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AC Aero (Higgs Diesel) E-330 Hawk Engine

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I don't think so, or at least anytime in the near future. He's got enough on his plate getting these out and in production for some time to come. Never know though.
 
We have finalized the fuel and cooling system layout which is pretty unique and pretty exciting. We really had to work at this to incorporate fuel as a coolant as Andy had envisioned. A comprimise was made to add a larger heat exchanger instead of only using the wings and tanks as heat exchangers, as there are times where the amount of fuel in the tanks just wouldn't provide enough heat dissapation needed.

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So following our super scientific Power Point, the fuel will come from the selected wing tank through a filter in the wing root to the duplex fuel valve. Airflow Performance boost pumps plumbed in parrellel will push the fuel forward of the firewall into a 1.5-2 gallon non-vented header tank and pressurize the tank and lines to 51 psi. Located on the header tank will be a pressure sensor, coolant outlet and return fittings, and injector rail outlet fitting.

The pressurized tank will allow the entire fuel rail to be pressurized at the required 51 psi controlled by a pressure relief valve located after the rail. The relief port will return to the selected tank via the duplex fuel valve. The ECU will control the fuel boost pumps which will have internal overpressure protection as well. In the event of a pump failure, the ECU will automatically turn on the secondary pump and provide annunciation to the cockpit.

From the header tank will also be a coolant circuit. Airflow performance pumps will be variable speed and controlled by the ECU depending on engine temperature. The primary pump, plumbed in series with the secondary pump, will not have flow throug capability to assist in keeping the engine temperature optimum. The secondary pump will have flow through capability and will be activated by the ECU if the temperature rises beyond limits and/or the primary pump fails. After the engine cooling jacket, a thermostat will direct fuel either to return to the header tank or to a heat exchanger (radiator) to dissapate excess heat.

Once challenge that this solution takes care of is a requirement to heat the fuel prior to the injector rail to a minimum of 130 degrees F. This provides better combustion in the cylinders, keeping in mind that the Jet A combusts via spark, not compression. We did not want to have an inline, power zapping, electric heater for the fuel. While the engine will start and run fine on cold fuel, the optimum performance will be gained once the fuel is warm. Testing will determine if we will need to add an inline heater for cold weather ops prior to take off, but no heater will be needed in flight.

Our next area of focus is on the details of the electrical system/controls/ECU. We're planning a call with Andy early next week to get a production update and discuss the cockpit controls needed as well as ECU interface with avionics.
 
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We have finalized the fuel and cooling system layout which is pretty unique and pretty exciting. We really had to work at this to incorporate fuel as a coolant as Andy had envisioned. A comprimise was made to add a larger heat exchanger instead of only using the wings and tanks as heat exchangers, as there are times where the amount of fuel in the tanks just wouldn't provide enough heat dissapation needed.

B8B73CDA-11BB-444D-BAF3-0BF92DBC2103.jpeg

5D162659-AA59-46A0-9A43-D09F5B22D216.jpeg


So following our super scientific Power Point, the fuel will come from the selected wing tank through a filter in the wing root to the duplex fuel valve. Airflow Performance boost pumps plumbed in parrellel will push the fuel forward of the firewall into a 1.5-2 gallon non-vented header tank and pressurize the tank and lines to 51 psi. Located on the header tank will be a pressure sensor, coolant outlet and return fittings, and injector rail outlet fitting.

The pressurized tank will allow the entire fuel rail to be pressurized at the required 51 psi controlled by a pressure relief valve located after the rail. The relief port will return to the selected tank via the duplex fuel valve. The ECU will control the fuel boost pumps which will have internal overpressure protection as well. In the event of a pump failure, the ECU will automatically turn on the secondary pump and provide annunciation to the cockpit.

From the header tank will also be a coolant circuit. Airflow performance pumps will be variable speed and controlled by the ECU depending on engine temperature. The primary pump, plumbed in series with the secondary pump, will not have flow throug capability to assist in keeping the engine temperature optimum. The secondary pump will have flow through capability and will be activated by the ECU if the temperature rises beyond limits and/or the primary pump fails. After the engine cooling jacket, a thermostat will direct fuel either to return to the header tank or to a heat exchanger (radiator) to dissapate excess heat.

