View Full Version : EA-81 Engine Performance Figures
Hello gyro nuts...<br><br>Does anyone here have or know where the dyno figures for a stock EA 81 engine can be found, I´m particularly interested in obtaining the RPM vs power and RPM vs torque figures for sizing a prop accurately.<br><br>Thanks in advance...<br><br>Nicholas Tomlin
12-04-2003, 05:12 AM
Hi there, haven't got any dyno figures but have read that you have 115 hp on 6'000 rev's and a max torque of 140 Nm at 3'200 rev's, apparently the most used direct drive prop is a 26 x 52".
Thank you for the figures, they are similar to the ones found on the sub4 web site, and reflect the performance figures for a mildly warmed up engine - ie, twin CV carbs, cam, head port and polish, etc, none of which I have.
115 HP would be nice but it wont happen without a gearbox, I´m just trying to arrive at the best possible solution without one.
The prop pitch you speak of are nominal, however, the performance of a prop is wildly dependent on its aerodynamic profiles, I have one which doesn´t seem to output the thrust that I´ve been told could be achieved, you could have two flat planks set at 26 x 52, and not get what you need, but maybe I should try....;>)
I did want to get a good comparison for the engine I have so I can see if it is the problem, then move onto the prop.
12-04-2003, 01:54 PM
Direct drive EA-81 engines - stock american version - will turn a 52 inch diameter by 26 inch pitch Tenn. prop. This combo will - if the engine is at peak performance - turn rpms up around 3800 or so. Much higher RPM will have the tips going supersonic.
The EA-81 engines out of Japan - so called 100 horsepower Truck engines - are slightly different, Intake manifold comes with dual carbs stock and the intake and exhaust valves are reversed in this version. This engine normally turns a 52 by 28 inch pitch tenn prop.
I have this japan engine on the gyro I just bought. It is turning a 52 by 30 inch pitch tenn prop. I haven't seen it fly in person or have had a chance to run the engine wide open since I got it so I am not sure if it will still turn the 3800 RPM target rpm. If it does then this engine is putting out some good power.
Now if your looking to put this engine on a airplane or something else, your choice of props may be a little different. But for a gyro this is what 99 percent of us use.
Have you ever done a static thrust graph for your machines - past and present?
What I´m trying to establish with my machine is whether I have a dog prop, dog engine, or both, it supposedly isn´t producing the thrust the prior owner said it used to, some 318#, the best I´ve ever got out of it is 275# with a 55 x 28 at 3300 RPM, at WOT.
I´m not sure if he is exagerating or if the machine has decayed.
My figures go like this:
160/125 jets Heat No Heat No Filter No Body Filter
RPM 55¨ 53.5¨ 53.5¨ 53.5¨ 53.5¨ 53. 5¨
0 0 0 0
1000 25 60 45
2000 75 125 90
3000 220 160 175
3200 215 210
3400 235 240
3600 255 270 Max Max
We arrived at these figures by tying the gyro up and running it up against a set of spring scales.
See if you can come up with some figures, it would be interseting to compare, that is if you have a direct drive.
12-06-2003, 03:40 AM
I am not sure I totally understand your question, For as far as a thrust test goes.... My old direct drive Subaru powered gyro pulled 305 lbs of static thrust turning the 52x26 inch prop at somewhere around 3600 Rpm.
Bottom line is a direct drive EA-81 is going to be a dog no matter what. If you are a light weight small person, and your gyro is made to be as light as possible with out a bunch of extras you will get pretty good performance, But a big guy with a heavy gyro and all kinds of Do Dads the direct drive is not going to be a hot performer.
Go to the larger subaru engines like the EJ-22, or the high output EA-81's or the best one the EJ-25 and these engines direct drive will do a lot better for not a whole lot more weight.
12-07-2003, 06:48 AM
Like Ron said, unless you have the 100 hp EA-81, it WILL be a dog as a direct drive.
A redrive is the only way to go.
