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Comment by Samuel McNair on August 15, 2017 at 4:26pm

How well does your 801 cool?

This is my second hot running Superior carbureted XP-360 in a CH 801.  The first (N801G) ran hot on all 4 cylinders and only by running keeping power down and leaning aggressively could I get it to at 400'F or barely under, often over. 

The latest 801 (N733 YD) also runs very hot. When I picked it up you could not get it much below 450'F. I got it down to in the 435 range by adding a lip to the cowl exit.  And I opened up the exit of the spring loaded  head baffles on the front and rear, which helped a bit more. BUT ONLYY ON THE FRONT 2 CYLINDERS.

The digital 4 cylinder EGT CHT has been verified as dead accurate. I tried opening up virtually the entire bottom of the cowl, with and without a lip. I got the measurements from the factory demo several other CH 801s which purport to run cool (but none have 4 cyl CHTs) and replicated those exit dimensions and configuration. And a host of other variations. The net result is the same:

In climb in 75'F to 85'F weather CHT will skyrocket to over 450'F very quickly. In cruise at 85 to 95 Knots at 70% power I can get it down to 425 to 435. If Cooler out (say in the 60's) I can get it down to the low 400's.

Here is the crazy part.  The front cylinders stay cool at about 375 to 385 - maybe just hitting 400 on a hot day and hard climb. But the rear 2 cylinders always run over 400'F.  On a cool day I actually had one front cylinder at 297 and one at 302 while the 2 rear were 425 and 415.  On a 80' degree day they run 375- 385 on the 2 front  and 425 - 435 on the 2 rear. In climb it will skyrocket to 450 and higher -ON THE REAR.

Engine has 40 hrs TTSNew and checked out perfectly when run in on the Dyno at factory. Fuel flows are correct.  Top baffle seals fit perfectly. Static pressure in the upper cowl is IAS+5 knots indicating  air getting in excess of the flow going out.  The "wrap around" baffles on the cylinders and heads compare identically to 3 other Lycoming CH 801's.  I have tried variations of the exit openings of the 'wrap around" baffles and I was able to cool down the front a little, but no change to the rear.

I have tried every cowl exit configuration from exactly matching the pictures Chris sent of the demonstrator cowl (and 2 other 801's I measured) to wide open exit clear to the front of the carb air box, with and without a turbulence lip, and just about every conceivable variation in between. I can make it run hotter, I can make just the front run hotter too, but I can't get the rear cooler. 

Superior has come up blank as well.

Anyone who can help me solve this is a real friend for life. 

Does anyone out there have an XP360 in a CH801 with a 4 cylinder CHT that can share some numbers, dimensions, and experience? 

Thanks

Sam McNair

ssm6791@gmail.com