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High CHT & EGT's

Jesse

Jesse

Well Known Member
I just got an RV-6A flying again after the engine hasn't run for about 1.5-2 years. The engine itself was replaced with a low-time O-320-E2A. The carb was the original carb with high time, although running well when last run.

On the first flight, CHT's on 3 & 4 went up quickly and higher than I wanted to leave them. The EGT's were in the 1400's with mixture full rich at sea level.

I am obviously wondering if I have a carb that's not delivering the right amount of fuel to the cylinders, causing the high CHT's. I am sure improvements can be made to the baffles, but a lean cylinder at high power will make the CHT's run high. I would like to get the mixture running right before I go much further, to see how the cylinders run with the right amount of fuel.

Next question is what the difference is between one MA-4SPA carb and another. There are a number of different part numbers. Is there a chart somewhere that tells the difference?

Thanks.
 
There are a lot of questions that need answered before any ultimate answer to your question can be fully addressed. You do not give the specific CHT numbers. Do you know them? If so, what were they? Just as a note, Lycoming considers 500 deg. high for CHT numbers. Most everyone runs below 400 deg but even 400 deg is really not "too hot" in most situations. Specific situations not withstanding. You state EGTs were 1400. Again this is not necessarily "too hot". I routinely run my EGTs 1400-1450 LOP. You mention those temps were at sea level. Assuming you were not flying on the deck at sea level what altitude were you actually flying when you saw these numbers? The more specific the data is that you provide, the more specific of an answer you are likely to find.

As the saying goes: "The devil is in the details!"
 
The CHT's were 445-455 climbing through 500'msl. The EGT's were about 1450-1470. Normally I like to see low 1200's on EGT's to keep the CHT's in control in full power initial climb.
 
It may also help to add that both engines are O-320-E2A's running low compression Pistons making 150HP.
 
RVbySDI said:
You state EGTs were 1400. Again this is not necessarily "too hot". I routinely run my EGTs 1400-1450 LOP. You mention those temps were at sea level.
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Jesse said:
The EGT's were in the 1400's with mixture full rich at sea level.
Click to expand...

With mixture at full rich, even if altitude was 2000 MSL, 1400-1450 is pretty high for EGT's

Start with simple stuff....
Make sure mixture arm on the carb is actually moving to full rich.
Make sure throttle arm is actually going to the full throttle stop.
Double check Ign timing.
etc.
 
Jesse,
You may be on the right track with checking the carb. My wingman bought a RV-6 and was really challenged on keeping the CHTs below 425 on climb out. Cruise was fine, well below 400. Climb out was the problem. Oil temps were never an issue.

We thoroughly checked all the usual suspects (baffles, timing, cooling fins, entrance and exit areas, ....) and came up empty. It wasn't until he called a carb overhaul shop and gave the shop the model numbers did he find out that his carb was jetted on the lean side. The guy at the shop immediately new that the carb was the wrong one for an RV-6. We never did check his fuel flow on take off. Had we did we would have found it maxing out in the 15-16 gphs giving us another clue that the carb was operating on the lean side. Flying at altitude compensated for the lean carb. That's why we never saw the issue in cruise. In retrospect, it all makes sense.

One of the local A&Ps offered to rejet the carb but it also had an AD out on the floats. He ended up trading his carb in for a rebuilt with a different jet size and the difference was like night and day.

Good luck, let us know what you find.

MD
 
Get leveled off at less than full throttle so that you're out of the enrichment zone. Then start leaning and see if you get any EGT rise. If any fall without a rise the carb is too lean. Check the throttle shaft for sloppy air suckage. Breakdown chart? I dunno, I usually go down the parts catalog breakdown and isolate differing parts.
 
actual egt numbers do not mean much. they very a lot by how far from the head they are in the pipe. now, for the cht's 455 is cause for concern, its not above lycomings limits, but is a lot higher than I would want to see. which i did in my aircraft until I did a lot of baffle work and other things.

1. first double check the timing on the mags. a couple of degrees to much makes a big difference.

2. do you have a good fuel flow instrument? what is the flow at take off? If you are seeing 15-16 gal/hr at take off I would not suspect a carb issue. ( i would have to look at the charts to see what lycoming says you should see at T/O on a 320, I know i see about 15-16 for a 360 and never get above 390 or so in the climb.

3. If you can get some altitude without the temps getting to high, check fuel flow at 70% against book. also check to see what the egt's do while leaning at 70% if you cannot get any rise in egt before it drops i would suspect that you are running to lean.

