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I recently collected data for a "GAMI spread" test on our newly rebuilt Aerovee, including my custom intake plenum and individual runners. The results show a mixture difference of ~15% at full throttle (fuel flow difference between peak EGT of leanest and richest cylinder.) The full write up is here.

(I realize leaning the engine to peak EGT at full throttle is not a good thing, but I think a few minutes of runtime for this experiment to confirm the mixture distribution is better than running some cylinder too lean for hour after hour due to ignorance.)

Has anyone done a similar test with the stock intake system? I'm interested in comparing real data on the mixture distributions.

Hi Patrik,

Your tests are very interesting. Thanks for the write-up!

Have to admit that I needed to lookup what "GAMI spread" meant. So to save others some time, the definition is: spread between fuel flows where the various cylinders achieve peak EGT.

I found a great article, by Mike Busch, that explains EGTs and GAMI in great detail. Link to article: http://gami.com/articles/egt_myths.pdf I found his analysis of why absolute EGT numbers are meaningless to be very helpful. Look for the paragraph that explains how the shape of the exhaust pipe can greatly affect the measured EGT readings. Good stuff.

-- Michael

Yeah Mike Busch has several articles talking about EGTs and the effect of mixture on both EGT and CHT. I'm reading his new book "on engines" now, it's a pretty good collection of all his talks and articles put into book form, if anyone's interested in learning more about this subject.

lutorm wrote:Yeah Mike Busch has several articles talking about EGTs and the effect of mixture on both EGT and CHT. I'm reading his new book "on engines" now, it's a pretty good collection of all his talks and articles put into book form, if anyone's interested in learning more about this subject.

I'm about halfway through the book and its def a good read.

peter
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