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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.
Copyright© French Grimes Race
Systems 2004
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