Noob question, sorry.

I am completely stock and wondering if running this stuff (or a mix) will hurt anything. I noticed it's leaded and was told the only harm it would do is to the catalytic converter. If it's safe, will it give me a noticeable performance increase?

Thanks!

 

It most likely won't do anything for you except screw up your 02s and your cats. Admittedly it might take a little time for that to happen, but without a more aggressive tune to take advantage of the 110 benefits, no point in really running it.

 

Noooooooooooooo!!! BAD NOOB!! BAD NOOB! (whacks noob with newspaper)

Running leaded will slaughter those cats and they aren't cheap.

Try to find some Sunoco 104 unleaded somewhere. That is the fuel of choice for most that wanna try race gas. May pick the car up a tick once she relearns the fuel but it will take some time for the car to relearn.

Only thing you may notice is a little tougher starts. No worries.

 

Even with unleaded race gas, on a stock car the only thing you'll gain is a wallet that empties faster.

 

Say hellllooooo to the CK engine light!

 

***EDIT BELOW***
Running a higher octane without a tune for it will not help your car at all. I tried running a few gallons of 101 octane (VP MS 109) mixed in with pump 91 at the track hoping the ECU would adapt a little bit but it didn't at all.

+1

 

This is one of those discussions that seems to get people on both sides of the fence.

I have run a 50/50 blend of 93 and unleaded race gas on occasion. I don't know if it helped the car's performance, but it did hit the rev limiter a few times after first filling up with the mix. The problem resolved itself after a half dozen short bursts at WOT and a few miles. It was almost like the engine was reving faster and the TCU had to adapt and did. I'm tuned for 93 by the way.

 

fwiw, I'm stock with no tune. I've run 100 octane with no noticeable anything going on. But I will mix a ratio of 100 octane and the 91 octane (highest we get in Cali) once in a while just to bring the fuel up to a 'normal' 93 octane as found in the rest of the world. But again, still nothing noticeable going on.

 

Could just be a coincidence on my part.

 

it will ruin the o2's and the cats.

and without being tuned for the leaded fuel and higher octane, you will not see an increase in power.

 

Do NOT use leaded fuel.... it will eventually fry your O2 sensors and kill your cats, which as Jim has mentioned, aren't cheap to replace.

Regarding the high octane fuel, the stock ECU (even without a tune) is able to adjust for a couple of points of octane when possible. It guesses when there is good (or bad) fuel is present in the car (usually) using the knock sensors and adapts accordingly. However, it is said to be a very minor adjustment in terms of adding or pulling timing - a range that is set by the factory before the car ships out. The ECU, therefore, will take advantage of a couple of points of higher octane, but it will certainly not adjust for a 15 to 18 points difference (from 91 to 109).

 

[QUOTE=MB_Forever;4430993]Do NOT use leaded fuel.... it will eventually fry your O2 sensors and kill your cats, which as Jim has mentioned, aren't cheap to replace.[QUOTE]

Curious. If your cats/ O2 sensors begin to go, any symptoms?

Thanks & brgds.

 

There are so many misconceptions about race fuel, race fuel tunes, and race fuel in a stock cars, race fuel in modern EFI engines and old carb engines.

In a modern car like the AMG, they are designed to run on all types of fuels, There are parts of the country were you can only get 89 (mostly at altitude) East coat guys can get 93 or even Ultra 94. In the west coast 91 is the highest you can get.

From the factory your car is designed to run on all of these fuels. It can do this because we have the lovely device called a knock sensor. If you put crappy gas in your car the knock sensor will detect some knock and start pulling timing. That means your car will feel slower and in fact will be slower. Less timing less power. Remember your knock sensor is communicating with the your ecu.

After you run your crappy gas just about to empty and fill up with good pump gas. You will feel your cars responsiveness come back. Why is this? Its because of your knock sensor. Your knock sensor is seeing that the fuel is taking longer to burn, or not pinging anymore so it adds timing. Adding timing will make more power. Your ECU will add and pull timing on its own based on the readings its getting back from the sensors places on your engine.

An AMG's ECU will handle octane swings up to about 95 octane. Anything more than that on a map not designed with more timing than the ECU can add on its own, will result in a negative effect. So its very true, you can over octane your motor. However running a 91 and 100 octane mix, (making about 95 octane) will result in a timing advance, thus making more power on an otherwise stock AMG.

Now in a old school chevy 350, fitted with a carburetor. Or no electronic management, the engine will have no idea what fuel you are running. To utilize a higher octane in this type of motor (based on C/R) you will have to manually adjust the timing to the fuel you are using. I'm sure we've all seen timing lights in action and people adjusting their distributors. Where as the AMG engine will do it on its own.

