Our Project Dirt Late Model team recently made the switch from a 112-octane race gas to VP's 113. We chose the 113 for a couple of reasons. First off VP does race fuels and only race fuels. Second, VP's 113 vaporizes extremely well and equalizes out exhaust gas temperatures. Think of your engine as eight individual motors (the cylinders). Each "motor" doesn't have the same cooling efficiency because of the water jacket design. If you could somehow even out the air/fuel ratio out among each cylinder then you can theoretically achieve a more consistent burn throughout the engine. The good vaporization characteristics of 113 would achieve just what we wanted.
Change those Jets
VP's Technical Director Freddie Turcza told us that once we made the change to 113 we needed to change the jets, because the octane rating of our new fuel is different than the old fuel. Changing the jets on a carb is probably one of the easier things you can do on a race car. But if you've never done it follow these simple steps. You may want to keep a metal bowl handy under the carb to catch any fuel that might spill out. Simply remove the four bolts and pull the primary fuel bowl assembly back resting it on the metal bowl, then you will be able to remove the metering body, exposing the jets. Removing the old jets on our carb required a flat head screw driver. But our new jets from Comp Cams would use a hex driver.
Here's a close up of the new jet on the right and the old one on the left. -Comp Cams
Conventional jets are mass produced with a wide tolerance, and then plated. Many of these
These mass produced jets also use a "slot" that requires a special, expensive tool to inst
Here's a close up of the Comp Cams Max Jet, note the 5/16-inch brass hex design that makes
The nut driver design results in zero damage to the bowl. -Comp Cams
The new jets from Comp Cams use a 5/16-inch nut driver, a much safer design. -Rob Fisher
That's right, I said Comp Cams. Among the general racing population the fact that Comp makes carburetor jets is not that well known. In fact, it's a pretty well kept secret, although not intentionally on Comp's part. In any event, Comp's virtually indestructable Max Jets are produced with 5/16-inch hex-stock brass that delivers a solid jet that can be installed with no damage to the inlet bowl.
Conventional jets are mass produced with a wide tolerance, and then plated. Many of these jets use the same orifice size with the only difference being different angle tapers to change the flow-rate characteristics. These mass produced jets also use a "slot" that requires a special, expensive tool to install, but most people just opt for a flathead screwdriver. Using a screwdriver on these jets can cause damage that creates a turbulence that severely affects the fuel flow as much as 50 percent. Max Jets' hex-stock brass uses a simple 5/16-inch nut driver resulting in zero damage to the bowl
With the old jets out of the carb and the new jets in, we can now replace the metering body, fuel bowl and put the bolts back in. Do not forget to change the jets in the secondary also.
Since we were changing fuels, we also took the opportunity to install a new inline fuel fi
The Future of Race Gas
The future for race gas is pretty wide open at this point. Some sanctions like IRL and ALMS are pushing full steam ahead with alternative fuels while others like NASCAR have recently made the switch from leaded to unleaded. In the short track world, fuel choice is still largely up to the racer. But what is clear is that technical development will continue on into the future.
"Every three or four years we go through this cycle of thinking we've topped out in terms of technology for race gas," says Burns. "Then some time passes and we develop several new formulations and say 'how come we didn't think of this three to four years ago?'"