EGT readings for uncompensated "cheap" gauges

[s johnson]

Hi Guys,

Question regarding uncompensated egt gauges. Cheap ones I bought at LEAF. I believe they are set up for standard day 15*/59F day.

If it's 20 degrees F out side and my EGT reads say 1300*F what is my actual egt temp. Would I subtract 20 from 59 = 39 F and then take the 1300F-39 to come up with the true egt of  1259*F or is it the other way around?? Dazed and confused...

My reason for asking is Yesterday I preheated my engine for about 45 minutes. Pulled it through 5 times with choke/enrichment on, mag hot.. fired and started first pull. Got to love these VWs. Warmed up for about 15 minutes advanced throttle with very rough running up to about 2300 rpm. Ran there for a bit and back to idle . it quit. Tuff time restarting and when it did start ran bad the entire time. would not take throttle or idle. Almost like carb ice. It was a nice dry day but very cold 12* F.
I guess what I'm hinting at is with these extreme temp changes do we need to re jet the carb for the really dry cold dense air? I've flow two years ago with temps in the mid 20's with no issue but that was with dual carbs behind the heads.

 My set up now is one carb mounted on top Engleman style with long intake tubes. It has a oil routed through an alum block to heat the air/fuel mixture after the fuel comes from the carb to the intake tubes. But I doubt the oil was never really hot enough to open the bypass to allow the heated oil to do it's intended job. could be ice build up in the intake tubes I suppose. The tubes get real cold on a good day before the oil heats up. Just thinking out loud here and look forward to any and all comments and sugestions.

EGT and carb jetting issues or Carb/intake tube icing??

Thanks
Scott J.
The Slug Musher

[Sam Buchanan]

My vote is for carb/manifold ice.

[s johnson]

Sam,

Thanks for the opinion. I am leaning that way also. There was a 2* C split yesterday but clear.
.
What is your though on the EGT readings? Not that is an issue at this point, just wanting to know what the real temp is and not worry if the egt spikes above 1400F when it really might be below the 1400F due to the non compensated gauges and very cold temps.  I don't know which way for sure to adjust the temp from what is actually being shown on the gauge, or even it it's a non issue.

Scott

[Sam Buchanan]

Sam,

Thanks for the opinion. I am leaning that way also. There was a 2* C split yesterday but clear.
.
What is your though on the EGT readings? Not that is an issue at this point, just wanting to know what the real temp is and not worry if the egt spikes above 1400F when it really might be below the 1400F due to the non compensated gauges and very cold temps.  I don't know which way for sure to adjust the temp from what is actually being shown on the gauge, or even it it's a non issue.

Scott

Scott, I have no personal experience with flying our engines in temps this low...I get uncomfortable at 55*F.  

But my thoughts are that even though the mixture is leaner at the low temps, CHT would also be lower than usual so it may be a wash. It is possible you are far enough LOP that the engine is developing less power than you would see in the summer and therefore have even more detonation margin than usual. If you can't achieve normal static rpm it may be necessary to richen the mixture a bit. But if the engine pulls as it should I would be ok with it.

 I would fly the plane if it is running smoothly and the pilot can keep from icing up.

[Dan_]

If it's 20 degrees F out side and my EGT reads say 1300*F what is my actual egt temp. Would I subtract 20 from 59 = 39 F and then take the 1300F-39 to come up with the true egt of 1259*F or is it the other way around?? Dazed and confused...

Scott,
Here is the info you're looking for...  Fill out a card and keep it in your pocket...

The EIS units keep up with the temp of of the cold junction and do the math for you in the microprocessor chip.

[Steve]

Two things Scott:



First, Mike Pastors single Mikuni on a cross top manifold would make ice in the manifold in summer wx big time...



Secondly, I'd get a dipstick heater and bring the oil up to temp before you fire the engine - I think you'll find it a different experience... I have the bottom of my fullcase wrapped in plumber's heat barrier in cool wx...




Steve

[s johnson]

Thanks Danny.... I was on the correct path...

Scott

[s johnson]

Steve,

Thanks for the info. I have heard mixed reviews on the dipstick heater. I have one but have not used it. I do pre heat for a long time. I might try the d.s. heater to see how it works as well as wrapping the bottom of the engine as you suggest.

Thanks

Scott

[s johnson]

I might try wrapping the intake tubes with a exhaust type tape to help hold the heat once they warm up .  I think the issue of running bad was ice.

S.J.

[Dan_]

Scott,
Yesterday in Oshkosh it was 16 degrees at 7:am with relative humidity at 73% and dew point 10 degrees (click hourly detail for dew point)...

That comes up bumpkus on the carb ice chart.

Could it be ice in the float bowl..?[/font]

[docmatt]

Scott,
I don't doubt that ice could be the culprit, but rejetting for cold weather will likely help.  Lot's of my friends race motorcycles on Lake Winnebago in winter, ( I work on my airplane).  Those guys all rejet or adjust fuel injection from the summer trail riding settings, whether they ride two strokes or four strokes.  The jet kit I bought for my trail bike came with a different needle jet for temps below 50 degrees.

[High Noon]

Scott,

Id be weary of Ice, AND poor fuel mixture with those long tubes.........
Remember VW ducted exhaust air around to get proper evaporation of fuel.

I had both problems before I heated mine. unequal mixture between sides, (left/Right) and Icing.
Both went away when i added heated pipe.

im Lost when It comes to the egt's though.

High Noon
SHANE