Jabiru power increase

[Paul davenport]

Does anyone have any ideas on how to clean up/ make more efficient for a power gain Jabiru cylinder heads/ engines ,I am not talking modifications here just tweaks for efficiency and perhaps a few free horses in the process ?.

[facthunter]

My view is the ports and manifolding are already good in a relative sense as far as surface smoothness etc are concerned. You can always achieve "something" but there's not a lot of surplus metal about. Uneven distribution is another matter and hard to deal with.. many have tried. Polishing combustion chamber surfaces helps for a short time and you can remove any sharp  edges.. Get your ignition timing right on.  Nev

[Thruster88]

More power always equals more heat, not what the jabiru needs.

[facthunter]

You are right. Both my recommendations reduce the heat . Perhaps a water methanol injector for high power settings? Nev

[turboplanner]

3 minutes ago, facthunter said:

You are right. Both my recommendations reduce the heat . Perhaps a water methanol injector for high power settings? Nev

I've always followed the principle that unless you want a real boost in the pants from the extra power, it's not worth taking the chances of side effects when you think about modifying an engine. What you said in your earlier thread I agree with; just clean up the things that are there. Boosting power from a standard engine is normally for racing where you accept an exponentially shorter life as you increase power.

[facthunter]

Spot on.. Most of the car stuff we modified was done far beyond the engines  inherent strength. You'd get 3 times the original horsepower. Crazy.

     To get more power from an aero engine you need to design it from scratch again or risk a dud. For some the short life  (Tens of hours) is no problem as you just get a new engine. Eventually you run out of new "OLD" engines.  Some of the "special" Lycomings (modified) aren't too good either.  Aero engines of the piston variety remain a challenge .Nev

[spacesailor]

Once you get up to the thinner air, a turbo really gets the power back.

No extra work on the motor, just the wastgate for lower altitude.

spacesailor

[Paul davenport]

So I take it none of you have actually tried any of this on a JABIRU. Engine and at best it’s speculation . My initial question stands what can be done to tweak without modifying to make it more efficient and possibly gain some free hp 

[lee-wave]

The only way you can gain a real increase in performance without modification or weight increase is to put on a more efficient propellor.  Fitting a 60X40 in place of a 60X42 results in static revs increasing from roughly 2670rpm to 2890rpm which is equivalent to a 7 % increase in horsepower (I think the maths is right) .Certainly the take off performance is blistering... but the offside is there is a reduction in cruise speed ...

[turboplanner]

8 hours ago, Paul davenport said:

So I take it none of you have actually tried any of this on a JABIRU. Engine and at best it’s speculation . My initial question stands what can be done to tweak without modifying to make it more efficient and possibly gain some free hp 

Well tweak is not an engineering term, so maybe you could explain yourself?

[FlyBoy1960]

just go with nitrous and your problems are solved

[SSCBD]

Without starting a war here - Rotax 915

[Paul davenport]

Tweak.  Any small adjustment to achieve efficiency and power increase without actually modifying motor ,including but not limited to ignition, head valve airflow, valve timing, engine balancing, piston reversal pin offset . No turbos, nitrous, and all other outlandish and obvious crazy things. No comparison with other engines, JUST Jabiru. If you haven’t any experience with doing this don’t bother adding your comments 

[Paul davenport]

SSCBD. no war started but not exactly the answer I am looking for

[Kenlsa]

I replaced one coil with a Rotec unit.

Better start (instant)  and no drop in idle rpm during ‘mag’ check.  So should be slightly better when opening the throttle and maybe fractionally more economical, not that I can tell.

Of course no advantage for cruise speed as 2800 rpm means 100 kts no matter what power is produced.

Ken

[WaterWings]

Sonex guys use exhaust headers and no muffler for Jab engines.
As well as Rotec TBI instead of Bing for mixture control and better mixture spread due to better atomisation.

[RFguy]

In my opinion, The Jabiru has NO thermal headroom for any more power. 

 

Zero zilch, none. More power and you will cook a piston, valve, a head, a seat.

I'll guarantee  it.

What you can do  to ensure best performance : 

-1) Verify that the timing is supposed to be where it should be, which in general will be assured by design (flywheel magnet location) .

-2) if a cold start kit is fitted, that it is operating as designed.

-3) Verify the prop is pitched in a way that satisfies the guildelines outlined in the Jabiru engine manual, and optionally, according to your needs. 

