Consistency is the name of...
Consistency is the name of the game in bracket racing and the same goes for the fuel used when tuning your car. We get our Rockett Brand 118-octane fuel by the drum, so we don't have to rely on what the track can supply. Remember that different brands of fuels, while having the same octane rating, have different percentages of lead, oxygen, and alcohol, which respond differently to jetting changes. By having our own independent supply of fuel we know we're using the same fuel we tuned our motor with, helping take the guesswork out of diagnosing fuel related issues if they occur. (Editor's Note: Notice the lack of long pants and use of sandals. Please do not try this at home, we are trained... something-or-other.)
With our jetting close, we...
With our jetting close, we bumped the ignition timing from our baseline of 36-degrees total advance to 40-degrees total advance, resulting in a gain of two-hundredths of a second and almost one mph. This engine definitely likes more ignition timing, and we will likely see further gains by experimenting in this area later. Remember, we found the timing tab on our timing cover to be some four degrees off true top dead center, so subtract four from our above numbers to attain our engine's true ignition timing.
Remember that we're limiting our rpm to 7,000 until we can install the second oil feed line to our oiling system, and our camshaft actually makes power up above 8,000 rpm. Once our oil system is complete, we will certainly shave some elapsed time by raising our shift points closer to 7,500 rpm. We will also add more ignition timing to the engine as it responded well to our first increase in timing. Our rule of thumb is to add ignition timing until no further increase in performance is seen, or until the engine begins running noticeably warmer (an indication of detonation) during a pass down the track. Our engine was happy and responded well to 40-degrees total advance, so we'll bump the timing again during our next test session. This may seem like a lot of ignition timing, but remember unless you have checked the tab on your timing cover for accuracy the numbers are somewhat ambiguous. We checked our tab during assembly when we were degreeing the camshaft and found it to be some four degrees off true top dead center, so our 40 degrees of advance is actually only 36 degrees. Optimum ignition timing varies widely from engine to engine and is dictated not only by compression and fuel octane, but by cylinder head and piston design, weight and gearing of the vehicle, and other variables. We always begin at around 36-degrees total advance on aluminum headed big-blocks and adjust to whatever makes the car run quickest without overheating.
So there you have it, our 500-inch wedge accomplished the goal we set of low-nines in our nearly 3,100-pound Barracuda. We will experiment later with more tuning and induction changes to try to improve our combination, but for now we're just going to race it. after our initial testing session we entered the Southern Nostalgia Nationals at Lakeland Motorsports Park and won our class both days of the two-day event! The following weekend we entered the Georgia Southern Bracket Nationals where we went several rounds each day among a field compiled of 90-percent dragsters (which in our opinion are purpose-built race vehicles, not cars) driven by the best bracket racers from around the country. The first race we'll enter at a quarter-mile strip is the Snowbird Nationals in Bradenton, Florida, and we'll keep you posted as to how we run at that event.
We shift our own gears in...
We shift our own gears in this car and use a tachometer that incorporates a shift light so we can be consistent. We only make one change at a time when tuning our cars so we know if the change we made actually helped or hurt. Missing a shift could skew the data on our time slip, so our driving technique has to be duplicated each pass down the track. Once we get the rest of our Milodon dual-line oil system installed, we'll bump our shift points up closer to 7,500 rpm to take advantage of our engine's top-end power.
Performing a consistent burnout...
Performing a consistent burnout is also important when testing or racing your car. We begin our burnout in second gear and shift to third as soon as the tires are spinning freely. Experience has taught us how long to perform the burnout in our car to get the tires sufficiently heated so they stick. Doing a simple count in our head proves to be the best way to time our burnouts so they are consistent. We also creep into the staging beams slowly and stage as shallow as possible so we know the car is in exactly the same place each time we launch. Deep staging can improve reaction time, but will slow the cars elapsed time because the car doesn't get the run on the track it does when shallow staged. Whatever technique you're comfortable with, just make sure you do it consistently so your timeslip accurately reflects the changes you make when tuning.
Traction is an issue anytime...
Traction is an issue anytime you're testing at the track. If the car spins your timeslip will reflect it by showing slower elapsed times. Most spinning occurs in the first 60 feet of the track, so the incremental times between 60 feet, 330 feet, 660 feet, 1,000 feet, and the traps can still be used to judge performance with some accuracy. As a measure against tire spin, we set our rear tire pressure with a couple of cars in front of us in staging so our tire pressure is consistent when we begin our burnout.