EGT SPREAD

[jetjr]

If theres a readout then theres a sensor??

 

I see they are advertising all come with EMS now so muxt be peetty common?

 

 

[Guest rv6ejguy]

The EFI CPU can track the injector pulse width and frequency to give fuel flow and totalizer amounts without any external flow meter or ist's restriction.

 

 

[spyfly]

Bruce .I tried a rotes. When I leaned out until the jab started to falter I had three on the lean side of peak and one still on the rich side.i.e. when I richened three went up and one down so I don't think that will cure your problem.

 

 

[spyfly]

Should be rotec. Bloody spell checker

 

 

[andrew lott]

Always bear in mind the two different octane measures used for Avgas and Mogas. Mogas is about 7 lower and subject to being adulterated by who ever wishes to. It's already variable in production in some instances Two stroke enthusiasts shouldn't let the fuel go stale especially after mixing where the life is more likely to be more reduced.A rich mixture will cool the engine by latent heat of evaporation, and increase power because there ia more mass of charge in there. Most engines ( Petrol) that are run at the limit of their power will enrichen the motor(s). Race cars and aero engines. Road cars would not be allowed as much leeway and they hardly ever go there anyway. Nev

This depends on how rich the mixture is. 50degF ROP will cause the highest CHTs. 80 - 100 deg F ROP will produce best power. The position of Peak Pressue relative to crankshaft rotation TDC is the big factor in CHTs. PP and its position is determined by the speed the cylinder charge burns and this depends on the fuel/air ratio. Lower and later PP can occur both LOP and ROP. The charge has to be very rich on the ROP side compared to the LOP side to get the same effect. Check the APS website for more detail.

 

 

[facthunter]

More charge density gives a more sustained push, same as with supercharging or water methanol addition. High compression may give a high peak pressure but still have less torque output than a lower peak pressure with more weight of charge burned. Nev

 

 

[Bruce Tuncks]

Here's the latest pics. The second is EGT on cruise-climb at 80 knots and the first is CHT on cruise at 90 knots .

 

I reckon the problem is solved, as the no 4 is no longer the hottest one and they are more even than before.

 

The best mod was the cross-vane in front of the distribution box.

 

Thanks everybody and especially Jab 7252 who designed the electronics and software.

 

 

 

[Jaba-who]

Here's the latest pics. The second is EGT on cruise-climb at 80 knots and the first is CHT on cruise at 90 knots[ATTACH]44715[/ATTACH] [ATTACH]44714[/ATTACH] .I reckon the problem is solved, as the no 4 is no longer the hottest one and they are more even than before.

The best mod was the cross-vane in front of the distribution box.

 

Thanks everybody and especially Jab 7252 who designed the electronics and software.

By in "front of the distribution box" do you mean between immediately after the carby and before the manifold induction chamber?

Just wanting to be sure because I might try it myself.

 

I've got cylinder 3 and 5 running hotter CHT than the rest and egts also a bit hotter. ( CHT only on climb but EGT all the time. ) I've already got a crossed baffle on the inlet into the carby. But if yours worked on the outlet might try the same.

 

 

[Bruce Robbins]

By in "front of the distribution box" do you mean between immediately after the carby and before the manifold induction chamber?....... I've already got a crossed baffle on the inlet into the carby. But if yours worked on the outlet might try the same.

Hi Jaba,

 

We recently installed a cross vane (from Jabiru) in a roller follower J230. We found that rotating the crossvane produced large changes in EGT behaviour between cylinders. After a fair bit of trial and error we finally narrowed in to a position that gave a nice even spread in both climb and cruise.

 

Regards,

 

Bruce

 

 

[Bruce Robbins]

... that's the standard Jabiru crossvane mounted at the carby inlet.

 

 

[jetjr]

What the standard vane?

 

Interested in how you made it so you could rotate

 

 

[Bruce Tuncks]

Yes, Jaba-who, the vane consists of 2mm brass tube filled with steel wire, in a cross and sunk into the rubber fitting which holds the carby. At the NS and EW positions I hollowed out the rubber fitting a bit where it joins the distribution box so the cross-vane is clamped between the rubber fitting and the distribution box, but fitted in so as not to let air leak in there.

 

Then I soldered 3 tinplate vanes, wrapped around the tube and extending about 12mm to the rear and curved so as to deflect the stream into no4 cylinder and no3 cylinder and away from no2.

 

It was jetjr who said that vanes downstream of the carby were more effective than upstream and this turned out to be the information I needed.

 

I have not seen the factory setup but I assume they have done something similar.

 

Nothing I did upstream seemed to have any effect ( remember the straws in the pipe) and even the extended pipe "catcher" from no4 pipe into the distribution box didn't change the temperatures much, so these things have been discarded and only this vane remains.

