Although the CHT's are perfectly normal in my Jab 3300/STOL 750, it's become a "mind game" with me to see just how low and how balanced I can get the cooling! So, with the annual coming up, I resolved to do some further enhancements to the cooling and modify the ram air ducts to accommodate other mods I've made.

One thing that has always irked me a bit are the ram air ducts' vertical dams below the front cylinders:

The left one (pilot's perspective) has a "bump" to clear the oil filter. I added the "periscope" scoop for the  ducted oil sump cooler of my own design. All that , coupled with the vertical "dam" behind, seemed that it must create chaotic turbulence and not be efficient! So, I cut all that out and glassed-in a ramp inlet. Not only does it smooth-out the airflow, it allows more clearance for the oil filter, which I needed since I also have a TOCA (thermostatic oil cooler adapter), and that necessitated a shorter filter. Now I can go back to the original full-size filter! Here's the new ramp inlet:

On the other side, I made the ramp from aluminum as it has to protrude beyond the silicon rubber seal (the inlet is shorter on that side due to the #1 cylinder is more forward). The lip catches just under the cowl inlet:

I also fabricated "butterfly" deflector baffles that deflect the air going down between the gaps between the cylinders, making the air flow through the cylinder fins. These are held by spring tension against the fins with a spring anchored to a hinge pin wire laying across the tops of the cylinders. Small deflections of the pin hold the springs in position and the springs are safety wired in case one breaks:

After the mods, I've seen temps as balanced as 5/6 cylinders in the mid to high 200's (F) with #5 at 305F! Very pleased with the results. While I was as it, I also cut the back corners off the ducts where the ignition wires pass through and added aluminum joggles with nut plates so I can remove a couple of screws and remove the ram air ducts without disturbing the ignition wiring. Previously, you had to unplug all the spark plugs to have enough mobility to completely remove the ram air ducts from atop the cylinders. (No pics of this.)

John

N750A