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  #31  
Old 12-02-2021, 03:49 PM
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rocketbob rocketbob is offline
 
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Thanks Don.

Now I am remembering the AFP innards. Slots cut with a wire EDM as opposed to the triangular holes in the Bendix.
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  #32  
Old 12-02-2021, 09:23 PM
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Quote:
Originally Posted by dpansier View Post
Photo of AFP divider
Quote:
Originally Posted by rocketbob View Post
Now I am remembering the AFP innards. Slots cut with a wire EDM as opposed to the triangular holes in the Bendix.
The slots are tiny.
.
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Last edited by DanH : 12-03-2021 at 05:17 AM.
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  #33  
Old 12-02-2021, 10:43 PM
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Really excellent discussion! Walt, humble apologies for the thread drift, but thanks for allowing it to be a springboard for the follow-on points.

Circling back to the original concept, having seen Ross's post that a 10:1 AV engine at high MAP and 29 degrees will very likely reach detonation, I'd like to ask, how high is too high? 24"? Higher or lower? And how much timing would one need to back out, in order to safely lean through peak at that same power setting? The 3-5 degrees that you mentioned (24-26 degrees?)...would that be safe? I'm sure its not cut and dry, but perhaps a rule of thumb would help other's avoid Walt's friend's troubles.

I've owned one plane with an AV Lyc. It was a TIO-580, but it was 6.5:1 for the turbocharger. I raced it at 67" MAP, but ran dual mags and leaned very carefully. I actually couldn't get the fuel flow high enough for the power I wanted to run, despite boost pump and mechanical pump changes to chase higher flow rates. Probably needed bigger pipes (#8 instead of #6). Ross will likely chuckle, as he's helped some of our Gold racers get far more MP and FF than I ran, along with the SDS and its cylinder tuning capabilities. The results showed it too...I was a distant third to Andy running SDS. But timing was back at 20, and it was not a great LOP flyer outside of racing, so I never really pushed into this danger zone with leaning.

The discussion of fuel flow/flow dividers, and airflow issues is great info! As Steve said, my AFP FM-300B and SkyDynamics cold air induction typically provide excellent flow. Good info from Greg on your AFR differences at different RPM. Greg, by any chance, do you have data that shows what happens to AFR in each cylinder (especially 2, the one I'm working on now), as you increase from 2200 to 2500?

The other curve ball in my engine performance, and this temp chase throughout the week in Reno, is the addition of N2O. I installed a system from AFP that injects both fuel and N2O into a spacer just behind the FM-300. There is one nozzle on each side, and each adds both fuel and N2O right into the cold air inlet plenum. Varying the jets in each line allows choosing a 50HP, 100 HP or a 150 HP shot. I used the 50 inserts. While my recent LOP test without nitrous showed the slight tendency of cylinder #2 to lean earlier at higher power (24 squared vs 22 or 23 squared), it was not as marked at is was at full race power (about 27 squared in Reno). Could it be that higher speeds, leading to more ram air pressure, could be forcing the air/fuel mixture towards the back of the cold air plenum, and #2 just isn't seeing quite as rich a mixture. I'm just musing out loud at this point...I know the time increments between cylinder firing are minute, but I'm wondering how the flow might be affected by all of this ram air/nitrous and other monkey motion going on. And wondering what, if anything, might be done (inlet pipe tuning comes to mind, as was mentioned earlier).

Dan, interesting graphic. What is the term "bleed" referring to in it (MP higher or lower than bleed)?

Thanks again for the discussion!

Cheer,
Bob
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Last edited by rvmills : 12-02-2021 at 10:47 PM.
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  #34  
Old 12-03-2021, 06:48 AM
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Quote:
Originally Posted by rvmills View Post
Circling back to the original concept, having seen Ross's post that a 10:1 AV engine at high MAP and 29 degrees will very likely reach detonation, I'd like to ask, how high is too high? 24"? Higher or lower? And how much timing would one need to back out, in order to safely lean through peak at that same power setting?
A perfectly stock angle valve can be moved in and out of detonation onset at will, with stock timing. Just supply the wrong conditions. I'm sure the same is true of the parallel valve, but I don't have comparable data. The manufacturers treat detonation info like a state secret.

Accurately knowing the limits for your race setup will require an off-season dyno session with a vendor equipped for detection. George Braly has a great setup, although Sky Dynamics might be a player, and Lycon should be.

