Thanks, Tracy....I should be able to find out in a few days. Today I removed the ram air scoop and fabricated an intake plenum for the 3 inch scat tubing. As soon as the NACA duct with the 3 inch outlet arrives, I will install it and be ready for testing. Today I measured the length of the scat tube that I will need....14 inches.  Thanks again for sharing your experiences.  Paul Conner

 

Paul,

 It is interesting that as you have noted your problem, there was on the other list comment made about exactly the same phenomenon you are experiencing. You have found the relationship between the effectiveness of the cowl outlet, and inlets. The rules of thumb that have been discussed on the list recently apply to pushers as well. You have some advantages, extraction assisted by the prop usually, and some disadvantages, often turbulent air near inlets often making flow paths difficult to predict. Ask Perry Mick to remind us of the oil cooler troubles he had.

 The real problem Paul is that when used without a sealed tube to the throttle body your ram air scoop pressurizes the cowl. The fact that you are seeing higher temps isn't so much a supprize, rather it's expected. The better your "ram air" scoop works the worse your problem. The pressure increase does help the engine make more power. That heats up your coolant and the increase in pressure inside the cowl makes it harder to get air through the radiator, making the engine run hotter. There is probably a point if you could reach a high enough speed that the pressure could prevent ANY air from going through the radiator! The fixes are to re-plumb the scoop as you are doing, or to enlarge the exit area to prevent pressure build up. Since enlarging the exit may be impractical, you should fix the problem by replumbing as you are doing.  It is a shame that you can't keep the other scoop easily. The type of problems you are having would seem to indicate that it is working well! I've been away for a while and couldn't comment, but my suggestion would have been to put a sheet of aluminum under the scoop with a 3" exit tube near the rear plumbed directly into the TB. You would probably see a HP increase at cruise. The NACA duct will probably solve the problem but you will lose some of the ram effect you could recover with the other scoop. Should be less drag though. Hang in there Paul.

Bill Jepson