Been there, done that.
I find it interesting that you blokes have these smaller props turning at the same revs as my prop but with a finer pitch and yet you are getting more thrust than I am.. I wonder about the accuracy of the scales now... and the tacho.
Some measurements on the existing prop has the inner portions of the prop with a negative angle of attack relative to the air flow, which is a little disturbing, do you have any details on the tennesy prop, ie, angle of attack at full power and the maximum flight speed at this power setting, what soes the leading edge look like, is it sharp or rounded, is it flat on the bottom with a blunt leading edge and about 12% thick wrt the chord length? Any of this ifo will be helpful.
ON the engine department - how about the EJ-18 I have in the back shed???-
Thanks for your comments to date.
12-08-2003, 05:22 AM
Nicholas, was the pic below your gyro at Forbes or am I out of my tree again!!!! LOL
12-08-2003, 06:51 AM
That gyro Paul has a re drive. I think he said his was Direct drive.
The Tenn prop is just a thick wooden prop. No tricks or weird shapes, just a standard prop you might expect to see on a airplane just shorter and thicker.
I am rather sure our thrust scale readings were ver close to what it was truely pulling.
The EJ-18 is the same size in cc's as the EA-81 so the power shoulc be close but higher of course in the EJ due to the more modern valve arrangement and better flowing heads. It may weight more though, and is possible it won't have as much torque and therefore not do as good as the old EA-81.
Down in Florida there was a gyrohead that was in love with Alfa Romero cars from Italy. He found some kind of Alfa engine that was made for racing, it was a Flat four like like a Subaru, but it was very hihg tech, with overhead cams multi valves per cylinder, and so on. Just looked like the coolest engine you'd ever seen. Anyway he tried to use it direct drive and it just couldn't cut it, it did very VERY poor. It would not make even close to enough trust to fly. It was later tried with a Re drive and still was far from a power house. In the end the machine never flew as far as I know. But it sure looked good!
12-08-2003, 05:16 PM
My Graph from Fuji Heavy Industries puts a stock EA81 at a maximum of 80hp at 5400rpm
Nicholas, was the pic below your gyro at Forbes or am I out of my tree again!!!! LOL
No Paul, you´re out of your tree again.... sorry to have to wake you up, it is reminiscent of one of the scenes out of ´Total Recall¨, come down to reality now, take the pill,,, aaaarrrgh..
My Graph from Fuji Heavy Industries puts a stock EA81 at a maximum of 80hp at 5400rpm
Any chance of posting it here so we can all see it??
12-09-2003, 05:10 AM
Could you please give some more details about the differences between the engines out of Japan contra the ones out of the US?
I live in Thailand and most likely a Subaru I pick up here will be the Japan spec'
Thanks a lot,
12-09-2003, 07:01 AM
I am not super sure how to tell the two apart. I will say that the US version comes with a single tiny carb so most of us over here take the stock small carb off and replace it with a much larger Holley-Weber carb.
The Japan version comes with dual carbs stock. they are pretty good sized carbs too. Most of us running the Japan version will leave the stock carbs on, so if it has dual carbs that is a tell tail sign.
I think the differences go much further than that, I think the Japan version is just slightly narrower and the location of intake and exhaust valves are reserved in compairison to a US Ea-81. But from the outside the Carbs is the biggest clue as to which engine it is.
I was told the US version was rated at 76 horsepower and the Japan version was 100. In direct drive gyros the guys running the Japan engine normally turn props with 2 to 4 degrees more pitch than the Us engine - 52x28 or 52x30 compaired to 52x26 on the US version.
Still no sign of a RPM versus power and torque curve - does anyone have one????
12-10-2003, 06:34 AM
Thanks for that Ron, really appreciate it.
For engine calculations below is a cut and paste:
Torque (in Nm) X RPM divided by 5252 equals hp.
Hp X 5252 divided by RPM equals torque.
Reduction ratio times torque equals prop torque.
