French Grimes Race Systems

The Motec/Grimes Cross-Ram Fuel Injection
Offers a broader torque band and increased horsepower

French Grimes Race Systems has been working with Motec, an Australian fuel injection company, to develop a new multi-piece cross-flow injection for small block Chevys.

(Excerpted from Doug Gore, Open Wheel Magazine, July 1995)

The maximum power that any engine can produce depends on the quantity of air that moves through it. Anything that increases the amount of air moving through an engine at a given speed always offers the possibility of additional horsepower at that speed. All engine induction systems are sensitive to intake tuning.

Fuel injected engines with individual intake runners are particularly sensitive to ram tuning effects. Relatively long runners have lower resonant frequencies than shorter runners, just like organ pipes, and they produce the greatest ram effect at lower engine speeds. That equates to increased low end torque. Short intake runners enhance an engine's high speed performance.

The cross sectional area of the intake runners is also important. For a given amount of airflow, meaning a given engine displacement and speed, the velocity of the airflow in the intake runners will proportional to their cross-sectional areas.

The larger the runner area, the lower the airflow velocity will be. Lower airflow velocities experience less flow resistance, or drag, within the manifold and thus moves air into the cylinders for a given vacuum signal. On the other hand, lower velocity airflows do not produce as great a ram tuning effect as faster airflows, nor do they carry fuel droplets along as well as faster airflows.

Numerous modifications and hundreds of dyno pulls were performed. In it's current form, the Motec/Grimes cross-ram injection system increases engine torque by more than 100 foot-pounds between 3500 and nearly 5000 RPM, and then maintains an average torque increase of nearly 50 foot-pounds out to 7200 RPM.

As impressive as the cross-ram injection's increases are, the relative flatness of the engine's torque curve between 4000 and 7200 RPM is even more impressive. This is not something that one might expect with a ram-tuned intake manifold, and it's a real benefit to the overall drivability of a race car equipped with this injection system. Engines with relatively flat torque curves just keep pulling throughout their powerbands.

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