Once challenge that this solution takes care of is a requirement to heat the fuel prior to the injector rail to a minimum of 130 degrees F. This provides better combustion in the cylinders, keeping in mind that the Jet A combusts via spark, not compression. We did not want to have an inline, power zapping, electric heater for the fuel. While the engine will start and run fine on cold fuel, the optimum performance will be gained once the fuel is warm. Testing will determine if we will need to add an inline heater for cold weather ops prior to take off, but no heater will be needed in flight.

Our next area of focus is on the details of the electrical system/controls/ECU. We're planning a call with Andy early next week to get a production update and discuss the cockpit controls needed as well as ECU interface with avionics.

Not to question the experts here, but one immediate concern would be a leak in the coolant system eliminating pressure for the injectors. A cracked block or cracked exchanger/radiator could effectively stop fuel flow to the engine by allowing the pressure to bleed off. Is there some type of check valve on the coolant inlet from the header tank? I suppose the leak would have to be more than a small crack with two pumps operating.

Also, Is there any concern that that radiator cannot give up enough heat in ground ops? What happens during the OSH departure parade, where you are idling for 30 minutes at a dead stop in 100* ambients? To make the worst case worse, assume you started the engine already heat soaked. Don't know the boiling point for jet A, but being a multi fuel engine, this seems to be an issue running on gas, even at 50 PSI. Maybe an electric fan?

Disregard the second paragraph. I see that the pressure relief is on the fuel rail, eliminating that heat issue.

Larry
 
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You say the primary coolant pump does not have flow-through capability - so if it fails how does the in-series secondary coolant pump continue to cool the engine?
 
Now we're talkin' something different.

Minor note...probably want good filtration between the header and fuel rail, given the circulation through block castings,
 
You say the primary coolant pump does not have flow-through capability - so if it fails how does the in-series secondary coolant pump continue to cool the engine?

So, it appears the coolant pumps aren't redundant, so I would assume there is coolant temp sensor in the block somewhere to indicate proper operation. What is the procedure if that primary pump fails and coolant stops flowing?

Larry
 
PWM on brush type DC motors could be a bad idea. Others have noted a serious reduction in pump life and some pumps plain don't like it and don't respond well at low duty cycles. Better test that thoroughly on the bench before getting married to the idea in the airframe.

Complicated system, lots of places for something to go wrong.

If you want to warm the fuel, a simple tubing loop in the coolant would do the trick. You won't be able to sink much heat into the fuel for long at high power with that small header tank capacity.
 
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Has one of these engines ever flown with this cooling system? Is it also for 100LL, autogas etc.?
 
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From an earlier post, I understood that a full scale prototype of this engine is yet to run on a stand, let alone fly. So, this is a good oportunity for feedback on the design concept.
 
PWM on brush type DC motors could be a bad idea. Others have noted a serious reduction in pump life and some pumps plain don't like it and don't respond well at low duty cycles. Better test that thoroughly on the bench before getting married to the idea in the airframe.

Complicated system, lots of places for something to go wrong.

If you want to warm the fuel, a simple tubing loop in the coolant would do the trick. You won't be able to sink much heat into the fuel for long at high power with a small header tank capacity.

I had a phone conversation with a tech at Walbro a couple of years ago, about PWM & their gerotor pumps. He told me that the issue was effectively 'hammering' (my word) on the gears due to the high frequency pulses from the PWM. (If someone needs info on PWM, it might merit its own thread.) He said that it's not an issue with their turbine pumps, which I assume also have brushed, DC motors. But: The turbine pumps will not self prime like the gerotor pumps, and are intended solely for in-tank use.

I regret that I didn't directly address with him the idea of trying to 'smooth' the PWM into variable DC to drive the gerotor pumps, but I did ask about using a true 'analog' variable DC voltage to drive them. He said that it would have no detrimental effect. He did not say, but I suspect, that using a variable DC voltage to control pressure using a gerotor in a dynamic environment would be frustrating, because you'd lose the full torque at variable rpm that's available with PWM.
 
Not to question the experts here, but one immediate concern would be a leak in the coolant system eliminating pressure for the injectors. A cracked block or cracked exchanger/radiator could effectively stop fuel flow to the engine by allowing the pressure to bleed off. Is there some type of check valve on the coolant inlet from the header tank? I suppose the leak would have to be more than a small crack with two pumps operating.

