A new well done video on the latest three Subaru Boxer engines

Homebuilt Aircraft & Kit Plane Forum

Help Support Homebuilt Aircraft & Kit Plane Forum:

jsharp

Member
HBA Supporter
Joined
Feb 28, 2019
Messages
11
Location
Augusta, GA / USA
The whiteboard analysis, includes the new engine for 2022. He goes over torque curves, turbo vs non turbo, and many other little details that I have missed from other sources. The channel is called Engineering Explained, It is the best public analysis of later model Subaru Boxer engines I have ever seen. If you know of a better source of third party analysis, please share.
If you are interested in what the future holds for these boxer engines, or what the current models turbo and non-turbo differences are, it might be worth a watch. The video is 15 minutes long and I feel worth every minute...


Joe
 

wsimpso1

Super Moderator
Staff member
Log Member
Joined
Oct 18, 2003
Messages
7,957
Location
Saline Michigan
Why? He is doing the stuff that is routinely done in auto companies, except that they run ALL the performance and fuel economy stuff on the computer.

Typical of this guy's stuff, he is telling us what he would like Subaru to do, which is set 2nd gear ratio to redline both engines at 60 mph... Nice idea, except that we know the final drive ratio of 4.3:1 is the same in both cars, so likely the gearbox is the same one in all three cars. Nice idea about postulating different gear ratios for the different engined vehicles, but I seriously doubt it. Far more likely the trannies are the same part number. The most likely thing for Subaru to modify for different engines is different final drive ratios, but our reporter is telling us that is the same. So, 50% more torque from one engine versus the other is probably true if you are in the same gear in both cars.

Better evaluation would be to run simulations through the gears, and look at the performance.

The other thing he keeps going back to is the extra weight. Hmm. Real driving weight of 3000 vs 3075 pounds. If the turbo engine only made 3075/3000 = 102.5% of the basic engine torque, it would equal the performance in the heavier car. 150% of basic torque gives a bunch more accel. The rest of the story is that both cars use up the same amount of tractive effort just rolling, and acceleration occurs with the torque above that needed for steady rolling. The 50% extra torque is a lot more reserve for acceleration. Do not let this guy fool you, the new NA engine is an improvement over the old NA engine, and may need less fuss to keep it running, but certainly nowhere close to the performance of the turboed version.

Billski
 

jsharp

Member
HBA Supporter
Joined
Feb 28, 2019
Messages
11
Location
Augusta, GA / USA
Why? He is doing the stuff that is routinely done in auto companies, except that they run ALL the performance and fuel economy stuff on the computer.

Typical of this guy's stuff, he is telling us what he would like Subaru to do, which is set 2nd gear ratio to redline both engines at 60 mph... Nice idea, except that we know the final drive ratio of 4.3:1 is the same in both cars, so likely the gearbox is the same one in all three cars. Nice idea about postulating different gear ratios for the different engined vehicles, but I seriously doubt it. Far more likely the trannies are the same part number. The most likely thing for Subaru to modify for different engines is different final drive ratios, but our reporter is telling us that is the same. So, 50% more torque from one engine versus the other is probably true if you are in the same gear in both cars.

Better evaluation would be to run simulations through the gears, and look at the performance.

The other thing he keeps going back to is the extra weight. Hmm. Real driving weight of 3000 vs 3075 pounds. If the turbo engine only made 3075/3000 = 102.5% of the basic engine torque, it would equal the performance in the heavier car. 150% of basic torque gives a bunch more accel. The rest of the story is that both cars use up the same amount of tractive effort just rolling, and acceleration occurs with the torque above that needed for steady rolling. The 50% extra torque is a lot more reserve for acceleration. Do not let this guy fool you, the new NA engine is an improvement over the old NA engine, and may need less fuss to keep it running, but certainly nowhere close to the performance of the turbo version.

