Velocity stack minimum clearance

[Riceburner]

Hi guys, just wondering if anyone knows the minimum clearance a velocity stack needs at the face before restrictions start to occur? I've read 25mm somewhere before.

 

I'm fitting the new airbox to my FCR's, it's going to require shortening of stacks on carbs for cylinder 5&6. I'll be running 105mm on cylinders 1-4 and then 80-90mm on 5&6.

 

Although not ideal will it cause any real issues?

 

Cheers, Gareth.

 

# Edited stack lengths.

[dat2kman]

What length are trumpets?

Are they full curl around type, ie like a donut sliced across in half, or slightly flared out Weber types?

 

The curl wrap arounds are better, and can be obtained in carbon fibre.

At narrowest point, ie bell mouth to the inner face of airbox, what is distance?

 

Aim for at least 40-50 mm clearance with weber type, can get away with 30-40 mm with full curl around type.

[Riceburner]

They are the EFI hardware full radius type. My airbox tapers front to rear, with 25mm clearance to the bellmouth I can fit 105mm long stacks on 1,2,3,4 carbs. Then only 80 or 90mm max on stacks for carbs 5 and 6. The taper is much more dramatic at the back.

 

So if I allow 35mm that will be 95mm for carbs 1-4. Then 70-80mm for carbs 5-6

[dat2kman]

Run the same length trumpets, you need to keep the total length from mouth to valve all the same.

If it requires run the shorter length ones.