Also, Is there any concern that that radiator cannot give up enough heat in ground ops? What happens during the OSH departure parade, where you are idling for 30 minutes at a dead stop in 100* ambients? To make the worst case worse, assume you started the engine already heat soaked. Don't know the boiling point for jet A, but being a multi fuel engine, this seems to be an issue running on gas, even at 50 PSI. Maybe an electric fan?

Larry, great point and question. Yes, there is a risk on having a cooling leak which would cause a drop in fuel pressure. We'll have to take a deepr look at that and mitigate risks. Initially, I'm thinking of keeping lines as short as possible, using quality lines and fittings, and layingout the air supply to minimize the impact of FOD damaging the heat exchanger if that's possible. It does bring up another concern that any leak or damage has the risk of creating a fire as well. We're looking at the potential for that to happen and evaluating the risk, as there are some common risks to other engine setups for fuel fires, just not as much as on this setup.

We will have the option to do a fan on the heat exchanger for ground ops. I plan to incorporate that into the cooling plenum design for the heat exchanger. The fan can be run by the ECUs just like in a car.
 
You say the primary coolant pump does not have flow-through capability - so if it fails how does the in-series secondary coolant pump continue to cool the engine?

Greg, excellent point, thanks for noticing that. As drawn out, I was thinking of a failure of the motor but still allowing fuel to go through it, but that's not right. I've changed it to a parallel setup and have no flow through either pump to retain flow rates that we need. This will mimic the fuel pump setup allowing redundancy. Good catch.
 
PWM on brush type DC motors could be a bad idea. Others have noted a serious reduction in pump life and some pumps plain don't like it and don't respond well at low duty cycles. Better test that thoroughly on the bench before getting married to the idea in the airframe.

Complicated system, lots of places for something to go wrong.

If you want to warm the fuel, a simple tubing loop in the coolant would do the trick. You won't be able to sink much heat into the fuel for long at high power with that small header tank capacity.

Ross, Don at Airflow said the PWM isn't a concern at all. I don't know all the technical details but he didn't anticipate any issues or longevity concerns with his pumps and variable speed.

We looked at a liquid to liquid heat exchanger for warming the fuel, but the most increase you can get is about 40F, not enough to get to the 130F. We're trying to avoid electric heaters since they pull so much power which could impact operations with a limited electrical system capability.
 
The engine has not flown at all yet, I may be the first in a manned flying machine. There will be plenty of testing before I give it a go, though.

These are all good points, and yes, this is the time to get feedback into the design process! Thanks for the points brought up here, it's a big help. There is some inherent complication but we are trying to keep it simple at the same time. If you want to see complicated, take a look at any of our Technical Orders for the C-17. Your mind will be fried with how many things can (and usually do) break! We'd like to avoid that.
 
Ross, Don at Airflow said the PWM isn't a concern at all. I don't know all the technical details but he didn't anticipate any issues or longevity concerns with his pumps and variable speed.

We looked at a liquid to liquid heat exchanger for warming the fuel, but the most increase you can get is about 40F, not enough to get to the 130F. We're trying to avoid electric heaters since they pull so much power which could impact operations with a limited electrical system capability.

That's good that Don's pumps work with PWM. Are these an impeller pump? Brush or brushless motors?

Should be able to get a lot more than 40F rise with oil or coolant to fuel HX. Commonly done on older GA turbine stuff.
 
Tim,

I played with this idea (fuel as coolant) quite a bit during my early building phase when it was looking like the Deltahawk might actually happen and I was drinking the Koolaid. You're right in that you'll need an air-to-fuel exchanger for at least part of the time, but you may be surprised how much heat you can dump in the wing if you'll take a couple things into consideration.

