velocity stacks
 

I am currently running dual 40 Webers in 74 1.8.Automotion is advertising Velocity stacks to add power. Questions: What mods have to be made to add these? How much more power can I expect? Still topless in Tennessee

I don´t believe that you can gain HP only with stacks.
In my race car I use different sizes in stacks (short, large) for diferent use in rpm band (diferent cicuits, trans ratios,city altitude).
But in a street car with airfilter I believe is not the same.
Larger are for torque at low rpm, shorter is for high rpm.

If you want install in your carbs is an easy job, you don´t tell what kind of weber (IDA,IDF,DCNF). In my IDA you only push and pull the stacks but in my IDF are with bolts and I need to change gasket.
If you install larger stacks you will need taller air filters.

Hope this helps, but I´m not a wise in this, In the forum exist a lot of people with great know how.

In my opinion save your money !
Buy K&N filter you will have better results !
http://temp.corvetteforum.net/c4/vet...ito_engine.jpg

I put velocity stacks from http://www.cbperformance.com/ on my 44s. I find that the engine runs smoother with them on-not too quantitative, just one of those 'feelings.' It's also easier to balance the carbs with a unisyn gauge with stacks. The stack helps to collimate the air before it enters the carb, and I think supposedly to speed up the air a little. There are tall and short stacks, so be aware when you order. You want 2 1/2 to 3" stacks if you run a standard 3 1/2" tall filter. They are cheap, and easy to install.

Velocity stacks (Air horns) will produce a modicum of additional power on any given engine. The stacks, in order to improve performance, must be tuned to the particular engine and application. Check out http://www.zhome.com/Care/airhorns.htm
This just gives am idea of the fooling around that should be done if one wishes to take advantage of the potential hp that might be gained.
Phil

V-Stacks
 

As the theory goes, velocity stacks are designed to "smooth" the air entering the carb (read greater volume/speed throughput). If the air is forced to enter over a 90 degee edge, the air becomes turblent in the venturi. Many hours are spent on race carbs to roll edges, etc.., to provide for smooth air entry to the venturi (where stacks are not allowed or can't be easily fitted).

The "tuning" is by length and the radius applied to the upper "lip" of the bell.

High performance airfilters try to provide some measure of smoothing.

Max airflow=greater volumetric effeciency=more power.