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Fuel Injection Jetting for Ram Air

For a mechanical fuel injection (MFI) engine with a forward facing air scoop, ram air into the scoop increases with speed.  At about 200 MPH, a 14% increase in air was determined in our drag racing car as an example.

A corresponding increase in fuel was the best way to maintain an optimum air to fuel ratio.  In our case, that was 3.4 to 1 for blown methanol.

For MFI, that increase can be done in several ways.

MFI WITH HIGH SPEED BYPASS

The high speed bypass can be shut off for ram air at high speed for the enrichment if it is the proper size.  The shut-off function can be done with a manual/valve, pressure/solenoid/valve, or timer/solenoid/valve.

EXTRA NOZZLE

For MFI fuel systems with a main bypass, an extra nozzle can be added.  It is off at low speed.  As the speed increases, the nozzle can be enabled with a manual/valve, pressure/solenoid/valve, or timer/solenoid/valve.

Note: Some MFI fuel systems are run without a main bypass.  Nostalgia Nitro drag racing is an example.  This method will not work in that case.  With the extra nozzle, only a drop in fuel pressure would occur.  No added fuel would be delivered with ram air increase.

ENGLER STUMBLE VALVE

The unique Engler stumble valve can be added to a bypass circuit.  It operates opposite to a high speed poppet.  As the fuel pressure increases, the stumble valve will shut down.  In the bypass circuit, that will richen the engine.  The stumble valve by itself will automatically initiate with fuel pressure.

Note 1: That would occur in low gear as well if the engine is revved high enough.  To disable that, a manual or timer controlled shut-off valve would be needed.

Note 2: The Engler stumble valve bypass requires an inline jet to restrict the fuel flow when the valve is open.  That jet restriction is part of the bypass circuit for tuning.

PROCALC

Jetting for proper enrichment for high speed ram air can be done with our ProCalc MFI jetting calculator.  Lining up the nozzle or bypass jet sizes can be done to maintain an optimum air to fuel ratio throughout a race.  Enabling pressures can be determined as well.  We can also provide this setup service and training with our ProTune & ProTune Advance services.

EXAMPLE

In a 225 MPH top dragster, a 0.060 in diameter high speed bypass was initiated during the low speed portion of the run.  At 200 MPH the high speed bypass was turned off to maintain a 3.5 to 1 air to fuel ratio above 200 MPH for the blown methanol engine.

Note: Without this function, the spark advance had to be reduced about 10 degrees as a band aid to the leaner running engine from ram air.  The car ran more consistently with fuel enrichment for ram air than with ignition retard for ram air.

WITH NITRO

Especially with low percentages of nitro for match racing, enrichment for ram air is better for tuning than an ignition retard alternative.  An optimum air to fuel ratio can be mapped & maintained throughout a run with proper enrichment for ram air.

 

Rons Fuel Injection FAQ’s

Ron Fuel Injection makes cost effective throttle body kits, throttle assemblies, fuel pumps, & other parts for both normally aspirated and supercharged engines; and EFI setups with HALTECH engine management systems.

Excerpts from their site to common questions about fuel injection:

“WHY SHOULD I SWITCH TO ALCOHOL (METHANOL) FROM GASOLINE?
… makes the car a more consistent performer.
WHY SHOULD I CHOOSE ALCOHOL INJECTION OVER AN ALCOHOL CARB?
… mechanical fuel injection does not utilize a venturi (restriction) to draw fuel into the engine … Without this restriction, and with no heavy fuel to deal with in the intake …
WHAT INJECTION SYSTEM IS BEST FOR MY APPLICATION?
… can be outfitted with the correct sized throttle body to work on virtually any combination …
WHAT ELSE DO I NEED TO PURCHASE?
… RONS prices their systems as complete units.  These kits include the throttle body, combination barrel valve/fuel shut-off, …
ARE USED SYSTEMS A GOOD DEAL?
… in most cases the system will need parts replaced or changed for your particular application …”

Click on http://ronsfuel.com/faq.cfm for the details.