I'd like to know what are differences and/or benefits of running a 1" 4 hole spacer and a 1" open spacer, and if any, running both at the same time. If there is a benefit of running both spacers, which one is on top and bottom? I'd like to try one out, let alone both. I've got a '71 Velle, my motor is a 388ci, 9.5:1 C/R, Holley 750 vac sec., edelbrock rpm intake, bowtie heads 2.02/1.60 valves, ported, and cam has a .488" I/E lift...not sure about the rest of the specs because I lost my spec sheet a couple years ago. I'm running a TH350 tranny, stock rebuild with a B&M shift kit, B&M Holeshot 2000 converter, B&M tranny cooler, and 4.11s out back in my 10 bolt rear. Any other questions drop me a line...email or on here. My car is my daily driver, drive it everywhere (and yes, even on the freeway where I rev right around 3200-3500rpm to keep up with traffic), and I take it to the track when I can. Thanks a lot, I appreciate all info graemlins/thumbsup.gif

Spacers. Some combos love'em, sone don't. And some don't care at all.
An open spacer increases plenum volume which may be helpful on a high rpm motor or an intake limited combo that doesn't have enough volume to start with.
A 4-hole amplifies the signal to the boosters and has a tendency to help bottom/midrange torque. But it can cause the mixture speed out of the carb to be too high and cause fuel separation when the mixture tries to turn toward the runner at high rpm.
My 355" race motor has a 1" open spacer on a ported Vic Jr. When I put a throttle stop which is effectively a 2" 4-hole spacer above the 1" spacer, everyone said that the stop would kill the power. Well, it ran 9.23 @144+ without the extra 2" 4-hole and 9.23 @144+ with the 2" 4-hole stop. Go figure.
Either way, the gains will be very small and only able to be verified at the track with back to back A-B-A testing, jetting and timing each combo, etc. or else on a dyno.
If using both, the 4-hole always goes under the carb.

Randy