Making maximum horsepower takes a package that includes the regulation of the mixture of air and fuel going into the combustion chamber. The most accurate way to monitor that element is to measure the ratio coming out of the exhaust.

We recently tested a Late Model stock car and used the F.A.S.T. Dual Sensor Air/Fuel Meter system to make sure we had the best A/F combination. You'll probably remember that in the Apr. '07 issue of Circle Track, we tested this system on an engine dyno in North Carolina.

Not long ago, we went to a chassis dyno and made several runs testing different air filters, timing settings, and carburetors. We learned a few things.

Dyno Test We borrowed the dyno from the racing shop run by Doug Elliot in New Smyrna Beach, Florida. After several warm-up runs, we did some serious dyno testing. First, we played around with a taller air filter and made a gain of about 6 hp. Then, we checked timing and found that we were off by about 5 degrees on the low side.

We increased the timing and pulled in another 5 hp. Things were looking up. Then we decided to try another carburetor that was brand new. This was a very good carb. That should have increased the horsepower, but it did not. In fact, it was around 8 hp less. We checked the jetting in both carburetors, something that we should have done in the first place, and the new carb had jets one size larger.

The F.A.S.T. meter told us the story, too. The A/F ratio was fatter (more fuel to air) with the new carb. We then changed jets in the new carburetor and gained another 4 hp over the old carb. Now we were getting somewhere. We were comparing apples to apples.

The next area we played with was pinion angles. We were off on the pinion-to-driveshaft-to-tranny shaft angles. We had way too much angle in the pinion to driveshaft, so we rotated the rear end to where our angles were around 4-5 degrees at both ends of the driveshaft.

The rule of thumb is to have equal and opposite angles at the two ends of the driveshaft. I read about that some 40 years ago in Hot Rod magazine as a teenager. I remembered it often as I helped the local hot rod guys work on their cars.

The rule is right on-we immediately saw a gain on the dyno of another 3 hp. That may not sound like much, but with a 335hp crate motor, it is significant. The harmonics should have been much better now with less vibration to wear and shake the U-joints.

Remember, pinion angle relates to the angle between the driveshaft and the pinion, and the angles between the transmission output shaft and the driveshaft must be close to equal that of the pinion, but in the opposite direction. Pinion angle relative to the ground is of no use to us.

Track Testing Once we had tuned the car on the dyno, we then headed to the track to do a test before the first race of the year. The car is an ASA Late Model Series South entry and our test was at Bronson Speedway, the location for the first race of the year.

After shaking the car down, we installed the F.A.S.T. air/fuel meter to see how the A/F ratio looked. The air was a little cooler than when we ran the dyno test, and the meter showed that. We found that there was more air density at the track test than when we did our chassis dyno test.

So we installed a set of jets that were one size larger to compensate, and the A/F ratio was then identical to the dyno test where we tuned for maximum horsepower. Lean is good for horsepower, to a point. Lower-horsepower motors need fuel, and going too lean is not only asking for trouble in the form of burnt valves, but also hurts horsepower at some point.

The F.A.S.T. meter can be used in most series and at most racetracks up until the cars are ready to qualify. I had a friend in the mid-'90s who had a small computer that calculated the correct jetting to use based on information from the dyno test compared to the air density, moisture content, and temperature of the air. That was, at the time, a good way to ensure the carburetor jetting was close.

With the A/F meter, you can precisely measure the ratio of air to fuel at any time of the day and make the necessary changes to the jetting to compensate, knowing that the engine will be performing to maximum horsepower. The addition of the chassis dyno test only serves to enhance the use of the meter.

We were able to find the exact A/F ratio that this motor liked and that produced the most horsepower and maintained that ratio at the racetrack. The unit is very easy to use and can tell you the A/F ratio on acceleration, differing rpm, and at coast-down. With that information, you can tune the jetting, power valve, and other settings that affect the final A/F ratio measured at the exhaust.

For peace of mind, knowing the engine is jetted properly and giving you the most power possible, this meter is almost a necessity. When we raced our car, we noticed several other cars that were belching flames out of the exhaust going into the corners. Those motors had to be running rich, and we know how much power is lost that way from doing our dyno test. Don't make that same mistake.

The crew makes adjustments to the Coleman third link in order to change the pinion angle in the car. We found that we had too much pinion-to-driveshaft angle and not enough driveshaft-to-transmission shaft angle. These needed to be equal and opposite for maximum power and reduced harmonic imbalance.



Marty watches the dyno readout as Dalton makes another run. To make all things equal, the water temperature and oil temperature should be the same for each run. We ran back-to-back runs where these temperatures were different and saw a sizeable difference in horsepower with no other changes.