For the average person, the takeaway from Walt's report should be two-fold. One, you can't just bolt stuff to an engine and assume everything will be OK, no matter what the vendors say. Two, with apologies to the poor schmoo who got the hard lesson, moving the knobs without first engaging the brain has consequences. In fairness to the nice folks at EMag Air, we should all remember it was possible to conduct the test without breaking the engine. The FAA, Lycoming, and Mr. Braly, for examples, do it routinely.

Quote:
Dan, interesting graphic. What is the term "bleed" referring to in it (MP higher or lower than bleed)?
You're looking at the output from a fast deltaP sensor, one leg tapped to the intake port via the primer hole, and one leg tapped to the butt end of a bleed air rail feeding shrouded injector nozzles. You'll recall the nozzles bleed upper plenum air into an annulus around the fuel stream just after the restrictor, to promote atomization of the stream as it enters the port. The goal of the experiment was to determine how often, and to what degree, does the nozzle suffer a reversal of bleed air pressure, something Don Rivera wished to see. Here there is some pressure reversal, for a very short period. The fun part is the ancillary data derived at the same time.

In the context of this discussion, bleed air pressure is assumed to be a constant, relatively steady value. That may not be completely true due to pressure oscillation in the propeller wake, and would probably vary quite a lot based on cooling air intake design. However, it's a close enough assumption here. It means the pulsing pressure seen in the plot is the wave action in the intake tract for that cylinder.

Below I've added two notes. Each little graph square is about 20 degrees. The positive waves are arriving at the port at intervals of about 117 degrees, mostly a function of intake tract length and diameter, and only optimum for one RPM. I've used spark as a marker, which allows me to identify TDC, and BDC, which lets me approximate intake valve open and close. Note that the wave is arriving twice during the intake period, once as the valve gets well off the seat, just after TDC, and again late in the stoke, as the piston nears BDC. Those positive pressure periods help cylinder filling...the whole purpose of the tuned runners used with the horizontal intake sump. Way back when, some engineer at Lycoming got it pretty close.
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  #35  
Old 12-03-2021, 08:23 AM
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Originally Posted by rvmills View Post

The other curve ball in my engine performance, and this temp chase throughout the week in Reno, is the addition of N2O. I installed a system from AFP that injects both fuel and N2O into a spacer just behind the FM-300. There is one nozzle on each side, and each adds both fuel and N2O right into the cold air inlet plenum. Varying the jets in each line allows choosing a 50HP, 100 HP or a 150 HP shot. I used the 50 inserts. While my recent LOP test without nitrous showed the slight tendency of cylinder #2 to lean earlier at higher power (24 squared vs 22 or 23 squared), it was not as marked at is was at full race power (about 27 squared in Reno). Could it be that higher speeds, leading to more ram air pressure, could be forcing the air/fuel mixture towards the back of the cold air plenum, and #2 just isn't seeing quite as rich a mixture. I'm just musing out loud at this point...I know the time increments between cylinder firing are minute, but I'm wondering how the flow might be affected by all of this ram air/nitrous and other monkey motion going on. And wondering what, if anything, might be done (inlet pipe tuning comes to mind, as was mentioned earlier).

Cheer,
Bob
Once you start shooting fuel in the intake plenum (i.e. the common area before the runners), you now experience the issues the carb guys do - way too small of a plenum and poor air flow distribution, etc. Your case is even worse than a carb, as the fuel is injected into stable air, where a carb injects it into the venturi, which helps a bit with atomization. While I don't understand the engineering of why, I do know that many with carbs experience it. Just looking at a modern automotive intake, shows that engineering principles matter here. An interesting experiment would be to see what happens at the same 27 squared combo (ROP) without the NO/fuel addition at the plenum. Does the lean condition on #2 lessen or remain the same. If it goes away, you are left with the same issues that plague all Lyc carb users. I suspect someone may have played with this and found some potential tricks to lessen the effect.

If you have the space, adding another spacer between the NO extentsion and the plenum will help to increase the plenum area and improve mixing, though it is critical that you match the walls closely. Remember the old hot rods with the carb(s) sticking out of the hood? Same concept here, though those also increased the runner lengths and made them more vertical as well as enlarging the plenum. Adding spacers between the carb and the intake manifold is a time honored trick to improve mixing and intake efficiency in the hot rod community.