4. also check that the right inter-cyl baffles are installed.

you can get it to cool by dumping more gas in it, but the best thing is to get the proper temps at the proper fuel flows.

bob burns
N82RB
RV-4
 
I will check for an induction leak. I had already thought that should be an early check. That would definitely make a difference. This carb was on this -6A for 1500 hours or more, so I can't imagine it has the wrong jet size. I was thinking there may be a common problem with carbs that sit for a period of time. I'll see how things go either Friday or next week.
 
As you mentioned there are several variations of the ma4spa carb. Which are denoted by the number and dash number. Much of which has specifically to do with which jet is inside of it.

I've never found a chart that correlates the carb number to the size of the jet, or a jet part number that correlates to the size of the hole in the jet.
 
If memory serves the -5317 is the richest carb. That's what ive got on an O320 with 9:1 pistons still had to ream the jet to get enough fuel at full rich at sea level. Lots of threads on it.
 
Carb

0 320 with 10-1 pistons and mags, no other mods. I think the carb is a 5009, no mods except a current float.
Very small cowl inlets, ground adjustable cowl flap. When I did my first flights the ambient temps were 90-110 F. I had to reduce power and step climb but was able to keep the CHT below 425. As the engine broke in I was able to do full power climbs.
Yesterday with surface temp of 17 C. CHT's were running 350 in low altitude cruise, about 75% power. Oil temp never made it past the 150 mark with the cowl flap partially open. I have done nothing with the carb jet, it is definitely too lean, I have to idle the engine for a couple minutes in the cooler weather before it will take much throttle. I also need to make the cowl flap in flight adjustable or maybe just eliminate it now that the engine is broken in.
It is all about baffling, I have a homemade plenum which works extremely well. The cowl inlets are not round but are well sealed to the plenum. I do have the timing set at 22 degrees which probably helps keep the temps down.
Wittman Tailwind with Sterba prop which was built for RV4 with 0 360, way too much pitch for the 0 320.
 
I checked the carb mixture arm and found that it wasn't hitting the full rich stop. That dropped the EGT's by 100 degrees at takeoff. I also adjusted the baffles a little bit for better sealing. CHT's dropped by at least 35 degrees. I have a little way to go yet, but it is improving.

For those that added an Anti-Splat cowl flap, where did they put them and how much did they help?
 
Jesse said:
For those that added an Anti-Splat cowl flap, where did they put them and how much did they help?
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I added one cowl flap on the bottom of the cowl where it as flat a surface as possible is provided. Mine is on the right side, where I could keep it slightly further away from the exhaust. Best I can tell, it drops CHTs and oil temps about 10 degrees when I use it, which is only on hot days and especially if engine is already heat soaked.

erich
 
On the left side

As far back and to the left that was reasonably posible. About 10 degrees in level flight, but I installed it for climb where it drops the CHT by close to 30 deg. I have a 9A with an IO-320 8.5
 
jj13 said:
As far back and to the left that was reasonably posible. About 10 degrees in level flight, but I installed it for climb where it drops the CHT by close to 30 deg. I have a 9A with an IO-320 8.5
Click to expand...

That's the kind of numbers that would solve what's left of my temp problems completely, I think, after I finish all other normal cooling fixes.
 
Jesse said:
I will check for an induction leak. I had already thought that should be an early check. That would definitely make a difference. This carb was on this -6A for 1500 hours or more, so I can't imagine it has the wrong jet size. I was thinking there may be a common problem with carbs that sit for a period of time. I'll see how things go either Friday or next week.
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Carbs that sit for a long time can develop varnish-like deposits left by the slowly evaporating gasoline. This experience is based upon auto gas, but I doubt that 100LL behaves any better. These deposits can reduce the size of key passageways and orifice's, such as the main jet. The problem can be amplified by other "trash" that makes it past the gascolator. If you believe that the lean condition hasn't always been there, you can use heavy doses of seafoam or other products to break down these deposits (I would add them directly to the carb, not the fuel tanks-let me know if you need a suggestion). I would go this route before tear down. The MSA's are easy to pull apart for cleaning and would only cost $20 in consumable parts to reassemble. My O-320 with MSA carb runs leaner on #3 & 4 and my research tells me that this is somewhat common. I run plenty rich at full power, but also drilled out my main jet 3 or 4 drill sizes.

