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Timing Sweep On A Dyno - Interesting Numbers

Toobuilder

Well Known Member
Some may know about my governor failure and major prop overspeed on my Rocket last year. Well, the mess is nearing resolution and a significant milestone was reached yesterday when the rebuilt engine ran across Ly-Con’s dyno. Since this engine has a fully programmable SDS EFI system, this allowed me the rare opportunity to validate “rich mixture” ignition timing insensitivity on an instrumented dyno. This experiment is a continuation of the flight testing I did in Death Valley a few years ago looking for any “peak” ignition timing point at 100% power. In that experiment, I did a 10 degree sweep from 20 to 30 degrees looking for any gains in speed. I was unable to discern any advantage based upon the IAS – it remained essentially flat. I opined that the airplane was hard against the drag wall and simply did not have the resolution to measure slight changes in power. It was admittedly a crude measurement.

Fast forward to yesterday when I once again did a 10 degree sweep, but this time I wanted to see how far of a retard from peak timing I could go before I took a big hit on power. Since I plan to run auto fuel in this thing, I want to retard my timing as a measure of detonation protection, but need to know where the “sweet spot” is. The results validate much of my in flight testing to date, but now I have hard numbers.

Disclaimer: I’m not going to defend the peak numbers shown here. This is Ly-Con’s data and I'm taking it at face value. What I’m more interested in is the percentage of power change with retarded timing. This data should translate well across the PV 320/360/540 fleet.

For general info, this is an otherwise stock 8.5 cr IO-540-D4A5 with the following modifications:

SDS EFI with 80mm throttle body
Ly-Con CNC ported heads
Piston oil cooling jets

The data as provided by Ly-Con:

Timing TQ HP
25° 620 320
20° 618 317
19° 615 316
17° 610 313
16° 606 310
15° 600 305


In this case, the peak power timing matches Lycoming's data plate value of 25 degrees. What’s interesting is the fact that I can pull a whopping 6 degrees out of the timing with almost no loss of power. So this tells me that I can program a huge retard into my takeoff curve and gain substantial detonation margin for no performance penalty.

Anyway, I thought you people might like another data point.
 
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Informative post Mike.

Amazing insensitivity to timing on these engines.

Appreciate you sharing this data.
 
Michael---excellent results. It will be great to have the engine back in the plane, so you can compare these dyno numbers to real world flight data. Will be interesting!
Tom
 
Yes, this was 100LL. I did not have the opportunity to try mogas.

But Bob, what numbers do you think will change, peak power, peak timing, or timing insensitivity?
 
Michael, great effort, and this is exactly as I would have expected.

I have mentioned this many times before, so while HP will be fairly static the peak pressure varies quite a bit, and this is why when fitting EI's it is a good idea to knock off a degree or two. The traditional mag has a bit of lag in it. The spark plug fires on average a degree or three later than the static timing. The dual mags on a chieftain even more so.

EI's hit the mark, and the SDS system is direct sensor, so even more so than the gear driven EI's.

If you decide to run on MOGAS, knock a couple more out, because HP is not the real issue here rather peak cylinder pressures.

If I don't forget to do it, I will dig in to some dyno runs and give you a guide to the differences you might expect with MOGAS, mainly with ICP, as this is the important factor.
 
Since Mike has an IO-540 parallel valve running 8.5:1, those who have a parallel valve 360, should see the same results as the cylinders are the same.

I would also suspect that a standard compression (8.5:1) (I)O-320 parallel valve (There is at least one angle valve 320 out there.) should also see the similar results.

Great info Mike, thanks for sharing!

(Bummer you didn't go to 26 degrees to see what the drop off would be up there, but it is understandable that you were conservative with your engine.)
 
Bill, they went all the way to 29 but it was really falling on it's face and hot by then. 26 was almost flat, but already starting downhill.
 
great data. Thanks for sharing! Impressive HP #'s. I would not have expect that big of an increase due to porting.
 
Tell us more Bob. Why?

Break.

Everyone note, Mike's motor is a parallel valve.

Lower octane, shorter burn. In one of my cars I have an aftermarket tune. I can select which octane I'm running and the tune is quite different.

I get that octane numbers are resistance to detonation.
 
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In the case of a car with a knock sensor, the higher octane fuel will sometimes make more power. But it's not the fuel that does it. As you say, it's the detonation resistance that allows more aggressive timing. If the lower octane fuel causes detonation and the computer regards timing below optimum, then power will suffer.

