Subaru Engine tuning 101

[automan1223]

Subaru ej 22. carb w distributor.

Finally got the new engine on my mount and have run it up. I was thinking it would be a easy setup as I had the same engine on it before. However I now know why the first engine went. Of course its all my fault. I assumed that...... and I got what I deserved.

For starters if you are running any engine on an aircraft or hd setup YOU MUST HAVE... There are no iffs ands or butts..... and this goes for you efi guys too.

A full set of exhaust temp probes. There is no way you can effectively tune an engine without them. they cost 35.00 a piece but are well worth it.

Westach makes a whole bunch of sender units that can be fitted to your exhaust pipes diff thread sizes and probe lengths. They have a good tech sheet that comes with every egt sensor. I am using a 712-4D2K
it is a 1/8 npt male threaded bung with an adjustable depth 2.5" probe and 48" wires. It has a millivolt output from 200 to 1800 degrees with a mv range of 26.03 @ 1200f to 32.90 @ 1500f. at 1400f it should have an output of 30.70 mv. Lockwood and aircraft spruce stock these sensors.

If you do not have them on all cylinders or only 1 or are sharing the output of 2 cylinders.... then you are sooner or later in for it. With the fuel we have now tuning by the spark plug color is out the window. The fuel burns too clean to be depositing anything on a plug to give you reliable readings before you cook the engine. Or you will have to tune the mix so fat that you have a boggy upper end by the time you bring down the hotest cylinder.

You must have egt probes on all the exhaust pipes. A gauge is not needed, just a dvom to read the output. Each sensor comes with a chart so you can set max volts and tune each cylinder.

I have discovered much to my surprise that what I thought was the lower efficency cylinder due to head design requires more fuel than the "higher" flow cylinder. This could be for many reasons and while it is contrary to my automotive education and real world experience I cannot argue with what the sensors say.

What this means is that I was burning up my 2 cylinders on my ej 22 because I had the wrong jetting and only 1 egt probe on the what I thought was the higher (hotter) flowing cyl. The other 2 cylinders run at much higher egt temps and that is why my first engine went away. It is not important which ones, I have photos in time but that you as a pilot and builder understand you have to check it or it will check you.

OTHER CHAOS.

I also learned that the intake manifold was bent and was leaking air on both sides of the manifold. I had to take a flat bar and jig and mill the manifold to get things to sit flat again. This like a dummy I knew months ago but disregarded what my very expensive snap on oscilliscope with vacuum probe was telling me. I sluffed it off as mechanical problems instead of checking the basics. The base of the carburetor was also bent from over torquing by a previous owner. Dumming the flange with silicone is a short term fix. I had to also remove the carb base plate and flat mill. Using a straight edge or putting the carb on the plate minus the gasket will show and bent base/flange. Buyer beware, when you buy used parts check them out before you install them. Do not assume anything. Even "new" parts come with problems more often than not.

On top of all of this the old engine must have had a crack in the heads or block or a sealing problem (headgasket) with the cooling system because with the new smaller radiator I am running cooler with less than half the core / surface area.

I also have to give myself the ultra dummy award. I should have known there was a problem when I saw the upper rubber rad hose pump up instantly with full throttle. I atributed this to new waterpump with a thermostat that had its element pulled out. Funny thing is the engine did not use any coolant under many hours of use. Which of course could still mean that the hd radiator I got (used) may be clogged in the core even though it looks clean when looking in the tank from the top of the cap......

Oil temps are a bit on the high side at 240 but I can hopefully bring that down with a cooler.

So what does this mean for

Carb guys: Most efficent system is to have a dedicated barrel for each cylinder. Set your ignition timing for best rpm when hot and then start to tune.

Sharing a barrel means that you have to tune the mix for the hottest cylinder in order to be safe but you sacrifice the power output on the cooler cylinder by adding too much fuel. In some cases the rpm loss is acceptable however for some of us who want to cull out the best power from our mill it is not acceptable.

I have a 2 carb dual manifold design in my head right now......

EFI guys: Listen up. While efi is more efficient I do not think that it alone can cope with the variances I have seen with flow rates at the top of the rpm band.

(up to 300 degree differences at above 5100 rpm. )

I also dont believe that the injectors are sized differently or the on time via ecm is different for each cylinder. Since subaru only used 1 o2 sensor for each side of the exhaust manifolds on the new gen... and only 1 on the old there is no way subaru has the setup tuned for wot or as efficiently as it could be or in my opinion is as safe for long term durability without at least 1 cylinder going critical with the higher flow exhausts and max rpm's......

Remember this engine is in a car turning low rpms. Only teenage kids looking to impress their girlfriends keep it too the floor for any length of time.

Anyway this post is long and I hope to put a web page together and show and tell with some photos when I have the time, which is short right now.

I have always suspected that while the subaru engine is tough it continues to suffer from tuning ignorance / laziness and while most of these engines do ok they could do better and the ones that have problems within the first 20 hours of wot, well I think you get the idea.

STRATUS engine which is no more ? anybody know what happened to stratus ? claimed 180 hp out of tuned 2.2 which is possible given race gurus are getting 300 hp per (1) liter displacement. Makes me feel small when I cant get half of that on more than 2x the displacement. Money & time....

Learn something new everyday.

Jonathan

[Mike Hook]

Great info Jonathan kep it coming, this is what we need from everyone that has expertice in different areas.