Larry
 
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Jesse said:
That's the kind of numbers that would solve what's left of my temp problems completely, I think, after I finish all other normal cooling fixes.
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Keep after the baffle work. My O-320 (160HP) and FP prop will now easily climb out under 400 in hot weather. I paid careful attention to baffle sealing during the build, but still needed quite a bit of tweaking to get the climb temps under 400 after I was flying. Lot's of great information here to help with a bit of research.

Larry
 
Im still working at the baffles and the mixture. Turns out the control arm was hitting the carb housing before hitting the full rich stop, so we should get a little more mixture yet. Cleaned up the baffles a little more. Took pitch out of the prop.

Another question for the technical ones. I was getting 2200 rpm for takeoff, which should have been close to 30" MAP at sea level. Will a low rpm like that cause higher CHT's or lower? I took pitch out and will see how that helps.
 
Jesse said:
...

Another question for the technical ones. I was getting 2200 rpm for takeoff, which should have been close to 30" MAP at sea level. Will a low rpm like that cause higher CHT's or lower? I took pitch out and will see how that helps.
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2200 RPM will be fine (I'm a little higher with my Catto Ubercruiser.) as you will transition through that RPM rather quickly on takeoff as your airspeed increases.
 
Jesse said:
Im still working at the baffles and the mixture. Turns out the control arm was hitting the carb housing before hitting the full rich stop, so we should get a little more mixture yet. Cleaned up the baffles a little more. Took pitch out of the prop.

Another question for the technical ones. I was getting 2200 rpm for takeoff, which should have been close to 30" MAP at sea level. Will a low rpm like that cause higher CHT's or lower? I took pitch out and will see how that helps.
Click to expand...

The more RPM's, the higher the HP, given the same MAP. More HP equals more heat. However, I would bet you only get another 100-200 RPM at T/O speeds and the HP increase won't be that great therefore Heat Output shouldn't increase too much. This is one of reasons you can't compare absolute CHT's across different planes. I take off with 2300 RPM (FP), while a CS prop'ed plane with climb out at 2700. Clearly the latter will produce more heat that must be removed.

Larry
 
I have some improvements to report. Turns out the fuel was 2 years old. New fuel made an improvement. Not huge, but a difference.

The EGT's still can sneak up close to (and one a little over) 1400 on takeoff. Fuel flow at 11gph. Not enough fuel getting through. I need to pull the carb and clean it as well as check the jet and maybe ream it out a little.

Also, in low power cruise, the temps are higher than they should be. CHT's in the high 300's to a little over 400. So the question here is, would I be better off installing a louver or two on the bottom of the bottom cowl, or should I install a cowl flap?
 
O-320 in low power cruise with CHT's in the high 300's to a little over 400....???

If it were my airplane, I would work to find the root cause of CHT's that are not normal when compared to many hundreds of other RV-6A's... rather than putting a band-aid fix on to try and solve the problem.
 
+1 on above. I have no problem cruising in mid-300's at 75% power in hot weather. I would start with the baffling as very few seem to get it perfect during the build and need to tweak a bit to make it optimal.

On the high EGT's, it seems many need to drill the jets out at least a drill size or two to get good fuel flow on T/O.

Larry
 
I would not be concerned with the egt's. They very a lot depending on how close to the exhaust port they are mounted. Keep working on it, you will get the chts below 400 in climb. At 70 percent wot how much egt rise can you get before peak egt when leaning? If you can't get a couple of hundred degrees I would say the carb is to lean.


Bob burns

N82RB RV-4
 
I haven't taken them to peak yet, but at 70% power and Mixture full rich at 1-2,000 feet they hang around 1275-1325. I think I am simply not getting enough flow at full power. I am seeing a fuel flow of 11gph at takeoff with a 150HP engine, and I should be seeing about 13.5-14.

I will continue to look for baffle leaks, but I think they are sealed fairly well. Not having wheel pants on can make a difference too, so I hope to get them on soon.

I feel like the cowl exit area isn't as big as it should be. Are there supposed to be any lovers on the bottom of the cowl?
 
I'm getting 30" of MAP and 2350rpm at takeoff. What percent power would that be? I'm guessing over 80%. I'm guessing in the 95% range. Should be flowing more than 11gph.
 
Just dug up the minimum flow chart for a 320. At 95 percent it should be just under 13 gal/hr

At 80 percent it should be about 11gal/hr
Bob burns

N82rb rv-4
 
I have an update. I drilled out the carb main jet 2 drill sizes to 0.096" and now my EGT's are in the low 1200's on takeoff. If I pull by MAP back to 25" at 500AGL and climb at 100kias, the CHT's stay below 400.

