Cowl clearance for engine ?

[Larry DeCamp]

I must modify my SJ cowl to fit a 360 w/dynafocal / AFP 150 updraft and custom FAB. I have read numerous opinions that the baffle/plenum should clear the top anywhere from 1/2" to 3/4".Same for FAB to cowl ( horizontal ) clearance 3/4" to 1".

Can anyone confirm how much clearance is 'required' ? I know a "bunch" would do the job but I am constrained for space and need to sharpen my pencil as much as possible. Thanks

[Raymo]

I had the same issue on my -7A, Larry, but managed to get about 1/8-1/4" clearance. This was only a problem toward the aft, left middle section. No rubbing has occurred.

[BillL]

RV7 - the outboard edges of the plenum/baffles (to cowl) 1/2" but 5/16" is good. The front corners are likely the tightest to the cowl due to engine rocking.

Just keep in mind what is happening - landing, aerobatics, and engine rocking due to starts or shutdowns.

Vertical clearance over the top center of my plenum is 5/16"

Longitudinal clearance between the cooling rings to the plenum - mine are 1/4" and work fine, no touching, the same for the engine air inlet ring to FAB.

The base of my conical (SJ) FAB is 1/4" or less and is rubbing a hole in the cowl. It touches at 3 G's.Recommend at least 1/2" due to G loading and deflection. Maybe when bouncing on landing -

Hope this helps.

[Raymo]

Another point to make (at least with mine) is that the engine will rise about a 1/4" in flight vs sitting on the ground, which means you can raise the upper cowl that much such that it will be even with the spinner in flight. YMMV