Intake length experiment.

[sonex1566]

Good evening guys,
I have just finished changing my Aerovee over to a Jabiru 3300 fitted with an AeroInjector. I've only done two flights so far but wahoo what a difference! I've had to tweak my cooling baffles and have now enlarged the outlet on the lower cowl which hopefully has got everything about right temps wise. The trouble I experienced was the same as quite a few others with my rear two cylinders running lean. Well sometimes my wack doodle ideas actually work....I machined up an intake manifold to extend the intake length by an inch. This was scientifically calculated by how room I had to still be able to get my big hands in there to adjust the injector. Now here is the amazing bit, it actually worked! My theory is that the airflow is different to the Bing which has the butterfly valve directing the airflow. I haven't flown it yet as I'm not entirely sure of the robustness of my test setup. I was too chicken to order a new manifold from Jabiru's in case they asked me why.....so I borrowed one from my club just to have a go with it. There is however one major 'BUT', I had the engine running without the cowls on, the outside temps were in the mid 20's (centigrade) but the aluminium tube was ice cold to touch which is a bit of a worry. So my next crazy idea is to make up an extended manifold copying the original, just longer. Hopefully this will allow the heat from the sump to radiate along it an prevent icing. I'm currently strutting around like a proud rooster at the moment!

[GraemeSmith]

Funnily enough..... I was about to try a similar experiment on my AeroVee where No 3 is consistently lean - though it is a little harder with the manifold sharing with the adjacent cylinder.

[lpaaruule]

Richard,

Do you have any pictures you can share?

[sonex1566]

Hi Paul,
Not at the moment, but think of what the fitting looks like at the front of the Bing carby and the AeroInjector, well I just made a double ended piece of tube 2" long to allow for 1/2" of overlap with the rubber insulator as an experiment. It worked a treat, but like I said I am a bit nervous about it icing up, plus the fact that the injector is now held on by two rubber insulators only which is a little bit dodgy. So version 2.0 will be the same principle as the standard adaptor fitted to the plenum chamber but increasing the distance of the AeroInjector from the plenum chamber by an inch. I reckon that Jabiru make theirs by machining it from a piece of solid using their fancy CNC machines. My machining is based on a Harbour Freight type lathe and Mill and me twirling the knobs in the right direction. I was planning on machining the tube and getting it welded onto a flat piece of plate by someone better at welding aluminium than me. I'll keep you posted, I'm hoping that I am on a winner with this.

[sonex1566]

Hi everyone,
Attached are a couple of pictures of my intake manifold ver 2.0. The good news is that the system works.....but there is always a 'BUT'! Now I've got to get my tuning right. The usual problem of getting the slow speed and high right at the same time. However I am a man on a mission! I tried a #4 needle as an experiment which worked much better, but I can't help being fussy. It cost me almost $100 AUD to land a $7 USD needle in Australia. Which means I'm making my own now! This is where Wes, Peter and the others are on the right track going down the EFI route. However I am a big believer in the KISS principle even if swallowing the Blue Pill kills me (Wes you are a bugger!).


Because of all this tinkering I have decided to inaugurate the International Sonex Golden Cowl Competition. Now a Formula 1 team can change 4 wheels in around 2 seconds.....my time to take my cowls off and back on again is more like 6000 seconds. Game on gentlemen.

[WesRagle]

That's some pretty work Richard. Wish I could do that.

Wes

[GraemeSmith]

So today:

Stock AeroVee 2.1
Stock intake manifold tubes
Stock Aeroinjector.

Left side cylinders always slightly richer (or at least EGTs lower).

I have consistently pushed the inlet tube tight against the red manifold casting and tightened the rubber boot. Both sides - make the same tube tight against the manifold. Both the same - should be good - right?

Did some reading about tuned inlet manifold lengths, shockwaves in the tube caused by inlet valves snapping shut and so forth. Long and short was my "guess-sumption" that lengthening a tube would lean the mixture slightly might not be true. Trial and error required.

So today I experimented with changing the length of the left side inlet and after lengthening it by about 3/4" by pulling the pipe off the manifold casting and securing the position with the rubber boot - I got a mixture that was basically the same as right side across most RPM's. Never seen the 4 EGT's basically all lined up before.

YMMV

[pappas]

So, are you saying that lengthening the manifold gave you cooler EGT's or hotter EGT's? Mine is a turbo and may have no effect but it would be fun to play with it. #3 is always 40-60 degrees hotter than my coolest.

[sonex1566]

Success at last! It's taken me 5 months from when I attacked my old engine mount with an angle grinder but I now have a Jab 3300 gen 3 thatbruns CHT's hovering around the 250 - 280 mark, oil temps running around 165 ish and the best thing is that it will happily idle all day and taxi around without touching the mixture control AND run rich enough from 1/2 to full throttle to easily adjust my mixture to keep my EGT's right. Sounds almost like an impossible dream, right? It only took an extended intake manifold, a homemade mixture needle that I'll call a #4.5 and lastly tweaking the angle of the throttle body a little to the left. The last change was to fix up the #6 EGT which still ran a little lean. Phew!

[karmarepair]

So, are you saying that lengthening the manifold gave you cooler EGT's or hotter EGT's? Mine is a turbo and may have no effect but it would be fun to play with it. #3 is always 40-60 degrees hotter than my coolest.

Turbochargers are really good at chopping up the mixture and homogenizing it. That is not to say that the fuel droplets can't fall out of suspension of the charge flow on the long intakes, but I SUSPECT that something other than poor mixture distribution might account for your hot cylinder.