According to my bro' (who is finishing his Ph. D in combustion engine optimization) above is correct -at least up until the prop torque.
12-10-2003, 02:06 PM
If you know the horsepower and the torque then you can work out what they are?
12-10-2003, 02:09 PM
I do have the Graphs you require but I am away from home for another 12 days.
Will post when I get back.
My thanks in advance.
12-11-2003, 12:03 AM
::)personally i would not bother with such a dinosaur engine but for those who prefer to i was told to check in the exhaust port, the small horsepower one has the divider come out to nearly the flange face and the bigger hp motor has the divider finish much deeper in the chamber and twin carbs, hope this is true and helps.
12-11-2003, 03:49 AM
Steve, that was funny ;)
Info that I have states that the engine has a max hp of 115 at 6'000 rev's, it would then have a torque of 100 Nm at 6'000.
The info also says that it has a max torque of 137 Nm on 3'200 rev's, the info in between is easily filled in by using Excel (yes finally soem use of that program)
Hp Rev Torque
115.0 6000 100.7
112.7 5800 102.1
110.5 5600 103.6
108.2 5400 105.3
106.0 5200 107.0
103.7 5000 108.9
101.4 4800 111.0
99.2 4600 113.2
96.9 4400 115.7
94.7 4200 118.4
92.4 4000 121.3
90.1 3800 124.6
87.9 3600 128.2
85.6 3400 132.3
83.4 3200 136.8
12-13-2003, 06:41 PM
Its the other way around. The twin carb has dual siamiesed exhausts ports per head and the standard EA81 has single outlet. The twin carb also has reversed valving arrangement, which means that the cams are not interchangable.
Incidently these "dinosaurs" from zero time, are capable of over 3000 hours of service in Gyroplane conditions. This puts them reliably ahead of Lycombing and Continental and way ahead of any Rotax.
"Dinosaurs"?? I have three of them - they are reliable, start easy, good fuel economy,don't foul plugs,cheap to re-build, enough power 2-up ...... on & on. Give me a "Dinosaur" anyday!
What powerplant do you use, Mr Wilkinson?
12-14-2003, 06:20 AM
Would be good to hear what set-ups you got for your engines, I am about to build one direct drive so any info would be helpful.
I have been experimenting with different carb setups- attached is pic of"truck" EA81 with 2 Bing carby's.
The difference in the heads to a 'normal' EA81 is what Tim said, the exhaust manifold needs to be made from 2" tube they are that much larger. If you look at the area above the two top middle head studs you will see that area doesnt have the bulge, it is flat. That is because the intake feeds straight down.
On one of my other motors, I have 2 flat slide Mikunis- they work well.
How many ponies are you extracting from this unit??
I suspect I see a sub 4 gearbox on the business end of the motor...
What is the reason for the extended manifold length on the carbs to the head?
It looks very tidy but aren´t you sacrificing some power and increasing the risk of carb ice by not having them as short as possible?
12-15-2003, 12:47 AM
;) Well that touched a couple of nerves. Mceagle that is what I thought I said, my current machine has a rotax, not my first choice, but thats what the machine came with, if it came with an EA- 81 I would have been happy with that. If i was building a new one, I would be using a late model Subaru fuel injected motor.
12-15-2003, 07:05 AM
Echo, thanks for the info.
Has anyone got any info about the difference in having long intake manifolds compared to short ones, a long intake manifold should increase the torque of some reason, SAAB made a model that had variable manifold lenght (a valve would shut and force the intake gases through a lounger routed "pipe" section), I don't know if this would work??
12-15-2003, 07:22 AM
Bottom line is if it is going to be a direct drive EA-81 and used to power a gyro, the best thing to do is to make it as light - the whole machine including the engine - and as simple as can be. Even then it will likely be underpowered.
Also Subarus are fairly trustworthy, but that is the internal parts. Most engine outs with Subarus are due to failures of outside parts or systems. use the KISS system and have better luck. KISS stands for keep , it , simple, stupid.
