Fuel ratios, Timing, and octane (a diary for a healthier engine)

[Dirk]

Before I start on this I should point out a couple of things.

 

1. Everything I am about to write is based on much research a little experience and what has worked for me. I have read through many articles about this subject and used many sources to form MY OWN understanding. If it is incorect then I welcome constructive critisism and ideas.

 

2. Disconecting or tampering with emissions devices may not be legal in some parts or may lead to failure of emissions inspections where you may live. It would be prudent to find out before making the following modifications.

 

3. Even if there are no legal emissions requirements in your area you may wish to consider the environmental implications of removing the following.

 

4. Sorry about the spelling.

 

And so...

 

Uleaded fuel became mainstream in most countries in the mid 80s. Therefore we can assume that cars made before this time were designed to run on leaded fuel.

 

EDIT:

 

This is a big assumption and not neccessarily correct depending on where your car was born. However it has been bought to my attention that any car with a factory CAT would have been designed for unleaded fuel.

 

That said, it would appear that the quality of fuel has changed somewhat over the last 30 years and therefore some aditional tuning may still be to the advantage of older soobs regardless of what fuel it was designed for at the time.

 

END EDIT.

 

Leaded fuel had an octane rating of about 100 RON. Todays pump gas has a maximum of about 96 RON.

 

NOTE: High Octane fuel DOES NOT GIVE MORE POWER!!!!!

 

Infact todays high octane fuel has less btu's than lower octane fuel.

 

However, High octane fuel is more stable and burns slower and more fully. This is the bit we are interested in if we are to have a happy little engine that does not knock or ping.

 

High performance engines require higher octane fuels because the engine compressions and temperatures are so high that lower octane fuels will spotaneously combust before time.

 

The EA engines are not performance engines but they do have a relatively high compression ratio and as I have already pointed out they where designed at the time of higher octane pummp gas.

 

EDIT: Disregard last sentence.

 

END EDIT

 

Also there are other factors to consider with an older engine. Mine has been re-built a couple of times and the heads were skimmed on each occasion. Therefore the compression ratio has been further increased.

 

If your engine has never been re-built then it is likely that carbon deposits in the compression chambers have naturally increased the compression ratio. These carbon deposits can also invite hot spots that can lead to pre igition.

 

EDIT:

 

Also, general wear and tear over the years will have taken its toll on some of the hardware. The carb may be leaking air causing a lean out. Jets may also be glazed causing lean out.

 

Aged distributors wil not help our cause either.

 

END EDIT

 

 

SO WHAT CAN WE DO TO HELP?

 

1. Using the highest octane fuel available is a good start.

 

2. Adjsuting the timing accordingly will aslo help.

 

3. Add more fuel

 

TIMING.

 

EDIT:

 

8 degrees is a good place to start but 'optimum' base timing is going to vary from engine to engine. Also it would appear that Timing marks on the flywheel are a guide at best. They are not necessarily bang on.

 

END EDIT

 

The following is in my opinion the most reliable way of achieving optimum base timing.

 

Hook up a vacuum gauge to the inlet manifold and run the engine up to operating temperature. If you don't have a vacuum gauge I strongly reccomend getting one. Mine cost me all of 10 dollars and has taught me a lot about my engine.

 

wind down the rpm as much as you can and then start to advance the timing and watch the vacuum increase untill it will go no higher.

 

This is the point at which your base timing would have been optimal for leaded fuel.

 

Now retard the timing by one inch of vacuum.

 

This should set base timing to allow for todays premium pump gas.

 

Now, go for a drive and see and hear how it runs. You may have to retard 1/2 or one further inch of vacuum.

 

 

MORE FUEL.

 

Having adjusted the timing it woulod be a good idea to keep an eye on the spark plugs.

 

If at this point they are uber white I would reccomend increasing jet sizes in the carb to richen things up a bit.

 

This will reduce the combustion temperatures which will help reduce pinging and may also afford you a little more power.

