race fuel = knock gone, Question???

[b15turbo]

My last thread I posted that I could not get rid of my knock even when my wideband was 10:6 it still knocked bad, well today I added 4 gallons of 110 fuel wow knock is gone =0 and a/f did get little bit richer around 10:4 but I have tried running richer before like that on 93 fuel and it still knocked. What’s going on with my car? Should I maybe put my wideband little closer to the turbo its around 35" from the turbo.. Can some one tell me why my knock is only gone with race fuel but running it richer on 93 octane doesn’t help it at all???WTF

 

[brute]

What is your boost currently set at?

 

[Staytuned]

Knock is about timing control not so much about AF ratio. Get your timing curve under control or drop the boost and knock will go away also. With race gas you have more control over knock because race gas burns slower and in control.

 

[b15turbo]

17psi boost. what should my timing be? i will check it tonight after work.

 

[The_EE]

I have the same problem. I tried a couple things.

I dropped boost from 20 psi on 91 oct down to 15 psi, still had knock

I lowered timing to down a couple degree's and still got knock at 20 psi on 91 oct

I add 100 oct, knock disappears from my logs.

No boost leaks. Only thing I can think of, maybe dying knock sensor or 130k engine dying.

 

[Staytuned]

17psi boost. what should my timing be? i will check it tonight after work.

I believe the 1G timing map is very aggressive in the midrange and that might be where you are having problems. If so you might want to get another keydiver chip with a more modest timing curve like a low of 9-10* at full boost ramping up to 16-17 by redline to start.

 

[b15turbo]

This is a stupid question but looking at the timing marks to set the ignition timing their is 4 marks witch way is retard witch way is advance???

 

[Staytuned]

That probably isn't the way you want to change your timing unless it is not set to stock base timing anymore. You are going to change the timing map all the way across the rpm range and it still may not be enough to curb knock at certain points. You have a Keydiver custom chip in your ECU why not just get them to burn you a new one that has a more appropriate timing curve.

 

[Fitz7099]

Just a tidbit on fuel:

In general the article says that as octane rating increases the rate of the fuel's burn decreases, also as octane increases the maximum compression ratio, before detonation, increases. Higher octane let's you run higher boost Here is a link and the article I cited

Taken from here

And so to fuel (or gasoline or petrol)

Petrol (or gasoline if you're American) is a distilled and refined oil product made up of hydrogen and carbons - a hydrocarbon. A long-chain hydrocarbon to be exact (so don't get it on your skin - its carcinogenic). It's designed to be relatively safe to handle, if you're careful. ie. it doesn't spontaneously combust without extreme provocation. When you have a petrol fire, it's not the petrol itself that is burning, it's the vapour, and this is the key to fueling an engine. The carburettor or fuel injectors spray petrol into an air stream. The tiny particles of petrol evaporate into a vapour extremely quickly, and combined in a cloud with the air, it becomes extremely combustible. The smaller the particles from the carburettor jet or fuel injector, the more efficiently the mixture burns.
Detonation, pre-ignition, pinking, pinging and knocking.

Remember I said petrol doesn't spontaneously combust? Well it can if the conditions are right, and the conditions are extreme heat and pressure - exactly the conditions you find in the combustion chamber. When this happens, it's called detonation or pre-ignition. Diesel engines rely on this process because they don't have a spark plug in the traditional sense of the word. However in petrol engines, when this happens (also known as dieseling), it's a Very Bad Thing. Engines are designed to have the fuel-air mix burn at a fixed point in the cycle, not explode randomly. Whilst it might look like an explosion, if you could film it on a super high-speed camera, you'd see the mixture actually burns up very quickly rather than exploding. Detonation, dieseling or pre-ignition are all terms for what happens when the fuel-air mix spontaneously explodes rather than burning. Normally this happens when the mixture is all fouled up, and the engine is running hot. The temperature and pressure build up too quickly in the combustion chamber and before the piston can reach the top of its travel, the mixture explodes. This explosion tries to counteract the advancing piston and puts an enormous amount of stress on the piston, the cylinder walls and the connecting rod. From the outside of the engine, you'll hear it as a knocking or pinging sound. The precise sound is very hard to describe because every engine sounds slightly different when it happens. But the best way I can describe it is a constant 'toc toc toc' type knocking sound.
Compression ratio.

The compression ratio of an engine is the measurement of the ratio between the combined volume of a cylinder and a combustion chamber when the piston is at the bottom of its stroke, and the same volume when the it's at the top of its stroke. The higher the compression ratio, the more mechanical energy an engine can squeeze from its air-fuel mixture. Similarly, the higher the compression ratio, the greater the liklihood of detonation.
Octane ratings - how to stop detonation

So you know that a fuel-air mix, given the right conditions, can spontaneously combust. In order to control this property, all petrols have chemicals mixed in with them to control how quickly the fuel burns. This is known as the octane rating of the fuel. The higher the rating, the slower and more controlled the fuel burns.
Put on the geek-shades for a moment and I'll explain octane in more depth. If you don't like being blinded by science, skip down a few paragraphs. For the rest of you, octane is measured relative to a mixture of isooctane (2,2,4-trimethylpentane, an isomer of octane) and n-heptane. An 87-octane gasoline has the same knock resistance as a mixture of 87% isooctane and 13% n-heptane. The octane value of a fuel used to be controlled by the amount of tetraethyl lead in it, but in the 70s and 80s when it became apparent that lead was pretty harmful, lead-free petrol appeared and other substances were introduced to control octane instead.
Measuring octane - RON, MON and the difference between America and the rest of the world.

