For the old 582 with 1250 short deck i used to run two- 1” spacers above the manifold. One being completely open and the other being the hvh version. Now going to a 598 and 1250cfm along with the tall deck sv632, wondering why or if anyone has some real reasons on what to use for spacers if any. Not even sure why i used them in the first place..... understand that they increase volume but does that affect jetting and throttle response? Bored at home

Rymo - Technically it will effect throttle response and jetting but the main reason I run a phenolic spacer is so I get a heat shield for the carb. I have switched back and forth between open, 4 hole, tapered and a weird combo by Gary Williams and I can't tell much difference. They say the only way to know for sure is to do back to back testing but I have never had the time to do that.

Depending on the combination, in most cases a 4-hole provides a taller column of flow under the boosters, and will improve booster signal, improving atomization, sometimes providing a crutch for a too large carburetor or reversion tendencies. The open spacer probably isn't necessary on better designed intake manifolds.
Heat insulation is always good.

Ryan,I would recommend using the HVH spacer by itself.The 4-hole gives a little more bottom end torque.FYI I had a 1250 0n my 582,took it off went to a tunnel ram and 2 1050s,picked up a solid tenth and 3mph.

Reher-Morrison anti reversion shear plate. You can run any open spacer of your choice under it. It's two pieces 1 1/4" tall altogether.

Anyone out there using APDs black widow?? I have the 2 inch on my 582 sr20 but have yet to try it out

Not performance related but we've always run a 2" open or HVH spacer that way it was an easy swap to put the throttle stops on. My 555 currently has a 1" open drilled for a lean out with a 2" HVH on top of that on an Edelbrock 2927. I know my car isn't the fastest but it runs decent for what it is.

I've tried them all over the past 30 years, wood, aluminum, phenolic, open, 4 hole, blended and upside down too. Never saw .01 or .1 MPH on any of the numerous engine combos I ran and tuned.

See lots of them out there varying in heights and shapes...