Lead for valve health required ?

[Larry DeCamp]

I asked Superior engines if leaded fuel was required for breakin and valve health for my IO EXP 360. Here is the answer I received :

"There is no metallurgical benefit to operating the engine during break-in on leaded aviation gasoline as relates to valve or valve seat lubrication. However, the brake mean effective pressure (BMEP) will be increased with the use of leaded aviation gasoline (AvGas). The slower burn rate of avgas compared to auto fuel will allow for a more efficient use of the ignited fuels pressure buildup to be converted to mechanical energy instead of heat. While not specifically noted, you may want to ensure the engine is operated on AvGas for the first 25 hours to ensure the highest BMEP during this time. Higher BMEP will assist in ring set and ensure a good rings seal."

While this is thought provoking, it does raise the question how much BMEP is your engine developing ( set aside MP/RPM setting ) considering magneto fixed timing, Pmag aggressive timing and EI adjustable timing ??

I hope this helps others like me that were "unfulfilled" by opinions on the Leaded Break-in Wives Tail.

[rv7charlie]

Originally Posted by Larry DeCamp

I asked Superior engines if leaded fuel was required for breakin and valve health for my IO EXP 360. Here is the answer I received :

"There is no metallurgical benefit to operating the engine during break-in on leaded aviation gasoline as relates to valve or valve seat lubrication. However, the brake mean effective pressure (BMEP) will be increased with the use of leaded aviation gasoline (AvGas). The slower burn rate of avgas compared to auto fuel will allow for a more efficient use of the ignited fuels pressure buildup to be converted to mechanical energy instead of heat. While not specifically noted, you may want to ensure the engine is operated on AvGas for the first 25 hours to ensure the highest BMEP during this time. Higher BMEP will assist in ring set and ensure a good rings seal."

While this is thought provoking, it does raise the question how much BMEP is your engine developing ( set aside MP/RPM setting ) considering magneto fixed timing, Pmag aggressive timing and EI adjustable timing ??

I hope this helps others like me that were "unfulfilled" by opinions on the Leaded Break-in Wives Tail.

Saay whaaaat? Do Superior engines have dylithium crystals or something now, so they can convert avgas directly to mechanical energy & skip that pesky heat step?

Sounds like what they're *really* saying is that avgas burns so slow, it keeps cyl pressure up all the way to the bottom of the stroke (where it's not really doing anything but pushing the main bearings sideways. Which will ensure proper breakin of the rings to the bottom of the bore.

edit: I agree that the old valve lube thing is hogwash; we should all realize it by now, since we all know someone that's had to ream the lead out of their valve guides.

Charlie

[BillL]

Originally Posted by rv7charlie

Saay whaaaat? Do Superior engines have dylithium crystals or something now, so they can convert avgas directly to mechanical energy & skip that pesky heat step?

Sounds like what they're *really* saying is that avgas burns so slow, it keeps cyl pressure up all the way to the bottom of the stroke (where it's not really doing anything but pushing the main bearings sideways. Which will ensure proper breakin of the rings to the bottom of the bore.

edit: I agree that the old valve lube thing is hogwash; we should all realize it by now, since we all know someone that's had to ream the lead out of their valve guides.

Charlie

Sounded pretty straight forward and technically correct to me. It means that the desired 3-4 deg ATC pressure peak (IIRC) is more advanced and will have higher peak pressure and temperature than 100LL. I did not know the heat release was faster for gasoline. That means it has a higher flame speed.

We also know from evidence presented by DanH and Nigel Speedy's that advanced timing is not beneficial below 8000'DA. And - - the Lycoming book would say not to break-in the engine higher than that anyway. (BMEP too low) Interesting Superior mentions BMEP, as you could just as easily (more easily) run at 2000 RPM to achieve the desired BMEP (and pressure) without the local friction heating of the rings moving so fast, at least with a CS prop that has adequate pitch range.

[DanH]

Originally Posted by Larry DeCamp

I asked Superior engines if leaded fuel was required for breakin and valve health for my IO EXP 360. Here is the answer I received :

"There is no metallurgical benefit to operating the engine during break-in on leaded aviation gasoline as relates to valve or valve seat lubrication. However, the brake mean effective pressure (BMEP) will be increased with the use of leaded aviation gasoline (AvGas).

BMEP is a theoretical yardstick derived from torque and displacement. The unit happens to be pressure, but it tells nothing about the location of peak pressure or pressure later in the stroke. A higher BMEP doesn't mean pressure is somehow more consistent throughout the stroke.