I was looking at a low-pressure header tank, with the pressurized fuel pumps pulling out of the header tank to the engine. The fuel/coolant in the header tank was only going to be about 10 psi and the flow rate was fairly high, displacing a lot of it through the header tank (which would have a coolant loop through the engine) back to the wing tank through a duplex valve, and with the return line going all the way to the far outboard bay of the wing tank. This forced the returned hot fuel to flow through the tank all the way back to the inlet and wet the entire tank surface to the fuel temp, providing a pretty decent heat sink, even with low fuel levels. You'll still need some additional air cooling though - but it's reduced. Your design is using the fuel pumps themselves to produce the flow through the header - you might want to put the fuel pumps AFTER the header, and use high-flow low-pressure boost pumps to move more fuel through that header and back to the tanks for thermal transfer.
 
You can sink a fair amount of heat into the full load of fuel on an RV but not a 2 gallon header tank with no recirculation to the mains.

Figure around 50-60,000 watts are being dissipated into the coolant at cruise power on a 300hp engine.
 
Ross, I believe they are brushed pumps. I'll have to check my notes from Don, as I can't remember off the top of my head.

Greg, so we are right there with you on some aspects. That was how we originally thought we'd dissapate the engine heat but to Ross' point, when you get down to 5-6 gallons of fuel left in a tank (which is a reality with an hour reserve fuel left on board), you run out of surface area in the tank to bleed the heat. Then it becomes a question of how to decide where the fuel goes based on heat, wing first then up through the system then to HX first or to small HX then to wing, etc. What we are afraid of is getting to a low tank level and running out of options to get rid of the heat.

So we played with the idea of a lift pump and then a boost pump from the header tank. That's still on the table as option B. I haven't gotten a 100% confirmation the cooling jacket of the engine will withstand 51 psi, so the pressurized header tank may or may not work. Our thought behind it was eliminating complexity with a need for four fuel pumps (two lift, two boost). But yes, we have a design setup with two lift pumps to the header tank, then using boost pumps for the fuel rail and cirulation pumps for the cooling cirtuit.

Ross, do you have any pics or designs for a HX? I'm only finding some diesel truck stuff at this point before trying to roll my own as a test.
 
Ross, do you have any pics or designs for a HX? I'm only finding some diesel truck stuff at this point before trying to roll my own as a test.

Ross has an excellent design for the air side, but you might want to provide information to the HX manufacturers (engineering sales dept) of thermal conductivity, specific heat, and viscosity to ensure the passages have adequate turbulence for your cooling fluid. You might not want to mention the actual fluid as they may not want to be involved. It might be called a "proprietary" fluid.
 
When I hear about using the fuel as a heat sink, all I can think of is TWA 800.

Please be careful...............
 
Mike, TWA went down because of fuel vapors exploding the center tank due to chafed wires arching. We won't have electrical inside any fuel tank! We also aren't looking at temperatures that will be close to boiling point or autoignition temperature.

We will follow your advice of being careful though!!!!
 
Then it becomes a question of how to decide where the fuel goes based on heat, wing first then up through the system then to HX first or to small HX then to wing, etc. What we are afraid of is getting to a low tank level and running out of options to get rid of the heat.

Highly recommend you take it direct to the air heat exchanger first - you get a much higher thermodynamic efficiency with greater delta T, which translates into a smaller exchanger, which translates into less cooling drag. Any heat left over can go the tank skins.
 
One point seemingly overlooked here (and it might be me) is the fact that aircraft using fuel for cooling "stuff" are dealing with thousands of gallons and rely on huge thermal mass. There is very little "cooling" due to the airflow over the wings. The concept was explored quite a bit with wartime development and found unworkable for engine cooling. Seems to me that pumping a high thermal load into a small and rapidly diminishing quantity of fuel is a thermal runaway event in the making.
 
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One point seemingly overlooked here (and it might be me) is the fact that aircraft using fuel for cooling "stuff" are dealing with thousands of gallons and rely on huge thermal mass. There is very little "cooling" due to the airflow over the wings. The concept was explored quite a bit with wartime development and found unworkable for engine cooling. Seems to me that pumping a high thermal load into a small and rapidly diminishing quantity of fuel is a thermal runaway event in the making.

The injectors on the early Ford Powerstoke Diesels (the HEUI injectors) bypassed fuel back to the tank. Many factors, but it got so hot as to melt the poly tanks Ford was using. And the purpose was not to cool anything.

