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-   -   Timing Sweep On A Dyno - Interesting Numbers (https://vansairforce.net/community/showthread.php?t=182190)

rv6ejguy 05-12-2020 07:32 PM

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.

RV10inOz 05-13-2020 12:53 AM

Quote:

Originally Posted by rv6ejguy (Post 1429776)
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!

Toobuilder 05-13-2020 07:38 AM

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.

rv6ejguy 05-13-2020 08:19 AM

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.

Toobuilder 06-06-2020 10:16 AM

Getting closer to validating the dyno numbers - had the first engine start yesterday. Just a touch of smoke from the presevative oil in the cylinders and thats it.

https://youtu.be/hXpzk2yLe6k

bjdecker 06-06-2020 01:18 PM

Quote:

Originally Posted by RV10inOz (Post 1429768)
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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