Just so you know, the octane number is actually an imprecise measure of the maximum compression ratio at which a particular fuel can be burned in an engine without detonation. There are actually two numbers - RON (Research octane number) and MON (Motor Octane Number). The RON simulates fuel performance under low severity engine operation. The MON simulates more severe operation that might be incurred at high speed or high load and can be as much as 10 points lower than the RON. In Europe, what you'll see on the petrol pumps is the RON. However, in America, what you'll see on the petrol pump is usually the "mean" octane number - notified as (R+M)/2 - the average of both the RON and MON. This is why there is an apparent discrepancy between the octane values of petrol in America versus the rest of the world. Euro95 unleaded in Europe is 95 octane but it's the equivalent of American (R+M)/2 89 octane.
In America, low altitude petrol stations typically sell three grades of petrol with octane ratings of 87, 89 and 91. High altitude stations typically also sell three grades, but with lower values - 85, 87 and 89.
What factors affect detonation?

There's a bunch of things that can affect how likely an engine is to have detonation problems. The common ones are ambient air temperature, humidity, altitude, your engine's ability to stay cool (ie. the cooling system) and spark timing. Fortunately, nowadays the engine management system of modern cars can compensate for almost all of these by advancing and retarding the ignition timing. This is where the computer slightly adjusts the point in the ignition cycle at which the spark is generated at the spark plug. With older engines that used mechanical points to send current to the spark plugs, adjusting the timing was a manual affair that involved adjusting the distributor cap orientation.
Knock sensors. Most modern cars have knock sensors screwed into the engine at multiple places. These actually detect the vibration or shock caused by detonation (rather than trying to detect the sound) and can signal the engine management system to change the ignition timing to reduce or eliminate the problem.
Octane and altitude

The higher the altitude above sea level, the lower the octane requirement. As a general rule of thumb, for every 300m or 1000ft above sea level, the RON value can go down by about 0.5. For example an 85 octane fuel in Denver will have about the same characteristics as an 87 octane fuel on the coast in Los Angeles. As a practical example of this, I currently live in Salt Lake City which is at around 4,200ft. We travel to Las Vegas from time to time which is at around 2,000ft. Our Subaru has a minimum octane requirement of 89 at sea level - so about 87 where we live. Last time we drove to Vegas, the petrol station we stopped at had run out of 'premium' products so we had to fill up with 85 octane. This, combined with the drop in altitude caused the 'check engine' light to come on because we'd effectively taken the engine from 87 octane at altitude to the equivalent of 83 octane at altitude - way below the minimum required by our car.
Octane and power

It's a common misconception amongst car enthusiasts that higher octane = more power. This is simply not true. The myth arose because of sportier vehicles requiring higher octane fuels. Without understanding why, a certain section of the car subculture decided that this was because higher octane petrol meant higher power.
The reality of the situation is a little different. Power is limited by the maximum amount of fuel-air mixture that can be jammed into the combustion chamber. Because high performance engines operate with high compression ratios they are more likely to suffer from detonation and so to compensate, they need a higher octane fuel to control the burn. So yes, sports cars do need high octane fuel, but it's not because the octane rating is somehow giving more power. It's because it's required because the engine develops more power because of its design.
There is a direct correlation between the compression ratio of an engine and its fuel octane requirements. The following table is a rough guide to octane values per engine compression ratio for a carburettor engine without engine management. For modern fuel-injected cars with advanced engine management systems, these values are lowered by about 5 to 7 points.
Compression ratio Octane
5:1 72
6:1 81
7:1 87
8:1 92
9:1 96
10:1 100
11:1 104
12:1 108

 

[b15turbo]

Well maybe that’s why I get knock when they burned the chip for me I forgot to tell them that my new pistons are little higher compression then stock.

 

[Staytuned]

Well maybe that’s why I get knock when they burned the chip for me I forgot to tell them that my new pistons are little higher compression then stock.

What is your CR? you should maybe add that to your profile. This could be very well be the problem when combined with high timing curves.

 

[CanadianTSi]

Check your Base Timing and Make sure its at 5 degree's BTDC.

 

[b15turbo]

Its wiseco and i think its 8:1 or something like that

 

[Staytuned]

You should look into this more, I am guessing 8.5:1 as that would be the same as stock 2G which works well with pump gas and decent boost levels.

 

[talon95newb]

As my name implies, I am an idiot, but if I'm right, isn't detonation caused by too much temp/pressure in the cylinders before they reach the point the spark plug fires? If that's the case, wouldn't a better intercooler help a lot since it cools down the air right before it gets to the intake manifold? Don't be mad at me if I'm totally wrong, I'm just supposing.

 

[Staytuned]

Pre-ingition and detonation as per Street Rod stuff:

Detonation
Detonation is the spontaneous combustion of the end-gas (remaining fuel/air mixture) in the chamber. It always occurs after normal combustion is initiated by the spark plug. The initial combustion at the spark plug is followed by a normal combustion burn. For some reason, likely heat and pressure, the end gas in the chamber spontaneously combusts. The key point here is that detonation occurs after you have initiated the normal combustion with the spark plug.

Pre-ignition
Pre-ignition is defined as the ignition of the mixture prior to the spark plug firing. Anytime something causes the mixture in the chamber to ignite prior to the spark plug event it is classified as pre-ignition. The two are completely different and abnormal phenomenon.

Many things can lead to these outcomes......including intake temps.

 

[1997gsx4sr]

Very interesting. Thanks!

 

[Jonnynitrous]

I would try the 2g timing map since you got the 2g compression.also you see alot of people have knock problems due to noisy lifters.go with the upgraded 3g's and try the 2g map and this should help..