Cooling Ramp Configuration for O-320-E2G
Marc Borom
©2004
I had been struggling over a five month period with high cylinder head temperatures in my LongEZ after recently swapping out my O-235-C1 engine for a more powerful O-320-E2G engine. Since the swap-out, I had been plagued both with high temperatures and with considerable imbalance of temperatures among cylinders.
I had tried numerous solutions without success. Among them were:
1) Adding GILL SLITS to the top of the canopy. This modification worked on the O-235, but created drag with a 5 kt. penalty in speed. I closed up the slits and did not try them again with the O-320 installation.
2) I added diverter ramps (see photos following) just after the NACA inlet lip giving an upward flow of air with about a six inch radius turn. This had some positive effect but little or no effect on the temperature imbalance.
3) I provided split ramps (see photos following) for each side of the inlet so that air could be better directed to individual cylinders. Splitting the air direction had little effect on either cooling or temperature balance.
4) I swapped out my Hal Hunt ram air box for a narrower profile, Van's Aircraft RV ram air box. There was some lowering of the CHTs, but not significant. I will post the installation details if there is interest. Email me.
5) I finally noticed that I could achieve a better temperature balance among the cylinder heads, if I reduced the throttle a bit during Lean Of Peak (LOP) flying. I monitored the thermal balance and found a setting that produced the minimal difference in CHTs among the cylinders. The balance was still off by 50 to 70 degrees. I measured the throttle back position in terms of fore-finger joints between the throttle and the Instrument Panel wall. One and a half (1.5) finger joints gave the best balance, but the differences were still too high. It was interesting to note that shifting from full throttle to a 1.5 finger joint setting switched CHT settings by as much as 100F; thereby, changing the hottest cylinder to the coldest cylinder.
6) As a last ditch act of desperation, I jury rigged a metal (.035" aluminum sheet) ramp toward the rear of the lower cowling (see photos following). The ramp fits within the tight baffling attached to the engine. The ramp is canted toward the rear on the left side of the cowling to direct air toward cylinder #1. The forward portion of the ramp was to direct air toward cylinder #2. The rear ramp did the trick. With a 1.5 finger joint setting, the cylinder head temperatures run around 340-350 and are in close balance.
Photos of Cooling Ramp Configuration at the NACA lip
For my O-320-E2G
I have no good reason to believe that the shape of the splitter between the sections of the ramps have any beneficial effect. They are a hold-over from an earlier configuration in which I could individually vary the angle of ramps on each side. The earlier mode is shown in the last two photos and demonstrated no beneficial effect.
The splitter also serves to set the angle of the ramp as the splitter is forced down by air pressure to contact the bottom of the cowling.
Click on each photo for an enlarged view
 Front Ramp (left side) |
 Front Ramp (right side) |
 Front Ramp (right side) |
 Front Ramp - Underside |
 Air Diverter Ramp Showing Possible Dual Mode |
 Dual Air Diverter Installed in Dual Ramp Mode |
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Photos of Cooling Ramp Configuration at the rear of the Lower Cowling For my O-320-E2G | |||||
This is definitely a work in progress. Showing it is like going to the emergency room wearing dirty shorts. Since it showed the best results I have had to date, I will show and describe the installation in spite of the poor cosmetics. The rear ramp is made from 32 mil aluminum sheet, cut and shaped to block and divert the airflow to cylinders #1 and #2 (the rear most cylinders). The sheet is connected temporarily to the cowling wall with four pop rivets through the cowling wall and the sheet. The top of the sheet is bent over in a smooth curve to minimize turbulence in the air spilling over the sheet on its way to the air exit around the cylinders. The sheet is mounted to turn the air at approximately a 60 degree angle. In addition, the sheet is attached further to the rear on the left (port) side of the cowling to accommodate the more rearward position of cylinder #1. The first photo below shows the location of the cylinders relative to the ramp. If you look closely, you will be able to see the line that defines the location of the rear engine baffle showing that the rear ramp lies within the confines of the baffle. One of the photos shows the location of the four pop rivets. Four rivets seemed adequate for attachment. The fact that the placement of the rear ramp had an effect on the cooling is somewhat of a mystery since the forward air diverter ramps should have been sufficient to direct the air upward. One might speculate that the rear ramp constrains the volume in which the air can move as well as limiting turbulence. Both effects may contribute to a smoother flow of cooling air and, thereby, produce more effective cooling. | |||||
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| Metal and RTV baffling for O-320-E2G | ||||
The following photographs show the construction and mounting of the metal baffling for my O-320_E2G. Your baffling will, more than likely, be different, since cowlings are seldom the same. The general ideas, however, should be applicable. I have chosen to baffle the bottom of the cylinders with aluminum sheeting that can be rotated around the cylinder to get the best exit position for the cooling air. The exit opening at the top of the cylinders is generally taken to be 1.5 to 2 times the depth of the cooling fins. | ||||
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| Details of the RTV baffling for O-320-E2G | ||||
The following photographs show the application of RTV/fiber-glass baffles for constraining the exit air around the cylinders in the most efficient way for my O-320_E2G. In my first attempt at constraining the air, I allowed exit areas to be larger than my final configuration. I have shown the original, more open configuration and have compared it in the photographs with the final, tighter RTV baffling. The final RTV baffling produced less thermal variation from cylinder to cylinder. | ||||
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