From our testing
We've run for over 20 years now and the HVH is the best spacer we've used with ET and MPH results that back it up.
We ran alot of runs back to back over the years testing with open, four-hole, 1 inch, 2 inch, "plastic", wood, aluminum...cheap ones and the top of the line HVH versions.
Quick generalization:
The 4 hole helped the 60 foot
The Open designed picked up the top end mph
The HVH versions out performed on both ends of the track...the top-side being a four-hole that transfers into the open design was a stroke of genius on their part.
Go with the aluminum if you do alot of street driving or circle racing...go with the phenolic (plastic) if your drag racing.
We do have these is stock if your interested...
See Ya,
G.