I think I have uneven airflow....

[bret]

do you have ram air intake, could the ram air be contributing to uneven intake pressure?

[BillL]

Originally Posted by Mike S

The problem with the individual injector "trim" as you call it, is getting a feedback system that accurately and swiftly responds to the change in fuel/air ratio.

In automobiles we can do this with O2 sensors in the exhaust, but our leaded fuel in aircraft will kill the sensor pretty quick. That leaves EGT or CHT.

CHT is too slow-----------so we are left with EGT. Not sure if anyone is using that to drive a cylinder by cylinder feedback EFI system------or if such a system would be feasible.

Considering the fact we spend the vast majority of our engine run time at a constant RPM, the need to have a rapid responding feedback system may be invalid even??????????

Ross---------what say you?

Mike, I was talking about just the trim, or compensating for a standardized AF across the manifold pressure and speed range by cylinder. Trim is typical another lookup table over that 2D (or 3D) map. There is no feedback control for trim, once it is matched to the engine, that's it, it's "fixed". Sometimes it is a simple % on-time shift for the PWM driver signal. It requires individual current drivers in the controller for each injector and is therefore more expensive. If they all fire at once, I don't know if they share a current driver or they are just triggered together. I think the former would cost less.

[rv6ejguy]

Originally Posted by bret

do you have ram air intake, could the ram air be contributing to uneven intake pressure?

The unequal air/ mixture distribution in stock Lycoming vertical manifold engines is well known and has been for as long as we've had individual EGT probes attached to them. Unequal runner length, almost zero plenum volume, unequal entry angle from "plenum" to runner plus heads which may also have airflow variances within the ports compared to its other brothers, all contribute to this. Ram air would simply change the manifold pressure ever so slightly.

I first heard this from a friend many years ago who built a beautiful 6A back in 2003 with an O-360. "Yeah, 4 one cylinder engines flying in close formation" he remarked after seeing a 190F EGT spread in cruise between coldest and hottest.

People spend $10-$30K on a bunch of glass for a day VFR airplane, $25-$30K on an engine and maybe $8K on a C/S prop but they have trouble coughing up another $2-3K for a proper manifold to get the best performance from their engine? I guess my priorities are different from most...

[rv7boy]

Originally Posted by rv6ejguy

...People spend $10-$30K on a bunch of glass for a day VFR airplane, $25-$30K on an engine and maybe $8K on a C/S prop but they have trouble coughing up another $2-3K for a proper manifold to get the best performance from their engine? I guess my priorities are different from most...

Filing this away for reference when I get to the FWF stage. Thanks!

[carrollcw]

Wow, this has become a pretty heated discussion. First of all, I want to make it abundantly clear that the EFII system designed by Robert and Ross is absolutely amazing and I would never go to one of the older antiquated systems. This is the technology of the future. Although I have a fairly large gami spread, I can still run lop much leaner than most RVs (almost a full GPH). That means my cylinders 1/3 are over 100 deg lop when 2/4 are 50 lop and the engine runs smooth and I cruise at about 170 TAS. From talking to others, they can't get anywhere near over 100 lop and the engine runs fine. The fact I can leads me to believe it is due to the superior fuel dispersion of the EFII. Yes, it would be nice to be able to individually tune each injector, but the root cause here is not the EFII, but instead the poor air supply of the Titan sump. So, it seems clear to me that I need to invest in the superior sump. Furthermore, my engine runs smoother and starts easier than any of my friends' RVs.

For those of you considering a Titan engine, just be wary of the updraft sump. I have heard the Titan horizontal cold air sump has much better airflow. However you pay the price of higher oil temps. Living in Houston, I knew I would have oil temp probs with a high horsepower engine, so I elected to go with the vertical induction. So, since I have chosen to stick with vertical imduction, I just need to find a sump with more balanced air flow. Seems the superior sump is the way to go.

[rcpaisley]

Bingo!
You nailed it Clarke!

Good job,
Robert

[DanH]

Originally Posted by carrollcw

Wow, this has become a pretty heated discussion.

One guy shows up and blows up. No big deal.

First of all, I want to make it abundantly clear that the EFII system designed by Robert and Ross is absolutely amazing and I would never go to one of the older antiquated systems. This is the technology of the future.

Actually, a batch fired speed-density EFI system is many generations in the past. At the fundamental level, it is the same as the Bosch system installed on a 1968 Type 3 Volkswagen. The technology of the future? Automotive is switching to GDI (gasoline direct injection) right now.

Yellowed page from a 1971 how-to manual:



Being an old idea doesn't make it a bad idea. Speed-density is simple and adaptable, which is why Ross sticks with it, and he has been building ECUs a long time. (A few readers might be surprised to hear that I have one here, for installation on another project.) As for the EFii branded system, Robert picked pretty good off-the-shelf components. It's all far more reliable than the vintage Bosch parts.

Back in 1968, a fellow could go to the hardware store and buy a pretty good claw hammer. Today a fellow can buy what is arguably a better hammer, with a comfortable rubber and fiberglass handle. It may be more pleasant to use, and harder to break, but it is still a hammer. It will not build a house faster than the 1968 version.

Therein lies the problem with EFii brand hype. It's a simple fuel delivery system, not a Magical Mystery Machine. It will not make your airplane do anything amazing. It will only do what the laws of physics allow, no matter how many exclamation points are added to the advertising. That includes both strong points and compromises, just like any design.