Billski
Excellent observations and conclusions. I posted this video because I thought it would be of interest to those considering a Subaru Boxer engine for aircraft.
In one place (video) there are examples of three modern versions of the Boxer engine. What I found most interesting at "first glance" related to aircraft, was one particular engine with a flat(ish) torque curve and the fact that rated torque was achievable at significantly lower rpm's, than the other two engines by design.. This in my experience, could allow for a de-rated engine that could produce substantial near-rated torque at a lower operational rpm. I don't need to explain all the benefits of this approach. I do however know that not everything is suited for everything else. All three engines may not be suitable for aircraft, certainly not for many however, contemplation begins the process of discovery.

It was my hope that some would find the data and other relevant information in the video somewhat interesting, if not useful. If you can ignore all the automobile vernacular, you begin to understand how the different engines could affect aircraft efficiency and performance.

Joe
 

wsimpso1

Super Moderator
Staff member
Log Member
Joined
Oct 18, 2003
Messages
7,957
Location
Saline Michigan
Those new engines will at best be starting points. The current light way to 200 hp Subie in an airplane is established and written about extensively by rv6ejguy. Similar setups at lower and higher power also exist. EJ257 short block (sturdy turbo set up) direct from Subaru, EJ SOHC heads as we do not need the high rpm nor weight of the DOHC heads. Then it is is custom manifolding, port injection and intercooler, a suitable turbo, PSRU, oil and water rads in a belly scoop and EFII from SDS.

The new base engine is just the starting point. Does anybody know what this base engine is? Is it the familiar and reliable EJ stuff or new?

Doubtless the 7500 rpm version has DOHC which is just extra weight. Perhaps the turbo version too. Manifolding would doubtless be replaced with lighter stuff packaged to fit in the airplane and with runner diameters/lengths more suitable to the 4500-6000 rpm speed range we would use with existing PSRU and props. Injection/ ignition/ sensors/ ECU from the car includes direct injection, which has no point in an airplane, and is just complicated by all of the car stuff. It would all be swept aside for a light, simple and ultra-reliable SDS. Then if the short block is new, we get to establish its reliability as an airplane engine while the EJ257 is a known entity.

Billski
 

rv6ejguy

Well-Known Member
Joined
Jun 26, 2012
Messages
4,285
Location
Calgary, Alberta, Canada
What I found most interesting at "first glance" related to aircraft, was one particular engine with a flat(ish) torque curve and the fact that rated torque was achievable at significantly lower rpm's, than the other two engines by design.. This in my experience, could allow for a de-rated engine that could produce substantial near-rated torque at a lower operational rpm.

Joe
You need the hp to accomplish the work. Now if you can get that hp at a lower rpm with these engines than an EJ engine at a lower weight, that's all good. Many of the torque and hp increases on new engines are due to the variable acoustic tuning of the intake manifolds and VVT- things which are not so important at the steady state conditions aircraft engine run at. Some of the design features of the new Sube engines don't make sense to me. The direct injection is a real stumbling point for use in aircraft also.

The EJs are readily available, inexpensive, a known quantity and have massive aftermarket support. Those things are attractive to those who would like to use an automotive engine.
 
Last edited:

sotaro

Well-Known Member
Joined
Feb 26, 2011
Messages
153
Location
San Francisco
Ross and Bill, are your concerns over direct injection the practicalities of adaption to homebuilt aircraft or are there more theoretical issues?If the former, is it primarily the complexities of the software? Thank you
 

rv6ejguy

Well-Known Member
Joined
Jun 26, 2012
Messages
4,285
Location
Calgary, Alberta, Canada
Direct injection involves high pressure pumps and injectors and complicated OEM ECUs for the most part which are not easily adapted for aviation use, being heavily tied into the chassis sensors as well. Once those sensors are not there, the ECUs usually throw codes, go into low power limp mode or shut the engine down. They weren't designed for this application.

If you follow the long term reliability of DI, you'll see lots of talk about severe intake valve carboning on almost all brands, VVT cam phaser issues, injector issues, pump issues etc. at higher mileages. This stuff simply hasn't proven as reliable as non VVT, port injected engines in the long term.

With aviation applications being essentially steady state rpm and power for the most part, VVT and DI offer few advantages in this application, especially for naturally aspirated engines.
 
Top