Jet A boils at 375F, EGW boils at 230-250F. Both depending on the pressure of course, BUT the numbers - specific heat of Jet-A is 43% of water, and thermal conductivity is 17% of water. Both of which will drive up operating temperatures for the cooling system. It is certainly possible too cool this way, and we wont engineer within this forum, but it is quite different and having AES involved for the whole system is a real advantage. They will have access to data that is hard to get otherwise.
 
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The driving requirement seems to be a need for 130F fuel at injection delivery. The question is thus how to heat the fuel.

Having brainstormed a fuel-cooled system, sit down and map out system components with conventional coolant. Make a hard comparison.

Fuel heating could easily be done via a simple tubular passage through one of the tanks on the water-to-air exchanger, just as transmission and engine oil is temperature regulated in automobiles. Very conventional, relatively safe, with high acceptance.
 
You are quoting data and products that were originally used to write the original papers.
Two strokes have notoriously poor fuel consumption due to "short circuiting" The papers you have read were based on engines that were using a simple carburetor for fuel supply.

AH

Actually section 7 of the report shows a predicted (but not demonstrated) BSFC figure of around .59 on Jet A using DI. Still nothing to write home about but a lot better than what the carb system delivered in testing.

It seems your design is far superior to this.
 
May 2019 Update

I wanted to give a short update on the Hawk V4 engine for everyone following along. Quite honestly, I have been too busy working and building so haven't gotten much information out to you all lately. Andy has been out of the country (Japan) for several months working on a few other projects including the V12, so progress on the Hawk has slowed a bit. All hands are on deck now since he?s back and progress continues. He?s requested a few components be reworked by the casting company as he had some fitment issues that did not meet his standards, so that has slowed the initial build up. He?s got the cylinders being touched up on the CNC now after recasting them and will be fitting the revised components next week. Needless to say, these things happen when producing a clean sheet design. While it is disappointing that the extra time must be taken, it?s comforting to know that the extra time is being taken! Andy is not compromising his standards to rush a product into the air. Importantly, the issues are minor and related to getting the manufacturing tooling setup, not anything with design of the components.

He is pressing hard to get a working engine to OSH for display in the innovation tent this year. I?ll be in OSH Saturday (pending WX) through Tuesday afternoon and will try to spend most of the day Monday with Andy in the tent to talk with folks about what we are working on.

While the case pictured (coming soon, I'm at work and can't post it) is still a prototype case he?s working on, the production run of cases is complete and my case (#20) is complete. He?ll begin running the engines once he is happy with all fitting and initial build up is signed off, hopefully in the next two months. Build up of the drive train is well underway and is progressing smoothly. This is a bit behind his original schedule.

After a lot of discussion and thought, I have decided to order a Lycoming for my RV-10 build and proceed with getting my airplane airborne. I made this decision based on two main factors, one financial and one personal. I am using a construction loan for the last part of my build and it is interest only payments right now. It also has a construction time limit of 18 months, so I am under a timeline that I must meet to avoid large financial penalties. Thus I could not wait any longer to get an engine on order nor did I want to put pressure on Andy to get the engine flying before it?s tested and proven ready. The personal reason is to get our airplane in the air so we can start utilizing it soon without the pressure of integrating the V4 on it before it flies. I really want to get some adventures going with family and friends!

So, I have reworked my approach to the V4 which will ideally make it a more enjoyable and less stressful project! I will be creating a test stand based on the RV-10 firewall and Show Planes cowl to create the firewall forward package for the Hawk. This will let me have a bit more freedom to make initial adjustments and some mistakes without it impacting my flying airframe. It also takes the personal pressure off of me to get the Hawk flying sooner since I can still go fly my 10. Once the engine mount is finished being machined, I?m going to start fitting and locating the systems and support components to prep for the V4 arrival. We will get a full setup going on the test stand and be able to really iron out the details along with creating documentation for those who select the Hawk for their builds. Andy has been really supportive of this decision and I appreciate his advice on this. He wants a seamless transition to using the V4 and if it takes a bit more time, so be it.

Once this tests rig is complete and we?re happy with the package, I will convert my airplane to the V4 and document that as well to create a firewall forward package which will be made available to other builders. The test stand will ideally stay in use for demonstration, testing future updates, and marketing at events.

