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03-18-2018, 11:30 AM
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Join Date: Mar 2015
Location: Greenville SC
Posts: 178
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Climb power and CHT?s
I have an 0-320 with a Hartzell constant speed prop. I just added two P-MAGs. I was wondering climb out settings? I use Full throttle on takeoff I get 2700 rpm 28.8 on manifold, after 500 feet agl I usually pull the power back to 2500 RPM for the rest of the climb at 600 ft per min, mixture full rich. My #3 CHT got up to 440 I lowered the nose pull powere a bit and opened the cowl flap and it came down to 393 in about two to three min. I have never had that cylinder get that hot. I was just wondering what others climb at with p-mags. Not sure how these P-mags should act? Maybe I should not climb so fast maybe climb at IAS.
I had a lightspeed before with a slickmag. Things seem a little different.
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Tim Crouch
RV-9A N626TC
"Merlin"
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03-18-2018, 11:44 AM
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Join Date: Oct 2012
Location: Clearwater, FL KCLW
Posts: 1,281
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What is your fuel flow at T/O power? The carbureted 320's are notoriously lean in RV applications. Having a C/S prop means you need even more fuel flow than us FP guys because you are getting much more power on T/O. I have drilled out the jet on my carb twice in order to get the fuel flow I need to keep things cool on takeoff.
Also, do you have all 4 cylinders wired for CHT? I say that because at WOT my front two cylinders (1 and 2) are the hottest ones, so if you aren't watching those, they may be even hotter than #3. Lastly, have you done the baffle mode to increase cooling for cylinder #3?
Chris
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Chris Johnson
RV-9A - Done(ish) 4/5/16! Flying 4/7/16
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03-18-2018, 11:45 AM
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Senior Curmudgeon
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Join Date: Sep 2005
Location: Dayton Airpark, NV A34
Posts: 15,420
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Quote:
Originally Posted by TJCF16
I just added two P-MAGs.
My #3 CHT got up to 440
I have never had that cylinder get that hot.
Things seem a little different.
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Well, pretty sure you have identified the issue.
Lots of folks here have experience with setting Pmags, but I am not one of them, so will let others advise........
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Mike Starkey
VAF 909
Rv-10, N210LM.
Flying as of 12/4/2010
Phase 1 done, 2/4/2011 
Sold after 240+ wonderful hours of flight.
"Flying the airplane is more important than radioing your plight to a person on the ground incapable of understanding or doing anything about it."
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03-18-2018, 12:02 PM
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Join Date: Mar 2015
Location: Greenville SC
Posts: 178
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I have done all the baffle mods. I doo have CHT probes on all cylinders. My front cylinders don?t get above 400. I think the jetting could be the answer. Allen at antisplat recommends the drill out the jet. I never looked at what the fuel flow was! Never had a carb apart!
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Tim Crouch
RV-9A N626TC
"Merlin"
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03-18-2018, 12:09 PM
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Join Date: Oct 2017
Location: Las Vegas, NV
Posts: 407
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Pretty sure your carburetor has an enrichment valve at wot.. try climbing out at full power, it'll run cooler. You're probably thinking that you are being more kind and gentle to the engine by pulling it back, but in reality, you're leaning it and probably adding stress (heat ).
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Tom
Las Vegas
RV-8 empenage almost finished
Horizontal Stab done! 2-15-2020
Vertical Stab Done! 5-27-2020
Rudder Done! 5-31-2020
Wings ordered!...
Last edited by Taltruda : 03-18-2018 at 02:16 PM.
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03-18-2018, 12:22 PM
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Join Date: Oct 2012
Location: Clearwater, FL KCLW
Posts: 1,281
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You can also retard the timing on the pmags (of course that will negate some of the benefits). And of course, give the baffles a very close look to make sure they are cooling as well as possible.
Chris
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Chris Johnson
RV-9A - Done(ish) 4/5/16! Flying 4/7/16
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03-18-2018, 12:27 PM
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Join Date: Oct 2013
Location: Schaumburg, IL
Posts: 5,298
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I am assuming this is new and appeared with the installation of the Pmags. What you are seeing is the byproduct of the pre-programed and unchangealbe
advance curves that are too aggressive. The curves are fine for cruise, but you need a more retarded timing for climb due to the reduced cooling available (optimum advance produces more CHTs than the more retarded settings of the mags). This is one of the reasons that I don't recommend products with a fixed and unchangelable advance curve.
I use a megasquirt system and have two switches to help control my timing. One is used for switching between A & B curves (curves of my design) that let me have either 25* or 34*, based upon ROP or LOP at my lower MAP ranges. I also have another switch that retards timing by 5* from whatever is called out in the map. I mostly use this for climb. I get high CHT's in the later stages of climbs to 8000', when the MAP goes down and my table starts advancing agressively. In the earlier parts of climb, my MAP is higher, so my timing is 25* and I am plenty cool.
I recommend the SDS product, as it allows the user the flexibility to manage situations like the one you are now experiencing. You are seeing the downside to a plug and play system where all decisions are made for you.
Larry
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N64LR - RV-6A / IO-320, Flying as of 8/2015
N11LR - RV-10, Flying as of 12/2019
Last edited by lr172 : 03-18-2018 at 12:37 PM.
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03-18-2018, 04:03 PM
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Join Date: Dec 2013
Location: SLC, UT (KBTF)
Posts: 240
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Tim,
You say that you, "usually pull the power back to 2500 RPM for the rest of the climb"
That's fine, just leave the throttle full open and the mixture full rich until you get to an altitude at which you'll start leaning in the climb.
I agree that the aggressive timing of the Pmags is responsible for the higher temps if that's all you changed. You can try accelerating to 120KIAS immediately after takeoff and climbing at that speed. If that doesn't help, you may want to do something with the timing/Pmags. Also, try to keep the CHT's cool before you start your takeoff. If they're already around 350 when you take the runway, you don't have much headroom to work with.
Have an engine monitor? Check the full power fuel flow both with and without the electric boost pump running and report back.
Good luck; summer is coming and CHT's will only get higher without some changes.
Cheers, David
RV-6A A&P
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03-18-2018, 04:41 PM
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Join Date: Aug 2015
Location: St John, Steamboat Springs, planet Earth generally
Posts: 96
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the troubleshooting guide from the horse?s mouth:
http://www.emagair.com/wp-content/up...leShoot-V4.pdf
Page 7, perhaps
You will see that you can easily make the timing equal to that of a regular mag and see if that cures the issue. Or change to a less advanced timing curve.
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Building a Panther, but lurking here, like many others
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03-18-2018, 04:54 PM
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Join Date: Oct 2005
Location: 08A
Posts: 9,500
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Quote:
Originally Posted by TJCF16
I have an 0-320 with a Hartzell constant speed prop. I just added two P-MAGs. I was wondering climb out settings? I use Full throttle on takeoff I get 2700 rpm 28.8 on manifold, after 500 feet agl I usually pull the power back to 2500 RPM for the rest of the climb at 600 ft per min, mixture full rich.
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CHT is much more dependent on RPM (i.e. mass flow, and number of firing events in a time period) than MP. You're doing it right.
Quote:
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I had a lightspeed before with a slickmag. Things seem a little different.
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As delivered, the P-mag A curve starts at 26.6? BTDC, while the B-curve starts at 30.8? BTDC. Both rise further as MP drops in climb. Install the jumper to run the A-curve. Report back.
__________________
Dan Horton
RV-8 SS
Barrett IO-390
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