T

Ted Farmin

Well Known Member
we have just completed phase 1 on our RV4 0-320 150 hp with Van's filter air-box and experience high egt (1540*) at full throttle 2600 RPM in level high airspeed flight. We think we are getting so much ram air pressure that it is causing a restriction or pressure on the main jet nozzle. We can apply carb. heat stopping the ram pressure and the egt drops to 1400. This is at 3000 ft. Would it be necessary cut a dump hole in the air-box?
Plane flys beyond our expectations, no trim needed for rudder or aileron.

Ted and Tim Farmin
27 hours and still
grinning
 
Typically we want to get all of the manifold pressure boost that we can (ram air). It is not likely that is the problem.
The improvement from carb heat is because the heated air produces a richer mixture condition.

As posted by asav8tor, more info is required.
It this condtion on all 4 cyl?
What EGT instrument are you using (not Westach hopefully)?
 
Is this a peak EGT number?
Not a problem. I see 1540 as peak at high rpms.
Will they rise on one mag? Turn a mag off and see if it rises. It should.
What ever the EGT number is, it really only relative to your engine/gage/probe/installation and should not be of any concern. Oil and CHT #'s are actual concerns. As long as the egt number performs properly. IE: lowers with carb heat, lowers rich of peak, lowers lean of peak. The actual reading is not important.

Best,
 
Ted Farmin said:
(snip)experience high egt (1540*) at full throttle 2600 RPM in level high airspeed flight. We think we are getting so much ram air pressure that it is causing a restriction or pressure on the main jet nozzle. We can apply carb. heat stopping the ram pressure and the egt drops to 1400. This is at 3000 ft. (snip)
Ted and Tim Farmin
27 hours and still
grinning
Click to expand...


As others have posted, more information is needed, but I seriously doubt that ram air is the problem.

What are the rest of the conditions of the test? Where is the mixture set?.

As an example, if the EGT rises another 200 degrees as you lean the mixture, you don't have a problem (well, maybe you have a poorly calibrated gauge). In normally aspirated airplanes, the absolute EGT numbers are unimportant--the numbers relative to peak EGT are very important.

At high power settings, you want to be very rich of peak EGT. This means an EGT 200 degrees cooler than the peak.

I would address this somewhat urgently, because if you are operating close to peak at high power settings, you are likely to damage your cylinders.
 
I'll try to ans. questions. We have a four port egt on the Dynon D180. Will temp. rise from 1540 wot level flight by leaning, NO by pulling mixture control
to the point where we get temp. rise at lower power settings it only starts to run rough and temp. seems to be peaked. We do get a temp. rise on one mag. at a little lower power setting but not at wot where we have the condition. I flew this morning to get more info and at 2500 rpm the egt was 1380 and I could lean to 1440 when eng. ran rough and at 2400 rpm the temp. was 1280 and peaked at 1380, but this was at 7000 ft. Was to turbulent at lower and I was having a hard time writing, should get a recorder.
At the beginning of this I should have told that I reamed the main jet nozzle in increments of .002 and .001 to .005 larger in other words from .088 to .093
This carb. is not the part no. for the 0-320 E2D but I went thru it and installed the -813 jet nozzle that is called for and also checked the venturi. I am thinking we have a mild condition of our old hot rod days where we had to put the carb. in a box when super charging (remember that guys). Also I just talked to Glassair owner and he said his air box has a large hole in the back side. When I apply carb. heat the manifold press. drops .8 in. and if I let go of the lever the air press. opens it. The question was asked, where was the mixture control during this, it was full rich.
Looking for your input. Thanks

Ted and Tim Farmin
28 hours
 
Ted Farmin said:
I'll try to ans. questions. We have a four port egt on the Dynon D180. Will temp. rise from 1540 wot level flight by leaning, NO by pulling mixture control
to the point where we get temp. rise at lower power settings it only starts to run rough and temp. seems to be peaked. We do get a temp. rise on one mag. at a little lower power setting but not at wot where we have the condition. I flew this morning to get more info and at 2500 rpm the egt was 1380 and I could lean to 1440 when eng. ran rough and at 2400 rpm the temp. was 1280 and peaked at 1380, but this was at 7000 ft. Was to turbulent at lower and I was having a hard time writing, should get a recorder.
At the beginning of this I should have told that I reamed the main jet nozzle in increments of .002 and .001 to .005 larger in other words from .088 to .093
This carb. is not the part no. for the 0-320 E2D but I went thru it and installed the -813 jet nozzle that is called for and also checked the venturi. I am thinking we have a mild condition of our old hot rod days where we had to put the carb. in a box when super charging (remember that guys). Also I just talked to Glassair owner and he said his air box has a large hole in the back side. When I apply carb. heat the manifold press. drops .8 in. and if I let go of the lever the air press. opens it. The question was asked, where was the mixture control during this, it was full rich.
Looking for your input. Thanks

Ted and Tim Farmin
28 hours
Click to expand...

Ted,
Your problem is not from getting to much air pressure into your airbox. With aircraft we do everything we can to get as much pressure as possible.
The problem is the amount of fuel your carb. is delivering, relative to how much air your induction system is supplying.
It could still be your carb is too lean as far as jet size goes or that it has another problem. An induction leak is also possible but not likely since all cyl are effected equally.
At altitude you should have at least a 200 degree difference between full rich and leaned to peak but still running smooth.
Do you know for sure that the mixture arm on your carb. is hitting the stop when at the full rich position? A throttle quadrant is sometimes hard to get the travels correct so that it hits the idle cutoff stop and the full rich stop.

This is the first thing I would check.

Once again... the result you see when pulling carb heat is not because you are getting too much air into the airbox. It is because for some reason you are not delivering enough fuel for the amount of air you are supplying.

You could restrict the airflow, but this would be robbing you of power output and would be a band-aid fix at best.

You need to fix the fuel delivery problem, to fix the problem. If you are running lean enough at high power (Takeoff) you could be causing engine damage.
 
rvbuilder2002 said:
Ted,
Your problem is not from getting to much air pressure into your airbox. (snip)
You need to fix the fuel delivery problem, to fix the problem. If you are running lean enough at high power (Takeoff) you could be causing engine damage.
Click to expand...


What he said:)

Really, your engine is running way lean, and you should fix this before you burn a valve or worse.

Are your CHTs OK?
 
other thoughts

With the assumption that you have the correct jet, I would definately perform a fuel flow test to verify that your fuel system can provide enough flow to the carb. I think the minimum safe number is 150% of max expected fuel flow, ie if your engine burns 10 gph at SL WOT, then the system better be able to deliver 15 gph to the carb. With as lean as your description sounds, I'd verify this prior to next flight...as others have mentioned, lean mixtures at T/O power can be a good way to meet your next overhaul shop.

Check for clogged fuel filter.

Tim
 
We have checked the flow to the carb. 22 gph with elec. pumping into measured container. Cyl. head temps. are 390 to 400*. We will pursue
enlarging the jet nozzle in small increments. Is there an enrichening circuit
in the Marv. MA-4SPA carb. that may not be working? But back to the info that the egt of 200* spread that we don't have confirms we are to lean
Thanks again

Ted
 
Ted Farmin said:
Is there an enrichening circuit
in the Marv. MA-4SPA carb. that may not be working?Ted
Click to expand...

Yes, there is.

Once again, I would double check that the mixture arm on the carb is hard against the stop when the mixture lever is at the full rich position.
This has been a problem in the past with other rv's that use a side quadrant.
 
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