Velocity stacks v Ram Air intake

[RX MIDGET]

Hi all,
I am contemplating either Velocity Stacks or a Ram Air method of getting cold air to the 48IDA on a 13b Extend Port engine.

Has anyone tried / tested either?
If so, what would you recommend?

I am not overly fussed re poor weather driving as the car is never driven in the wet. My main concerns are sucking in bugs etc.

I am currently running a K&N filter and housing.

I ask as I have no room for a cold air intake and a damaged bonnet that will be resprayed shortly.... a very small scoop will cover existing damage.

[PercentSevenC]

So you're not using any velocity stacks at all right now? I can tell you that getting some will add quite a bit of airflow.

I've always heard that ram air doesn't really help much, and will increase drag somewhat. You say you have no room for a cold air intake, but there are all sorts of ways to route ducting to the carb. Pic of your engine bay?

[t_g_farrell]

I assume your rotary is in a midget. Not much room I'm guessing.

You should have velocity stacks, even shorties will make a difference. They
are required to make the air flow good coming into the venturies. If you
run an airbox or a cold air intake, make sure there's at least 1.5 inches
clearance above the stack openings or it will impede the flow. Also make sure
your running a filter or your carb will get messed up.

And yes, we want pics

[vex]

'Ram air' style scoops can help, though if sized incorrectly large amounts of drag can be manifest; negating the benefits of the scoop. Furthermore 'speed stacks' implicitly accelerate air into the combustion chamber for additional pressure effect. If you're mathematically inclined you can figure out the 'ideal' size of the 'ram air' scoop as well as installation of the 'speed stacks' (though technically speaking they're nozzles).

Use Bernoulli's equation for the incompressible flow regime (basically anything less than 0.7 Mach) which gives you pressure at a specific speed.

P=1/2*rho*v^2

If you're hoping for increased operating pressure you can then add atmospheric pressure to the dynamic pressure calculated above and get the stagnation pressure (or the point where air's velocity becomes 0 in the scoop). The proper sizing of the scoop should ensure that all nozzles get the same pressure of air--no sense in getting increased pressure on one nozzle while the other is still stuck in ambient pressure. Doing this will also help you understand at what speed the 'ram air' scoop will become most effective. If you have the means drag force profiles can be plotted and the ideal scoop criterion can be selected from both Bernoulli's equation (will give you the operating speed for effective pressure) and the drag profile (at what point is the scoop a hindrance as opposed to a benefit).

[RX MIDGET]

Thanks guys, much food for thought...

In short, yes it is in a MG Midget, I have a K&N "oval" filter with small stacks.
All, my thought was stacks through the bonnet (just), sucking straight through with a basic filter set-up.

VEX, you have turned a somewhat simple train of thought into something my simpleness struggles to comprehend... (lol). However I sorta knew the Ram Air option was not as "uncalculated" as I first thought. To be honest, I was thinking.... the more cold air supplied to the carb, the better it goes (basically speaking) right?

The car has a Toyota Tarago Diesel radiator that takes up 95% of the grill, so I ruled out the cold air intake idea. I guess I could do something with a smaller radiator perhaps or have the CAI inlet through the beaver panel.

If I went Cold Air Intake, is there a kit available for the 48IDA connection, or do I fab up something??? Has anyone got pics of a CAI connected to a 13b non turbo?

Is rejetting likely to be needed with CAI?

I have attached pics of the engine bay - excuse the untidiness.. car is ex race car 40 years old that in currently undergoing a ful tidy up.

Thanks guys....

[PercentSevenC]

You don't need to take air from in front of the radiator, though that is a convenient high pressure zone for most cars. What I would do is build a box around your filter and have a duct leading through the fender well for cold air.