Rotec TBI issues

[rocketbob]

Timing is perfect, I check that as part of the condition inspection and am running EI on one side. The only possibility is a decrease in pressure inside the spray bar due to the top four row of holes on the WOT end being exposed in a "leaner" orientation since they don't line up with any other holes. I may silver braze the top row closed as an experiment at some point but right now its running great and I don't mind the elevated WOT EGT since oil temp and fuel flow are stable. A slight throttle reduction drops the EGT big time. I'm sure many on this forum would rejoice with a stable 405 CHT and 195 oil temp on a hard climb to 7500 burning mogas. Normally I never do that and always go 25/25 cruise climb as soon as obstacles are clear, so I have zero concerns about it.

[RV10inOz]

That makes it even worse. An EI will reduce EGT, so it carries some advance even at WOT most likely, plus reduced fuel flow.

It is a bad idea to use the CHT as a direct proxy for cylinder pressure, you may have good cooling compared to someone else with poor cooling but they have much lower stress than you, but the same CHT.

I would not be happy.

Is it going to kill your engine any day soon, no. Is it a good result? sub-optimal at least.

Just trying to help you get it better having seen a lot of fully instrumented dyne data over the last few years.

[rocketbob]

1450 EGT is no problem for a Lycoming...many turboed airplanes run much higher TIT (EGT) than normally aspirated engines do. Couple hundred degrees higher.

I believe that the superior atomization of this system is moving heat out and away from the combustion chamber and hence the EGTs are higher. Its a different animal.

Collect some dyno data on a Rotec install then talk to me.

[RV10inOz]

Originally Posted by rocketbob

1450 EGT is no problem for a Lycoming...many turboed airplanes run much higher TIT (EGT) than normally aspirated engines do. Couple hundred degrees higher.

I believe that the superior atomization of this system is moving heat out and away from the combustion chamber and hence the EGTs are higher. Its a different animal.

Collect some dyno data on a Rotec install then talk to me.

Bob, The EGT itself is not a problem?.TIT's run up to 1750 max continuous on some systems. But that is not the point.

You are not flowing enough fuel by my estimation, and so far you have not confirmed this by quoting your numbers. The higher CHT you are noting confirms this.

Collect some dyno data on a Rotec install then talk to me.

Gladly, lets start with a $20,000 deposit and your engine in a crate ready to ship. The laws of physics apply equally to all things Bob.

I believe that the superior atomization of this system is moving heat out and away from the combustion chamber and hence the EGTs are higher. Its a different animal.

Explain your belief please, as it seems at odds with the science. You are quite likely getting better atomisation compared to the old carby but the rest of the science of combustion and the rest of your engine remain a constant.

Just trying to help you out here.

[rocketbob]

Originally Posted by RV10inOz

Explain your belief please, as it seems at odds with the science. You are quite likely getting better atomisation compared to the old carby but the rest of the science of combustion and the rest of your engine remain a constant.

The combustion event is happening so slowly now with a lean but stable mixture therefore more spark advance is required to move the peak pressure point back closer to TDC. EGT is higher because the combustion event is continuing after the exhaust valve is opening. Adding more fuel will move the peak pressure point back and reduce EGT but as I stated previously with little benefit. More spark advance would be more advantageous in this situation.

Since the airplane has an older Electroair I can add a pot and a resistor to advance the timing for cruise conditions.

[flyboykelly]

Originally Posted by RV10inOz

Gladly, lets start with a $20,000 deposit and your engine in a crate ready to ship. The laws of physics apply equally to all things Bob.

just curious, but what's your background RV10OZ?

[UH1CW2]

After a few more flights I made the following changes to my Long EZ induction set-up. Added a K&N Filter between the NACA inlet and the Carb air/heat box. That helped with over-leaning issue at lower RPM's. However, the last flight I took I noticed some surging of the engine. it almost sounded like when you're flying a twin and the props are not in sink. I determined that the TBI was running lean at full rich above 2800 RPM. So, I ordered the #80 drill bits and the hand drill. I will open up the holes in the TBI spray bar so I have some mixture to play with. As it stands right now I can not pull back the mixture at all. the engine is running on the lean edge at Wide open throttle. Now most of you would not agree but I am an engineer that design's engines for Chrysler, Detroit Diesel and PACCAR engine, So I will tell you that I run my Lycoming up to 3200 RPM's. So long as the valves, springs, retainers and guides are strong the engine will run like that just like any other engine does at 2600 RPM's. Lycoming's like running under load so-long as you can maintain cooling and lubrication. When I built my engine I balanced the rods, pistons, wrist pins and crank to under a gram. I know I will get a few squaks about the RPM but I would appreciate any negative comments come with Facts and not Hear-say.

[rocketbob]

On the four row of holes at the WOT end, enlarge only the holes parallel and below (to the rich side) of the double row of holes. I believe the other holes do nothing but drop the pressure inside the spray bar. And enlarge all the others. #80 won't help much, at least that's what I observed. But they helped.

I was enlarging by hand and it took forever so I got a chuck from McMaster to go in an air pencil tool. Then it was a breeze but took a steady hand.

Here's what I ordered from McMaster...

30585A96 3 Each Uncoated Hss Jobbers' Drill Bit, Wire Ga 78,7/8" Oal,0.2" Drill Depth,118 Deg Point
2 30585A95 3 Each Uncoated Hss Jobbers' Drill Bit, Wire Ga 77,7/8" Oal,0.2" Drill Depth,118 Deg Point
1 30585A98 3 Each Uncoated Hss Jobbers' Drill Bit, Wire Ga 80,3/4" Oal,0.1" Drill Depth,118 Deg Point
2 30585A97 3 Each Uncoated Hss Jobbers' Drill Bit, Wire Ga 79,3/4" Oal,0.1" Drill Depth,118 Deg Point
3 30505A5 1 Each Small-hole Drilling Adapter, #99 To #60 Cap, 1/8" Shank Dia, 1-5/16" Oal

[UH1CW2]

I purchased a drill pencil and a complete set of 60 thru 80 number drills. I will follow your instructions as best as possible. I have a good idea where the fuel delivery needs to be increased on the spray bar. Your suggestions are very much in line with what I was going to do. So thanks for the info. I know that eventually this TBI unit will be a very much appreciated device on my engine. I also know that some times it takes a bit of Trouble-shooting to make things work as designed especially if the engine is not stock and has been modified. I do believe if I had a stock 0320 150 HP engine this unit would be a winner right out of the box. but like all of us understand, once you start modifying things, everything else requires a bit of tweaking to work correctly with other parts.

Phil

[deej]

Originally Posted by UH1CW2

I do believe if I had a stock 0320 150 HP engine this unit would be a winner right out of the box.

That's what I have, and yes, it worked fine "out of the box". Going on a year and half now, no issues so far.

-Dj