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Faulty Intake Tubes

SHORTRV7

SHORTRV7

Well Known Member
Has anyone had trouble getting to Lean of Peak causing the motor to stumble? On my IO 540 Barrett cold air sump and after consulting with two AI's we think we have found the problem. The intake tubes are not sealing with the gasket only. I'm not able to put pictures up on this, but the flange of the tube sits lower in the collar and the lip of the tube is not constant all the way around.
 
SHORTRV7 said:
Has anyone had trouble getting to Lean of Peak causing the motor to stumble? On my IO 540 Barrett cold air sump and after consulting with two AI's we think we have found the problem. The intake tubes are not sealing with the gasket only. I'm not able to put pictures up on this, but the flange of the tube sits lower in the collar and the lip of the tube is not constant all the way around.
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Not going to comment on the condition of the seal of your tubes, but if you are LOP, it's assumed you are at altitude, and the throttle is wide open. In this condition there is hardly any difference in pressure between the port and the outside air. In other words, there's not much pressure differential to cause a "leak". I have had the two bolts come completely out and the tube fall away from the head in cruise and didn't notice anything until closing the throttle to land.

If you are having a stumble at LOP, it's more likely you have a different problem.

And yeah, grab the SDS O ring flange kit. Fixes the leaks for good.
 
LOP ops place a large load on the ignition system---harder to ignite the fuel/air mix.

What ignition are you running?
 
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Toobuilder said:
Not going to comment on the condition of the seal of your tubes, but if you are LOP, it's assumed you are at altitude, and the throttle is wide open. In this condition there is hardly any difference in pressure between the port and the outside air. In other words, there's not much pressure differential to cause a "leak". I have had the two bolts come completely out and the tube fall away from the head in cruise and didn't notice anything until closing the throttle to land.

If you are having a stumble at LOP, it's more likely you have a different problem.

And yeah, grab the SDS O ring flange kit. Fixes the leaks for good.
Click to expand...

+1

quite unlikely the problem is related to intake leaks at high MAP. We would need some EGT RPM MAP and FF data showing the problem to offer much help. It could be many things.
 
bjdecker said:
Mike -- Why is this?
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I read that as well but made assumptions as to his intent. Ign system load doesn't change with AF mixture; however,

the ability to take advantage of a lean AF mixture requires good spark energy; (no need to get (back) into diminishing returns argument on spark energy). Without such, unstable/incomplete combustion and the expected, related losses will result.
 
You didn’t mention: Have you balanced the cylinders (e.g., do they all reach peak egt as you lean, at (nearly) the same time)?
 
bjdecker said:
Mike -- Why is this?
Click to expand...

Freemasm said:
I read that as well but made assumptions as to his intent. Ign system load doesn't change with AF mixture; however,

the ability to take advantage of a lean AF mixture requires good spark energy; (no need to get (back) into diminishing returns argument on spark energy). Without such, unstable/incomplete combustion and the expected, related losses will result.
Click to expand...

Poor wording on my part---Freemason explained it.

If the spark energy is borderline weak, you could have misfire with a LOP operation. EI usually has a much greater ability to fire large gap plugs, and hotter spark.
 
I have what’s sounds like the same setup. Barrett/CAI/slick/surefly.
I also have the SDS intake oring flanges.
Mine stumbles faintly LOP as well and for the life of me I can’t work out what it is.
My GAMI spread is nice and tight (all 6 cyls peak within 0.5 gph or better)
I’ve shop vac pressurized the entire intake looking for leaks with soapy water. No leaks. Im sure my issues aren’t intake related.
I’ve flowed the injectors with AFPs help. That’s all in spec. No divider issues.
I’ve shrunk the nozzles down to nominal 0.025 (+/-) to increase the back pressure at the spider.
So I’m at a loss. The last thing on my list is ignition. But I’m not sure what to change. The plugs all look fine but I haven’t put them on a tester (champions) so I can’t be 100% certain.
 
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