Here, in return for simplicity and price point, one of the compromises is lack of individual injector fuel trim...the equivalent of restrictor insert swapping in a constant flow system. As Ross has stated, it's available with more expensive systems, but not this one. Here a user must accept the compromise, or find a way around it. ((EDIT, 2017...in-flight injector trim is now available from SDS....nice work!

Maybe the Superior sump will even up air delivery. Heck, I hope so; although not directly comparable, being sure about a better sump would be a big plus for the carb guys as well as EFii users. Please do take the time to fly and record a few specific repeatable test flight profiles before the swap.

[rv6ejguy]

Originally Posted by DanH

One guy shows up and blows up. No big deal.



Actually, a batch fired speed-density EFI system is many generations in the past. At the fundamental level, it is the same as the Bosch system installed on a 1968 Type 3 Volkswagen. The technology of the future? Automotive is switching to GDI (gasoline direct injection) right now.

Yellowed page from a 1971 how-to manual:



Being an old idea doesn't make it a bad idea. Speed-density is simple and adaptable, which is why Ross sticks with it, and he has been building ECUs a long time. (A few readers might be surprised to hear that I have one here, for installation on another project.) As for the EFii branded system, Robert picked pretty good off-the-shelf components. It's all far more reliable than the vintage Bosch parts.

Back in 1968, a fellow could go to the hardware store and buy a pretty good claw hammer. Today a fellow can buy what is arguably a better hammer, with a comfortable rubber and fiberglass handle. It may be more pleasant to use, and harder to break, but it is still a hammer. It will not build a house faster than the 1968 version.

Therein lies the problem with EFii brand hype. It's a simple fuel delivery system, not a Magical Mystery Machine. It will not make your airplane do anything amazing. It will only do what the laws of physics allow, no matter how many exclamation points are added to the advertising. That includes both strong points and compromises, just like any design.

Here, in return for simplicity and price point, one of the compromises is lack of individual injector fuel trim...the equivalent of restrictor insert swapping in a constant flow system. As Ross has stated, it's available with more expensive systems, but not this one. Here a user must accept the compromise, or find a way around it.

Maybe the Superior sump will even up air delivery. Heck, I hope so; although not directly comparable, being sure about a better sump would be a big plus for the carb guys as well as EFii users. Please do take the time to fly and record a few specific repeatable test flight profiles before the swap.

All true but Lycomings won't be adapted to GDI any time soon as it involves very high pressure (hundreds of Bar) injectors mounted into the combustion chamber and high pressure pumps as well. While the demonstrated fuel burn reductions are certainly there as are increased detonation margins (substantial), the jury is still out on long term reliability of the systems compared to port injection. Audi and others had widespread problems initially with severe carboning of the backside of the intake valves since there was no fuel there to wash off deposits. Lexus discovered this problem in long term testing and employed both GDI AND port injection (together) on some of their V6 engines to solve the issue. Not sure where that stands now but GDI is certainly the way for automotive use. Some people found the injectors were not lasting like port injectors due to the high pressures and carbon buildup as well. Like you say, advantages and disadvantages to everything.

One primary focus is not to obsolete previous models or radically change the physical layout. Yes, the 5th generation ECU and software is very advanced from the 1st one but for 18 years, the hardware could be inexpensively upgraded to the latest software and most of the wiring would still plug in. We don't like to create orphan devices like many other electronics firms have if we can help it.

We've installed EFI on a lot of automotive engines and never saw any mileage or power drop with batch fired injectors over "sequential" (timed) types. That technology was developed mainly for emission reasons which we don't care about much in the aircraft or racing world.

In the end, it works pretty well when combined with a proper intake manifold. You get better hot and cold start and should have virtually zero maintenance compared to legacy aircraft fuel and ignition systems just as we saw in the automotive field starting in 1967 with the Bosch D Jetronic, some of which are still running today with original components.

Anyway, it's just another choice in the market. Some people will want it, others won't.

We have some new ideas on how to make the systems even better for aviation applications in the future as we concentrate more energy on that market. Will have to see how the R&D and testing goes first...

[Toobuilder]

Originally Posted by carrollcw

...From talking to others, they can't get anywhere near over 100 lop and the engine runs fine. The fact I can leads me to believe it is due to the superior fuel dispersion of the EFII...

Just as a data point, I have run the 200 HP 360 in the RV-8 to 100 LOP with standard Bendix injection (and Pmags). This is also with the stock Lycoming horizontal, tuned sump.

At 100 LOP, it ran smooth as glass, but power was way down. No way I got anywhere near your 170 KTAS.

[skylor]

Originally Posted by Toobuilder

Just as a data point, I have run the 200 HP 360 in the RV-8 to 100 LOP with standard Bendix injection (and Pmags). This is also with the stock Lycoming horizontal, tuned sump.

At 100 LOP, it ran smooth as glass, but power was way down. No way I got anywhere near your 170 KTAS.

I too have an RV-8 with a stock factory Lycoming IO-360A1B6 and Precision Airmotive RSA-5 Injection + Slick Mags. At low altitudes and high manifold pressures, I can easily run 100F LOP (1.3+ gph LOP) and make 170 kts TAS (with 26 or so inches manifold pressure) and the engine runs smooth as glass and very cool even on hot inversion layer SoCal days.

Of course, at normal (for me) cross country cruising altitudes of 8500-12,500 or so, I don't run this lean because you're right...power levels are really low. The point is, 100F LOP and 170 kts is a meaningless data point without knowing the actual manifold pressures...and also the stock mechanical injection system is plenty capable of running smoothly far lean of peak at least with the forward facing Lycoming sump. The real limitation for me is the slick mags will start dropping sparks when the mixture gets too lean.

Skylor
RV-8