Plenum height above cylinders

[runstrong92]

I’m getting ready to install a Sam James plenum on my O-320. The directions on the Sam James website don’t give a height or any point of reference for how high to sit the plenum above the cylinders. For those of you that have a plenum, Sam James or not, what kind of height do you have? Any “gotchas” with this? It’s going on my RV-4. Also looking to cut down my current baffle setup and utilize it instead of having to reform all of the aluminum parts if anyone has any advice/experience/wisdom on that. Thanks in advance for the help.

 

[rockwoodrv9]

I sent you pm

 

[Ralph Inkster]

I would think you could use the existing baffling to determine height clearances. If not, attach something to the baffle sides to measure your heights, allow for about 1/2” clearance between plenum & top cowling. You are in custom mods & custom solutions mode here, your cowl to engine clearances are probably unique to your plane only.

 

[PilotjohnS]

Just me

We dont need no stinking badges...

I did not use a plenum for my io320, but I did have a problem with the ramp being too close to the #1 cylinder on the right side. There was insufficient airflow over the number 1 cylinder to keep #3 cool in climb. I had to move my ramps forward. i would think a plenum would suffer the same fate.

 

[wirejock]

Plenum

I used 1/2" but it hasn't flown yet.
The paperclip method works pretty well to get close enough to get the baffle clear of touching. I found a sharpie in a section of CPVC pipe worked best for precision. Reach in through the inlets and drag the pipe along the surface while drawing a line on the baffles. Then measure and redraw the line and cut. Perfectly matches the contour.

 

[Carl Froehlich]

My experience is with the James Cowl plenum on an IO-540 (RV-10). On that plane I did make the aluminum following Sam James’ hand drawn instructions. It worked.

For the new RV-10 I told Jimmy at James Cowl that I’d use the standard Van’s baffle kit for the aluminum sides and such. The plenum will most likely need to be modified to do this, but Jimmy will take my modified plenum to make a new mold.

So - if you want to use the standard baffles I suggest:
- Follow the baffle instructions - trim the top of the baffle aluminum sides and back to get a 3/8” to 1/2” clearance to the top cowl.
- You may find the front of the plenum to be better if you do not use the front aluminum plate. Instead, I put clear packing tape on the engine, installed the plenum, and then use flox to fill in any gaps between the plenum and the front of the engine. This was a lot easier than I thought - and the result was very good.
- Depending on the plenum you may need to modify it to fit the baffle sides. Here decide what is easier - modify the baffle or replace the offending baffle side and or back with one you make.

Carl

 

[rvbuilder2002]

Any “gotchas” with this?

Yes
Put it too low and you can have poorer cooling performance than with standard baffling because of there being a choke point between the top of the cyl. and the bottom of the plenum cover.
My opinion is that the cover shape should be such that it has just enough clearance to never contact the inside of the top cowl.
An RV-4 (and 3) probably has the biggest challenge of doing this well because of the need to fit the plenum within the cowl cheek area, but still maximize clearance over the front cyl.

I would think you could use the existing baffling to determine height clearances. If not, attach something to the baffle sides to measure your heights, allow for about 1/2” clearance between plenum & top cowling. You are in custom mods & custom solutions mode here, your cowl to engine clearances are probably unique to your plane only.

I think your advice is good Ralph, as long as someone doesn't follow the first part and skip the rest.

I have seen plenum covers made of aluminum that just bridged in a straight line from the baffles on one side to the other. Cooling was very much compromised because of the choke point this caused on the top of the front cyl. Particularly # 1, since it is the furthest fwd.

In my opinion, to assure good cooling performance, any closed cooling plenum needs to have a top that parallels the inside surface of the cowl with just enough clearance to assure no contact with the cowl.

 

[RV7Guy]

Not the problem

While everyone is focusing on the height above the cylinders, you also need to make sure your plenum has adequate clearance from the top cowl. This is very important since the motion of the engine can be considerable during shut down and start up. You don't want the plenum beating up the cowl.

My suggestion is get it low enough to insure at least 1/2" clearance from the top cowl. You will have plenty of cooling air coming through. My plenum is hand made and I have minimal clearance from the top cowl. (wish I had a little more). Although everything is fine, I wish I would have lowered it a little more. The 390 cools absolutely fine in the AZ heat. I don't think my temps have ever hit 400 degrees. The seal is complete.

In summary, don't worry about getting too close to the cylinders. Make sure you have adequate clearance from the top and you'll be fine with cooling.

 

[bonefishdave]

My 7 with angle valve engine and james plenum. It sits low and tight over the cylinders. You can actually see through the plenum and see how the plenum is actually sitting on top of the cylinders.

My cylinder temperatures run a little under 300 degrees on climb out.
And around 330 in cruise rich of peak. If I go lean of peak they will drop below 300.

 

[DanH]

My 7 with angle valve engine and james plenum.

My cylinder temperatures run a little under 300 degrees on climb out.

Under 300 in climb?

 

[bjdecker]

Under 300 in climb?

K type probes, J type wire or maybe a MeatStick 4X thermometer...yeah, that's the ticket...

 

[bonefishdave]

For the doubters and naysayers
Here are screenshots of climb power, and cruise both rich and lean of peak

 

[scsmith]

For the doubters and naysayers
Here are screenshots of climb power, and cruise both rich and lean of peak

The condition you want to demonstrate is climbing at Vy to 9500 ft on a day where the sea level temp is 100F. That is the only meaningful test. My angle valve with stock Vans baffles and cowl exit reduced to 37 sq in with modified ASA cowl flap, sees 350F at that condition. Oil about 215F.

