egt's and tuning

[Yves]

i have a discussion going on at another forum about the effectiveness of egt's in balancing cyls.

I have read here that they do a good job, but some people seem of the opinion that they are not worth the hassle. So how is it irl ?

[subwoofer]

No first hand experience, but from what I have heard from the aircraft side (GAMI etc), absolute values are of little use - you have to adjust mixture while monitoring EGTs to find peak EGT for each cylinder.

But as I just said, I have no evidence to back this up.

[kaeman]

when my engine was dyno'ed the builder had egt probes in each cylinder and watched the temps very closely during the pulls, he said that the temps should be within about 100 to 150 degrees of each other and that you didn't want egts above about 1300 or 1400 degrees... I cant remember which, because if the temp was elevated to that point for more than just a few seconds you would start to damage pistons and such... I just cant remember the temp that he said to watch out for on the high side. the temps also depend on how far from the exhaust valve you are measuring the temps at.

[shaodome]

when my engine was dyno'ed the builder had egt probes in each cylinder and watched the temps very closely during the pulls, he said that the temps should be within about 100 to 150 degrees of each other and that you didn't want egts above about 1300 or 1400 degrees... I cant remember which, because if the temp was elevated to that point for more than just a few seconds you would start to damage pistons and such... I just cant remember the temp that he said to watch out for on the high side. the temps also depend on how far from the exhaust valve you are measuring the temps at.

EGTs are useful for balancing cylinders and I use them for this on a regular basis. You would be amazed at how far off fueling can be depending on manifold designs, boost pressures, etc. As for the EGT temp there are a lot of variables that factor in to what is "considered" safe. 1400 degrees is fine, but it definitely is NOT the max limit of the pistons and the related boundary layer directly above them. Hell, a standard bosch LSU sensor wideband has a max sustained operating temperature of 950c (1740f). I'm not saying to run it that hot, but just as a point of reference.

150 degree variance to me is on the high side and it wouldn't be uncommon to see 30% or more correction in particular cylinders. Also keep in mind that exhaust manifold pressure (turbo apps) will skew the readings as well.

[Yves]

How much smoothing does a balancing/trimming act cause on an engine ?

[Matt Cramer]

We've used EGTs for testing cylinder to cylinder fuel distribution before. They're not as accurate as one wideband per cylinder, but they are not as expensive, either, and can hold up much better in a turbo application.