High CHT's

Dan,
I wish now that I had done a better job of recording specific temps on all cylinders, but I did not. I recall a small reduction in temp on #3, but I was focused on #1 as it was my problem child! I should also note that I had previously trimmed the air dam in front of #1 quite a bit before moving the ramp, but that had little effect on cooling #1. I was also breaking in a new engine at that time.
Now, in cruise flight, my #3 is typically the hottest cylinder, but only by a few degrees, and all are below 380 and within 10 degrees or so, depending on leaning.
So to answer your question, there was a small drop in temps on #2 and #3, but I don't recall anything on #4. It is my coolest running, so maybe I don't pay enough attention to that one! Sorry I don't have more specifics...Bottom line is, for me, after I moved the starboard air ramp forward, I had a dramatic (25 degrees or so) reduction in the #1 CHT, and that was my biggest concern at the time. If I were to build another 7, I would trim the ramp and move it forward to match the gap on the port side, from the get go...
Jim

Jimzim said:

So to answer your question, there was a small drop in temps on #2 and #3, but I don't recall anything on #4. ...after I moved the starboard air ramp forward, I had a dramatic (25 degrees or so) reduction in the #1 CHT, and that was my biggest concern at the time.

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Overall, that would suggest an increase in mass flow, although it's probably not huge.

It's all theory without pressure probes, but the 'ole educated guess says the pinch was increasing velocity and reducing pressure in the immediate vicinity of #1. In addition, a high velocity jet into the right side plenum space may have been wasting a lot of the kinetic energy in turbulence rather than appearing as increased static pressure. Moving the ramp forward relieves both issues.

A mass flow increase created by increased upper deck pressure may not result in much of a a cooling drag increase, as pressure remaining after the drop across the cylinders/oil cooler is transmogrified into exit velocity.

It's all magic really.

Jimzim said:

I originally had only about an inch or maybe a bit more on my starboard side. I simply cut the ramp out, trimmed about an inch or maybe an inch and a quarter off the front end of the ramp, then epoxied it back in place, filled and smoothed things out, and that was it. Now I can just get my fist through the gap. So now my port and starboard ramps have similar gaps to their respective cylinders. The temp on #1 was my problem, and it dropped dramatically. Again, I don't claim to have any expertise in this area, but it worked for me. In any case, it was easy to do, didn't affect the paint finish on the outside of the cowl, and can certainly be undone easily. There is some talk of a small cooling drag penalty, but I could detect no performance change in speed.
Jim

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My #1 runs about 30* hotter than my #3 and I suspect the issue you discuss here with the smaller gap is the cause. I would like to move my ramp as you did here. Could you share how you "cut the ramp out." I have been wondering how to do this without hacking everything up.

Larry

Larry, I just took my Dremel with a cutting disc and cut the ramp off, both fore and aft. Then, I used the Dremel drum sander to smooth out the remnants on the inside of the cowl. Trim the ramp to provide the increased clearance, then epoxy the ramp into its new home. Easy!
Dan, that stuff about volume and pressure is pretty much what I was thinking, too!
Jim