 

 

[Bruce Robbins]

What the standard vane?Interested in how you made it so you could rotate

Hi Jetjr,

 

The vane is a modified version of the cobra head fitting that attaches the scat hose to the carby mouth on a standard Jab install. They have fitted intersecting plates that run the length of the cobra head, effectively dividing the tube into 4 sections. Normally you would install the cobra head so that the outlet sits nicely in line with the outlet from the air box, keeping the scat hose run nice and straight.Because it clamps to the carby mouth you can rotate it a little either direction.

 

 

jabiru cobra head - Google Search

 

 

[Bruce Tuncks]

Sorry, I didn't really answer jaba-who about what I meant by the distribution box.

 

Here is the bit I mean, some call it a plenum chamber.

 

The vane is between the rubber fitting and the cast metal part, which is part of the sump on my early model engine.

 

You will also notice how the hose-clamp is too far from the carby rubber end. The carby can actually fall out with it like that... I hope I didn't fly with it.

 

The hose clamp should be flush with the end of the rubber.

 

 

 

[Oscar]

Bloody hell, Bruce: there should be TWO hose-clamps there, one holding the rubber sleeve onto the carby and one holding it onto the plenum chamber. You are one VASTLY lucky person if you flew with that set-up and the damn carby didn't come loose, it would have been only the cobra-head holding it in place.

 

 

[Bruce Tuncks]

Nope Oscar, the rubber fitting is fixed to the plenum with 2 socket screws. They just don't show up well in the photo.

 

I have thought about wiring the carby to the plenum so that even if the rubber split then the carby would stay in place.

 

Has anybody done this? I would like to see how they did it.

 

 

[Bruce Robbins]

Jetjr,

 

This is what I was trying to post this morning before rushing off to work.

 

 

 

 

 

[Oscar]

Ah, my apologies Bruce - that is a rubber coupling bonded to a steel (or alloy) flange? (Maybe Rod nicked them off BMW bikes..) Jab changed to a flange and dual hose-clamp arrangement with the CNC plenum ( and four cap heads to retain the flange to the plenum).

 

 

[Ultralights]

if you want a good EGT spread, wouldn't it be easier to move the probes in the exhaust to get the numbers you want?

 

 

[Oscar]

Now, Ultralights, you are being contentious! However, that's nowhere near as facetious a comment as some might think..

 

The standing wave pattern that develops in an exhaust system - particularly one with a combination of straight runs and fairly sharp bends as the Jab. has - not only can be quite sharp in its definition, but will change in position with revs and load. If one were to put a stripe of temperature-indicating paint on each exhaust tube, I will bet $10 that nobody ( me included) has managed to get all their probes accurately centred on the highest EGT position for any particular flight.

 

Exhaust design is well into the realms of the arcane; only those with incredibly sophisticated facilities can get within a bull's roar of 'best'. Anybody remember the Honda v12 F1 engine exhaust system: Honda F1 engine exhaust - Google Search

 

Or: here's what Honda did, to tune its exhausts to the different rider requirements for engine performance characteristics between its two factory team racers in 2013: Honda motogp exhaust - Google Search BTW: those exhausts are fabricated from welded titanium segments.

 

OK, the motoGp engines produce around 260 hp/litre, Jab engines produce less than 45 hp/litre. But: dead set: why would we think we can get it absolutely right for shoving on our EGT probes?

 

We are not trying to extract the last few hp from our engines - we are looking for reliability. That comes from keeping CHT (and also the top few inches of the barrels) within limits. The actual numbers being reported by the EGT probes is fairly irrelevant - particularly since we don't have mixture control requiring EGTs that indicate ROP /LOP necessary for mixture control. What full EGT monitoring DOES offer, is a very quick alert to a sudden change in engine operation - such as detonation, or a dropped plug lowering effective combustion.

 

The CHT reporting is far more useful to us as an indication of engine performance. Provided you have a set of calibrated probes (and that is fairly easy to do for the temp. range for CHT), and you have validated your CHT reporting all the way through ( i.e. the instrument reporting, IS reporting accurately ) then you have the basis for good engine management. Get THAT part right, and the EGT reporting is a supplementary 'check' factor about instant engine performance condition - but EGT reporting on any engine other than a certificated engine running certificated installation and TSO'd probes and instruments, is no more than 'indicative'.

 

 

[Xavier]

Apology if the link has been posted before: EGT Myths Debunked

 

- PDF

 

 

[Yenn]

The maion use of EGT is to control mixture, but the added use is as a diagnostic tool. To can find out which plug is misfiring very easily. Run too rich at idle and lycomings will oil a plug. Use the EGT to find which one and it is a quick job to replace and be on your way.

 

 

[Bruce Tuncks]

I take your point Ultralights, there has to be quite a gradient between the combustion temperature and what you measure in the exhaust pipe. I tried hard to make them all 11 cm from the exhaust flange measured along the pipe centerline but the pipes have different bends so they cannot be exactly equal. Jabiru say 10 to 12 cm.

 

Suppose I was to try moving the no4 exhaust probe 2cm further down, so the other 3 were at 11cm and the no4 was at 13cm. What do you think the reading would change by? And don't forget that the rear ( 3 and 4) pipes have similar bends, as do the front (1 and 2).