Engine setback

[keeks]

When dealing with a dlm on a fully constructed chassis how do you define setback? If the rule states "up to 6" setback" is that from the chassis manufacturers motor mount?

What advantages can be gained by moving the motor back if this is the case?

[TALON75]

It is usually from the upper ball joint to #1 spark plug. Advantage is more rear percentage.

[Matt49]

It is from the upper ball joint back to the #1 spark plug measured in a line parallel to the centerline of the car (not straight from the ball joint to the plug).

The most easily understood advantage to more setback is that it is easier to get your percentages where you want them if you have a steel block or all steel motor.

The not-so-often discussed advantage is that you decrease the car's moment of inertia. Google it for a scientific explanation but the best way I can explain it is that it's easier to rotate an object that has the bulk of its mass primarily at the center versus rotating an object (of the same mass) with its mass out near the edge.
Think about a spinning figure skater. What happens when they bring their leg in?

So a car with the bulk of it's weight closer to the center of the car will rotate (turn) easier, steer better, be easier to catch, etc.

[grt74]

It is from the upper ball joint back to the #1 spark plug measured in a line parallel to the centerline of the car (not straight from the ball joint to the plug).

The most easily understood advantage to more setback is that it is easier to get your percentages where you want them if you have a steel block or all steel motor.

The not-so-often discussed advantage is that you decrease the car's moment of inertia. Google it for a scientific explanation but the best way I can explain it is that it's easier to rotate an object that has the bulk of its mass primarily at the center versus rotating an object (of the same mass) with its mass out near the edge.
Think about a spinning figure skater. What happens when they bring their leg in?

So a car with the bulk of it's weight closer to the center of the car will rotate (turn) easier, steer better, be easier to catch, etc.

someones doing there homework,very well said

[roe dale burton]

well said matt!

[keeks]

Thanks everyone.