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  #1  
Old 10-29-2021, 03:43 PM
JDBoston JDBoston is offline
 
Join Date: Oct 2007
Location: Boston Area
Posts: 311
Default Unleaded fuel for the IO-390

I debated putting this post in the Engines section but my question is a little more specific so I am leaving it here for now.

Also I am not looking to get into a debate about unleaded fuel or "if it will ever happen" because we are building these airplanes hopefully for a long future rather than the next 5-10 years only.

Does anyone know the feasibility of running the IO-390 on the proposed unleaded fuels that exist out there? I am thinking the GAMI one, but I am not as familiar with any others.

Let's assume that some modification could be done to the IO-390 (ignition, fuel pump/injectors, etc) to make it work.

Now, what about the EXP119 variant and changes that Vans made?

I am asking this because I chose the EXP119 and have the finish kit on order for January. If there is potential that we will need to switch eventually to unleaded fuel I am wondering if the EXP119 choice is going to limit this potential given the higher performance optimization.

If you were thinking of somewhat future proofing in this area, would the EXP119 be a good choice?
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  #2  
Old 10-29-2021, 04:01 PM
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rv8ch rv8ch is offline
 
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Quote:
Originally Posted by JDBoston View Post
...

If you were thinking of somewhat future proofing in this area, would the EXP119 be a good choice?
From everything I've read the EXP119 will be able to run G100UL and the other 100LL replacements without problem.
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  #3  
Old 10-29-2021, 08:15 PM
lenlou lenlou is offline
 
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Default I-0360

Interested to follow this discussion, I do hope that you receive your Finish kit in January. Still waiting for me EMP that was ordered in May.
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  #4  
Old 10-29-2021, 11:34 PM
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HAL Pilot HAL Pilot is offline
 
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https://www.ac-aero.com/gladiator/

Gladiator 390 liquid cooled lycoming compatible cylinders can run auto gas
87/89/91 & up, 100LL, MOGAS
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  #5  
Old 10-30-2021, 08:46 AM
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DanH DanH is offline
 
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Quote:
Originally Posted by JDBoston View Post
Does anyone know the feasibility of running the IO-390 on the proposed unleaded fuels that exist out there? I am thinking the GAMI one, but I am not as familiar with any others.
I do not think there will be a serious issue, as the whole point was to develop a drop-in replacement. A lot depends on exactly which new fuel, because they are certainly not all the same, regardless of octane rating.

The FAA ran a full test series for Swift fuel, and published detailed results, a nice example of public money for public benefit. In general terms, the detonation performance was acceptable. The report is available from various web sources. Search Full-Scale Engine Detonation and Power Performance Evaluation of Swift Enterprises 702 Fuel

GL100UL doesn't seem to have as much data available to the public, a situation which appears to be based on competitive advantage, not lack of performance. Information released by its developer suggests it is superior to minimum spec 100LL:

https://gami.com/g100ul/Excerpts_FAA...rch_7_2021.pdf

Some will find this patent filing interesting:

https://patentimages.storage.googlea.../US8628594.pdf

Quote:
Let's assume that some modification could be done to the IO-390 (ignition, fuel pump/injectors, etc) to make it work.
The IO-540-K is the accepted baseline engine for NA Lycoming detonation testing. The direct connection to the 390 is its angle valve cylinders. However, the 390 has a slightly larger bore, and CR is 8.9 rather than 8.7. The result is a few more HP per cylinder at the same 2700 RPM. In theory, a bore increase and higher CR are both pro-detonation, making the 390 a tad worse than the baseline.

Fuel pump and injectors are not relevant, and here we'll assume owners will not change pistons to lower the CR. That leaves two items within our control, operating temperatures and ignition timing. Detonation tests are run with oil, intake air, and cylinder head temperatures at or near the maximum, something a smart operator won't do. Less ignition advance is almost always an effective option, and it's easy to implement.

Quote:
Now, what about the EXP119 variant and changes that Vans made?
The key differences, as compared to C and D models, involve weight reduction, the installation a dedicated exhaust, and the use of an Airflow Performance FI system rather than an AvStar. The rated power boost really isn't huge (like 2.5%), and I doubt it will make any difference in the big picture. As an RV owner, the keys to operating on any unknown fuel will be careful installation of cooling components, and not allowing a lot of advance.
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  #6  
Old 10-30-2021, 09:29 AM
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rv6ejguy rv6ejguy is offline
 
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In case you haven't seen this in the other unleaded fuel thread, the FAA has just added a bunch of engines to the list to run on the GAMI fuel: https://www.aopa.org/news-and-media/...unleaded-avgas

A tiny reduction in ignition timing at high MAP should allow the 390 to use this as well, retaining factory detonation margins or maybe none at all is required.

There are several supercharged radial engines on the list now which operate at much higher cylinder pressures than a 390.
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  #7  
Old 10-30-2021, 10:00 AM
JDBoston JDBoston is offline
 
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Fantastic information everyone, that puts me at ease. Clearly the 390 came out of modifying I believe the 360, and my lack of experience in this area made me question as everything I have read in the past is that the “higher performance” engines “may have a problem” which is clearly imprecise at best. Excellent info, thanks!
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  #8  
Old 10-30-2021, 12:53 PM
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DanH DanH is offline
 
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Here's a nice illustration of how ignition advance affects detonation onset, in this case with Swift fuel. Although the numerical values may change with another fuel, all of them will have a similar response to timing.

Here note that at 26 BTDC, it entered detonation at max power (not good!), but at 23 and 20, detonation was roughly 1.5 GPH on the lean side of max power.

Who might have trouble? Best bet is a few clueless 390 owners running P-mags without clocking the install and installing the jumper, i.e running with 30.8 degree base timing. Hey buddy, here's your sign...
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Last edited by DanH : 10-30-2021 at 01:11 PM.
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  #9  
Old 10-30-2021, 01:50 PM
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rv8ch rv8ch is offline
 
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Quote:
Originally Posted by DanH View Post
Here's a nice illustration of how ignition advance affects detonation onset, in this case with Swift fuel. Although the numerical values may change with another fuel, all of them will have a similar response to timing.

Here note that at 26 BTDC, it entered detonation at max power (not good!), but at 23 and 20, detonation was roughly 1.5 GPH on the lean side of max power.

Who might have trouble? Best bet is a few clueless 390 owners running P-mags without clocking the install and installing the jumper, i.e running with 30.8 degree base timing. Hey buddy, here's your sign...
-
Looks like only 2hp difference between 20° and 26° of advance at peak power. I guess the benefit comes in at lower power settings. I know my pmag advances up to just over 32 degrees when I'm at altitude and leaned out. Mine's an io-360.

https://www.youtube.com/watch?v=iN5AmdAmySs
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