Maximizing Performance

   ~In reading several reviews from other UL Power owners, it becomes painfully obvious that these aren't engines that you can simply throw under the cowling, slap a prop on it and get wow performance. These engines are designed and finely tuned at the factory to give maximum HP under very precise conditions. No, I don't mean SAE, I'm referring to correctly installing the engine, cooling ducts, ECU, and air filter. It's not rocket science but critical for best performance. I want to address each one in detail, so get comfortable.

1. CHT's and Oil Temps

   ~Yes, I know CHT's and Oil temps don't make you go faster, but they do play a critical role in how happy your engine is when driving it hard. Efficient cooling can drastically reduce your overall drag, which in turn allows more speed, and therefore a higher RPM range. I won't go into NASA explanations of cooling your beast, as there are more qualified people to do so, but in my experimentation, I've learned some ground rules that certainly make a difference.
   First and foremost, you must know that the UL Power engine is completely different than a Lycoming or Continental. For example, the Lycs and Conts have twice the oil capacity as a UL, giving it a much better chance of running within ideal oil temp ranges. Also, the UL Power cylinders are limited to a maximum continuous temperature of only 320F, compared to 440F. So while the traditional piston engines can rely on higher CHT's and more oil for heat dissipation, the UL engines require a much more precise cooling setup to stay within limits. Knowing what the UL needs is key.
   I've spent over a year trying to get my CHT's UP, while my oil temps have been too high. Currently I'm using a dual pass 8 row SW cooler, and am just now seeing temps in the green, while my CHT's struggle to see more than 280F in cruise. I've limited my intake plenums to only 9sq. in. per side of open area, and will have to choke them down even more to hit the target 300F in cruise. (More on that in another post) So, why has UL Power chosen such a small oil capacity while relying heavily on the oil for cooling? I don't know, but I've had sources tell me it was a fast way to compete in the weight category. Cheap trick if you ask me.
   To expand on the CHT's for the UL, I've had great success running a small opening and allowing the air to expand into a dedicated plenum for each bank of cylinders. Again, the opening is still too much at 9sq. in. per side for the 390is 160hp model. The same rule applies when talking about oil cooler ducting. A ram air intake, using a 3 to 1 expansion ratio has proved to be the most affective setup yet. I've been told the bigger 200hp model (520is) requires a minimum 13 row cooler. We're talking IO540 cooler sizes here!
   So there you have it. Plan on buying and installing an oversized, high quality oil cooler while keeping your CHT plenum openings to a minimum. This will allow the best all around engine temps and a low drag solution at the same time.  Keep in mind that using an expansion chamber will always create LESS drag and BETTER Cooling. This is critical for performance.

2. Air intake setup

   ~I cannot stress this section enough. I will even venture to say that a poor vs. good air intake setup is easily worth 100rpm if not more.
   I won't forget the day I took my father-in-law for a joy ride. At the time, the air filter was located inside the cowling with just an NACA air vent opening blasting the filter with outside air. After finally rotating around 2000ft down a 5,000ft strip, I noticed my climb rate was only about 400ft/min and the trees were getting closer. By the time I was at the end of the runway, I was no more than 50ft above the trees and wondering how a 160hp long ez was struggling so much. After reaching altitude I could only do 165kts WOT which was far slower than I'd been in the past. That flight didn't have to happen that way and I want to show you how to avoid being in that position.
   The UL Power engine is like a car engine in that it has a TPS, MAP, an Air temp sensor and a static pressure port located on the ECU. That day, my ECU was getting signals from the air temp sensor that the OAT was HOT, and instantly leaned the mixture, retarded the timing, and reduced power in effort to avoid knocking. Smart engine, but only as smart as the information you feed it, in this case HOT air from inside the cowling. In a Cessna 150, it would be like taking off on a summer day with the carb heat on. No one does that and no one should!
   I finally realized later what was going on and designed an intake that was completely sealed off from the engine compartment. The new intake was a forward facing ram air scoop, sized for the CFM my engine required at 3300rpm. This setup did not include an air filter (Which i don't recommend) due to the space constraints. However a future design, including an air filter is in the works. In the meantime, I needed to test out the new scoop. The first thing I noticed was an additional 50 static rpm. On roll out I also noticed the engine was unloading a lot more and takeoff performance was sensational. Climbing out, now at 1300fpm and 150rpm more than before, I knew I was on to something. Finally, reaching 3500ft I leveled off and went for top speed. After hitting 179kts, I was convinced that this engine was starving for cold ram air all along. Now the ECU was getting the right signals to richen the mixture, advance the timing and let her go. I'd also like to note that my original  intake system was also an enclosed system, but using a flush NACA duct, which also did not perform as well as the ram air scoop.
   Another very important thing to mention is the path the air must take before arriving at the throttle body. I experimented a lot with this and found that, like the manual says, going beyond a 45 degree angle bend will reduce performance. The location of the TB isn't too friendly in this scenario, as bringing air into the rear of the engine requires at least a 90 degree bend at some point. However, the difference in running a SCAT, CAT, or any other flexible hose compared to a smooth bore aluminum or silicone hose is noticeable. I could easily reduce static rpm simply by attaching a SCAT hose and bending it 90 degrees or more.
   The moral of the story is that these engines need to breath fresh, unrestricted ram air in the most direct path possible. Any deviation and the engine will take a vacation from RPM.

