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glenn654

Well Known Member
I'm planning on entering the Race to Ridgeland for my first race, but I have a fuel distribution problem. While testing my engine at full throttle and full mixture at low altitude (1500') cylinders 1,2 and 4 showed EGTs of approx. 1250 with CHTs at or just above 350. While cyl 3 showed an EGT of 1450+ range and CHT of approx 325. This leads me to think it is running LOP.
I have an O-320-D1A, 160HP with an Ellison TBI better than a carb but I still have the distribution problem at high power(65 percent +).

Is the condition of my #3 cyl bad enough to burn a piston if run like this for an hour or more? The last thing I want to do is ruin a cylinder playing.

I have been considering some experimentation at evening out fuel mixture distribution but don't have the needed parts (cost). What I thought of was making inserts to restrict the flow for # 1,2,&4 and hopefully allow #3 to draw a little more. To do this I would get four junk intake tubes and cut a piece about 2" from the lower ends.Then cut the pieces lengthwise removing some metal then welding the cut closed. When inserted into the existing runners fitting snuggly I hope reducing internal diameter enough to improve flow to #3.

What do you think? Does anyone know of any other method to redirect fuel flow?


Glenn Wilkinson
 
Recommendation

Glenn:

Call Airflow Performance in Spartanburg, SC. I've found they are very good at these types of issues. Good luck.
 
glenn654 said:
I'm planning on entering the Race to Ridgeland for my first race, but I have a fuel distribution problem. While testing my engine at full throttle and full mixture at low altitude (1500') cylinders 1,2 and 4 showed EGTs of approx. 1250 with CHTs at or just above 350. While cyl 3 showed an EGT of 1450+ range and CHT of approx 325. This leads me to think it is running LOP.
I have an O-320-D1A, 160HP with an Ellison TBI better than a carb but I still have the distribution problem at high power(65 percent +).
Click to expand...

The Ellison unit is a TBI-----fuel is introduced at the throttle body, not individual injectors at each cylinder head. This pretty much assures that the mixture going into the plenum is equal for all 4 cyl. Not a guarantee, but pretty good probability.

To me, it sounds like an air leak in the induction leading to #3, causing that one cyl to lean out.

Another cause could be timing issue for that one cyl-----not too likely.

Do you really mean LOP??? Or, just lean??
 
Yeah, higher EGT would indicate LEANER, rich of peak, or RICHER lean of peak.

I second the induction leak, but just do a lean test on it. Remember, the VALUE of the EGT isn't as important as how close all three cylinders peak with respect to one another. A few other possibilities are:

Bad probe/Gauge
Installation of the probe CLOSER to the port on one cylinder (measure location).
 
The Ellison unit is a TBI-----fuel is introduced at the throttle body, not individual injectors at each cylinder head. This pretty much assures that the mixture going into the plenum is equal for all 4 cyl.
Click to expand...

Single point fuel pretty much assures unequal mixture. Close enough to run ok, rarely close enough, for example, to peak all cylinders at the same time.

Just polishing the pins old bean <g>
 
Dan, he was running at full rich, had high EGT, and Low CHT on one cyl.

Assuming the probes and gauges are accurate, I still see an induction leak as most probable cause.

A TBI at full lean may be subject to distribution unbalance, but full rich????

As I said before---"going into the plenum"-------
 
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It is OK to procedurally deal with the problem

Glenn,

It is OK to throttle back and take it easy on you engine in the Ridgeland race. You can always take care of the problem physically at some later date.

A competitor
 
Exactly Glenn. Just throttle back...depart after Bob and keep the airspeed down. The thrill is just entering and running the race. No need to go fast if you have concerns.

On my one and only race I did not go full throttle since I had a new engine. Just finding the turn points was thrill enough.
 
