Something I came across that might be of some interest.
Flattop

Well those pesky Dellortos look good. But hard to say if that is because they are bigger (do the math on the area of a circle by increasing diameter), or just better. MikeV

And they don’t have those odd threads on the bolts to deal with. And we don’t weigh them in stones. MikeV

Hi Mike....What I found interesting was the small change there is between the bare stack and the stack inside the filter, and the biggest drop with stand-alone filters. I always assumed adding filters created a "suffocating" effect on the intake, whereas these tests would suggest, filters only, are more of an inefficiency. Then there are the CV's. No change no matter what you do to them.
Flattop

And i noticed that the long stacks flowed better than the short ones.

But there is no room for them in an F1 or TT frame!

MikeV

I probably should have posted in Bevel or Pantah. I've seen comparisons of other bell mouths/stacks. The "pancake" style commonly found on TT's are actually quite good.
Flattop