That is the same thing I had when I first flew my Rocket. I changed out the Positech for the much more expensive SW and it made no difference. I did a major redo of sealing all the small leaks between the engine and baffling. This helped some. I added louvers on the belly of the cowl. No impact. I took some ideas from the Long-Eze guys (yes I know, plastic airplanes). Look at their oil cooler installation. I hammered and wheeled a small half dish with a flange. I drilled a series of 0.5" holes in the side of the upper cowl just aft of the cooler. I mounted the half dish on the side of the cowl covering half of the drill pattern with the opening facing back. I added an air ramp directing the air down into the cooler on the underside of the upper cowl. Using kinectic energy in additon to static pressure. Voila, success and polished it looked cool. No noticable impact on speed. My primary problem was lack of exit air space. I had a lot of things on the engine and firewall in that area. That could be another approach is to clean up that area if it is crammed. My Rocket has since gone north to Calgary and I am building a 7. I am going to great lengths to avoid this problem again. A local friend is having the same problem with his 7. I never had a problem with the 3 or 4.
The biggest problem I had was that so much air was going through it right over my #4 cyl that I had to put a small air plate to divert the air between the cylinder and oil cooler. Lowered my CHT and only affect the oil cooler by 5degSW 8432R
Single air pass, Two oil pass.
Core:
8 oil fin channels, flow length 5.64".
9 air fin channels, flow length 3.22".
Stack height 4.34"
Collectors: Sheet metal with welded extrusion ports
Approximate unit weight 3.8 Lbs
By the way, I'm getting ready to post the Niagara for sale. Nothing wrong with it but just didn't work for my installation. Anyone here interested?
Would you have a photo of the air plate you installed? I would like to see your instalation