Volumetric Efficiency Real Example 1995 BMW M3

Volumetric Efficiency Real Example 1995 BMW M3

November 7, 2023


CUSTOMERS CAR – 1995 BMW M3 Manual fitted with a built engine 9.5:1 compression, head work, upgraded camshafts, Vortech V2 TI supercharger kit, front mount intercooler, 775cc injectors and a Link G4+ stand alone ECU tuned by FLI.

Today’s example includes a customer’s very nice car running California 91 Octane fuel and methanol injection. This article is summarized using the exact engine, power package and fuel system in the shop. The internet will tell you all types of information. You can find detailed articles written by engineers, engine builders, computer scientists, mechanics and professors specializing in the automotive industry. You can find fuel calculators, turbo flow sheets, compression ratio calculators, rod to stroke ratio calculators and computer electronics datasheets with detailed info. That is easy. What is NOT easy is to create a Volumetric Efficiency engine with a power package in the real world. This takes expertise and a tremous amount of experience to achieve . FLI has been doing this for 23 years this month, 22 years of which includes a chassis dyno used for testing.


The current engine and power package is close to being as best as you can get given the fuel used. The 3 liter engine (head work, compression, camshafts, valvetrain) is flowing the amount of air that the current Vortech V2 TI supercharger is supplying through the front mount intercooler setup and exhaust system. You can tell because as boost increases so does wheel horsepower. The ignition system seems to be fine along with the wiring of the engine to Link ECU. The fuel system is on the edge and should be upgraded because the current volume of fuel supplied to the engine is not enough. Any hiccups in fueling will cause engine damage. How do we know this? We can install a fuel flow sensor and amperage meter which we use as shop tools and datalog it on the dyno, however, we do not need to perform this because we can look at injector duty cycle and lambda readings under wide open throttle to keep things simplicit.


Below are dyno graphs and a screen shot of a datalog which were taken during a COLD (50 degrees F, 44% humidity) morning where volume is at the highest. As you can see, when we spray belt dressing to eliminate belt slippage, fueling gets richer but the injector duty cycle reaches 100% at 6500 RPM. You NEVER want to go above 95%, In fact you want to stay between 80-90% to give the injector some head room for error. This is because overtime injectors create build up and flow less. A good way to combat this is to send out the injectors to be clean and flow tested once a year (marking each cylinder for reference). What Injector Duty Cycle DOES NOT tell you is volume, just how long the injector stays open. Just like a supercharger / turbo with a certain engine, ignition, intake and exhaust system combination, the only way to find out if that combo works is to tune the package on a dyno and study the graphs. The only way to find out if your fuel system is adequate is to measure fuel volume, amperage to the fuel pump and fuel pressure during the dyno run. FLI could have done this but given our experience we did not have to in this particular situation. FLI recommends our Stage 2 Rear Fuel System and Front Fuel System IF the current pulley stays on and adjusted NOT to slip. FLI’s S2 front and rear fuel systems include new fuel pump(s), surge tank, hardlines, fuel rail, fuel regulator, dampers with Goodridge crimped soft lines and electronics to support. The current fuel injectors can be used to start with and maybe they will need to be upgraded, we will not know until we make some runs with tuning to find out the results with the new fuel system.

If the current belt continues to slip, then the current fuel system is on the edge but is safer. Even with the belt slipping, this car is EXTREMELY FAST.

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