In my street racing days, throttle back was called sandbagging.:D

Nobody likes a bragger, but everybody likes an underdog. So throttle back for your first race or two, then when you've got your power/cooling issues fixed, go out there and blows some doors....tail feathers off the competition. :D
 
<<As I said before---"going into the plenum"------->>

Ah, so you did. Sorry, my bad <g>
 
On my last annual I replaced the rubber hoses in the induction sys along with the gaskets at the heads...so I tend not to believe there is an induction leak but will double check it. At 65% power and less the EGTs and CHTs are nearly dead even, only at higher power settings does the variance show, increasing to full throttle which makes me think it is a matter of less efficient mixture distribution at higher power settings. The TBI was sent to the factory for SB compliance two years ago and has always run like a champ.
Instrumentation appears to be working properly through experience but has not been tested. I have read that with a carburator or equivalent that EGTs can vary as much as 200 Degrees F between cylinders due to the nature of the induction system and fuel distribution.
I was hoping some of the racers using carbs/TBIs may have already dealt with this and have some information for improvement. Maybe an efficient flow divider or a way to even the flow through induction runners was my idea of a solution. I've got vertical induction and looking at how the distribution thru the sump to the runners is designed appears to be poor but adequate.
I suppose I'll have to take prior advice to throttle back (sandbag) and accept the limitations of the engine but I REALLY want to run hard and up front. This is where FI comes in handy.

Thanks for all the input....I always learn something here.

Glenn Wilkinson
 
Glenn,

Here is a thought...

Assuming there is no intake leak on #3, would putting some type of vortex generator in that tube help keep the fuel and air swirling and help with our high CHT's?
 
N941WR said:
Glenn,

Here is a thought...

Assuming there is no intake leak on #3, would putting some type of vortex generator in that tube help keep the fuel and air swirling and help with our high CHT's?
Click to expand...

Bill, you beat me to it.

However, I would put it between the TBI, and the plenum, not in a single intake runner tube.

These have been used in the past for poor fuel atomization distribution problems, but they can be restrictive to the overall flow------I would suggest trying it as an analysis tool, more than a perm fix------of course, if there is a big improvement, well then..........

I keep going back (mentally) to the original statement of high EGT, lower CHT------sounds like a late timing issue. Just seems really strange to have only one cyl out of time, however.

Ross----any input here???
 
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Cooler CHT indicates that the cylinder is either getting more cooling air (not likely on number 3, if 3 on the gauge is actually 3 on the engine) or it's running richer. If it was running a cooler CHT because it was LOP, the engine would be shaking like all get out because thats a pretty darn big spread (3 cylinders ROP by 300? and one LOP 100?).

I really think it's most likely a instrumentation error... I don't see a timing problem being it, and I definitely don't think you are acutally running LOP in that one cylinder
 
Just kidding

Glenn, when I said pull back on the throttle earlier I was just kidding - you always want the other guy to slow down. I have the old common Precision Airmotive up draft carburetor on my O-360 in my RV-6A. I did modify it with the "Mooney Mod" (richer) very early in the flight testing to deal with a very high EGT problem on the only cylinder I was monitoring (#4). I do not ever recall seeing the coolest cylinder having the highest EGT but until a few years ago I only had the EGT in one cylinder and no CHT instrumentation. I don't know anything about the system you have but I get the most speed when I lean the mixture for around 1300F on the hottest EGT. The CHT of cylinder #3 usually runs higher than the rest if I have the heater air source and blast tube ports behind cylinder #3 uncovered - when I cover them for racing CHT #3 drops a little (I believe this is because of the cooling air bleed robs air from the cylinder). Your CHT for Cylinder #3 is lower than the rest so it is not being robbed of cooling air and the rest of the cylinder temps seem about right for the max power situation and the cooler CHT condition could come from fuel cooling - richer rather than leaner than the rest. That conflicts with the high EGT indication so if the instrumentation is accurate I don't have a clear answer. What I would do with my plane in your situation is lean based in cylinder #3 EGT to keep it ROP under 1400F and go with what I could get as far as CHTs are concerned. I am most suspicious of the CHT on cylinder #3 and if it bothered me a lot I would move the probe from cylinder 3 to 1 and and the probe from cylinder 1 to 3 and see if the low temperature follows the probe. In truth when in a race I run the engine as hard as it will go as long as the temperatures and pressures are not alarming. My cylinder #1 CHT and EGT are always much lower than the rest and at max power settings cylinder #2 CHT rises to compete with #3 for highest temperature honors. I can usually hang in there with the pack and if by chance I pick the right strategy for winds and other weather conditions I can do a little better than average. For the race (less than a month away) as you setup right now I would keep the EGTs below 1400F and the CHTs below 400F and I think you would be OK. There will be plenty of time to treat it as a science project.