 

[bonefishdave]

The condition you want to demonstrate is climbing at Vy to 9500 ft on a day where the sea level temp is 100F. That is the only meaningful test. My angle valve with stock Vans baffles and cowl exit reduced to 37 sq in with modified ASA cowl flap, sees 350F at that condition. Oil about 215F.

Yeah my engine and oil temps don’t run that hot. If I climb full throttle and leave everything full forward I can climb at Vy to at least 5500 feet with temps under 300. And I live in south Florida where temps are in the mid to upper 90’s all summer.
Obviously differences in cowls and baffles can attribute to how well the engine cools along with how the engine is operated.
For example if I am doing a Vy climb, which I seldom would do as my normal climb profile is 120 knots, I do it will throttle and mixture full forward and do not touch mixture until climbing through 5500. Under those conditions cylinders will remain under or close to 300.

 

[DanH]

So Dave, tell us about the rest of your configuration. Inlet area, exit area, special efforts at baffling, etc?

 

[rockwoodrv9]

Im also interested in how you keep the temps so low too. I have a great plenum and system but I have to pay close attention to keep below 400 on a hot day climb.

I would love to see some pictures of the plenum, inlets, and temp sensors. Thanks.

 

[DanH]

Keep in mind...Dave has an angle valve. Lots more fin area. The cruise CHT numbers are not unusual for a good system.

 

[bonefishdave]

Angle valve engines by design will run cooler than parallel valve engines for several reasons. Pistons are oil cooled and the cylinders have larger area of cooling fins.
Generally the oil temps run higher and cylinder temps run cooler for angle valve cylinders.
There are additional factors that come into play.
I have the sam james plenum and I was very attentive to the baffling under and around the cylinders to fit tight and to have proper distance spacing under the cylinder head and barrel.
I have a primary and secondary oil cooler to control oil temp as the oil naturally runs hotter on angle valve cylinders due to the oil cooling of pistons.
The plenum sits low and tight on the engine.
Airflow is not the only consideration when dealing with cylinder temp.
Fuel flow has a major impact, and timing advance will affect temps.
I have dual P-mags and they are set so the advance is limited to 29.6 degrees.
At full power 19.6 degrees.
I generally do not reduce power or RPM after takeoff on climbs, and don’t start leaning until climbing through 5000 feet.

 

[rockwoodrv9]

Thanks Dave. I didnt realize you had the angle valve engine or did I know it ran cooler. Great job with the entire cooling system. Im sure there must be reasons most dont have that engine but you have it figured out!

I have the James cowl and think I have a pretty tight system but still have to pay attention to temps. Except for my oil. It rarely gets over 160 and never in the winter with it completely shut off from the plenum. I have a dehydrator running from the time roll the plane back into the hangar to pre flight and hope that helps!

Edit - I love the polished covers!

 

[bjdecker]

For the doubters and naysayers
Here are screenshots of climb power, and cruise both rich and lean of peak

I'd love to see all the flight parameters on one screen shot -- AoA, IAS/TAS, Alt, RPM, MAP, OAT, DALT, Baro, GPSALT, etc etc.

 

[bonefishdave]

I'd love to see all the flight parameters on one screen shot -- AoA, IAS/TAS, Alt, RPM, MAP, OAT, DALT, Baro, GPSALT, etc etc.

Here is cruise flight. Pretty typical altitudes that I fly. Shows most parameters you are looking for.
I don’t think I have any that shows flight parameters in climb, only engine parameters as posted earlier.

 

[bjdecker]

Here is cruise flight. Pretty typical altitudes that I fly. Shows most parameters you are looking for.
I don’t think I have any that shows flight parameters in climb, only engine parameters as posted earlier.

Cool ( )

Was that LOP, and how much (°F) approximately?

 

[bonefishdave]

Cool ( )

Was that LOP, and how much (°F) approximately?

No, that is rich of peak. Lean of peak the temps would be lower than that.

 

[DanH]

inlet diameter and exit size? Cowl flaps(s)?

 

[bonefishdave]

inlet diameter and exit size? Cowl flaps(s)?

No cowl flaps, as far as inlet and exit areas I really can’t say. It’s legacy Sam james cowl and plenum, first generation, circa 2005.
If you look closely at the head on picture of the plenum you can actually read Sam’s signature embedded in the fiberglass

 

[DanH]

Next time you're near it, just measure the ID of the inlet ring.

The cruise CHT numbers are not unusual. I dug out some old notes from the first year flying, working with larger exits.

May 15th, 2011
No bottom cowl air outlet panel
CHT's 267 270 274 286

2760 feet, 174 knots true inlet 81F
CHTs 282 293 319 297
10" deltaP

OAT 86F @ 2500 ft
307 313 321 313
January 15th 2012
OAT 50F
185F oil temp
Exit Air Temp 186.5F
CHT 319 313 340 317

Your plenum is very low in the center, but the volume above the cylinder heads is about the same. With an angle valve, none of us can get much higher than the ears. With the more narrow RV-8 cowl, I have no baffle tin above the front cylinders...the plenum attaches directly to the mount ears.
.

 

[bonefishdave]

Next time you're near it, just measure the ID of the inlet ring.

That might be a while. Stopped in KGAD last week. I’ve been told 6 more weeks.

 

[Planecrazy232]

Nice toes Dave