 

It may be interesting to note that pinging is more likely to occur at stoich fuel ratios and also that petrol egines produce maximum power with 10% rich fuel ratios. Therefore you have nothing to lose by doing this.

 

DISCONECT VACUUM ADVANCE...........

 

Having done all the above to my EA71 had a happy smooth running engine with pots of power through the rev range.

 

And yet I was still haunted by slight pinging under light load at low rpm. I desperation I dissconected the vacuum advane and.......VOILA!

 

No more pinging AT ALL.

 

So what is it that I have done? and what does the vac advance do?

 

Well, it would appear that under light throttle the vac advance was advancing just too much for the engine to cope.

 

The mechanical advance in the distributor takes care of the advance timing requirement through the rev range.

 

Vac advance is connected via a port on the carb.

 

This means that at idle the vac advance is not active and nor is it at wide open throttle when there is little no vacuum present.

 

The vac advance is most active when cruising under light load and partial throttle. Its job is to ensure a fuller burn thus reducing emissions.

 

Essentially this is all it is. An emissions controll device. Although I am told that it also aids fuel ecconomy.

 

In any case it is obviously has a negative impact on my engine under these circumstances.

 

LASTLY

 

These procedures have worked well for me. Depending on the setup of your own engine they may or may not be of benefit. But I hope at least that it has been an interesting read.

 

I guess that a re-curved distributor would be a more perminant solution however this is finance permitting. Right now finance does not permit!

 

I will keep you updated with notes on fuel ecconomy.

 

Regards

 

Dirk.

Edited July 15, 2011 by Dirk
correction of facts and additional info

[Dirk]

Notes on fuel ratio.

 

I will start with another preface. I have been working on the same engine (EA71) in the same car for the last 4 years. In this time I have taken almost as many steps back as I have forward. But slowly after much reading and even more experimenting the engine is running smoother and with more power with each step forward.

 

What I mean to say here is that I do not believe that even with the most knowledge and equipment at ones desposal is it possible to perfectly tune an engine first time.

 

The concept of making one change at a time is a good one. However one must not forget that this single change will affect many other aspects of the engine that may also need adjusting at this time in order for the change to take effect in the desired way.

 

For example: Making changes to fuel ratio's will not change the base timing of the engine BUT it will affect how the fuel mixture is burned.

 

So.....

 

'Richer' fuel mixtures tend to igite reliably and also more quickly. This means that you are getting one big bang very close to the moment of ignition. This means that you may be able to afford slightly more advanced timing......

 

'Leaner' mixtures can be less reliable and also take longer to burn. This can lead to pinging as flame fronts collide with each other in the combustion chamber. The longer burn time can have the EFFECT of retarded timing.

 

If the mixture is too rich then the combustion chamber and spark plugs can foul up. Dirty plugs will cause eratic igition. Carbon deposits can cause hot spots to pre-igite or ping. Carbon buildup can also increase compression ratio's and compound problems. This is an interesting situation since your spark plugs may be telling you that the engine is runnning rich or too cool but the overheating and pinging is telling you that the engine is running too hot. Care in diagoses is important.

 

 

If the mixture is too lean the combustion chamber temperature will rise and a over hot plug can again cause pre-igition. Sharp edges in the combustion chamber can also heat to the point of pre-igition.

 

Back to timing again.

 

As I have already pointed out, Different fuel ratio's will affect the burn cycle.

 

If you think that your fuel ratio's are about right then you can fine tune the burning cycle and indeed the colour of your spark plugs by adjusting the timing.

 

Advancing the timing tends to brighten up the plugs a little.

Retarding the timing tends to dull them up.

 

If you have to adjust the timing well beyond its perameters then it is likely that your fuel ratio's are incorect.

 

The reverse of this procedure can also be adopted.

 

If you are happy with the base timing of the engine then you can fine tune the fuel ratio's to suit.

[Dirk]

Carb tuning.

 

This notes are based on Hitachi carbs and assume optimum timing.