12-15-2003, 02:37 PM
Longer (or smaller diameter) intake tubes are one possible strategy for lowering the RPM at which maximum torque is produced, which might help a direct-drive, but it's hard to imagine any advantage when using a reduction drive.
Since aircraft engines are never called on to make high power at RPMs just above idle, the way cars and trucks are, variable-length intakes like Saab or Ford use would be not much more than ballast.
That´s a scary picture you´re touting there...
How does the induct manifold length affect the torque and power - I am most intrigued.
12-16-2003, 06:12 PM
This is going to be a little oversimplified, but here goes...
The challenge at any RPM is to get as much fuel/air mix into the cylinders as possible during the period the intake valves are open. The factors determining the rate at which air will flow into the cylinder are (a) the difference in pressure between ambient atmosphere and the space in the cylinder, and (b) the resistance met by the flow of air through the intake system.
If you want to optimize high-RPM performance, you'll want large-diameter intake runners just long enough to organize the airflow into the desired direction, and no longer, since airflow restriction increases with length.
At low RPM, the airflow volume through these short, fat runners will be too low to maintain directional integrity, and the velocity of the flow will be low, reducing the efficiency with which it fills the cylinder. A longer, smaller-diameter tube does not contribute much resistance to the flow at low airflow rates, and results in more efficient filling of the cylinder. This longer, narrower tube will lower efficiency at high RPM, and improve efficiency at low RPM. It will thereby lower the RPM at which maximum torque is reached, a big advantage in vehicles in which the engine is expected to start moving the vehicle from a full stop at low RPM.
In an aircraft, the engine is air-coupled to its load, and free to rev to near redline before the vehicle even starts moving, so there's little point in adding weight or complexity to improve low-RPM torque.
In cars, where weight-savings is a low priority, manufacturers have resoted to some interesting means to maximize torque at all speeds. Dual-plane manifolds have been used since the early 60s with four-barrel carbs. They have two layers of intake runners, one small-diameter set fed by the primary carb bores, and a larger-diameter set fed by the secondaries, both terminating at the same valve port. A full-throttle low-RPM start opens the throttle butterflies on all four barrels, but a second set of butterflies in the secondaries seals off their barrels, as well as the larger set of intake runners. When engine speed rises to a point at which the restriction of the primary bores and intake runners becomes significant, a vaccuum motor reacting to falling manifold pressure opens the secondaries and their large intake runners.
There's a similar compromise made by engine designers when choosing valve sizes, camshaft profiles, and exhaust systems. The biggest valves you can fit within the bore diameter of a cylinder, or adding the complexity of four valves per cylinder will allow maximum flow, but low-RPM torque can be so poor the engine is hard to start and idle. Ford had this trouble with the high-output, aluminum, 32-valve version of the 4.6L V-8, which in its early days would lose drag races to the cast-iron 16-valve version of the same displacement, despite having 45 additional peak horsepower (305 vs 260.) Ford has experimented with alternate plumbing and butterflies in the head itself to alter effective port diameter, allowing higher low-speed torque.
Chevy has gone the other way in that compromise, and decided to stay with two valves per cylinder in its current performance V-8s.
Honda pioneered techniques in varying valve timing to balance low-RPM efficiency with high-RPM capacity.
I apologize for the somewhat rambling answer, and there are also resonance effects based on tubing lengths which affect the RPM at which they are most efficient, but I hope this helps. If you're in a position to experiment with intake plumbing, you can fine-tune the length to maximize torque and horsepower at take-off speeds. No matter what length and diameter you find appropriate, it will almost certainly work best if you can keep bends in the tubes as few, gradual, and far away from the intake ports as possible.
Re-drive is a NSI.
Pics of inlet tubes may be a bit misleading,tubes are similar length to standard manifold.
The only reason I made them that length is that is where I wanted the carbs- close together to make a single airbox for carby heat.
