Racing Tuning Evolution vs Status Quo Tuning

We studied the evolution of racing over the years and watched dramatic mechanical fuel injection (MFI) tuning differences over multiple seasons of racing.  Within a short time period, however, MFI tuning was very uniform between most competitors in a given racing class.  A status quo combination emerged almost every year, with tuning information exchanges between rounds, between competitors, as well as between manufacturers.

Status Quo Tuning Limitations in MFI Setups

Participants in racing categories often become expert in the status quo setup.  However, many racers do not ever gain a real understanding of the science to make more power beyond the status quo practices.  That includes tuning practices for various fuels as well as mechanical fuel injection where it is used.  For example, methanol has a dissociation characteristic that few racers are aware of.  Yet, tuning changes can affect power and backfiring from unintended chemical dissociations that occur in methanol fueled racecars and boats.  Experienced racers are often unable to go beyond the status quo setup common within that season.

Many engine builders and tuners are good at ‘connecting the dots’ for a new combination that is in-between other combinations that are known.  Some are good at ‘extrapolating’ a combination from one that they experienced.  However, we witnessed some very successful racers who were completely lost on new combinations where ‘connecting the dots’ or ‘extrapolation’ did not work.  Some racers are the first to admit little understanding of fuel injection science or racing fuels science.  They often proceed slowly and many times do not go beyond a conservative combination.

Others exaggerate the value of their experience and take blind shots at new combinations.

The myriad number of racing engine failures that occur at just about any racing event around the world are an indication of that frequency.

New MFI Tuning Problems from Several Rows of MFI Nozzles

For example, ‘exhibition’ nitro classes in drag racing along with ‘outlaw’ ProMod racing are categories with new tuning challenges.  These combinations open up new tuning tasks and ranges beyond those developed for racing within common class rules.  Outlaw ProMod, for example, may have several rows of engine nozzles:

• idle dribblers that may be ‘on’ or ‘off’ for the high end
• port nozzles that may be ‘off’ or ‘on’ for idle/low end
• blower lubers that may be added to traditional MFI nozzle layouts.

One setup had fogger nozzles just beyond the throttle plates of the hat injection throttle body, well above the inlet.  New tuning problems emerge such as fuel split between different layers of nozzles.  I saw hat-to-port nozzle fuel splits range from 90-10 to 10-90 and every ratio in-between.  Engine failures are common.

Endless Fuel Distribution Problems

A problem is the fuel distribution influence from each row of nozzles.  I saw some ridiculous combinations with fuel bias to the front of an engine from larger front hat nozzles together with fuel bias to the back of the engine from larger rear port nozzles.  It looked like the port nozzle arrangement was a band aid for a poor hat nozzle layout.  The well experienced tuner for this setup could not describe how he got to this result.  Trial-and-error tuning for air density corrections seemed to be endless.  Spark plug readings varied indicating a moving target for engine temperature management.  The engine frequently banged the blower at the finish line.

Gordon Tarbell, drag race auto & motor cycle MFI tuning expert, has experience with good fuel bias in MFI hat nozzles by turning a deflector tip nozzle a few degrees from vertical, toward the front or back, to better distribute the fuel.

Row of Nozzles with Pressure Poppet

Another tuning problem is from different rows of nozzles that are enabled or disabled by fuel pressure poppets.  The engine speed is the major contributor to MFI fuel pressure.  In one case, changes to bypass jetting done ‘between rounds’ messed up fuel distribution in the subsequent round.  Closer examination revealed a pressure poppet in the port nozzle feed line intended to disabled the port nozzles for idle.  A change to the main bypass dropped fuel pressure, holding the port nozzles ‘off’ for a greater part of the run.  Port nozzles were then unable to compensate for the fuel distribution coming from the hat nozzles alone.

When the fuel pressure is changed from any jetting adjustment, pressure poppets throughout the system will open or close at different engine speeds.

