seb7701

Yep, I just took the pre-fab easy way out!! Lol. Bruce - what can you tell me about the cross vanes in the cobra head? Seen a bit about this to stop the swirling mixture into the diffuser. Did it change things much? I am guessing at the moment that there may be a leaner mixture on the left side, but not quite certain.

Bruce - the cooling kit is a nice little item from CAMIT which more or less closes in the gap between tappet covers do direct flow between the cylinders which would otherwise just be wasted.

Here's the link - you can't quite see them completely in my shots.

Cooling Kits

Nice work Oscar! I will be particularly interested to see the results of the plenums depicted in the last piccie. I am fascinated by the effects of oil cooler 'exhaust' on the happenings inside the lower cowl, so your duct makes some sense. I did see a similar setup on a U.S website, so must be something in it.

In the mean time, given that I have been cruising around this afternoon with 108/120 on the right bank of my engine, I would say that success hopefully won't require me renting the NASA wind tunnel just yet, but we'll see... If that is what is achievable with my fairly standard setup, there is scope for success yet.

After I check pressure differentials, I would say it might be time to enlarge the left intake yet again, as my mod, whilst effective, seems modest compared to some I've seen, so should leave some room to stuff some more air in there! The results from the right cylinders indicates that the cowl lip is working just fine, so if I can get it in there, I reckon it'll come out!

Some more shots from this arvo- the only thing I didn't mention, is that I added CAMIT 'cooling plates' to the sides of the cylinders. They just make sense.

O.K. - sounds like you have achieved nirvana with your temps! If you have an pics, I would be curious, particularly if the top of the engine is totally clear!

Thanks Bruce - likewise, your temps are looking really quite good to me with no.4 not being overly outlandish. Bruce - I have read about the cross pieces in the cobra head. Did that actually lower some temps for you?

Just went for a lap since that last post and found no. 1 really probably too cold to be flying. With a little defending here and there (power left on as best I could...), it was actually in the 80's and 90's at times!!

The temps quoted are straight and level @ 2900.

Please don't judge me on duct tape, as the fence was strictly trial only and now to be permanent! It is possible to go too big, as I also trialled a bigger fence which covered the triangular outline of the head and instead it added about 11 degrees to no 2, but did drop the rear cylinder by 10 degrees to 140. (These figures are around 20 degrees ambient BTW)

Just trying to find some other pics, but you may be able to gauge somewhat how much the intake has been opened. (I only have a 'before' pic of the left side I'm afraid...)

Well, here's an update following a few different strategies: simply opening up the intakes did do wonders - it dropped around 10 degrees off things and adding about a 1 inch 'fence' on the base of the duct directly in front of No. 2 dropped it a further 10ish degrees also! At this stage, 2 & 4 are my warm cylinders, whilst 1 & 3 are bordering on too cold (has this ever happened in a Jab?????)

On the last run, at 20 degrees celsius ambient (ground temp), cruise temps @ 2900 were as follows:

CHT's.............EGT's

No 1 -108....... No 1- 664

No 2-155.........No 2- 713

No 3-120.........No 3- 602

No 4-150.........No 4- 656

Has anyone had experience with the left side being substantially higher than the right? From a duct perspective, both sides are almost identical, so it's got me scratching my head for sure. I am waiting on a Manometer, so will check the pressure differentials, but going on 1 & 3, the cowl outlet situation looks just fine...

I have actually tried the 'carby tilt' technique, with nil effect, so at this stage jetting is my next curiosity. It seems I have older jets, with a 255 main and possibly 276 needle?

From the EGT's, I gather that 2 & 4 may not be getting as much mixture....

Any thoughts??

2200A -solid lifter. Got my base line figures today for cruise, so tomorrow will check what it's like after stuffing more air in...

As far as the exhaust is concerned, I was thinking of trialling a straight through just for a brief test to see the effect, as I note the likes of Sonex etc don't use a muffler with their Jab installations.

Thanks Oscar - love to see what goes for cowls these days and what mods people have down. Quite simply, if the increase in the intake size isn't effective, I will know to go back downstairs to the outlet and perhaps increase lip size etc or add some tab style lips as a trial. So far, anecdotal evidence indicates that intake enlargement is quite successful, so we'll see. The fact is, there are perfectly satisfactory LSA cowled Jab in existence, so I am not of the impression that drastic measures are required, just some tweaking. Next after that though, I am curious to remove that big barrel muffler from behind the trusty oil cooler, as I imagine it could be creating all sorts of complexities in terms of air output from the cooler striking it, as well as the radiated heat.