My tandem machine has two flat slide Mikunis pointing forward wiyh a real short intake- I'll take some pics & post them.
Tim Mclure gave me some info on tube lengths- where are ya Tim?
12-17-2003, 03:39 AM
Longer inlet tubes can reap benefits in a high performance engine but generally only when each branch feeds one cylinder. In the case of an EA81 the breathing problem is compounded by the fact that the two cylinders on one side induct the inlet charge one after the other and then there is a lull while the other side induct their charge. Increasing the induction length would probably only advantage the second cylinder in the food chain and lead to uneven compression pressures. This is the reason why all the later Subarus have dual port heads and longer intake tubes. Some have successfully converted EA81 heads to dual port for reasonable gains.
01-10-2004, 03:43 PM
There seem to be quite a few variations on the EA81. I have one that was a real dead duck. When I bought the gyro the owner said it was an imported from Japan one.
I could never get much power out of it. He flew the thing but was somewhat lighter than me. ???
On investigation I found that it had a low lift cam- 4.95 mm compared to the standard 6mm. Also the inlet valves were smaller than usual. I haver been told that there was an "economy" model produced when the original oil price rises occured.
The cam lift coresponds with that of the turbo cam, so that and the smaller valve would have certainly limited the amount of fuel it could suck!
I got some ordinary sized valves and had the inlet throats opened up to suit. I also replaced the cam. Believe it or not this can be done without pulling the pistons out. The cases have to be split to give enough room for the cam gear to clear the crankshaft sprocket.
Care must be taken on reassembly to ensure there is a good seal between the crankcase halves.
The cam I used has 6.5 mm lift and would probably be called a stage one.
Some may be critical of my not replacing the rings and bearings, but I see them as just being nicely run in, so why disturb them? :D
It runs very well now with quite good power output on the original carburettor. That will eventually be replaced by single point fuel injection- making ice a little less likely I think. ;D
01-13-2004, 03:29 AM
Thanks for that info John, I will look out for the cam type when I get out and look for engines.
I checked with my local garage and they say that they will be able to get the wiring loop and such for injection for it, would this be worth it instead of going with a (couple of?) carb (s)?
I don't have to worry about carbs icing where I live but I want it light weight and reliable.
Appreciate your comments,
01-16-2004, 02:09 PM
Just a couple of things to consider Hasse.
Carby ice is more a function of humidity than just ambient temp. Now I've only been to Bankok once, and while it was hot, it was certainly very humid. It is possible to get ice up to 30degrees C :o.
While we have not had them here in Oz, I understand there was a model of the EA82 which came with Throttle body fuel inj. I understand this fits straight on the EA81.
However you will need to get the whole fuel system, i.e. pump in tank, computer, distributor for crank angle info, etc.
01-17-2004, 11:21 PM
I have set up quite a few multipoint EFI EA81's but I have never seen a single point EFI system on an EA81. I would be curious to know more about it if anyone has any info. It should be a lot easier to set up than a multipoint.
We have not yet recorded any iceing problems with fuel injection.
01-19-2004, 04:22 AM
Thanks for the info, I will see what I do when I get that far...
Agree, Bangkok is one hot, humid, ****ty place, outside Bangkok it doesn't get that humid though, you'd be surprised what a difference it is.
All the best,
04-15-2011, 04:59 PM
I'm new to gyros and the site. So please be gentle with my lack of knowledge.
I would like to build a Little Wing Autogyro. I'd also like to use an EA-81 or comparable engine equiped with an electric 5psi boost supercharger. I live in the California High Desert and the summer DA can easily approach 10,000' in the winter we see temps in the teens and a bit of snow. I would not need a turbo charger running all of the time but could see a valid use for a supercharger when the DA required it.
Right now I'd really like to get a line drawing of the EA-81 or equivalent so that I can see whether it will fit or not. Weight of the engine would also be much appreciated.
