[Cliff R]

I've done a LOT of spacer testing, street, strip and on the dyno.

W/O exception all single plane intakes I've tested respond very well to a fully open 1" spacer nicely blended into the plenum area.

I've noticed smooth off idle and at lower RPM's with 4 hole and fully divided spacers on dual plane intakes for "normal" driving. Fully open spacers on dual plane intakes have never tested well anyplace. I've also observed hesitation/stumble/bog going very quickly to full throttle using them on dual plane intakes.

On the dyno spacer testing the best to date has been a semi-open 1" spacer similar to what is shown in Jim Hand's Book. The same spacer also logged the highest MPH at the drag strip verifying the engines we've ran them on really like that deal in the upper mid-range and top end.

At the track w/o exception 4 hole spacers on dual plane intake were the worst at every point on the track.

Kind of interesting but on several private track rentals using two different cars we did carb and spacer testing. On my car the best ET was with no spacer at all! Highest MPH and just about as quick in ET was using a Tomahawk intake with a 1" fully open spacer and Holley 850 DP carb. It ran a solid 2mph faster than all other intake/spacer combinations tested but gave up enough in 60' and short times that my factory intake, Q-jet and no spacer ran just a tad quicker (.02-.03" seconds) in ET.

I'd add here that ALL street or "seat of the pants" testing favors 4 hole and fully divided spacers on dual plane intakes. They "feel" very smooth right off idle and at very light throttle openings but take a back seat at WOT and making best power across the loaded RPM range.

From what I've seen you have to be very particular about how much area you can allow for one side of a dual plane (divided) intake to see the other side. I've lost count of how many folks I've helped out putting dividers back in dual plane intakes when their engine builder or beer drinking buddies removed them!

We even had a FAST Class iron intake evaluated after being professionally ported by a very well known Pontiac "guru". They removed the entire divider in the intake. This resulted in a couple more HP on the dyno WAY up at the shift point (5900rpm's), but the engine was WAY down in mid-range torque, nearly 40 ft lbs nearly as I can remember. With the divider missing it was also IMPOSSIBLE to launch the car as not having it there produce a HUGE hesitation going quickly to full throttle, which instantly went away when we made an aluminum divider for the intake putting all the material back in it.

Track testing on my own engine shows that it is beneficial to remove about half a 50 cent piece right between the secondaries and run a 1/4" thick fully open gasket. To date this set-up has produced the best ET, MPH and average power on the dyno......FWIW.........Cliff