Greg in Oz

On many discussion forums we have have read of the "free horsepower upgrade" available to those with M102 and M103 motors by way of removing or changing the value of the R16 ignition reference resistor. Many who perform this simple modification (generally removing R16) claim great results using the "seat-of-the-pants meter". It is amazing what we can make ourselves believe if we want to. Well, I have got some bad news for those who have simply removed R16. Read on.

It is generally accepted that maximum power and fuel economy will result from using the maximum amount of ignition advance possible without causing pre-ignition (knocking or pinging) for a fuel of given octane rating. The EZL ignition modules fitted to the M102 (1.8, 2.0 & 2.3) and M103 (2.6 and 3.0) motors follow different advance curves dependant upon a programming resistor known as the R16 reference resistor. Most threads suggest that a higher value resistor results in more advanced ignition timing and thereby deduce that removing the resistor completely will give maximum ignition advance. NOT TRUE. A higher value resistor can give more advance up to a point but an open circuit (resistor removed) is read as a fault condition and sets the most retarded ignition curve. Many falsely believe that R16 can just be a variable resitance that will dial up whatever ignition advance you wish. This is not the case. The ignition module has a finite number of ignition advance curves or maps that are selected by certain fixed resistor values (0, 220, 470, 750, 1300, 2400 ohms).

As an owner of both M102 and M103 powered cars I decided to test the effect of different values of R16. As a temporary arrangement, I removed the plug containing R16 and removed the resistor (220 ohms in my 300TE and 470 ohms in my 190E). I then connected a 2-core cable to the plug of sufficient length to reach into the cabin of the car where I had a box containing a rotary switch with all the above listed resistor values as well as an open circuit position. I then test drove each car (with 98 RON fuel) and noted the effect of different resistor values. Most obvious was how little effect different resistor values had. Only at higher engine speeds at full throttle on long hills was any change noticeable at all and only then by repeatedly switching from one resistor to another. How anyone could notice a change after stopping the car, getting out and removing or changing the resistor, getting back in and driving further, escapes me. Also interesting was that the best performance was not necessarily obtained at the highest resistance setting and certainly not when open circuited.

I then decided to verify my findings with a timing light. As suspected, greatest change occured at higher speeds (> 3000 rpm) and high load (simulated with vacuum hose disconnected from ignition module). R16 has no effect on ignition timing at idle. As also suspected, an open circuit R16 gave the same minimal advance as a short circuit. At the intermediate values different amounts of advance occured and this was dependant upon which motor. For my M103 six, 750 ohms actually gave the greatest advance. In my M102 four, 1300 and 2400 ohms both gave the same result so I went with 1300 ohms. The original lower values were presumably to suit our low octane (92 RON) regular unleaded fuel here in Australia. We also have 95 RON premium unleaded and more recently some suppliers have changed their premium to 98 RON (which I now generally use). In the 300TE (which we use for long journeys) I have fitted the R16 plug with a small switch which is normally set to the 750 ohm position (for premium fuel) with a 220 ohm position available for the situation where only regular fuel may be available (eg. when travelling in country areas).

My reason for posting this is to alert those who are contemplating or have performed this modification to take a measured approach with their car. Ideally a dynanometer would give the most valid readings but at the very least a timing light should be utilised. Without such equipment to verify the effect of any change of the value of R16, I would leave it untouched. I would certainly advise against removing it unless you can measure results different to those obtained with my cars. Possibly, different results may occur with different models delivered in different markets. It comes back to not modifying something unless you fully understand the implications of doing so.

E-Klasse

How are you increasing the compression ratio of your 190Es engine to take advantage of the advance in timing and the higher octane fuel. It sounds like one can adjust the timing to use higher octane fuel and then put the more expensive fuel in the tank but where is the power gain? Your engine compression is still the same.