Bob Axsom
 
As others have mentioned, be real careful using the EGT numbers in comparison with one another. Very minor placement differences of the EGT probe can cause drastic changes in the EGT reading.
 
I may have missed it but you should run a lean to peak test. Use a power setting of 65% or less. 23 squared at 6000 feet pressure altitude should work nicely. This will let you know if that cylinder is peaking before the other cylinders, and if so, by how much. check this link http://www.gami.com/gamijectors/leantest.php for lots of information on how to do a test.
 
glenn654 said:
On my last annual I replaced the rubber hoses in the induction sys along with the gaskets at the heads...
Click to expand...

Did the problem exist before you replaced these items? Is it possible you received up a bad part?

I have the Marvel/Precision carb with a stock O-360-A1A, and in races my observations are pretty similar to Bob Axsom's. However, I'm not sure the carb experience means much with respect to the Ellison. For example, I would not expect to see CHT's grouped closer than ~25° while running wide open and rich, whereas this may be possible with the Ellison? 200° hotter EGT on just one cylinder does sound like a problem.

What kind of inlet/airbox setup do you have? The TBI is reputed to be more sensitive to inlet geometry, airbox design, etc. than a Marvel carb (also see the Ellison web site). I'm not sure if this would affect only one cylinder though.
 
I was NOT kidding about powering back. IF you have an issue that could damage the engine running WOT in a race, then prior to the race run at a setting that is comfortable and safe. Use that as your race speed to determine takeoff position.

Run the race at that setting. You still get the benefit of racing and once you determine if there is a problem..and correct it, then you can up the power setting.
 
Just found this thread while trying to research a nearly identical problem on the front engine (O-320 B1B) of my Rutan Defiant. (Sorry, plastic airplane guy infiltrating here..). This winter I had a set of tuned headers built, which exit out the right side. Ever since this installation, my #3 EGT has risen to above 1400, sometimes to 1450, on takeoff/climbout. I have tried almost everything you could imagine, swapping probes, checking timing, compression check, etc. etc. and nothing helps. I am now thinking that the scavenging effect of the tuned exhaust has unbalanced fuel flow even more, causing the high EGT. CHT's are all lower than before, and #3 is no exception, in flight I only see about 350 max CHT. I have read the threads about drilling out the main jet, but I'm wondering what effect that might have on the other 3 cylinders that stay around 1200-1250 at full rich. Would these then run way too rich? Another surprise is that there is no additional power than before, based on static and takeoff rpm (fixed prop) Harry Manvel
 
I have come up with another theory of my problem.....if #3 has a bad plug or ignition lead, could the combustion mixture be exhausted w/o being completely burned and then complete its burn while in exhaust stroke and cause greater heat to be applied to the EGT probe while causing the cylinder to run cool because there is less heat generated there.
I'm going to get my plugs tested. I only cleaned and gapped them at annual.

I won't make the race this time...need to get this problem solved.

Glenn Wilkinson
 
Pierrie,
I hate having to miss the race cause of some problem with my engine which I hope to have corrected soon. I am now waiting for your friend w/ the Pitts to come back for some aerobatic instruction. Put me on the list and give me a call when ready.

478-452-96813 work
478-456-3090 cell

Thanks
Glenn Wilkinson
 
another chance to race

I don't know where you are based but the Tennessee Valley race/speed dash would be a great opportunity to test your plane and engine. If you don't want to run all out for 45 mins just do the speed dash and only run all out for a few minutes.

Chris Murphy RACE34 RV-4
 
Thanks Chris...I'm working in that direction, I'm from GA (MLJ) so it's close.
Expect to have it ready by then.

Glenn Wilkinson
 
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