Mike

[mceagle]

Johnathon, just a few small points from your post above.
You stated - "the lower efficency cylinder due to head design requires more fuel than the "higher" flow cylinder".
I have not experienced such a variation in cylinder head design in a 2.2 that it requires individual cylinder mixture consideration. I would not expect that the USA engines would be any different to the Australian engines (barring possible emission considerations). Are you sure that the problem is not in the "home made" manifold?

Also I would not be too concerned about the oil temp running at 240 - sounds OK to me.

[automan1223]

There are 2 maybe 3 different cylinder head designs. All of my heads are 2 port exhaust designs. If you are running a single port exhaust then you might not have as much a variance.

Cylinders 2&3 have a straight shot out of the exhaust. Cylinders 1&4 do not they are routed in the head over and down. This alone will cause pressure differences of a considerable nature. Depending on the exhaust you have you may be able to balance the flow that way. I am running a raf style can exhaust.

Do you have a full (4) egt probes for each exhaust pipe ?

If so which are the hotter cylinders on your engine? and by how much ?

The sub 4 engine redesigned the heads for the ea 81 style and made all the intake and exhaust port symmetrical if I recall. If your you are running fuel injection then you might have less of a variance but you will still have one.

[Aussie_Paul]

I agree Tim. It is rather silly not to use the standard manifold. I am sure that there would have been considerable R&D conducted by Subaru to "get the manifold right". What makes any of us amatures think that we can do any where near as well?

With the Raf manifold and the carb I had quite different plug colours. With the standard manifold and the fuel injection the plugs are all the same colour.

Aussie Paul.

Aussie Paul.

[automan1223]

Well this tells me one thing. The intake flow rate demand based on the exhaust flow is critical but not the only thing that determines fuel mix. I forgot to mention that I am running the hi po cams with a bit more overlap than the stock. I think that alone could excacerbate the differences I am seeing. If the stock efi has a better mix control it has nothing to do with intake design, it is the placement of the fuel injector, close proxmity to the intake valve that contributes to the even flow. The stock efi manifold has tons of room for improvement but is functional. THey also use a unique fuel injector to better atomize the fuel. Than a standard pintle or motec design injector.

Using a carb which is dependant on the intake signals. then you would have to have a more balanced intake design. Either way my point is I am the first to put egt sensors on all 4 cylinders and see what is going on . The subaru heads are very hard and tough. But the exhaust valves are the failure area I have seen more often than not.

[Harry_S.]

Jonathan: I am running my 2.2 with a 350 Holley for over 6 yrs. now with no problems.

I have an EGT on #1 cyl. and it always shows 1200-1300 degrees...gyro shaking. Every time I pulled the plugs, the color was all close together; light chocolate shade. I put in new plugs every 50 hrs. This last time I pulled the plugs, #3 plug was lighter in color than the others. Electrodes on all plugs were clean. One of the hangar rats said, #3 plug was getting more air. I checked the manifold bolts and they were all torqued good.

Do you think a shot of carb cleaner would help? Any thoughts?

[automan1223]

Number 3 should be the more efficient cylinder. along with number 2. The reason being is that the exhaust ports have a straight shot out and all things being equal should have a better exhaust flow. Thus increasing airflow into the cylinder. This is established cook book engine tuning. Why it is reversed on my application I can only think that the intake is not symetrical, which it is not and hi po cam issues along with exhaust. At least it proves the law of chaos. Given enough things in one direction you can change the known outcome, or at least what it should be.

The short answer is starting in January the epa mandated cleaner fuel. The chemistry has changed on the gas and so brands and regional blends will show different burn characteristics. Some will not even show on the plugs. Marine engines running around here have changed plug color reading skills considerably. A local outboard race guy and I had a very interesting discussion today. He confided in me he blew 2 power heads and is now gone fully digital. to monitor all temps. He blames it on the new fuel too.


The other short answer is that over time deposits will form in the venturi of the carb and the internal circuits feeding from the fuel bowl. This WILL cause leaning out of the fuel mix.

I am curious what your jetting is.

It makes sense to me that the number 3 plug is going light as it should be the first plug to show signs along with # 2 on the other side of the engine.

^
2------1
4------3
Prop

If it is just number 3 then I might check for intake manifold leaking Just because the bolts are tight they do not sit symmetricly over the flange. In fact the sohc early heads have the bolts on the outside of the flange by each valve cover the inside of the flange has little clamping force over it due to bolt location or lack thereof.

(DOHC heads reworked the bolt location and it sits on each side of the ports, at least a plus for dohc heads)

DO NOT SILICONE FACTORY SUBARU GASKETS. They have a graphite coating that is like trying to glue teflon or tupperware. Nothing will stick to it for very long, fuel will eventually wash it out. Use any adhesive sparingly (thin film) to hold a gasket in place only. DO NOT RELY on it to seal your steel manifold to your aluminum heads.

A few shots of carb spray on the venturi area and the small air bleed tubes next to the venturi,

should be good maint every 20 hours. Dont drown the engine.

Lastly larry, I would have at least 2 probes to verify you are monitoring the hotter cylinder. I bet you are not. 1 egt is playing roulette. You could make more power if you moved the jetting to the edge of the hottest cylinder. I believe brad king told me his engine runs above 1400F.

Jonathan