I would challenge any local AMG to come down to the shop for some dyno pulls. We can do a base line on your standard pump gas. Then bump the octane up to about 95 octane... And if you dont make power on the dyno I'll pay for your dyno run

My rule of thumb is: If you are not tuned for race fuel do not run more than 95 octane. If you are tuned for race fuel don't run less than what you are tuned for.

 

MBH, can you elaborate on your statement "you can over octane your motor"? What are the physics behind this? Otherwise and excellent explaination for a subject that has so much misinformation fueling it.

 

where does the 95 octane number come from? personal experience?

 

The higher the octane the slower the burn rate. This is required as the brake-mean-effective-pressure (BMEP) of the engine increases. In other words, you want an even burn and a lower flash point in order to prevent pre-ignition. Tetra ethyl lead (T.E.L) is still the best (and least expensive) additive. That said, there are some pretty exotic unleaded fuel blends such as those being used in F1 engines which have been limited by rules to 18K RPM, but in fact are capable of RPM's in excess of 22K. I can only imagine what those BMEP's are.

So, bottom line, if you use an octane rating higher than what the engine is tuned for, you will get a slower, colder burn and you will also notice a decrease in MPG (L/100km) and, of course, a reduction in power.

 

Thanks for all the info guys, much appreciated!

 

The 95 octane number comes from the percentage the of timing the ECU can add on its own... Based on a stock ECU. Basically if you use 95 octane, your motor will be at full advance. Or at the max value the ECU can add on its own. Anything more than 95 octane or about 95 octane, the stock ECU wont be able to advance the timingm because it has already reached the max advance.

So running a full tank or 100 octane race fuel, on a stock ECU wont help because your ECU can not take advantage of it. Then you get into over octaning your motor. That is another discussion all in itself. I recently read on motortrend someone saying "you can't over octane an engine". I'm not sure what I think about that statement. However if you can't advance the timing enough to burn all of the race fuel. I guess the rest just shoots out your tail pipe? Sounds like a waste of money to me.

Another note: Don't go to your local airport and use their 100 octane airplane fuel. Its fulled with stuff you don't want to run in your car.

 

In the summer I run 7 gallons 93 and 2 gallons 104 when I can find 104

 

I am VERY familiar with gasoline and high performance engines. I am also familiar with the Internet fueled idea that high octane fuel burns slower than low octane fuel. It is so often repeated that it has become the truth. In reality, this is not always true for a quality fuel blend. I cannot say the same thing about home brewed high octane blends where large amounts of Toluene, Ethanol or AVgas are added. In fact, burn rate has nothing to do with the fuel's ability to resisit pre-ignition. It is the fuel's ability to handle higher temperatures and pressures.

I know how the inability to advance timing to compensate for slower burn rates (whatever their cause) could result in less fuel being burned in the combustion chamber and more heat energy going out the exhaust pipe. This was bigger problem prior to computer controls but even so, I have never seen an appreciable decline in power on the dyno when using fuel from a quality source (VP, Sunoco, 76, etc) with a higher AKI than an engine needed. Having said that, it has been more than 12 years since I wore that hat. What has changed in these engines and or fuels that makes it a real problem now?

By no means am I advocating using higher AKI/Octane ratings than necessary to achieve maximum efficiency. I am just trying to keep the air clear of misinformation.

 

Leaded gas smells like a little slice of heaven.

 

It is safe to run Unleaded race gas. You will do damage to your cats if you run leaded race gas.
I mixed in 3 gallons of MS109 race gas to 91 octane and felt some noticable power.

 

I do the same mixture. And in my subjective opinion, I do feel a noticable improvement.

My car makes more noise and feels faster after the car adapts to the higher octane.

And it makes sense after all, considering the C63 is not meant to run on 91 octane. It's meant to run on minimum 93 octane, so my ECU must be in a lower octane fuel table when I'm running 91 and it likely switches to a higher octane table when it recognizes at least 93 octane.

Also, I have heard my engine knocking before on crap 91 octane. It was Shell, but still must have been a bad batch. I drove (lightly) to the 100 octane pump and mixed some in, and the knocking went away.

This is when my car was stock.

 

Great points. And it makes me feel more comfortable with my own experiences with mixing 100 unleaded and 91. I like to reach a 93-95 octane mix.

 

This makes perfect sense. I've filled up a few gallons here in AZ on 100 Octane mixed with my current tank of 91 creating 95. The engine was much, more aggressive but this is proablly due to the tune and mods I have.

Related question, the $3.00 "Octane Booster" you can buy at a store, does that really do anything if you're running for example, 91 in your tank or is that just a scam?

Great thread by the way!