High CHTs

[GlennBfromOz]

I note that you have P-Mags, and that they're correctly timed at TDC.

This won't be the ultimate fix, but may give you some relief till you find it: since the timing on the P-Mags is so easy to adjust, may I suggest retarding by 5 degrees or so? The power loss will be minimal, but the effect on CHTs is significant.

My own experience in this area (RV7, IO-375) was a long series of tweaks to control CHTs, particularly at low speed and high power. The single biggest change, with about a 30F reduction, was a friend's recommendation to time the P-Mags 5 degrees after TDC.

[Walt]

Originally Posted by kaa

Thanks!

Yeah, I'm starting to think that the whole induction leak theory isn't that great. I'll do proper cruise checks.

Walt, are you saying that EI is 40 degrees lower steady state or that it's slower to react?

Yes steady state, the older ones are a different probe style, not the spring loaded bayonet commonly used now.

[kaa]

Thanks everyone for the help, much appreciated. I tried to plug some holes behind cyl #3 and #4 (around the dipstick and symmetrically on the other side) and it may have helped a bit, but not much. Still running 425F on #4 during the initial climbout. I guess I'll put more RTV around.

I did an induction leak test at 5000'. Here is a picture: https://photos.google.com/share/AF1Q...lwVWJiOUNHVTNB

Full data here: https://apps.savvyaviation.com/fligh...0-9ee0a3c4d357

Interesting that the first two times #1 and #2 went up, and the third time all of them did. Is this typical for induction leaks?

I tried to spot the leak by pressurizing the intake system through a cylinder's intake valve, but no luck - cannot see any bubbles anywhere. I'll replace the gaskets and rubber tubes (the tubes haven't arrived yet), but I'm a little uncomfortable that the leak doesn't show up with soapy water. I also replaced intake gaskets on #2 and #4 recently, when I was installing CHT probes, so they should only have a few hours on them.

I also verified that the probes are configured correctly.

[rv8ch]

Hi Kosio, I can't add more on the induction leaks, other than to fix them. You may not have seen the product that Ross sells - if you are looking for something else cool to add to your engine, he's got some very nice induction tubes and gaskets. (http://www.sdsefi.com/aircraft.html)

Also, on the pmags, you probably know that you can get serial data from them and can program them. You can use a laptop, or pick up Bill's EIcommander (https://eicommander.com) or EngineBridge (https://www.enginebridge.com/product/engine-bridge-ei/) Good luck!

[kaa]

Thanks, I just ordered a kit from Ross. Hopefully it fixes things.

I have an EICommander, and it shows that advance increases as MP is reduced, as expected.

[lr172]

Originally Posted by kaa

Thanks everyone for the help, much appreciated. I tried to plug some holes behind cyl #3 and #4 (around the dipstick and symmetrically on the other side) and it may have helped a bit, but not much. Still running 425F on #4 during the initial climbout. I guess I'll put more RTV around.

I did an induction leak test at 5000'. Here is a picture: https://photos.google.com/share/AF1Q...lwVWJiOUNHVTNB

Full data here: https://apps.savvyaviation.com/fligh...0-9ee0a3c4d357

Interesting that the first two times #1 and #2 went up, and the third time all of them did. Is this typical for induction leaks?

I tried to spot the leak by pressurizing the intake system through a cylinder's intake valve, but no luck - cannot see any bubbles anywhere. I'll replace the gaskets and rubber tubes (the tubes haven't arrived yet), but I'm a little uncomfortable that the leak doesn't show up with soapy water. I also replaced intake gaskets on #2 and #4 recently, when I was installing CHT probes, so they should only have a few hours on them.

I also verified that the probes are configured correctly.

#2 is definitely showing symptoms of an induction leak. Maybe #1 to a much lesser degree.

Larry

[kaa]

Could you explain why? Don't #1 and #2 show the same amount of EGT increase?

[lr172]

Originally Posted by kaa

Could you explain why? Don't #1 and #2 show the same amount of EGT increase?

#2 rises much more than #1, when viewed across the average. Also, #1 EGT is not stable like the other 3 under high MAP, which indicates that something else is going on with that cylinder. The incosistent behavior makes it difficult to see what part of the rise is related to induction leak. Notice how crisp the changes are on #2 compared to #1. You can see the clear correlation between MAP and EGT and how much larger the rise is on #2 relative to 3 & 4.

Larry

[kaa]

Well, I installed the no-leak kit from Ross, and nothing changed. The graphs looks exactly the same with #2 showing a big rise on throttle reduction. I guess it's something else then?

Could it be the primer port plugs? What's the correct sealant to use there? Although even with no sealant the potential leak path seems very small.

On the plus side, I think I might be able to bring the temps down by using copious amounts of RTV and speed tape around the baffles.

[Tom @ N269CP]

Am currently upgrading the 20 year old 10-3878 carb on my O-360-A1A with a rebuilt 10-4164-1 carb.

Spoke with the tech support engineer at Tempest/Marvel-Schebler today. They advise the 10-4164-1 carb should flow about 4.4 gph more at full throttle, full rich mixture, at sea level versus the 10-3878 carb.

Just chiming in here to provide for future reference some quantitative Sea Level flow data for the 10-4164-1 carb.