That can change the fuel distribution.  Add a high speed bypass, fuel pump sizer on a pressure poppet, or a pump saver, and the fuel curve can quickly become unmanageable.  That was also the case in the first example.

AFR Mapping With ProCalc (now named MFIcalc) Analyzes Jetting When Nozzles Are ‘Off’ or ‘On’

We are now doing air to fuel ratio mapping using our calculator, ProCalc (MFIcalc).  This mapping can really sort out a fuel system.  In some cases, we are finding ridiculous combinations of air to fuel ratio changes.  They can occur at different engine speeds and fuel pressures. as a result.  Engines are set up to go overly rich, then overly lean to compensate, then overly rich to recover.  This is called ‘teasing the engine’ by some.  Fuel distribution can change with bypass jetting adjustments for air density.  The tuning practices in many combinations are based on a lot of experience, but a better understanding of fuel injection science is needed.

Air to fuel ratio mapping with our calculator can provide jetting changes to straighten out many combinations.  Smaller high speed bypass jet sizes, fewer poppets, or different poppet pressure settings are the outcome that makes tuning really simple.

The air to fuel ratio of an MFI system is like a speedometer to a car or truck.  Tuning MFI without knowledge of the air to fuel ratio is like driving without a speedometer.

Only On-the-Job Training (Tuning)

In summary, racers throughout various competition categories with MFI operate from combinations often established by the status quo with tuning information exchanges between rounds and competitors.  Many do not become familiar with MFI science.  A simple tuning routine evolves: ‘run it til it breaks.  Fix or adjust whatever all the others are doing.  Then run it til it breaks.  etc…’

Jetting selections from air to fuel ratio & fuel pressure mapping using ProCalc (MFIcalc) is an alternative tuning tool that can help performance.

Tuning Tip For Blown Engines

Our 6 second blown alcohol drag racing setups were all very simple — without port nozzles.   We had excellent luck with higher fuel pressures.  Distribution of the highly atomized fuel was excellent as a result.  We maintained a constant total jet area with ProCalc (MFIcalc) that sustained a uniform, high fuel pressure.  We also maintained tight control of air to fuel ratio using ProCalc (MFIcalc) to keep a target air to fuel ratio.  That target was in the middle of the operating range of air to fuel ratios for our combination.  The operating range was established by the following limits:

• the lowest numerical ratio that dropped cylinders formed the rich limit
• the highest numerical ratio that melted pistons established the lean limit.

With jetting adjustment discipline to maintain good air to fuel ratio & fuel pressure, the tune-ups were simple.  Running all of the fuel through the hat also kept the blower cool and well lubricated.  It kept manifold boost to a minimum that reduced blower drive power loss.  Low RPM power was spectacular & flat, all the way up to the shifting RPM and in high gear, all the way to the finish line.

Air to Fuel Ratio Target Remains Consistent

While jetting was different for different air densities, we found that the middle of the air to fuel ratio range remained the same numerical value.  While jetting was different for different blower sizes and blower overdrives, again the middle of the air to fuel ratio range remained the same numerical value.

Tuning for an air to fuel ratio target at a consistent high fuel pressure was really easy with ProCalc (MFIcalc) for any variation in air density, altitude, blower wear, blower size, or blower overdrive in our simple setup.

For variations in all of the above going on at the same time, trial-and-error jetting is almost impossible without the calculator.  However, jetting combinations are really easy to determine with the calculator to maintain both an ideal air to fuel ratio and a consistent high fuel pressure.  In fact, specific blower overdrive changes can easily be determined with the calculator to compensate for altitude or air density changes.  The same low altitude power level can be maintained at high altitude with an appropriate blower overdrive change determined with the jetting calculator.

Case History

In previous 7.9 second bracket drag racing class outings, most of our rounds were maintained at 7.90 with only blower overdrive changes to compensate for air density changes.  No changes were done in the racecar setup or jetting.  Air to fuel ratio was maintained to a constant value as the air density changed.  That is one advantage of a Roots blown bracket racer with appropriate blower overdrive determinations.