Increasing pressure later in the stroke (assuming the goal is to increase ring seating pressure further down the bore) requires only a delay in combustion. However, since peak pressure will be reduced, the overall result will typically be a reduction in torque, and a corresponding reduction in BMEP.

There may be some difference in torque output when comparing mogas and avgas at the same ignition timing and equivalence ratio. I don't have that comparison data, so I'd like to ask your contact at Superior for a reference source.

The Swift fuel tests (DOT/FAA/AR-08/53) are illustrative of two fuels. To obtain approximately the same peak pressure (psi) and location of peak pressure (degrees ATDC) at 2450 RPM, Swift fuel required 3 degrees more advance. Same pressure at the same point would result in the same torque. The rest of the PV diagram would probably also match, thus the same BMEP.

In a practical sense, I doubt the choice would make much difference for break-in. Without the timing change, the actual HP difference (torque*RPM divided by a constant) was roughly 2% for the Swift fuel. If you're worried about it, add some manifold pressure.

[pjc]

I also agree the Superior info makes sense, and with the additional color from Dan and Bill. Particularly that fuel choice is not material to break in results, and that all else being equal, running higher MAP will achieve higher cylinder pressures if you believe that is beneficial (or necessary for ring seating).

Now to run off-topic, I?m interesed to learn more about this statement (I presume by ?advanced timing? you mean relative to Lycoming?s suggested fixed mag timing).

Originally Posted by BillL

We also know from evidence presented by DanH and Nigel Speedy's that advanced timing is not beneficial below 8000'DA.

Can you provide a pointer/link (I was not able to format a specific enough search to pick this out).

Thanks
Peter

[DanH]

Originally Posted by pjc

Now to run off-topic, I’m interesed to learn more about this statement (I presume by ‘advanced timing’ you mean relative to Lycoming’s suggested fixed mag timing).

Can you provide a pointer/link (I was not able to format a specific enough search to pick this out).

You want Nigel's article written for Kitplanes, May 2017 issue. His is a parallel valve. Angle valve heads seem to require less advance.

[Toobuilder]

Originally Posted by pjc

...Now to run off-topic, I?m interesed to learn more about this statement (I presume by ?advanced timing? you mean relative to Lycoming?s suggested fixed mag timing).

Can you provide a pointer/link...

Bill's statememnt is a bit too broad in this context. While it is true that lower altitudes and rich mixtures require less advance, the truth is each engine, each fuel type, each mixture setting and every foot of altitude will require an "optimum" ignition setting. We often use the data plate ignition timing as a baseline, but the fact remains this factory setting itself is a significant compromise and will really only be optimum in a very narrow set of circumstances. Move one or more variable (altitude, mixture, RPM, etc) and its no longer optimum. There are a few of us who have done flight test and posted results on this site.

In the context of the OP, it is nice to see the confirmation that the valve faces and seat material no longer need the sacrificial lead deposits to prevent valve seat recession (remember the issue with old cars when we switched?). However the secondary issue of lower BMEP was raised. Most of us who have played with race cars know that different fuel formulations require different ignition settings - and this is secondary to detonation margin. Some fuels burn slower than others and those of us who would dump 100LL in the tank for a night at the track know just how slow it burns compared to pump gasoline. We needed a change in timing to get the BMEP back. So if you take an aviation engine with fixed timing set for 100LL and use a faster burning fuel, then of course it will no longer be "optimal". You will need to change the timing. How much? Depends. Flight test or instrumented dyno time in an environmental chamber will be required.

[lr172]

Originally Posted by rv7charlie

Saay whaaaat? Do Superior engines have dylithium crystals or something now, so they can convert avgas directly to mechanical energy & skip that pesky heat step?

Sounds like what they're *really* saying is that avgas burns so slow, it keeps cyl pressure up all the way to the bottom of the stroke (where it's not really doing anything but pushing the main bearings sideways. Which will ensure proper breakin of the rings to the bottom of the bore.

edit: I agree that the old valve lube thing is hogwash; we should all realize it by now, since we all know someone that's had to ream the lead out of their valve guides.

Charlie

They may have assumed the alternative to avgas was E10 gas. The energy output of E10 is around 5-10% less than E0 or whatever you call gas with no alcohol.

FYI, the need for lead years ago was not for lubrication, it was heat transfer. The lead coating helped to better transfer heat from the exh valve to the seat. Modern alloys and hardening allows this to work well enough without the lead.

Larry

[pjc]

Originally Posted by DanH

You want Nigel's article written for Kitplanes, May 2017 issue. His is a parallel valve. Angle valve heads seem to require less advance.

Thanks!
Peter