3. ECU installation

    ~Several years ago, a Sonex builder took off with his new UL Power engine and experienced total engine failure above the runway. The aircraft crashed and was totaled. This guy was lucky to walk away from the crash site. The NTSB did their thing, and after a thorough investigation, it was found that the ECU was mounted on the Firewall. The UL Power ECU is not designed for such extreme temperatures, and it was assumed to have been the cause of the engine shutting down. Since then, UL Power has directed people to make sure the ECU is mounted somewhere safely away from abnormal temperature ranges seen inside the engine compartment. I personally have mounted mine inside the cabin with no problems whatsoever. And while installing the ECU somewhere safe and convenient is simple enough, there is more to the ECU than just a box to be mounted.
   As stated in my previous write-up, the UL engine uses several sensors to ensure the engine is running safely. One of the sensors mentioned doesn't get much attention from what I've seen, but is quite important nevertheless. The ECU incorporates a static pressure port, clearly seen on the front of the case. A brass nipple if you will. I've got mixed reports from UL Power reps about plumbing this port or just leaving it open. The Static port on the ECU is meant to give the ECU a barometric pressure reading in order to compensate for altitude changes. As we climb up to altitude, our engines need less fuel as the air becomes thinner. For the most part, having the port left open to the air inside the cabin is close enough to allow the engine to run pretty well, however, the air pressure inside the cabin is rarely if ever, the same as the air outside. Up until recently, the UL power manuals have not advised to plumb this port, but to leave it open inside the cabin. Now, the installation manual states on page 53 something entirely different:

 "On the ECU is a small connector for a hose. This is for the “altitude sensor” integrated in the ECU. Install a hose and bring it close to the inlet air filter. (Certainly when you use an extra “Inlet air box”)

   Prior to seeing the statement above I tried plumbing this sensor to various locations, attempting to get a proper pressure reading to match the outside air pressure. Out of the several locations, my first attempt was by far the most successful. The idea was to take a pressure reading from a location that would be virtually identical to the air coming into the engine. I installed a brass nipple just aft of the intake scoop opening. I then used some 1/8"ID radio control aircraft fuel tubing to connect the ports.   
   During flight testing I noticed a slight decrease in Static RPM, but as the aircraft began rolling down the runway, the RPM would recover. This may have been due to a slight suction on the port, but more likely was due to a small change in the mixture. I'm assuming the later because I also noticed a much better throttle response indicative of a leaner mixture. After takeoff, on climb out, no other changes were noted, however, in cruise, the most notable change was an increase in fuel economy, again due to a leaner mixture. The proof was also evident in the color of my exhaust pipes being closer to white than tan. Obviously the slight change in Pressure was making a noticeable difference in throttle response and fuel economy, without affecting overall performance. Maybe UL Power did their own tests and decided to update the manuals after coming to the same conclusion. I must add, though, that Ray Lawrence of UL Power is not a fan of plumbing this line at all in that an incorrect installation could lead to a very lean mixture and potentially dangerous situation. I agree with his concern, but as long as the installation is done correctly, the benefits are there. 
   I'm sure running the ECU port open to the cabin air works ok, but imagine an OAT temp of 40F, and the cabin being a toasty 80F. This would most certainly constitute a change in pressure, and in my testing has shown to make a valuable difference.   


4. Prop Selection

   ~I have tried 8 different propellors from 3 different manufacturers, all yielding wildly different results. So much so that I've dedicated an entire page to it. For Prop reviews and detailed info see the Prop Selection page.


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