I also added a louver on each side of the bottom of the bottom cowl. That dropped my CHT's about 15-20 degrees in cruise.

3 and 4 still run 30-40 degrees hotter than 1 and 2 in climb.

I also don't have my wheel pants on yet, so that may help a little more yet.
 
Another update. I now have several hours since I drilled out the main jet. I think I went too big, so I would like to hear some ideas on whether or not this could be causing my small remaining problems.

At takeoff I see 1100's on EGT 1, 1200's on 2 &3 and 1300's on 4. When I pull back to 25" MAP they even out quote a bit, with 1 at least 100-150 cooler than 2-4. I haven't actually done a lean of peak test yet, but to get 2-4 to me to high 1300's in low altitude cruise at 65% power, I am within 1/2-3/4" of mixture ICO. I will do it, but I want to run it a little bit more first. I have proven in my mind that the original jet was not putting out enough fuel and it was running too lean.

I climb at 105kias and CHT 1 & 2 are low 300's and 3 & 4 are high 300's, sometimes sneaking up to 402 or so. They maintain this in the climb at 25-25.5" MAP and around 2250 rpm. When I level off 1 & 2 come up to the mid 300's and 3 & 4 come down to the 380's. I'm very happy with that.

Back to EGT's. When cruising at, say, 3,500', things are nice and stable at 65% power. If I go full power the EGT's go up as I would expect, but #4 goes way higher than the others, like high 1400's sometimes. I haven't done a lot of checking to see if I have an intake leak. I have heard others talk about the carb acting different at wot than it does pulled back a little. Does this sound like I am sucking air through a leak in the intake on cylinder 4 at higher power settings, or is something going on in the carb somehow that is causing this. I personally do not worry about CHT's up to 420 (recommendation from Allen Barrett) since the engine has already been broken in, so nothing about my CHT's bothers me in regards to being too high, but it is strange that 1 & 2 run so much cooler on climb and come within 30 degrees in cruise.

I'm open to all suggestions of simple things to check, although I am having so much fun finally having a plane of my very own to fly that I hate to take it down for maintenance of any kind if I can avoid it. Plus it takes me away from the other work in my shop that pays the bills.
 
I have another update. I was able to substantially improve my CHT's in the past by opening up my Carb jet and adding louvers to the bottom cowl, but I just got the thought from a couple of others lately that mentioned mag timing that maybe my mags were a little too far advanced. I put this engine on without modifying anything from the plane it came off except adding one Pmag to the right side, and leaving the impulse coupled mag on the left side. When I checked timing, the Pmag was set a couple of degrees (maybe a little less than a tooth) before TDC instead of right at TDC. I fixed this. When I got to the mag, however, I noticed a real big difference. It was probably 2.5 teeth before the 25 degree mark, making it 31 degrees BTDC instead of the required 25 degrees. Naturally, I fixed this.

I buttoned things up and flew (being one of the hottest days of the year at 95F). It probably dropped my CHT's by at least 25-30 degrees. I have never been able to climb full power at 110Kts without getting to 420 at which time I would pull way back and add mixture. Today I saw 407 max and as I climbed it dropped. I can live with 407 at full power at 110Kts.

Thanks to those who brought that to mind in other threads recently. I can't believe I didn't think to check that earlier.
 
O-320 Carb Issue

You may be interested in my report on this problem to our LAA, here in England. They now warn builders and test pilots of this issue.

Here's the link:

https://drive.google.com/file/d/0B-SOSxyKpCQoMFlmenI4WnY0cXc/view?usp=sharing

Latest news: Gus Funnel told me Vans now have a permanent solution - they are no longer selling the O-320, just the IO-320. Wish I'd known about this common problem - I would have gone for the IO-320 too!

Stan Hodgkins
G-DMPL RV7-A
G-DUDE RV-8 sold
G-HOBO Kitfox 4 sold
 
Captain Midnight said:
You may be interested in my report on this problem to our LAA, here in England. They now warn builders and test pilots of this issue.

Here's the link:

https://drive.google.com/file/d/0B-SOSxyKpCQoMFlmenI4WnY0cXc/view?usp=sharing

Latest news: Gus Funnel told me Vans now have a permanent solution - they are no longer selling the O-320, just the IO-320. Wish I'd known about this common problem - I would have gone for the IO-320 too!

Stan Hodgkins
G-DMPL RV7-A
G-DUDE RV-8 sold
G-HOBO Kitfox 4 sold
Click to expand...

