No, I don’t believe carbon build up could raise the compression to have any benefits in performance or efficiency.
Yes it performs better than a lower compression (regular) engine of the same displacement. No it doesn’t require premium fuel. According to the manual 91 octane is recommended, but not mandatory, as low as 87 is acceptable.
@PvtPublic We all know what you said and meant. To avoid stupid arguments, maybe just ignore.
No, I don’t. I fabricated one for my 2007…never got anything in it. At 84K miles my intake looks pretty clean with a borescope. The compression is still very strong and it doesn’t use any oil worth noting. I don’t have direct injection so I am not worried about buildup on the intakes…for THAT car…
Now the '14 Audi 2.0 turbo has direct injection. I’ve Seafoamed it at about 33K miles. Haven’t scoped it yet even though it has 42K on it.
For what year? Is that a newer throttle by wire vehicle? Throttle by wire vehicles can operate on lower octane fuel. Older vehicles with carburetors sometimes said to not use full throttle unless premium fuel is used.
Irregular carbon deposits in a combustion chamber causing knocking are very different than a carefully designed high compression engine. My '95 Suburban knocked a bit on regular because of carbon deposits, I noticed no improvement in power or mpgs.
That is not the reason. ECU controlled cars with knock sensors can operate on various octanes of fuel because they can sense knock and reduce spark advance. They pre-date the common use of throttle by wire.
I have never heard that one before. Any way to document it?
it’s in the 1971 Jaguar XJ6 owner’s manual I believe.
My point is that throttle by wire vehicles can prevent the use of full throttle when lower octane fuel is used in a high compression engine. This is equivalent to driving in high altitude when you can use lower octane fuel.
??? I doubt that .
Octane rating has nothing to do throttle by wire, fuel injection or carburetor. What octane is needed is determined by engine design.
Removed by me.
If 87 octane fuel is used and the compression ratio is high enough, at full throttle at sea level pre ignition will occur. If I’m using that word correctly, it means that the fuel air mixture will ignite before the spark, so no amount of delayed timing can fix it. Reducing the manifold pressure by preventing the use of full throttle can prevent it. Maybe some variable valve timing trickery could be used as well.
I have a JLT 3.0 catch can on mine, I wouldn’t call it elaborate, but it catches about 1 oz (give or take) of condensed oil/blowby every 5k miles or or so.
Yes reduced timing can prevent pre-ignition. Retarding the spark cools the combustion chambers so the next cycle is less likely to pre-ignite.
But that is not how it is done in a modern ECU. My OBD2 data collection sends “spark retard” data out as a signal. Under high heat and high load on track days, 93 octane will still knock at times. Since it tends to run a bit hot, (245 degrees head temp, it can still suffer pre-ignition at times.
My ECU retards the spark but not the throttle (I have that data, too). I tested this to prove the need for a little octane booster (or unleaded race gas) in my fuel tank to kick the octane up a couple of numbers.
Can you provide anything to back up the claim that knock sensors are used to reduce throttle opening? No source that I’ve found (including Hella, who makes them) says this.
Why wouldn’t they do it that way? I admit I’m not familiar with how modern throttle by wire vehicles operate. Delaying the ignition would reduce power while keeping the fuel consumption the same which would hurt fuel economy.
What’s the compression ratio of this engine? Do you run it on 87 octane?
In an old car with a carburetor you could just back off on the throttle if it started knocking because of low octane fuel. It would then perform like it was running on premium but full throttle would just not be available.
I can’t because I don’t know much about how they work and I have very little experince with them. That it not to say that it would be impossible or wouldn’t work. They sell 86 octane mountain grade fuel in the mountains. Reducing the manifold pressure would accomplish the same thing, that is allowing lower octane fuel to be used. So in theory any throttle by wire vehicle can do this if the software is made to.
In other words, this is an idea in your head only, that seems to make sense to you. Doesn’t make it true.
Because backing off the throttle will cause an unexpected loss of acceleration, potentially leading to an accident. If I’m merging in front of a semi, I don’t want to suddenly slow down.
Can you say… throwing something at the wall to see if it sticks. 
what is mountain grade fuel? never heard of it.