Carb to FAB spacer

I'm installing a Van's O-320 FAB and am considering inserting a 3/4" spacer between the MA4-SPA Carb and the FAB mounting plate. This would allow using a mounting plate without the cutouts for the accelerator pump and drain plug bumps with the advantage of not having to cut a notch in the filter and use silicone. I believe that in my particular case the extra 3/4" will not interfere with the cowl.
1) Might there be any air induction issues with using such a spacer?
2) Does any one know the official dimensions of the bolt spacings and the throttle opening? By my measurements, the 4 carb bolt centers are 2.5" apart and the venturi entrance opening is 2.594" diameter.

I saw one installation where a collar was mounted under the FAB mounting plate, forming a velocity stack sort of affair inside the filter area & and act as a reinforcement for the FAB mounting plate. This would preserve the original FAB placement in the cowl.

Yeah, I didn't think the 3/4" spacer would have any negative induction effect, but wanted to get other opinions, so thanks. If I can fashion a bell shaped entrance in the spacer, it might even help. However, my primary intent is to avoid the standard cutouts in the mounting plate and the filter.
I hope I got the hole and bolt spacing accurate enough.

Maybe not

Great idea but You may not want to spend a whole Lotta time on that project because the nose of your Fab air box usually Has to be tipped up as much as you were talking about , I know mine and a buddies both had to be cut and bent up to align with the opening in your bottom cowling , I’m sure others will chime in with similar experiences

SPACER

Hello Radio, I made a 1.35" spacer for my O-320, but I had an O-360 cowl on my plane. Therefore, I had plenty of room to work with. Also, I developed other solutions for common problems with the FAB. All the mods worked great! PM me your email and I will send you some pics and a drawing of the spacer.

Ron B.

I have a 1 inch spacer on my fab mounting plate but I am using RSD5 Bendix FI servo. My fab intake lined up perfect to my o-360 cowling. This gave me spacing for the mixture control arm or I was going to have to modify the FAB.

Thanks everyone for the encouragements. Glad to see this has been done before on the RV6's.

I just did this mod to a new FAB on an RV-9A. I made a 0.700" thick spacer out of phenolic which moved the FAB mount plate down far enough to avoid having to cut the filter or cut outs for the MA4SPA accel pump / aft protrusion. After 5 hours of flight testing it, it seems to be working better that the original. Fuel flow at max power / RPM went up 0.4 GPH and temps went down, so it might be flowing more fuel / air than the previous FAB.

Cowl clearance on some models.

On my -4 that wouldn't have worked due to cowl/snorkel clearance. The little trim outs were no big deal to me, but ultimately, I would be really tight on clearance below the snorkel and definitely would have to angle it upward If I had a spacer . With no spacer, mine is perfectly aligned with the inlet.