An aftermarket "tune" in a car typically tweaks timing and mixture for more power at the expense of reduced detonation margin. A tune that requires race fuel will be right on the limit of detonation anyway, so when fed low octane fuel will quickly experience a detonation event, the knock sensor will tell the computer to remove a bunch of timing and add fuel, and the power will be reduced as a result. But it's the timing and mixture changes that cause the reduction in power, not the chemistry of the fuel itself.
 
great data. Thanks for sharing! Impressive HP #'s. I would not have expect that big of an increase due to porting.

Yep. That's why I posted the disclaimer in the initial post. Even if we took Ly-Cons advertising claims of 5 HP per cylinder for the CNC porting at face value, that still only accounts for half of the 60 HP gain. The bigger, RSA-10 sized throttle body might be worth a bit of power as well as the slight plenum volume increase from the TB adapter - but 30HP? I'm not buying it.

That said, even with some Dyno error this thing is a bunch stronger than the 260 it left the factory with!
 
Mogas-Timing

You say you want to run Mogas. I too run Mogas, but a mixture of 2 parts 90 octane non-ethanol and 1 part 100 LL, providing a theoretical 93 octane result. I have an 8.5 CR as well in an IO-320

Are you using 93 octane ethanol, or 90 octane non, or a mix?
Ed
RV9A IO-320 8.5 CR
 
Lower octane, shorter burn.

Cryptic, but appears to relate flame speed with octane number. Can you suggest a data source measuring the difference in flame speed between mogas and 100LL? I suspect the difference is very small.

There are significant differences in flame speed for other fuels, alcohols being notable in our context.

Flame%20Speed%20Various%20Fuels.jpg
 
You say you want to run Mogas. I too run Mogas, but a mixture of 2 parts 90 octane non-ethanol and 1 part 100 LL, providing a theoretical 93 octane result. I have an 8.5 CR as well in an IO-320

Are you using 93 octane ethanol, or 90 octane non, or a mix?
Ed
RV9A IO-320 8.5 CR

I have not run a drop of mogas through this engine yet. The governor blew up before I even broke the rings in last time. However, it is my intent to gradually flight test my way down to running straight pump gas from the local station down the street. If it can handle the evil chemical concoction that passes for pump gas in California, it should be able to handle anything sold as "Gasoline" in the rest of the country.
 
Bill, they went all the way to 29 but it was really falling on it's face and hot by then. 26 was almost flat, but already starting downhill.

Thanks Michael, that is what I would have expected.

With the P-mags, we have found that reducing the firing angle from 26.6 to 25.2 pilots have picked up a little bit of speed but the bigger thing was their CHT's dropped 10 to 15 degrees.
 
Lower octane, shorter burn. In one of my cars I have an aftermarket tune. I can select which octane I'm running and the tune is quite different.

I get that octane numbers are resistance to detonation.

The higher the octane rating, the greater the fuels resistance to igniting, in general. I don't know the chemistry or science involved, but wouldn't be surprised to find that the chemical differences create a change in the speed at which the flame spreads with that particular formulation, and therefore have different optimal timing values in any given condition.

Larry
 
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Can you suggest a data source measuring the difference in flame speed between mogas and 100LL? I suspect the difference is very small.

Yes, how about having Mike test this and we find out. :)

The detonation margin and power output is large when running E85 in turbocharged automobiles with tunes specifically tailored for this. Are we talking about the difference between 87 mogas with 10% or more ethanol and 100LL? Here we could have an opportunity to see if there really is any difference in power. I suspect the power output differences would be negligible but the timing differences might be significant.
 
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I would have done it but the engine is off the dyno now and ready to pick up. I guess we'll have to wait until the next person from this forum with programmable ignition or EFI has Ly-Con build them an engine.

Im done playing on the dyno and ready to FLY!
 
Thread drift at intermission 😊

I recently tested 90 oct no alc mogas against 93 oct pump gas. Switching from one to the other made no difference at ROP cruise. But, when leaning (dual pmags) the engine is ?fussier? on 93 pump gas, and fuel flow apears higher to get things happy. 😡does this make sense ?
 
I've done hundreds of dyno pulls with 100LL vs. non-ethanol 91 mogas on various automotive engines. Best torque was obtained with the same total timing in all cases and the same jetting or maps if EFI.

Switched my Sube over from 100LL to 91 mogas years ago and noted no differences in EGT at the same power settings and found best speed was still obtained at 32 deg total timing.