I have no dog in this fight, but this is a great document for Doug to post in the archives for future readers with this issue, I have seen a half dozen threads on this same thing. Well done on the documentation.

Alternatively, you could repeat this very post and ask the moderators to make it a sticky with a catchy title (like "New Builders: O320 Carb Jet Warning !!!") in the appropriate engine section. Just a (meddling) thought.
 
Jesse,

Good to see you making progress here. I had terrible mixture problems with my carb and, like you, they were worse at WOT - T/O power. I also drilled my jet and had a spread of over 150* EGT between #1/2 and #3/4 at initial climb power. I don't believe the issue was with jetting, but poor performance of the very small plenum and intake routing in the sump. I resolved by going FI.

Advanced timing will definitely increase CHT's. It is optimizing the burn rate which means more heat in the combustion chamber, producing more energy. Later timing allows more of the heat to flow out the exhaust. So, increased timing generally increases CHT and reduces EGT. Others have shown, through testing, that this increased energy is not translating to increased performance in high MAP conditions and therefore, it is all negatives, with no offsetting positives in these configurations.

Larry
 
late

Sorry I am late to this thread, but this is not an 0-320 problem but an RV problem. Maybe problem is too harsh a word, an issue.

As the story in the link kind of said. The carbs supplied with Vans engines are just a carb that was designed for a certified airplane. It would have been nice for Vans to ask the carb manufacturer to design a carb for the RV's. Pretty sure that might have added to the cost of the kits, etc.
There is plenty of info in the archives and the yahoo groups on this subject and usually ends up with drilled jets. (against all professional advice).
I went through this years ago with my 0-360/CS set up and after all the usual things like baffling/timing/exit area, etc. Drilling fixed it.

Part of the problem is some people don't have the problem. Some don't watch very close, some limit climb, some don't fly on hot days and some just got richer carbs, etc. Some are located at higher elevations that allow the leaner carb to perform adequately. I am located at just above sea level and have a C/S prop with the leaner 10-3878, lean carb, so I had to address the issue.

If you look long enough, you will find Mooney aircraft ran into this issue a long time ago, not sure why they started with a lean carb instead of one designed for the job, but the carb manufactures made a kit to alter the carb and called it the Mooney mod....and still sell the kit today for the o-360 carbs. And yes, it is mainly a larger jet!

This whole issue is about getting proper fuel flow for you application and should be found/address in the very beginning during phase one testing like the OP in the LINK found. If you search much on the issue and reading John Deakin-Pelican Perch articles are great. The FI guys are not immune to this problem either.
 
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Bob Martin said:
If you search much on the issue and reading John Deakin-Pelican Perch articles are great. The FI guys are not immune to this problem either.
Click to expand...

To your two points above:

I agree, I have read the Pelican's Perch articles you've referenced, and they are great...very good read!

And to your second point, I will also agree. After purchasing my already-built RV-7 with a brand-new IO-360-M1B, it was a constant struggle to keep the CHT's to a "reasonable" (<410F) level on a hot day takeoff. It was an immediate level-off after T/O to get some smash (100KIAS+) and then pulling power when CHT's started going over 400F.

At cruise, all temps were perfect.

When I brought the aircraft to Walt Aronow for its first condition inspection after I bought it, when he pulled the plugs he emailed me and asked if it had been running hot, as the plugs condition appeared that it had been running lean. Of course, I replied in the affirmative...and after looking at some engine monitor history, he strongly suggested sending the servo out to get re-flowed.

He stated he had run across a number of them (even brand new, like mine was) that just were not getting the FF to the engine as they should.

While I didn't like spending $600 to fix something that should have worked right from the git-go, getting it done has made a big difference in what I'm seeing now. While last summer I would be pushing 400F on T/O leg before the end of the runway, now most of my temps are in the 390's, and the rate of rise is much lower. GPH at WOT went up about a gallon or so vs before the mod, and that seems to have helped, a lot. If you read the Deakin articles, you'll understand why...

Finally, I talked to Mike Busch after one of his presentations at AirVenture last year about Lycoming engines and CHT's, and I will pass along the info that while he feels the recommended "time to do something to cool things down" for Conti engines should stay at 400F, with Lycomings he would raise that to 425F, as I recall because of the head design, sodium filled valves, or something related to that. Still, he made the point, cooler is just about always better and if you can work to keep it 400F or less, you'll put less stress on your engine.

Rob S.
 
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