Greg in Oz

I am not altering the compression ratio, only the ignition timing. Generally speaking, optimum engine performance (power and economy) is achieved with near to the maximum amount of ignition timing advance that can be used without pre-ignition (pinging, pinking or knocking). It is for this reason that newer cars use "knock sensors" to cause the timing to be constantly run as advanced as possible and to retard it slightly when knocking is detected. Higher octane fuels will allow greater advance before knocking occurs. Assuming you have such a system, or one like I describe for the M102 and M103, greater engine efficiency can be realised with greater ignition advance and higher octane fuel. Higher octane fuel can allow for higher compression ratios as you suggest, and for greater ignition advance which is what I am describing.

mbr129

Interesting that this was just posted. I did remove the R16 on my 1990 190E 2.6 and I felt not so much power, but better throttle response. Maybe it was just me. But I had no adverse effects. A few months later (a couple of weeks ago), I filled up with 93 (as I alwasy do) and 8 miles later, whenever I took my foot off the brake to hit the gas after a full stop, the revs would dip before the car started going. It almost felt like it was about to stall. It did this for the next 6 miles until I got home whenever I went for the gas after a full stop.

I also felt a slight knocking. I immediatelly reconnected the R16 and reset the battery. The car feels great again, and much smoother. Also, for a couple of months, my check engine light was on. I had tried resetign the battery, but after a few miles it would go back on. After reconnecting the R16, the light hasn't come back on. It has been a couple f weeks and several hundred miles.

Even if there is some gain, in retrospect it is not worth the problems.

E-Klasse

I still think that you are fooling yourself that there is more power without an increase in the compression. All you are doing is adjusting a car that runs on cheep gas to run the same on the expensive gas.

Greg in Oz

Then why do the Euro spec cars with M102 and M103 engines have a selector plug that allows easy adjustment of the ignition timing dependant upon the available fuel?

My original post was questioning whether open circuit or high values of R16 are valid, not whether or not greater ignition advance used with higher octane fuel will result in better engine efficiency, this has generally always been accepted.

E-Klasse

Nothing has been generally accepted. Euro cars have the adjustment because the grades of fuel are different depending upon availability. Otherwise they would just leave it set for high octane if it was such a benefit.

mbr129

That makes little sense. If there was no difference, MB would set it for the lowest grade fuel. Why allow to switch it for a higher octane? For the pleasure of spending more in gas in a land where gas is already ridiculously expensive? That makes no sense. There MUST be an improvment.

jff2k

There is a sense: In Germany you have several unleaded fuel sorts:
91 octane - Normalbenzin
95 octane - Superbenzin
98 octane - Super Plus
100 octance - e.g. Shell V-Power

For every used fuel you can adjust the ignition in seven steps, from 7 to 1! --- 7 for worst fuel quality, below 91 octane.

6 is for 91 octance fuel (N for Normalbenzin)
4 is for 95 octance fuel (S for Superbenzin)

maybe it's possible to drive with 100 octance V-power and adjust it to 2 or 1? And yes, if you drive with 91 octance fuel (Setup N) your car is slower, with 98 octane (Setup S) it's faster! But it is noted in the owners manual: "While driving with unleaded normal fuel (91 octane) the adjustment has to be N (Danger of motor damages)"

So if you remove your R16 plug, do only use high quality fuel! Because it is set to setting 1 then!!!

I've attached the owners manual page about the adjustment of the ignition timing.

E-Klasse

The facts on High Octane Gasoline
Do you buy a high octane gasoline for your car because you want to improve its performance? If so, you should note: the recommended gasoline for most cars is regular octane. In fact, in most cases, using a higher octane gasoline than your owner’s manual recommends offers absolutely no benefit. It won’t make your car perform better, go faster, get better mileage or run cleaner. Your best bet: listen to your owner’s manual.
The only time you might need to switch to a higher octane level is if your car engine knocks when you use the recommended fuel. This happens to a small percentage of cars. If it was designed for regular gas, but knocks, often that means you need a tune up.

Unless your engine is knocking, buying higher octane gasoline is a waste of money, too. Premium gas costs 15 to 20 cents per gallon more than regular. That can add up to $100 or more a year in extra costs. Studies indicate that altogether, drivers may be spending hundreds of millions of dollars each year for higher octane gas than they need.

What are octane ratings?
Octane ratings measure a gasoline’s ability to resist engine knock, a rattling or pinging sound that results from premature ignition of the compressed fuel-air mixture in one or more cylinders. Most gas stations offer three octane grades: regular (usually 87 octane), mid-grade (usually 89 octane) and premium (usually 92 or 93). The ratings must be posted on bright yellow stickers on each gasoline pump.