Have some customers flying with one tank of 100LL and one with mogas reporting little if any change in speed or EGT when switching tanks.

All this would seem to indicate that clean mogas and 100LL have similar burn rates. Maybe Mike could run this test in the future for another data point.
 
I recently tested 90 oct no alc mogas against 93 oct pump gas. Switching from one to the other made no difference at ROP cruise. But, when leaning (dual pmags) the engine is ?fussier? on 93 pump gas, and fuel flow apears higher to get things happy. 😡does this make sense ?

From my research, alcohol has a lower energy output than std gasoline, though it has a higher octane rating. Thererfore, when using E10 you should expect a somewhat higher fuel flow for the same power levels. I have done no testing, but wouldn't be surprised that E10 is a bit more challenging when agressively LOP, due to the higher octane (the higher the octane, the hader it is to ignite the mixture and and agressively lean mixtures are already harder to ignite than richer mixtures.

Larry
 
From my research, alcohol has a lower energy output than std gasoline, though it has a higher octane rating. Thererfore, when using E10 you should expect a somewhat higher fuel flow for the same power levels. ...

Larry
Larry is correct here. Ethanol is used as an anti-knock agent to get the octane rating up, besides being mandated.

I notice the difference in my pickup; when I run ethanol tainted auto fuel my mileage drops around two to three MPG from when I run non-ethanol gas (both low octane). There is less "energy" in ethanol, thus the drop in mileage.

The odd thing about fuel is that there is more "energy" in lower octane fuels. The reason for the higher octane is it is required for high compression applications to provide knock margins. It is the high compression that produces the extra power, not the high octane fuel that those engines require to avoid knocking. From what I researched years ago, the difference was so slight as to only really noticeable in the lab.

Interesting science to be sure.
 
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(the higher the octane, the harder it is to ignite the mixture...

Larry

I have never seen any research or results to indicate this is true. Have run some crazy high lead content and, high aromatic home brew race gasolines and M85 fuels in cars and Reno aircraft at stupid levels of boost. Still light off just fine with inductive discharge ignition systems.

Folks erroneously think high octane fuels burn slower. They just have higher resistance to knock.
 
Pmag management next step ?

The above threads suggest 22 to 25 BTC timing doesn't lose much power and 32 yields max benefit lean. So, to get the best performance and lowest fuel price on my 7:1 compression 0320, I just retard the pmags 3 degree on the flywheel ( ie -3 from TDC) and use 87 oct pump gas. Correct ?
Thanks for all the smart attention to my question.
 
Hold on Larry - Ross' 32 degrees is for a turbo Subaru. Whole different animal!

This thread is dealing with validation of a long suspected timing insensitivity at full rich, 100% power conditions for the Lycoming parallel valve engines only. Its only a small piece of the puzzle. Yep, you can be very safe in your assumption that 20-25 degrees of timing is going to work well in your 320 for takeoff, but cruise and LOP numbers are a more complex issue (and fodder for other threads).
 
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Folks erroneously think high octane fuels burn slower. They just have higher resistance to knock.

I thought that was the result of the slower burn, they resisted preignition due to burning slower.

Methanol has less specific energy and density than gasoline, will have to burn more to make the same power.
 
Ross, just to clarify
did you mean "32 deg. total timing" as 32 deg BTDC - or - 16 BTDC plus 16 ATDC (point of peak pressure) = 32 deg. total timing? (Which would come within the low end of the scale of Mikes dyno numbers) Remember Ross's application is a boosted engine.

Also, Mike's dyno results are at near sea level 100% power levels. Conditions at lesser % power levels with variations of density elevations, MAP & RPM should have a varied effect on optimized timing point, & should be viewed only in their specific context.

A question to the masses - A small engine with a small piston & combustion chamber compared to the typical Lycosauris with it's big old piston & combustion chamber, plus lets rev the small engine twice as fast as the the big guy. Should the timing be the same in both the small and big engine so the flame front delivers the peak pressure on the piston the same, at the theoretical optimal point of 16 - 18 deg ATDC?
-Assume variables like fuel type, A/F ratios and MAP are the same for both engine.
-Factors I see playing out in this scenario - small combustion volume vs bigger one, smaller piston area vs bigger one, flame front speed same, basically half time slot for combustion event in small vs big due to rpm differences, and you want to deliver the peak pressure at the same point in both engines.
 
