[F-1Rodder]

I have read dyno articles and note that sometimes a HP and Torque improvement comes from adding a spacer, usually some sort of plastic material, in between the manifold and carb.

What are the flow dynamics that explain this result. Why does it work sometimes to produce more power and sometimes not?

[unstable]

METHINKS (don't know) that it has LESS to do with the flow dynamics and MORE to do with cooling off the fuel by seperating the carb from the manifold.
Cooler fuel = good.
Hotter fuel = bad.

[sheppard00]

it also gives the fuel more time to drop and helps with mixture. it also gives you more plenum volume which alows each cylinder to have access to a bigger gulp of air and fuel.

the reason it somtimes doesn't help is because of the head cam and intake combo itself. if the amount of plenum is enough for your combo adding more won't help

[bullheimer]

sounds good to me. i have also read dyno results in HRM where they said they made less torque/ also agree that making air cooler would always help, it seems! it looks like you have to put one one, run it and see what happens. a $30 experiment.