Larry
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Last edited by lr172 : 12-03-2021 at 08:40 AM.
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  #36  
Old 12-03-2021, 10:41 AM
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As Dan correctly points out, the dyno with knock sensing capability is your friend here.

There are many inter related factors here- CHT, IAT, timing, MAP, CR, squish, piston shape, fuel droplet size, fuel octane, ADI amounts etc, cylinder to cylinder AFR variation etc., so there is no easy answer to as how much timing is safe- it depends as they say.

As far as the top Reno Sport Class turbo race engines go, most have multiple non-stock parts in them and have been dyno developed over several years. Pinnacle and Lycon obviously know what they are doing, having taken all the Gold Class wins over more than a decade where Lyconentals have been running.

The top engines are making a lot more power than the ones running even 20 mph less given the cube hp function and lowering prop efficiency.

As related to stock engines where ultimate hp is less important, it simply doesn't make sense to push timing that last few degrees for very minimal gains and higher risks. Conservative will serve you well here.

I will again mention that 30-50F LOP and low MAP (less than 25 inches) with CHTs below 370 and IATs below 100F isn't a place where most Lycomings have a high likelihood of detonation but as Dan said, you can still do it under the right or should I say wrong, conditions.
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Last edited by rv6ejguy : 12-03-2021 at 10:50 AM.
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  #37  
Old 12-03-2021, 11:38 PM
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Dan, Larry and Ross, thanks for the replies and info...very good stuff!

Dan, makes sense now on the bleed vs MP. Don and I recently discussed all this as well, and we may end up trying turbo rails like I had in the Super Glasair...if fuel distro appears to be the (or an) issue. This discussion of intake air issues may slide that back in priority order, but it's still on the table. Another system of systems approach...as always. I spoke with a Sport racing couple today, and they recommended George as well. I talk to Ken at Lycon often, and look forward to chatting with George. He's close by in OK too, so that's a good opportunity. Thanks!

Larry, interesting points. I will compare 27/2700 data with and without N2O...good call. On the spacer install...I actually had to use a 3/4" spacer between the FM-300 and the N2O/fuel plate, because the butterfly was impacting the nozzles. Don made that for me just before leaving on vacation (I was running out of pre-Reno flight test weeks...what a great guy, eh). But that doesn't buy me extra space between the nozzles and the plenum...you have me thinkin. I believe I can fit another 3/4" or 1" spacer in behind the N2O/fuel plate. I have the room to the cowl inlet...but I need to check the clearance on the lower cowl bottom and side clearances to the nitrous and fuel hoses and nozzles. It's pretty tight up there. Yay...another new project, er I mean opportunity!

Ross, concur on Lycon and Pinnacle, and the great engineering. You've been a big part of that success as well...just want to make sure that gets mentioned too! I was one of those 20mph back in Gold (or 30+ in some races) for a few years, and knew the quantum HP leaps (and $) needed to catch them. Its fun territory!

When Don and I discussed LOP testing at 24/2400, I expressed my concerns about detonation. We planned and executed the test to be done at the highest altitude I could get 24". That turned out to be 8500' that day. As I mentioned earlier, I had advanced my mag timing back up from 20 (in Reno) to 22.5, and did the same with the base timing on the Electroair. But I did turn the MAP sensor on for the EI before that test flight, so it did go to 29 during the test. Perhaps a better (and more safe) approach would have been to leave the MAP sensor off, and essentially run fixed EI timing, like I did in Reno. Might be a more valid comparative test too. I watched CHT closely for rapid trends during the test, and saw none...and actually the CHTs stayed relatively cool for the power setting, given the leaning exercise.

The original post from Walt really got my attention, after having done what, on the surface, appears to be a similar exercise. Really good to know that what works with one engine/fuel/ignition system may not be apropos for another. I'd still be very interested to know what MP and timing actually was when the gent ran into detonation. It certainly reinforces my caution about leaning at moderately high to high power. Good info guys...thanks again!

Cheers,
Bob
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Last edited by rvmills : 12-03-2021 at 11:42 PM.
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  #38  
Old 12-04-2021, 12:25 AM
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It would be interesting to hear what manifold pressure, RPM, CHT's and EGT's were. Was he below 75% power?

He tried to lean? A new engine I'd stay 100-150F ROP. Problem is you peak EGT first. So if below 75% power I'd lean to just see EGT start to move and leave it. Too late now.
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