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Ross, just to clarify
did you mean "32 deg. total timing" as 32 deg BTDC - or - 16 BTDC plus 16 ATDC (point of peak pressure) = 32 deg. total timing? (Which would come within the low end of the scale of Mikes dyno numbers) Remember Ross's application is a boosted engine.

Also, Mike's dyno results are at near sea level 100% power levels. Conditions at lesser % power levels with variations of density elevations, MAP & RPM should have a varied effect on optimized timing point, & should be viewed only in their specific context.

A question to the masses - A small engine with a small piston & combustion chamber compared to the typical Lycosauris with it's big old piston & combustion chamber, plus lets rev the small engine twice as fast as the the big guy. Should the timing be the same in both the small and big engine so the flame front delivers the peak pressure on the piston the same, at the theoretical optimal point of 16 - 18 deg ATDC?
-Assume variables like fuel type, A/F ratios and MAP are the same for both engine.
-Factors I see playing out in this scenario - small combustion volume vs bigger one, smaller piston area vs bigger one, flame front speed same, basically half time slot for combustion event in small vs big due to rpm differences, and you want to deliver the peak pressure at the same point in both engines.

I mentioned Subaru (one centrally located spark plug) in the post which requires more advance than a Lycoming. My point was that gasoline type has little to no effect on the advance needed to achieve max torque as others were postulating. Total timing refers to timing BTDC, a composite of rpm timing plus or minus MAP advance or retard with EI systems.

We've run a bunch of tests on Les Kearney's RV10 with regards to timing vs. MAP vs. AFR as have other customers. Nobody has reported seeing any gains in TAS (power effectively) running any more than 33 deg total even LOP and below 15 inches MAP.

Revs, counter intuitively, don't seem to make much difference in required advance for best torque. Timing required on most engines I dynoed liked to be the same from about 3000 rpm to redline- up to 9000. The thought is that chamber turbulence increases with increasing rpm and this may increase flagregation rates.
 
I have never seen any research or results to indicate this is true. Have run some crazy high lead content and, high aromatic home brew race gasolines and M85 fuels in cars and Reno aircraft at stupid levels of boost. Still light off just fine with inductive discharge ignition systems.

Folks erroneously think high octane fuels burn slower. They just have higher resistance to knock.

I didn’t say higher octane fuel burned slower only that it was harder to ignite. That is what provides the increased detonation protection. Mild Detonation is typically a less powerfull force than a spark and increasing octane can help prevent the weaker detonation impulse from igniting th charge while still allowing a spark to ignite the charge. I only speculated that ethanol, being chemically different and with less energy, could possibly have a different flame speed than gasoline. Clearly yuo have more experience with this and have shown that it is the same.
 
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Fuel is an interesting subject, often not well understood.

Probably the best web resource on gasoline has been around a long time.

http://www.faqs.org/faqs/autos/gasoline-faq/part1/

Returning to topic...timing.

Mike's data is best power, ROP, with a ported parallel valve head. Chamber turbulence and swirl are key factors to increasing flame speed, thus reducing the ignition advance requirement. We don't know the details of Lycon's port work, but I imagine they try to improve both. It's possible that an unmodified head might like a little more advance. Theory, no data in hand.

Reported torque here is less than 1% difference, 20 vs 25 BTDC. I do have some data from another dyno running a highly modified parallel 360. I do not know exactly what was done internally, but it was a showpiece hotrod; 430 lbs ft is 201 HP at 2456. The reported torques were...

20 411@2424
25 430@2456
30 422@2461

...which is still only about 4% between 20 and 25.
 
I didn?t say higher octane fuel burned slower only that it was harder to ignite. That is what provides the increased detonation protection. Mild Detonation is typically a less powerfull force than a spark and increasing octane can help prevent the weaker detonation impulse from igniting th charge while still allowing a spark to ignite the charge. I only speculated that ethanol, being chemically different and with less energy, could possibly have a different flame speed than gasoline. Clearly yuo have more experience with this and have shown that it is the same.

No, I didn't say say that alcohols need the same advance. Methanol does require a bit more timing for best torque. I was only saying that high octane fuel is no harder to ignite than low octane stuff in my experience. Cylinder pressure from high boost pressure is a much more significant factor in required spark energy than the fuel octane.

Mild detonation still produces much higher peak pressures than normal combustion events, even ones started say 10 degrees early. Have a look at some cylinder pressure plots to see the differences.

