Jabiru ignition leads

[turboplanner]

My problem is that one side runs 20 degrees cooler than the other. The right-hand cylinders 1 and 3 are cooler than the left-hand 2 and 4.  I have tried an extender lip on the left-hand ones, to try and divert more of the prop air into the duct, but this had no effect. The hot cylinders have the upgoing prop, and they are further back. 

 

Maybe discarding the ram-air ducts and putting in a plenum chamber would solve the problem.  But apart from the uneven cooling, those ram air ducts sure do make for a tidy setup.

 

The engine does not run real hot, on climbout the max ( no 4 ) can be kept under 160 C by being careful.

 

Maybe another scoop just feeding into the hot side duct? Maybe an electric fan helping the cooling flow?

 

You told us previously the engine failed on the ground after idling for some time, and said that was your fault, but at major city airports, taxy and waiting time is a lot longer, so you could run into a situation where this will happen again. If its egt you're talking about with one side 20 degrees hotter, that's going to reflect in uneven power output putting more pressure on two cylinders. It's a pit aircraft have props or you could put some tufts of wool in the ducts and stick your head in. Maybe you could mount a small camera on the hot side to see what the air is doing. I never had any success with electric fans. What are the spark plugs telling you?

 

 

[coinz]

Plug leads ended up inside my Ramair ducts was not initially planned,but these early ducts were very restrictive to airflow over the top 6 fins,

 

compared to D model, i wanted to keep them outside but the 90 deg spark plug caps ($146 for new set) were too short,so i routed them the same

 

as the later model . I would have used longer straight caps but they would have needed complicated sealing on an angle and removal would be near

 

impossible ,i imagine that would be an issue to be solved, Paul .

 

 

[facthunter]

It's a little difficult to understand why Jabiru didn't adopt the "conventional" method of close fitting baffles around the engines cylinders and blast tubes onto individual items as required.  All the air above the engine is at the same pressure in a largish space. . You do need rubber seals around the edges to sit against the cowl but that's not rocket science. Nev

 

 

[Paul davenport]

T88 was no 8 on a 230 

 

 

[Old Koreelah]

... you could put some tufts of wool in the ducts and stick your head in. Maybe you could mount a small camera on the hot side to see what the air is doing...

 

I've heard of a bloke doing pretty much that. I believe he was in western Sydney and after much careful study of the airflow around the heads, got his temps just right. From memory, Oscar described it on this forum.

 

 

[Bruce Tuncks]

Turbs, you got the story wrong yet again.

 

I did NOT overheat the engine taxying on the ground.

 

I did overheat the engine running it at cruise rpm on the ground trying to dynamically balance the engine/prop system.

 

This meant running the engine MUCH  harder than you would when taxying.

 

I am at a loss to explain how you get these things so wrong so often.

 

 

[turboplanner]

Probably because that's the first time you've mentioned cruise rpm on the ground?

 

 

[facthunter]

I think he did mention power runs with the cowl off and I warned of head problems.  Once you overtemp a head, its suss no matter what engine it is.  Inserts can come loose and the metal rendered soft(er) Nev