Throttle body stacks … Air flow and performance

[eight-six]

The basics from what I understand are … the longer the stack the more mid range and torque, and a shorter stack means more top end and power.

However are there any thoughts around how much air space you have in front of the stacks? Does it matter?

If I had some long stacks fitted to a set of throttle bodies and the end of the stacks was close to a bulk head etc would that be an issue, will it affect performance etc? Were talking maybe 2 / 3 fingers width close.


On another subject what can be done to improve air flow into the stacks? From what I have seen a flat plate mounted behind the radius edges of the stacks is recommended. Obviously some form of cool air feed would also be helpful. Any other pointers? The stacks will be run open so no filter considerations to worry about.

Cheers

James

[jondee86]

As I understand it, it is the total tuned length from the valve
head to the open end of the trumpet, that is important. The tuned
length determines at which rpm bands you will achieve torque peaks
due to the "ram" effect of reflected waves in the intake.

Having the open end of the trumpet close to a bulkhead can have two
effects. The first is simple interference with the airflow into the open
end, and the second is interference with the reflected waves. If the
distance from the bulkhead to the open end was adjustable, you may
even be able to obtain some benefit from "tuning" the gap.

A trumpet with a fully rolled lip is said to improve the airflow from
behind the stack. This air has to make a 180 degree turn. However,
the improvement in flow is somewhat less than obtained by just
having a nice trumpet with an elliptical curve or better still, parabolic
curve. Allowing air to enter evenly around the whole circumference
of the trumpet would be good for efficiency also.

Using a trumpet with a plain flaired lip and putting a flat plate hard
against the back of the lip would be a nice arrangement.

Cheers... jondee86

[F0Bman]

Depends on what type of cams and tuning you want to do. Look up Helmholtz Resonance to find the right power band.