A good education on this subject can be had from the old texts by Taylor and Liston.

Back to Mike's data, running mogas, as he plans, with decreased advance, will certainly increase detonation margins at almost no cost in power. That's a good thing to know.
 
Since detonation has been mentioned several times in this discussion, it should be defined. It is the abrupt combustion of the END GAS in the cylinder. In normal combustion, as the flame front propagates from the spark plug it travels through the mixture until all of it is combusted, normally at the cylinder walls and piston crown. Higher octane fuels (lots of iso-octane, lots of tetraethyl lead, alcohol fuels) have a higher resistance to this abrupt combustion of the END GAS. In a combustible mixture, higher octane fuels are not harder to initiate combustion than lower octane fuels.

For a more complete discussion see the Lycoming article:

https://www.lycoming.com/node/17607

This article has more depth:

http://www.contactmagazine.com/Issue54/EngineBasics.html
 
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Finally found some time to study real time engine data off the Carl Goulet engine test facility at GAMI in Ada OK.

Engine was a TIO540 Chieftain engine at 29.5"/2220RPM and full rich. Sorry, I know it was not your O-320 :)

First Question was Avgas Vs Mogas.
100LL Vs 91R+M/2 or 95 mogas. (98RON for the Aussies watching.)

Horsepower remained constant at 193GCHP/182BHP. BSFC=0.561 BMEP 120.4 and Toque at 431 ft. lbs.

Theta PP averaged about 18-20 degrees ATDC on Avgas 100LL but decreased as you would expect by around 2 degrees to a range of 16-18 degrees. This value bounces around a lot due to cycle to cycle variability.

Peak cylinder pressed ranged from nominally 600 PSI to 650-660 PSI which makes sense with the Theta PP change.

Interestingly when run on the mogas, and left in this condition, and with fixed spark timing of 20DBTDC (on spec) as the CHT's warmed up to what many consider acceptable 395-400dF and running a less rich mixture (BSFC 0.52-0.53)but still rich enough for Avgas, some cylinders started to knock (detonate).

You cannot assume that acceptable CHT means no knock, it might be minimal or low intensity, but it could be there and you would not know.

Part of this test was to reduce the ICP and correct for the fuel by using PRISM, and the result was 13-14 DBTDC and the knock vanished.

I know of an engine with all 6 cylinders that were run on 28+ degree timing and premium mogas that have valve recession to the point it had to be overhauled. (Ross, you might recall this one). If you consider the above observations with ICP being the key factor, you will not view spark timing the same way ever again.

Please note the Chieftain engine is normally a 20 degree engine compared to our typical RV engines being 25 degrees. Also note the spark timing I am quoting is actual plug sparking, not the static mag timing which has nominally 2 degrees of lag.

Lessons from this: If you want to run Premium Mogas, be very aware of vapour pressure problems, and these are not insignificant. Also spark timing needs retarding appropriate amounts, and EI's typically do not have the lag a regular mag has.

Last point I should make is and Ross has spoken about this a bit in previous posts, there is no gain in running much advance except when LOP and high altitudes / low MAP. And even then 28 degrees is more than enough.

Hope that is useful.
 
More data

The numbers in the OP were a subset of the full dyno printout and provided in an email with the premise that the particular run was pretty rich, and when leaned to best power it would make more.

That said, I now have the full dyno sheet in hand and can say the 320 HP figure (and timing sweep) was done pretty fat - the FF was 29.8 GPH for a BSFC of .5. MP was 29.38.

As a way of comparison, best power was found when leaned to 24.3 GPH and it turned out 331HP (.42 BSFC). And when leaned further, to 22 GPH even, it made 330 (.38 BSFC).

Not much to do with ignition timing here, but thought the BSFC numbers compelling.
 
I am curious but that HP number, was it Gross corrected horse power not BHP?

If so then I am going to stab at it that is still in the 310 BHP range :eek:
 
David, your example TIO-540 is an angle valve engine which we've seen from flight testing requires somewhat less timing than the PV engines to make best torque.

Also, were you running the mogas at the same MAP as on 100LL? If so, I'd certainly expect some detonation with the CHTs over 380.

I see some EI manufacturers dialing in over 40 degrees of total timing under some conditions and I can only conclude they have no idea what they are doing. I can see no benefit to this strategy, just more likelihood of damaging something.