How is octane rating determined?
Gasoline is subjected to two testing methods to establish its octane rating: one, called the motor method, runs the gasoline in an engine under load; and a second, the research method, runs the gasoline in a free running engine. The research method gives slightly higher ratings, and the octane number displayed on the pumps is an average of the two methods.

What’s the right octane level for your car?
Check your owner’s manual to determine the right octane level for your car. Regular octane is recommended for most cars. However, some cars with high compression engines, like sports cars, old cars and certain luxury cars, need mid-grade or premium gasoline to prevent knock.

How can you tell if you’re using the right octane level?
Listen to your car’s engine. If it doesn’t knock when you use the recommended octane, you’re using the right grade of gasoline. Knock occurs when cylinder pressures are high. It is normal for an engine to ping a little at full throttle because cylinder pressures are very high at full throttle. Engine knock, however, should not be ignored since it can result in serious damage to the engine. High octane gasoline burns slower than low octane gasoline. The slow burn prevents engine knock when cylinder pressures are high.

If your engine runs well and does not knock or ping on low octane gasoline, there is no advantage in switching to higher octane gasoline.

If your engine knocks or pings, it does not necessarily mean something is wrong with the gasoline. It could be a problem with the car's ignition timing or exhaust gas recirculation. On high mileage engines, a carbon build-up in the cylinders can increase cylinder pressures and cause knock.

Will higher octane gasoline clean your engine better?
As a rule, high octane gasoline does not outperform regular octane in preventing engine deposits from forming, in removing them, or in cleaning your car’s engine. In fact, the U.S. Environmental Protection Agency requires that all octane grades of all brands of gasoline contain engine cleaning detergent additives to protect against the build-up of harmful levels of engine deposits during the expected life of your car.
Should you ever switch to a higher octane gasoline?
A few car engines may knock or ping - even if you use the recommended octane. If this happens, try switching to the next higher octane grade. In many cases, switching to the mid-grade or premium-grade gasoline will eliminate the knock. If the knocking or pinging continues after one or two fill-ups, you may need a tune-up or some other repair. After that work is done, go back to the lowest octane grade at which your engine runs without knocking.

Does high octane gasoline improve mileage?
In general, if your car is designed to run on 87 octane gasoline, high octane gasoline will not improve mileage. If switching to high octane gasoline does improve mileage, you might find that a tune-up will give you the same improvement on 87 octane gasoline.

Does high octane gasoline achieve quicker starting?
No, it doesn't.

Does high octane gasoline increase power?
If your car is designed to run on 87 octane gasoline, you shouldn't notice any more power on high octane gasoline. Again, if it does make a noticeable difference, you may need a tune-up.

Is high octane gasoline more refined -- is it just a better product?
Additional refining steps are used to increase the octane; however, these additional steps do not make the gasoline any cleaner or better. They just yield a different blend of hydrocarbons that burn more slowly. The additional steps also increase the price.

The facts on High Octane Gasoline

Contrary to what the gasoline companies advertise, engines never need to change octane. If a new engine is happy with 87 and at 40,000 miles starting pinging, that means is time for some maintenance, not higher octane. Many european cars and bikes need higher octane because of their better fuels. The US has the "worst" fuel in the world. Germany starts the fuel grades at 96 octane, the their engines are designed to need it. Now, many foreign manufacturers "de-tune" their engines to run on our 87 octane gas. If your engine needed 89 or 92 octane new, then that is what you must run. If it didn't need 92 new, and does now, look for a problem.

mctwin2kman

BEfore you go on about how ignition timing works on cars you should educate yourself on how they actually work.

http://auto.howstuffworks.com/ignition-system.htm

Advancing engine timing actually can increase power at higher RPM's. Compression and timing are two sperate things. The higher the engine revs the faster the piston is moving, therefore the spark can occur to late, so advancing the timing can cause the spark to occur at the proper time at higher engine RPM's thus giving you more power at higher RPM's. Just go look at the advances of changing the valve timing on modern engines, hence the VTEC and i-VTEC engines from Honda, this is just another way to get more air/fuel in the cylender at higher RPM's, now the old engines such as the ones we are disussing here can only advance timing to get gains at top end RPM, but you will have less power at lower RPM's due to the spark plug firing way to early, so you must find a happy medium.

jff2k

@E-Klasse, I'd like to translate you another paragraph of the German owner's manual:

Do you think this is written just for fun? As the 190E was made, the best available fuel was 95 octane... So how could there be a better value in the owners manual?

