D

DSmith

Well Known Member
Patron
I have an RV-7a with the standard Vans cowling for a forward facing sump on a TMX IOF-360 (FADEC). My CHTs and OT run high on climb but I can manage them to keep them from red lining but want to cool them down some. I was about ready to put louvers in the bottom of the cowl then I really took a close look at the air intake area of the cowl and realized the #1 cyl. side is way too close. I don't remember anything in Vans cowl instructions about cutting the top cowl intake area back before glassing in the ramps but it looks like that is what I should have done? I can't even slide my hand up over the top of the #1 cyl. ! #2 cyl. has plenty of space.

I'm planning to pull the top cowl, cut the ramp out then cut back the intake lip on the top cowl, then glass the ramp back in to give more area for air flow over the top of the #1 cyl. - I wished I had thought of this when I did the cowl the first time!

Is that what most of you did to get better airflow?

Danny
 
RV-7A Cooling

DSmith said:
I have an RV-7a with the standard Vans cowling for a forward facing sump on a TMX IOF-360 (FADEC). My CHTs and OT run high on climb but I can manage them to keep them from red lining but want to cool them down some. I was about ready to put louvers in the bottom of the cowl then I really took a close look at the air intake area of the cowl and realized the #1 cyl. side is way too close. I don't remember anything in Vans cowl instructions about cutting the top cowl intake area back before glassing in the ramps but it looks like that is what I should have done? I can't even slide my hand up over the top of the #1 cyl. ! #2 cyl. has plenty of space.

I'm planning to pull the top cowl, cut the ramp out then cut back the intake lip on the top cowl, then glass the ramp back in to give more area for air flow over the top of the #1 cyl. - I wished I had thought of this when I did the cowl the first time!

Is that what most of you did to get better airflow?

Danny
Click to expand...

Before you go cutting the ramps out, try this: On the lower cowl air exit area, on the part that steps down and where the exhaust pipes protrude from, cut 2" off and taper the sides back to the are where the cowl meets the firewall. This essentially increased the lower cowl air exit area, and increases the pressure drop across the cylinders. You should see a major difference in the cooling, and it will also reduce drag in that area.....
Additionally, be sure that you have the area on the sides of the ramps (on the top cowl) closed. This is the area on both sides of the ramps that would allow upper cowl air to escape into the lower cowl area without going through the cyclinder cooling fins. The upper/lower cowl inlet are is fine per the production parts.....
 
I'm with Jim

Fred, I would also like to see a picture in case I have this problem..! Look twice..cut once..thanks!
 
One of the reason you see more room on #2 cylinder is that they are offset and your #2 sits a bit farther back then #1. Also your left side draws more air (I believe due to prop) then right side.
 
I just started a thread on the this very topic. Search for "High CHT resolved"

Check the gap at the forward outer portion of your inlets (between the two cowl halves). If you have any gap at all put a piece of 100mph tape over the gaps and go fly. My CHTs and OT dropped significantly and so did several others who taped their gaps.

Good luck
 
Hi All,

I to have been bothered by high CHT's especially #3 cyl. I did the calculations and had a 1:1.01 Inlet to outlet ratio. Checked with a Embry Riddle profesor and he recommended a minimum of 1:1.75. OK so what would be a quick way to try this out?

Broke out the whizz wheel and cut the exit ramp foreward at a 45 Degree angel. Didn't take the measurements but did fly the RV9. Another RV grin moment when during a hard climb out with a OAT of 98. The temp of #3 was down from a previous 456 to a very comfy 409. The others ranged between 385 to 395. At cruise they all stablized at 340 +or - 5 deg. All in all a very worthy change and took all of 15 minutes to complete.

John H
RV9 N194JH
 
I put a good bit of time ensuring my baffles fit the cowl all around the sides, back and front. Also I blocked the ramps so air could not escape to the lower cowl without passing by the cyl.s. I understand why the #2 cyl. has more room and clearance and why the #1 has less space. It just seems to me that if we are going to go nuts over air leaks around the baffles up front and around the ramp then maybe I should be concerned about how much air can get in in the first place!

Danny
 
Bruce said:
Look under louvers and you can see pics that I just
posted on cutting the lower cowl and reduced temps
by 50*.
Click to expand...

Look where? Dont see a recent thread on VAF with this title, and I dont see a link to louvers on your Kitlog website either. What am I overlooking?

erich
 
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