New billet parabolic velocity stacks now available

[Sam-Q]

UPDATE: Now done and available, see post #28 for a pic



Thought people would find it interesting to see what I have been doing regarding some development work on velocity stacks.

Recently I for the first time had the option to get velocity stacks made by being machined out of a solid billet of aluminium instead of the current way of getting rolled and then fitted into flanges.

Due to material costs this was only feasable on the shorter sizes, the first batch is 50mm which is ideal for the RHD Corolla and Sprinter owners who wish to run slide on filters. They will also fit inside a blacktop airbox with a light shave on #4 and work better than anything else out there.


Right so being machined I have the liberty of choice in designing something new. From previous research I knew that the ideal design was a long taper to a parabolic opening and a full curved edge. This also known as a expodential, elliptical or variable radius curve. This gives the highest theoretical net airflow out of any of the designs.

Most of the velocity stacks on the market usually have some sort of taper but with a fixed radius rolled/machined edge, this has the highest velocity on the inside at the end of the rolled edge at the transition before slowing down again further down the tube. The parabolic design however lets the air keep speeding up all the way to the opening face.

More about the technical side of that here:




Knowing all that I came up with this:




Which I then had 3D printed along with a different design and a prototype exhaust mount alternator mount:



I sanded these smooth and had Jamie "Frak" being nice enough to put them on a flow bench for me. Here are the results in order worst to best, of note the OEM stacks where checked on a different day so the results might be a little off.

- Blacktop OEM: 320

- Silvertop OEM: 342

- HRC: 445

- IMEC: 483

- SQ model #1: 483

- SQ model #2: 489

All tested at 28 inches of water.

Two things really surprised me about this- first that silvertop flows better than black when to me they look terrible and second how bad both OEM designs flowed. This explains why people pick up power even when running short stacks in the OEM airbox.

Picking the better of the two and taking the chance at making a small adjustment to improve it further I gave the go ahead for a batch of both silver and blacktop sets to be made. This is when I was last at the machinist and only the outside profile had been cut:



Next up is them getting the flanges cut.

Once done I shall have them back on the flow bench, this time all at once.

This is the part of my job that I love, I really look forward to how they turn out not just in flow numbers but how they look with a little bit of a polish.