This shows exactly what I have in mind. There appears to be quite a few people I know of locally who have success to the amount of 10-22 odd degrees reduction.

No probs Oscar - always fascinating to hear this stuff. Good point re the MGL, as it does actually appear to be reading similar to the last one, which is simply ambient...

You mentioned something I wondered, and that was to overlap the firewall with the cowl extending past it, as I have seen often before a few times. In all, I think opening the intakes is on the cards, along with making sure that the low pressure area underneath is sufficient to do justice to the intake.

Ha! Thanks Danny - might be the go!!

Thanks again Bob - CHT's are measure from hole drilled between plugs. Yep, 170 is too hot, but bear in mind engine is about 45mins old with completely new top end, so needs to settle a little before I get too carried away. That said, 2 & 4 need cooling! Ahhh, laser thermometer - bloody good idea!!! New air cleaner done, using AVGAS, but have to check jetting. Saw 16l/h on flow meter at around 2850ish on downwind, but really only glimpsed, so have to go give it a good run and see what's really happening!!

Very early days into the testing, but cruise (not much more than downwind leg so far...) are mid 150's, but max values recorded are in the pic. Note - no 3 CHT not working... Buggered if I know why 2&4 are so much warmer, albeit nicely simiar!

Thanks for the insight Oscar- yep, your friend did what I dream of...oh for a wind tunnel and the knowledge to use it!!! Given your points above, what are your thoughts on adding an inch or two to the lip (pictured above), perhaps at a less acute angle and opening the front intakes by lowering the bottom edge by around another inch, to match the duct openings? Seems to be a few success stories from such a tactic.

Here's the lip - I think it needs increasing...maybe angled further backwards now?

There aren't any fences at the front of the heads, as these earlier ducts only extend down as far as halfway anyway, but thinking I might install some 2cm x 2cm angle pieces there anyway to send the air over the top of the fins/barrels??

Thanks Bob. I had a lip glassed on the lower cowl whilst up at the Jab factory, but I am thinking I'd like another inch or so on it!

Always a bugger to hear when someone's had a fender bender, but in honesty, more pleasing to hear that the plane was the only casualty and that the trusty x-air can be patched up in no time thanks to a few brackets, bits and pieces! At the end of the day, these minor slip-ups happen and you're wiser for it!

Hi all.

Just in the process of playing with the cooling on my newly re-vamped Jab and was wondering how many owners are using the original LSA style top cowl with the smaller front intakes, as well as the earlier plenum chambers / ram air ducts with the plug leads running externally?

While I have every intention to open up the front end a little more to match the ducts, I am wondering whether they can do the trick or not, given that I've read a few articles which suggest that they just won't cut the mustard.

Apologies in that I know Jab cooling has been done to death, but doesn't seem to be much on the old vs new ducts/cowls and I'm very curious to know who has the early stuff and if so, what was their keys to success!!

Cheers, Seb

Bloody ripper! Glad you've put Mellow Yellow to good use already- perfect for that stuff!!

Went up Thu night and brought it back Fri!! Hope to have wings back on by next week!

Well done - didn't think it would take you long!!!

Truly terrible to hear - such a wonderful pioneer in Australian rec flying and a definite character by all accounts. RIP.

Thanks OME - it's no wonder I now stay away from this forum these days...people now cruise forums looking for a barney?? Bloody hell...

In truth, you didn't actually tell him who is technically responsible for paying for a UACR or how to find a L2, so I guess it's a 'no'. No malice was ever intended for what it's worth...

Hi Oz. To answer the actual questions:

1. Buyer arranged the UACR.

2. Cost should be very reasonable

3. RAA did have lists of L2's available online - haven't looked lately though.

It's fine to have the seller arrange a L2, but not all L2's are created equal, so a perhaps a call or email to RAA tech manager may put you in touch with a good one at the location you need!

Yep, sure do. Very STOL too!

Yenn - there is RecFly at Roma also in Sth Western Qld.

Wasn't sure that there were any in Oz?