On the RV-10 flight tests, WOT, LOP, low map up at FL180-200 best TAS was obtained at around 30 deg total timing. Down lower you probably need a bit less than that. This is a PV engine.

It seems too many folks think more timing should make more power- nope just higher CHTs and less power usually.
 
David, your example TIO-540 is an angle valve engine which we've seen from flight testing requires somewhat less timing than the PV engines to make best torque.

Also, were you running the mogas at the same MAP as on 100LL? If so, I'd certainly expect some detonation with the CHTs over 380.

I see some EI manufacturers dialing in over 40 degrees of total timing under some conditions and I can only conclude they have no idea what they are doing. I can see no benefit to this strategy, just more likelihood of damaging something.

On the RV-10 flight tests, WOT, LOP, low map up at FL180-200 best TAS was obtained at around 30 deg total timing. Down lower you probably need a bit less than that. This is a PV engine.

It seems too many folks think more timing should make more power- nope just higher CHTs and less power usually.

Yes they are an angle valve, and they do run slightly more CR and less timing, but that is not the point, it is the comparative difference between the 91R+M/2 and avgas.

Yes of course the MAP/RPM/FA were the same...... you know me better than that :p

As for other manufacturers, you and I have discussed this before and yes I agree!

And once again, violent agreement with me, about 28 is the max anyone needs LOP. :)

My data mining was to reinforce your statements based on the actual cylinder peak pressure change from avgas to mogas and that people should not discount that. Same for timing.

All the best mate!
 
Thanks gentlemen for your input. And while I completely agree with the general consensus that many people and some EI manufacturers load too much advance into their canned curves, I stand by my position that in situ testing is the best way to determine what an individual engine "likes". The statement that "28 degrees is about the limit" for LOP ops does not agree with my testing. Back when my Rocket engine was "stock" (save for the dual CPI) it "liked" 33 degrees when LOP. I offer this from an earlier thread:

...Cruise at peak EGT, 9500 MSL and a sweltering 70 degrees OAT resulted in 12 GPH and just at 200 KTAS. In this rich condition I run without the LOP switch advance active (30 degrees advance). Well stabilized, I advanced the timing to 33 with the LOP switch and within a minute or two I saw zero change in TAS, but the CHT settled in 8 degrees hotter and the oil temp increased a couple of degrees. This is expected behavior based upn my earlier flight test. If you are rich, too much advance only drives more temperature into the engine. after flying in this condition for about 10 minutes, I deactivated the LOP advance to see if the temps would drop to their prior levels. Almost immediately after pulling the advance out, the temps started downhill, settling in at their prior levels after just a few minutes. Ok, that result was confirmed as repeatable.

Next test was LOP cruise. As much as I hated to give up my 200KTAS, I dialed the mixture back to 10 GPH and the speed and temps plummeted, eventually settling in at 188 KTAS and a full 20 degrees cooler on CHT and close to 10 on oil temp. I flew for close to 10 minutes in this configuration to establish stability. Without touching anything else, I activated the CPI LOP advance switch taking the ignition from 30 to 33 degrees. The EGT dropped immediately, and the CHT started climbing. Within 5 minutes, the TAS climbed from 188 to 191 knots and stabilized, with the CHT finally settling in about 8 degrees warmer than before (still a very comfortable 375). I flew the remainder of the mission in this condition and it remained stable for the next 30 minutes until the TOD into Sedona...


I'm certain that David and Ross have validated their results like I have, so the only conclusion that I can draw is that individual installations might drive some significant variation. I also expect that with my "new" engine sporting EFI and ported heads (not to mention a substantial increase in power), my timing curve is largely invalid now. This version of the engine might not need nearly the advance of the old.

But you can bet I'll find out and report it here.
 
Agree, nothing like accurate flight testing to determine best performance. Most dynos can't simulate all variables present in flight. Lower OAT, ram rise and especially lower exhaust back pressure.

I have some customers who've done extensive flight testing on PV engines and report that best TAS running LOP was obtained between 30 and 33 deg. The question is how much LOP, leaner requires more advance to achieve PCP at the optimal crank angle, due to progressively slower flame speed.

Look forward to your flight test data Mike. The more good data points we have, the better recommendations we can make to our customers.
 
I am curious but that HP number, was it Gross corrected horse power not BHP?

If so then I am going to stab at it that is still in the 310 BHP range :eek:

I've heard it called "California Horsepower" by a few other folks that did work with that engine builder...No first hand data tho. I just thought it was amusing :)
 
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