I?m sure this sounds like other engines that have been saying it for a decade or more now. I can?t honestly say I know it won?t be true! I can say that Andy is still 110% committed to the success and production of the engine. I?m happy to see he isn?t compromising on quality and wants to see folks use his engine safely and reliably.

Stay tuned for another update around the end of the month. In the meantime, keep building! I finished my doors, windows, and now have avionics powered on. I hope you all are well and look forward to seeing you at OSH this year!
 
Neither the Hooper or E-330 are diesels, they are heavy fuel capable, SI designs. I am confused...

The Hooper engine has dreadful BSFC- especially on Jet A.

Just spotted this thread. Interesting engine design!

This range of BSFC is typical for smaller engines used in UAVs. As power levels drop BSFC gets worse due to thermal efficiency effects of worsening surface/volume ratios.

I was heavily involved for a time on a SI heavy fuel engine for a Scandinavian UAV helicopter and we saw a best effort of around 300g/kWh on JP8 and Jet-A1 for about 55kW. SI on heavy fuels isn't an easy problem to lick due to the poor and generally uncontrolled octane rating of the fuel. On the up side, two-stroke engines can tolerate a lot more knock intensity than a four stroke given the much lower cylinder pressures.

Anyway, I wish Andrew well in his endeavors! It's a challenging project in many areas.
 
Nothing really new to report. Oshkosh saw a lot of interest and a mock-up but the engine hasn’t run yet. Fingers crossed Andy is working hard and will run and produce once the design is proven and prototype is successful. I’ve been busy flying off my phase 1!
 
andrew higgs project update??

I have emailed back and forth a number of times with Andrew over the past couple of years. I was also able to visit Andrew at Osh Kosh and I'm really looking forward to seeing him get into the production stage of his 4 cyl.
I sent him an email after the holidays but I have not had a reply as of yet. I'm guessing he is up to his eyeballs in all the tasks required to keep this project moving forward.
Does anyone have any updates on the current status on the testing / certification / availability of his 4 cyl engines.

I'm dying to get any info that anyone has.... Jeff

Andrew if you happen to read this I'm the guy in Minneapolis with the motorcycles :)
 
I have emailed back and forth a number of times with Andrew over the past couple of years. I was also able to visit Andrew at Osh Kosh and I'm really looking forward to seeing him get into the production stage of his 4 cyl.
I sent him an email after the holidays but I have not had a reply as of yet. I'm guessing he is up to his eyeballs in all the tasks required to keep this project moving forward.
Does anyone have any updates on the current status on the testing / certification / availability of his 4 cyl engines.

I'm dying to get any info that anyone has.... Jeff

Andrew if you happen to read this I'm the guy in Minneapolis with the motorcycles :)


While I sincerely wish them all the luck and fortune in the world, just be aware how many promising developments over the decades have never made it to production. For over 15 years I believed the Zoche diesel was going to make it someday... :)
 
I wouldn't be looking for a certified version any time soon. That process will likely take years more and many $$ more after prototypes run for some time and pre-production examples with all the final changes made get some serious testing time on them.
 
just saw The HIGGS HAWK V4 E330J/G Diesel is taking orders.
is anyone putting one of these in an RV10?

A. Mekler
N668G
 
Definitely would like to hear more about this here on VAF, especially after the article in EAA Sport Aviation. I also don't use Facebook, so I'm not going to find it over there.
 
Hi Folks,

So a quick update, Karl Grove has become the US representative and point person for AC-Aero. He's working hand in hand with Andy for the distribution and support of the V series engines. He has a wealth of knowledge and expertise that will really come in handy getting the initial production off the ground as well as setting up a support infrastructure.

I will be working with Karl and Andy to still develop a firewall forward kit for the RV-10. My goal hasn't changed, to create a turn key solution including full documentation and support to install the Hawk on the RV-10. I'll do the initial prototyping and most of the testing on a test stand then hopefully transfer to my plane for flight testing once proven.

At this time, I haven't gotten any further updates regarding the engine itself. I know Andy had some dyno time scheduled for late last year but I haven't heard any results. Covid really affected production in 2020 since he is in Japan, but things are opening back up. As I get confirmation the engine has begun testing, I'll definitely pass that along. Until then, I'm waiting patiently to get an engine in my hands so I can start integration tasks.

Stay tuned!
 
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