The engines are the same in the USA and Germany... Because in the US the fuel is so poor in quality, Mercedes-Benz removed the above shown adjustment of ignition timing and inserted an constant ignition setting (based on the poor fuel!). So if you change your ignition timing, the engine runs faster, with fuel not made for this fast ignition timings! If you don't believe it, contact your Mercedes-Benz technican.


Oh, and another reason, because Shell introduced the 100 octane fuel (V-Power) here in Germany there have been many tests, because Shell promises to rise the engine power by 10%. The test made by various car magazines, TÜV and the ADAC showed a rise in power by 6 percent average versus 95 octane fuel...!

E-Klasse

Octain rating is a measurment of how fast the fuel will burn.

Note: fuel can be ingnited by heat"spark" and pressure"compression"

It's a balance game, a motor built for a low octain fuel has a lower compression ratio and will develope less horse power because of it.

If the compression is raised when the spark plug fires the initial burn pressure will cause all the fuel to burn all at once "like a diesel motor" and that is that ping noise you here on acceleration.

Because the fuel burns all at once you will experience a power loss "The ideal burn will happen for the entire stroke of the pistion". So to keep it form burning all at once they raise the octain of the fuel "that makes it less volitable so it takes more pressure for it to ignite"

There are other variables that apply also. Motor Timing is one, you can retard the timing thus causing the burn to begin at a lower compression ratio "when the piston is on it's way down already" but this will cause a loss of power so it's a trade off.

Euro spec. cars have higher compression ratios than US spec. cars do. This is because the available octane level is higher in Europe.

You can't get higher Horse Power unless you raise the compression ratio.

Using too high an octane can cause carbon build up.
If your car isn't designed for high octane fuel, the lower compression, and slower burn, can increased carbon and actually make your car run worse in the long run.

Doing your engine a "favor" by using the premium fuel may make it run worse.

Those with engines that "ping" or "run on" (diesel), and have been using premium where regular is called for, may already have carbon build up.

The European version of the 190e 2.3-16 ran a 10.5:1 compression, versus 9.7:1 for the US version. European versions also had a higher redline (7200 rpm vs 6800 for the US) from a different fuel pump cut off relay, and also had a lower ratio rear axle which gave higher top speed. The Euro version achieves 185hp with the same displacement by using cams with higher lifting (longer duration) and also uses an euro exhaust. This exhaust looks the same as the US version, but is more free flowing.

Higher compression needs Higher Octane and that is what creates more horse power.

Running high octane in a regular 8:1 engine is nothing but a waste of money, but high octane in an 11:1 engine, is necessary to extract the maximum horsepower.

jff2k

Oh I see. Sorry, didn't know that the compression ratio is different in US models... If it would be the same, the car will have more power by adjusting the ignition timing.
So simply get a euro spec engine...

Greg in Oz

E-Klasse,

I accept the point you are making. I would be the first to agree that there is no benefit in using higher octane fuel unless the engine was designed for it. But that IS the point here. Most MB engines were (and are) designed for higher octane fuel than the regular stuff we get in Australia (and you get in the USA). As the owner's manual states, operating with low octane fuel in position N (the equivalent of a low value R16) should only be considered a temporary situation. Unfortunately, Aus deliveries came without the R16 selector and only a simple plug with a resistor equivalent to position N. I am prepared to run premium fuel (that the car WAS designed for) with R16 changed to the equivalent of position S and benefit from the improved engine efficiency it brings.

The more modern engines do the same with knock sensors. They operate with the maximum posible ignition advance up to the point where knocking occurs. This allows for maximum efficiency. If an owner chooses to operate with lower octane fuel than for what it was designed, the ECU retards the timing to the point where knocking does not occur and the owner suffers the loss of efficiency that results.

E-Klasse

Very well put Greg. So many people here in the USA are not paying attention to their compression ratio when chosing their fuel.

mctwin2kman

Yes, but we are not talking about just putting better gas in the vehicle we are also talking of changing the ignition timing. So as stated this could increase power, until there is a dyno done though we will not really know. But by changing the timing we could increase power, but we could also lose power at lower RPM's so there is a trade off in this.

E-Klasse

You are not going to get any more power out than what the engine was designed for.