 

Idle jet: This can be fine tuned via the idle mixture screw. Consider the screw to be like a shower mixer. Turn the screw too much in either direction and the mixture will be incorrect. ( too hot, too cold/ too lean, too rich)

 

If you are able to turn this screw fully in one direction then it is likely that you have the incorrect idle jet.

 

Fully clockwise means the jet is too big. Or the needle at the end of the screw is worn r damaged

Fully anticlockwise means the jet is too small.

 

The idle jet is just that. It has a small influence at part throttle but less and less as you open the throttle more. It can NOT be used to compensate for incorrect main jets.

 

more to come...............

[NoahDL88]

I hate to poo poo your advise on running the highest octane available, but the EA-81 was designed to run on plane old 87, it runs great on it, and will get the most power out of it, provided the engine is stock.

 

Leaded gasoline was starting to get phased out in 75, when manufacturers started putting in cat converters, it made the new cars unable to use leaded gasoline. Your theory that any Subaru, EA series or newer was designed to run on leaded or higher octane fuel is incorrect.

 

If you're old enough to remember, the leaded and unleaded filler nozzles at gas pumps were a different size, so you couldn't fill your unleaded car with leaded gas.

 

As far as adding more fuel, the bottleneck with any I.C.E. is airflow, liquid fuel is easier to pump, and takes up much less room than the air it's mixing with. For emissions 14.7:1 is the best bet to burn all your fuel and not have any leftover emissions, however with carbs it is true that you want to run a little bit rich, 13.2-13.5:1. But it is a fallacy that adding more fuel and timing will increase your power if your airflow remains the same.

 

Timing is of course set conservatively from the factory, but how much is a matter of debate, and leaving your EA-81 at 8 deg BTDC is not a bad idea, atmospheric pressure, temperature and humidity can all vary day to day and what timing was on the ragged edge of detonation one day can easily pole vault right into broken piston land without so much as stopping to get its passport stamped.

 

These are of course my own opinions, based on my experience, what information I could glean from the internet, as well as from my automotive engineering degree. ETA, This would be more pertinent to those of us in the USA, I don't know when NZ made the switch to unleaded.

Edited July 12, 2011 by NoahDL88
Hey, you're from NZ, that kinda changes things.

[Dirk]

Hey Noah,

 

Thanks for the feedback.

 

Indeed New Zealand was a late starter with unleaded fuel. The reduction of lead in fuel started in the early eighties. Leaded fuel was only made ilegal to sell in this country in Sept 1996!

 

However I still think that my comments are relevant to US engines produced before 1980. This would more or less exclude the EA81 but still include EA71s and earlier.

 

Do you think this is fair?

 

I chose the vacuum method of timing since it has been most useful to me. Particularly since my timing marks are incorrect. Are you suggesting that this may be too advanced for the engine to be reliable?

[NoahDL88]

Unless you can confirm your timing with a light, I wouldn't know how far advanced you are.

 

Like I said though, any car with cat converters, or the smaller fill hole for the gas tank was not designed to run on leaded fuel, so any speculation to that effect is really irrelevant.

[Dirk]

Unless you can confirm your timing with a light, I wouldn't know how far advanced you are.

 

I understand. But what do think of the Vac method for setting base timing?

[Dirk]

Like I said though, any car with cat converters, or the smaller fill hole for the gas tank was not designed to run on leaded fuel, so any speculation to that effect is really irrelevant.

 

My car never had a CAT nor does it have a smaller filler.

 

But what I am trying to achieve is a smooth and happy engine. Lower ocatane fuel in my case does not allow for this.

 

I'm sure I am not the only one with a GEN 1 soob that has found this to be the case.

 

And ofcoarse the engine is no longer stock. But then no 30 year old engine is going to be.

[Quidam]

Hi,

 

Concerning fuel these days compared to what was run when your car was new.

