to require running a larger fuel cell, but Turza says he has seen situations where a racer needed to upgrade their plumbing from the fuel cell to the fuel pump.
A properly tuned engine running...
A properly tuned engine running oxygenated fuel will burn more than a standard race gas. Beyond tuning the carburetor for the application, make sure the rest of your fuel system can handle the increased load. Quality AN fittings like these from Aeromotive are guaranteed to maximize flow for the size, but off-brand fittings may create a restriction with a smaller id.
You can run oxygenated fuel...
You can run oxygenated fuel by simply increasing the jet size in your carburetor, but you will probably notice you engine will start stumbling when you get on the throttle. Carb tuners like Willy’s offer carburetors built specifically to handle the unique requirements of oxygenated race fuels.
As proof of the quality of...
As proof of the quality of its oxygenated fuels, VP has a large stable of drivers that have made it to victory lane burning the stuff. This includes Mike Pegher Jr, who won an incredible 12 of 36 crate races in 2011 driving for Geisler Racing.
"I can't say you have to run at least a -10 AN line or something like that," he says. "And really it's never the fuel line that's the problem. But sometimes your AN fittings can be a problem and limit fuel flow. It's never the quality name brand stuff like Earl's, Brown and Miller, Goodridge, or guys like that, but the private label or import stuff that's really cheap. Sometimes the inner diameter (id) on those fittings isn't as large as the name-brand stuff and it can cause a restriction in the fuel flow from the cell to the pump. You may not notice it with standard race gas, but when you move to oxygenated fuel and are trying to move more through there, you may wind up with a restriction you didn't realize you had before."
Oxygenated fuels can also be harder on components in your fuel system. It's probably because oxygenated fuels typically contain greater amounts of methanol in the blend, but you will need to keep an eye on rubber components like the power valve plunger, carburetor gaskets, and your fuel pump and pressure regulator. Oxygenated fuels aren't as corrosive as alcohol fuels, but they certainly are more aggressive than standard race gas. And if you are racing an older fuel cell, you may need to consider replacing the foam. Newer foams are unaffected by new fuel blends, but older foam can be dissolved by oxygenated fuels. If you start running an oxygenated fuel and notice your engine stumbling or trash in the carburetor, make sure to check your fuel cell.
Besides needing to burn more of it compared to a standard race fuel, oxygenated fuels are also a bit more volatile. That doesn't mean that it's going to blow up in your face or anything like that. It simply means that it contains more "stuff" in the blend that will evaporate into the air more quickly than a standard gasoline.
"The shelf life of an oxygenated fuel is going to be less than a standard race fuel," Turza says. "One thing that we highly recommend at VP is it's OK to put the fuel in those plastic jugs going to and from the racetrack. They make life a lot easier when trying to fuel the car at the racetrack. But when you get back home, you want to get any leftover fuel back into that steel drum and get the bung back on nice and tight. The light ends of the fuel will evaporate into the atmosphere. And you may not realize it, but those plastic jugs are porous to that stuff, and over time the light ends of the fuel will evaporate right out. When that happens the fuel will still burn, but it has lost some of what gives it its power enhancement. So make sure to keep it in the steel container we package it in for storage."
If you aren't already, Turza also recommends running a return line from your fuel regulator. That's because oxygenated fuels are more susceptible to heat. "These fuels sometimes have a tendency to go into vapor lock because of the increased under hood temps on these race cars," he explains. "I have seen guys run a deadhead regulator where the fuel is stuck in the carburetor and fuel pump when the car is under caution and the engine is barely running above idle. The fuel isn't getting used as fast so it has more time to pick up heat, and that's what leads to vapor lock. The oxygenated fuels are more sensitive to this, so I definitely recommend insulating your fuel lines and running the extra fuel back to the fuel cell by using a return line. That keeps the fuel circulating under caution so it won't heat up as badly."
Thankfully, Hendren says that after many hundreds of rebuilds, he hasn't seen any signs that running a good quality oxygenated fuel is any harder on a race engine than standard race gas. So if your racing class allows it, you are willing to make a few changes to your race car (and can stomach the higher fuel bill), an oxygenated race fuel may be an easy way to help squeeze a few more horsepower out of your racing engine and give you an edge over the competition.