Instead of going over this again, just read the posts above again.

There is no point in changing the timing to run higher octane fuel in a low compression engine

You must like giving your money to the gas stations.

mctwin2kman

I wish I could run less octane in mine but I can not or I lose power. As for the engine design, I doubt that MB designs two diferent versions of the same engine, and as stated the European model has a higher compression ratio than the US version. This is most likely accomplished by retarding the timing to adjust for lesser fuel's that were common in the US at the time. So by advancing the timing to European spec and then running the better gas, that should make up for it somewhat. The compression ratio can easily be change with a new head or by changing the valve timing, but this is just ignition advance, and I am no mechanical engineer so I have no idea if an advance of timing causing the fuel/air mixture to iginite earlier would increase compression, but it will give you an earlier combustion causing the piston to go down sooner and therefore increasing power as the combustion cycle could be closer to perfect at that point in the RPM range. Remember that on a vehicle with a cap and rotor that timing can be off causing you to lose power due to late combustion. And of course timing is everything in this case. So maybe you are not truly gaining horsepower but more of bring the power back to its intended level due to age and of course the cap and rotor no longer being in the ideal position.

E-Klasse

Compression is determined by the distance from the top of the piston at Top Dead Center to the underside of the part of the head or button that forms the combustion chamber. More commonly refered to as head clearance.

This clearance can be altered to increase compression. Euro spec engines are different because of the quality of the fuel is much better over there. They can have different pistons, harder crank shafts, and smaller head clearance than the same US spec engine.

Changing the timing does not increase compression. You would have to rebuild your engine to Euro spec.

The US engine spec changes the components so that compression is lower so that it can run on the poor quality gas. The Euro manual says that their engines are designed to run 95 octane. The US engines are designed to run 87. The engines are different. This limitation is why the horse power specs are always higher on the Euro cars. The fuel grade and timing are secondary changes caused by the difference in compression.

Read this question from HOW STUFF WORKS:

"I would like to increase the horsepower of my car's engine. What's the best way to do this?"

http://www.howstuffworks.com/question395.htm

Increase the compression ratio - Higher compression ratios produce more power, up to a point. The more you compress the air/fuel mixture, however, the more likely it is to spontaneously burst into flame (prior to the spark plug igniting it). Higher octane gasolines prevent this sort of early combustion. That is why high-performance cars generally need high octane gasoline - their engines are using higher compression ratios to get more power.

jff2k

Compression ratio:
190E 1,8: 9,0:1, for US market: 8,0:1
190E 2,0: 9,1:1, for US market: 8,0:1
190E 2,3: 9,1:1, for US market: 8,0:1
190E 2,3-16: 10,5:1, with catalytic converter: 9,7:1 (same in the US)
190E 2,5-16/EVOI/EVOII: 9,7:1 (same in the US)
190E 2,6: 9,1:1 (same in the US)
190E 3,2 AMG: 9,1:1 (same in the US)

i don't know, wether the compression ratio has been different in the USA the whole production period or has been raised in the late 80s... If some one has got more/other information, please post them.

E-Klasse

This would be true for your 2003 Pewter C230K but not a stock US spec 2.3L 190E.

mctwin2kman

Thank you sir. I know think I learned something today. Anyway, yes I know my valve timing would adjust as well as the timing to compensate for the lesser fuel and stop pinging and knocking. I am looking for a mid 80's 190E 2.3 for a play around vehicle and to drive while my wife has my C230 which is everyday but Friday. SO I hang in this forum to learn some stuff on the 190E's. So thank you for your input E-Klasse

jff2k

Dear E-Klasse,
I'd like to correct what you've written: Your example with the 190E 2,3-16 was wrong. The 10.5:1 compression has been used in all cars without catalytic converter! All 2.3-16 with cat have 9.7:1, also in Europe. But of course you are right with the 1.8 liter up to the normal 2.3 liter M102 engine (according to my information 3 posts above).

Have a nice day.

E-Klasse

Thanks for your input. The information I posted that you quoted were specs from another Mercedes web page and it must have been references to cars without a cat in the exhaust.

I am not trying to pick apart one spec from another. The only point I was making is that power doesn't come from the octane rating of the fuel. Power comes from compression and that is the determining factor for what fuel grade to use and what the timing needs to be set at.