 

"4) Fuels have changed. Modern fuels are no longer designed for carbs, but for EFI. It makes a big difference. The most important change I know of is the lowering of the evaporation point. Simply put, fuel now has a lower boiling point than it used to. This results in float bowls drying out and harder starting. It causes accelerator pumps to fail when the fuel and additives and wet/dry cycles destroy the pump cups. It causes vapor locking, overheating and detonation from lean mistures."

 

5) Alcohol. There's a big push to add alcohol to fuels. We all know the reasons that this is happening and, frankly, I'm not going to debate it one way or the other. What I do know is that alcohol changes mixtures in carbureted engines. It takes almost twice as much alcohol as gasoline to produce the same amount of power. That means that to feed your engine, if alcohol is added, it will require more fuel and a richer mixture. You either have to de-tune the engine or re-jet the carb. Sometimes jets, siphon tubes, internal passage sizes, power valves, and more need attention.

 

EFI works differently because these systems look for proper mixtures by sniffing the exhaust and listening for knock and sensing heat. Carbs can't and don't make adjustments like EFI does. In my daily driver, if I use straight non-alcohol regular I can get 20 MPG all day long. If I put the alcohol fuel in the tank this drops down to between 14 and 16 mpg. A 10-20 percent drop in fuel mileage is not uncommon. However, EFI will accommodate this change in fuel quality and simply add more fuel to normalize conditions."

 

I'd have to read that again after sleep. I want the highest vac reading and cranking compression I can get. They go hand in hand. What produces that high cranking compression also produces the strong vac. signal. That draws in the most fuel/air possible.

 

Doug

[Dirk]

Hey Doug,

 

Thanks for the feedback.

 

FYI: My VAC at idle is 20-21 inches. Not sure what my compression ratio is anymore but compression shows about 162 to 165 psi

 

The high-ish vac reading made me wonder if the vac advance was messing with my part throttle too much.

 

Cheers

 

Dirk.

[Quidam]

Hey Dirk,

 

YW. Hope it helps. You figure this all out like you've been doing and tuning with a laptop isn't much difference.

 

The vacuum can you have, the spring isn't tight enough for the compression ratio you're running. Allows to much advance too soon.

 

For now, what you can do is disconnect the vacuum line and plug it. Bump the initial timing to probably 10, 12* or so. Only limit is keep it from dieseling, kick back/hard starting, and ping. That increases the total timing, but the motor will tell you what it wants.

 

You don't even have to use a timing light for that. The recurve on the distributor can be done in the car. Just a matter of having the parts on hand. The most essential is two lighter springs. Adapting an adjustable vacuum advance can would be my choice as well. Makes that setting a snap.

 

Got to go for a while, I'll check back though.

 

Doug

[Dirk]

Further notes:

 

The Vac advance has been somewhat of a distraction. For the moment I will leave it disconected while I continue to tune. I will have to go in search of a heavier diaphram when I am ready to reconect.

 

Setting base timing with a vacuum gauge has been very useful for me. However I am still using my ear to confirm good running.

 

Another indication of good base timing has been how smoothly the engine runs at full rpm. Regardless of timing curves, if my total advance (base timing plus full mechanical advance) has been too much the engine has not been able to achieve full rpm without wanting to rattle itself off of its mounts.

 

At the moment I feel I can hold 5000rpm for a good length of time. I can run up to 6000 with confidence but I would be reluctant to hold that rpm for more than a few seconds. This suggests to me that my total advance is in the right ballpark.

[Dirk]

Jet selection.

 

This has been an ongoing challenge for me. The closer I get to a good jet size, the more subtle the colour changes are on the sparkplugs. Also the longer it takes for the plugs to show their true colours.

 

Soon it will be time to invest in an O2 meter.

 

Cruizing at 100km/h (60mph) on part throttle has allowed me to select the correct primary jet based on plug colour.

 

Power valve and secondary jets have been more difficult to tune. Again monitoring plug colour has been a help. But largely it has been down to the feel and sound of the engine at full throttle.

 

My spark plugs are now maintaining consistant colour throughout all throttle postions and engine loads.

 

Can't be far away. Like I already said, time to get an O2 meter.