Here is the Racepak unit installed...
Here is the Racepak unit installed in our Late Model. We finished this temporary installation in time to do some testing the following day. The unit can be removed for races in about 20 minutes.
Many stockers run from 4,400 to about 5,800 rpm, with an engine acceleration rate at about the 300 to 400 rpm per second mark. Axing 20 pounds out of a stock diameter Chevy flywheel resulted in an average gain of almost 8 hp. We have not even considered the effect of reducing the weight of an equally heavy clutch yet.
So far we have established the worth of low MOI in terms of output as measured at the flywheel. But what the Super Flow dyno tests don't take into account is the fact that they only include the MOI of the engine's rotating mass and the dyno's absorber mass. In the real world, cars not only have flywheels, but also a clutch, transmission, and wheels-all contributing to an increase in MOI. Although the reduced flywheel mass as measured on the engine dyno looks good on paper, the reduction of 20 pounds or so of flywheel mass may become insignificant, or even actually get lost, when both the MOI and friction losses from all the other components downstream of the flywheel are taken into account.
The engine dyno has certainly pointed us in the right direction, but a chassis dyno test under accelerating conditions would be needed to deliver a final and indisputable verdict. Some dyno tests I did with Cerra Racing in Rock Island, Illinois, on its Dynojet chassis dyno revealed what we can expect the rear wheel power output to do when a change is made from a stock 23.75-pound flywheel to a 10.8-pound Fidanza flywheel of the same diameter. Our test vehicle, powered by a small-block Ford engine, had a little more power than a Street Stock or even a Late Model car powered by a crate motor, but the results are nonetheless relevant. Within the speed range we tested, the lighter flywheel was worth around 10 hp at the rear wheels.
It would be difficult to make...
It would be difficult to make a stock diameter flywheel much lighter than this.
Some track testing backed up the validity of the chassis dyno tests. Here, a data acquisition system is a boon. At present, we are evaluating the latest Racepak system on Losito's car. Data taken from the Ford-powered test vehicle revealed that the lighter Fidanza flywheel shaved 0.08 second over the speed range from 60 to 130 mph. This may not sound like much, but when it's put into terms of a measurable advantage down the straightaway, it takes on added significance. That 0.08 second represents a lead of 14.4 feet over an otherwise identical car with the heavy flywheel. If you are a racer, you will understand what a big advantage just a few feet is, let alone almost a car's length.
Using some Racepak data we had already gained from track testing at Hickory showed that the speed range we were interested in was nominally from 60 to 95 mph. Plugging all the data at hand into a vehicle-modeling computer program indicated that the lighter Quarter Master clutch and flywheel assembly should be worth about 2 feet per lap. Again, that does not sound like much, but remember we are going from a relatively light race clutch and flywheel to a very light one.
This is the kit we received...
This is the kit we received from Quarter Master. The small diameter of the clutch relative to the proportions of the flywheel is demonstrated.
At most, we are talking about something equal to nearly 5 pounds off a stock flywheel. This 2-foot advantage translates into a lap time reduction of 0.018 second. If we had installed the Quarter Master clutch for our previous race at Hickory, we would have qualified Fifth instead of Tenth, as the qualifying numbers through the field were that close.
We made the clutch and flywheel swap between races. It would have been wise to do a chassis dyno test on the before-and-after effects of the swap, but fixing race damage took all the time we had just getting ready for the next event.
Since we had to take out the engine to put a new front clip on the car, changing the flywheel and clutch assembly only took a few minutes. Along with the flywheel and clutch assembly, a Quarter Master clutch throwout bearing and steel bellhousing were installed.
After practice at the next event, I got Nick's take on the pedal feel. He reported it was just fine and said he could feel the difference in the way the car picked up out of the turns. Maybe we did not need to do that before-and-after chassis dyno test after all!