AIUI, the main reason for this is that the airflow is not the same to all cylinders, plus cylinders “steal” air (and thus fuel) from the adjacent ones.
But this pattern should be the same for all engines of a specific type.
The differences might be casting flaws inside the inlet manifolds?
AFAIK that’s only the case for Lycomings. Not for Continentals where it’s predictable, or so Braly said in one article I recall. Lycomings run lean so badly mainly because of poor tolerances in the injectors themselves, or so the same article said. But that doesn’t explain why a custom set is needed (presumably injectors are not the only thing with poor tolerances).
The term you are looking for Peter is “manifold robbery”, one of my favourites.
Gami injectors, as I understand it, are simply standard injectors, which have a wide tolerance range, whose delivery rate has been accurately measured and then an injector can be matched to the measured performance (by recording temps) of a particular cylinder.
So, let’s say an injectors design delivery rate is 100 units but with a tolerance of +/-5. That gives a spread of 10 units from 95 to 105.
By measuring and recording your cylinder temps you can identify which of these injectors will give identical temps across all cylinders.
Eg: cyl 1: 96 unit injector, cyl 2: 103 unit injector, cyl 3: 100 unit injector and cyl 4: 98 unit injector.
I’m sure you know this already but it doesn’t hurt to have the discussion.
I still don’t get why the variation between identical engines. The only obvious difference is a difference in the inlet manifold casting flaws.
Volumetric efficiency can vary quite a lot between cylinders, especially after a few hours are accumulated.
The condition of every component of every cylinder would have to be identical to get exact matches.
So, rings, bores, plugs, valves and inlet tracts.
I think you have to be doing a lot of hours to recoup the investment in Gami injectors but perhaps for some it’s more a matter of perfectionism.
Stickandrudderman wrote:
I think you have to be doing a lot of hours to recoup the investment in Gami injectors but perhaps for some it’s more a matter of perfectionism.
For some planes, it is the difference between being able to fly the engine LOP, and not being able to do so because it would shake off the engine mount before. Of course you could try to do without injectors ordered from GAMI by just switching yours around until you hit a lucky spot, but there’s no guarantee that will yield a good outcome. How much is a set of GAMIjectors?
I believe about £600 for 4.
Could someone explain to me how I go from having a datafile that I have output from my EDM700 (which I have on my Mac) to having a valid order for Gami injectors. I can’t find such an obvious question answered on the Gami website. I was expecting their website to have an email address to which I could send my EDM data file and a webpage on their website which invited me to do just exactly that in order to create business for them.
Thanks
Howard
Howard, they do in the first item on the side menu. Have you done the lean test however? Normal engine data is not what they need.
Thanks Jason…..quite why they would hide it on a page called “Take the GAMI Lean Test” is beyond me. I have would have a page called “How to obtain and send us your data to order your Gamijectors”… but what do I know :D
I’ll make sure I have the right data and send it to them. (I think I have it already.)
Much appreciated.
Howard