The engine plenum that we showed you above was a little too big, it was for the 300HP IO-540-K “angle-valve” motor. We have the IO-540-D, which is normally a 260HP motor, although ours is pumped up with high compression pistons and electronic ignition to above 300HP. Here are pictures of us glassing the fore and aft halves of the plenum, so that there’s a lip from the aft section over the lip of the ore section. This will have nut plates installed for screws later.

Preparing the Fore Plenum to Release Fiberglass Lip

Lip being Glassed onto Aft Plenum

Here we’re glassing flanges onto the runners. The runners have lips on the firewall end on both sides and the bottom, the top has to be flush against the cowling when mounted, and it shares the retaining screws with it on top. On the plenum side, the runner has flanges on top and sides, and the plenum gets a flange on the bottom side to allow for easier installation and removal. Once the runners are glassed, the plenum is trimmed inside the runner mouths to allow for the cooling air to pressurize the top side of the motor, and flow down through it’s cooling fins.

Runner to Plenum Flange Preparation

Runner to Firewall Flange Preparation

Glassing Lower Runner Flange

Finished Flange and Runner Opening

Next we need to make access holes for routine maintenance items so that we don’t have to remove the plenum to check the oil or change a spark plug. Here we’re preparing the oil dipstick access hole and cover. I started to make a screw-down cover for the dipstick, but after seeingĀ Rich Guerra‘s setup I decided to go with the ‘recessed cup’ configuration. I took a wax cup that I cut the bottom out of and then cut the side of to create this cup. I taped the wax cup wall back together in the diameter that I needed, and then made a 4 BID layup on the outside. I then cut that to extend just below the dipstick, where the diameter of the dipstick tube changes, and glassed to the plenum. I think took a piece of 2 Triax that I’d laid up flat previously and cut a dipstick-tube sized hole in it, and cut the outside diamter to fit the bottom of my cup, and then glassed it to the plenum as seen below. Sound tedious? I assure that it is. The upside is I got mine tight enough that I have to remove the dipstick to pull the fore section of the plenum off. NICE.

Oil Dipstick Access Hole

Abandoned Oil Access Cover

Oil/Dipstick Access Cup

Oil/Dipstick Cup Internal Detail

Posted By: Brett Ferrell
Saturday November 6th, 2004 at 2:34 PM

Categories: Cooling
Tags: Building Cooling Engine Fuselage

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