I am a real Subaru fan, BUT!, at those altitudes you really need about 25% more power that the guys down at SL. To get a EA-81 to do what you need can, and will, cost more that a used 0-200 Continental. Think about a 0-200 !
04-16-2011, 08:39 AM
...I would like to build a Little Wing Autogyro. I'd also like to use an EA-81 or comparable engine equiped with an electric 5psi boost supercharger...
Glen, welcome to the forum!
Be wary of the electric superchargers. They often advertise a PSI rating which can only be maintained at low airflow rates. A dead giveaway that you're reading a scam is if they claim to improve miles per gallon.
If you do find one that will make 5 PSI at 300 CFM, make sure you know the current required. It's likely to exceed the capability of a light aircraft electrical system.
The concept of a supercharger driven by an electric motor is appealing, in part because it would lend itself to experiments with electronic regulation. But it's not efficient. By the time you generate the required power with a belt-driven alternator and incur two sets of loss in the alternator and motor, you might as well just drive the supercharger with the belt in the first place, and save the added weight.
A properly sized and gated turbocharger will be more efficient, since much of the force to turn the turbine comes from expansion of hot exhaust gas, which is normally wasted. It also makes a great muffler!
The best strategy for dealing with a DA of 10K' might be to just choose an engine with 30% more displacement than what you'd need at sea level, and keep the external systems more simple and reliable.
Early Bird Dave
04-16-2011, 09:26 AM
Go to www.autoflight.co.nz, contact Neil Hintz. This is one of their specialties.
They have a long term running example, I think Neil said it has crossed 500 hours of a boosted 2 place Dominator run by his mate Grant.
04-16-2011, 02:24 PM
Thanks for the information. I'm building the Little Wing Autogyro, and it would seem that too much wieght up front will change the nature of the beast. The Turbocharger is a posibility. I'll find the electric supercharger information that I found and post it for review.
We are 15 miles north of Palm Springs, California and the summer temperatures even at 3,800 MSL can get to 100+ in the late summer. On the other side of things we had snow on April 9th.
04-16-2011, 02:27 PM
Thank you, I'll consider that as well. In any case I think I will want to boost it.
04-17-2011, 12:12 AM
I too am building a little wing, LW5 single place to be exact. I started about 2 1/2 years ago and started down the Subaru path but when i learned about Todd Reick and his Yamaha conversion i took note and followed his path. I now am 90% complete with my build and have a Yamaha Genesis 120hp up front for power. Here in the Denver area we routinely get DA days at above 9,000' so extra HP and long rotorblades are the rule here.
I purchased Todd's Rotax gearbox adapter kit to mount a "c" box and will use a clutch to dispell blade shake at idle and low RPM. The only down side i have encountered using this engine is to keep the thrust line were Ron Herron designed it (on Datum "A") the engine sticks up over the top of my 26" tall firewall and boot cowl by 2.5 more inches so i have this pregnant looking nose but that is that big of a problem. I just built a scoop facing backwards to accommodate the engine height.
All up my firewall forward package will weigh in at about 150LBS which is fantastic for 120HP! and a very realistic flying weight will be 780 to 800 so that is about 6.66LBS per HP at full throttle and at 75% power the Yamaha dyno's at 100hp so even at 8lbs per HP that is very very good! You wont get that out of a Subaru! I cannot post pictures here as i used "reply" so here is my email if you would like to see any pics just send me a message and i will send pics of my build.
You may want to look into using a Yamaha!
Just my 2 cents!
04-17-2011, 12:13 AM
...We are 15 miles north of Palm Springs, California and the summer temperatures even at 3,800 MSL can get to 100+ in the late summer. On the other side of things we had snow on April 9th...
Glen, not so different here. We don't often hit 100ºF, but we get close, and our airports in the greater SLC area are between 4,200 and 4,900 MSL. Density Altitudes of 7-8,000' are common in summer.
A Rotax 503 on even a light single-place wouldn't get most guys off the ground in the middle of a hot summer day in Utah.
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