-4) Verify air filter, induction system, esp. carb heat, plug performance, fuel quality  are in spec.

-5) Verify the mixture settings are suitable and the carb is set up correctly.. Needles and mixtures and carbs vary. 

-6) Keep your aircraft skins clean and prop in top condition.

-7) If you have a wooden prop, get the composite prop, it has much better efficiency/performance.

 

That's as good as it gets. 

-Glen. 

Edited May 22, 2021 by RFguy

[danny_galaga]

It's it carb or fuel injection? Fuel injection will get you a gain without creating more heat

[facthunter]

Jabiru engines always seem more happy when fitted to faster planes. Anytime they looked like getting a bit hot I increase climbspeed.  I pull them through prior to each flight.. You need to know what a good compression  feels like. . I don't like hydraulic lifters. It doesn't hurt to lift the rocker covers and check things.  Unusual Changes to valve clearances mean something's happening that should be checked. Nev

[skippydiesel]

To get more ponies; There are a host of engine modifications which always result in more heat, greater pressures, shorter in service life. Then there is what we used to call "Blue Printing" which I understand to be, pedantic/anal attention to engine build (fit, finish, matching component weights/balance, etc), ignition timing , fuel delivery and exhaust flow all without changing the engine specifications. The later should not create additional heat and if anything has the potential to extend the service life of the engine - if you have the time & dosh this might be for you.

[turboplanner]

5 minutes ago, skippydiesel said:

To get more ponies; There are a host of engine modifications which always result in more heat, greater pressures, shorter in service life. Then there is what we used to call "Blue Printing" which I understand to be, pedantic/anal attention to engine build (fit, finish, matching component weights/balance, etc), ignition timing , fuel delivery and exhaust flow all without changing the engine specifications. The later should not create additional heat and if anything has the potential to extend the service life of the engine - if you have the time & dosh this might be for you.

Blueprinting is very expensive; worth it for a race engine, but not for an aircraft engine you're going to replace every few hundred hours. Holman and Moody used to go through hundreds of pistons at the Ford factory to find 8 matched to what they were looking for. You can only buy so many and get a credit. In some areas you're removing resistance, so power gain through eliminating power demand, in others you might be bring one cyclinder up to the performance of the other three, so the other three cylinders get an easy life, and if you set the installation up so you only use the same power, then logically you could expect the engine to run cooler, but if you're going to cash in and use the extra power available, the cooling you gained may well be offset by the higher power you demand. For example, if blueprinting gets you 10 hp, so you put a coarser prop on the engine's going to work harder.

[facthunter]

IF you equalise power from all cylinders you get more power without exceeding any  temperatures. In some engines there is a wide variation of output on delivered engines. due to casting  (coring) dimensional accuracy etc. the Jabiru is all CNC'd ports and they are most likely to a very close tolerance . Same as the crankshaft  is from a solid billet and doesn't need balancing. Getting the mixture even and the timing more precise won't up the heat. You set the engine to RPM settings anyhow and if it makes them easily you use less throttle. Better alignment means less friction so do more precise fits all round. Nev

[onetrack]

I used to have a workshop mechanic working for me, who was formerly a Cummins head mechanic. I have never seen a man so anal about engine rebuilding. He would check every single component intensely, to ensure it met factory specifications.

 

And every engine he rebuilt performed immaculately and ran to maximum service life without any failures. The simple fact remains, that engine manufacturers provide detailed specifications for every single engine component - and many a time, components are fitted that are never checked, and which are outside specified parameters. There are a multitude of parameters that many engine rebuilders never check - flywheel runout, and component balance are typical areas that are neglected.

 

Conrods must be checked for alignment, concentricity, twist, dimensional limits, surface finish, roundness, nicks and flaws. Pistons must be measured in multiple positions. The amount of effort you put into specification checking upon engine assembly is directly relative to the life and performance of the engine.

 

https://goodson.com/blogs/goodson-gazette/inspecting-measuring-the-pistons-pins-connecting-rods

[facthunter]

You do and MUST get an advantage. One thing hard to check is material specification. Some supplier cuts corners and you get failures. "out of the blue " so to speak. . Core shift in castings and porosity as well as not having the right spec alloying metals  and casting at the right temps. Nev

[Paul davenport]

All good information and I take your point about attention to detail and your Cummins referral but I caution you about wandering away from my initial question and remind you I asked about Jabiru and nothing else and would ask you keep to ONLY Jabiru