Wait a minute. Ok we've established that low octane in a force inducted car will cause the PCM to pull timing, KR. And you say that running a lower octane will not hurt an engine. So this insinuates that knock is a good/neutral occurance?

If you can afford to buy a SCed car and the insurance that goes with it, why fret over spending money to take advantage of the blower?

No knock is not a "good" thing. The sensor retards timing and "learns" so fast you won't even hear it. Hell tons of you are probably running around all the time with engine knock and don't even realize it. One or two knocks every so often is a "neutral" occurance yeah. Matter a fact in some older cars its considered "normal."

"If you can afford to buy a SCed car and the insurance that goes with it, why fret over spending money to take advantage of the blower?" ---- Ok screw it, take a difference stance then. Figure it out in the pursuit of knowledge, not cost savings.

Actually, I believe the pcm even adds timing until it sees a knock then backs it off and repeats.

Will low octane fuel damage your engine. I will say that depending on how you drive the car you "may" get away with it. Let me ask you this way Doc. Is it good for your supercharged car to run low octane fuel? Is it beneficial to the motor to run low octane fuel? Show me examples please. Are you willing to say that if every blower motor was run on low octane fuel that engine failures would not increase? You see, you can probably get away with it but that doesn't mean it'* the proper thing to do.

I have seen rotors run all the way to the fins metal to metal. I mean the backing to the pads were gone and the car was being stopped by the pistons. No problem right? The car was still stopping. Some people just get lucky.

[quote="DrJay"]In the spirit of friendly debate, I'll have to agree with Don. I've played around with Octane more than anyone here. 'mixing my own'. I can FEEL the difference between 91 and 92, 92 and 93, and 94 and 95. And I've repeated the process several times. Partly MAYBE because of the high boost and sensitivity to KR and Octane that I have in my situation? Maybe.

Debate?

Stranger things have happened. It'* hard to debate what you say you feel. I still think blind testing it you wouldn't know which is which. Are you talking seat of the pants or using meters? This is like the stereo forum where the guy was saying he could hear the difference in his system after polishing the 3 prongs on the power cord. I know I couldn't tell the difference. If you can then more power to you.

Buzz, I have an Actron Scantool. I log KR. Each 5 degrees of KR is worth 3hp the last I checked. 5 hp is commonly the 'seat of the pants' dyno threshold. I might have my numbers mixed up a bit, but you see the point. It'* quite easy to characterize this by watching KR on a scantool, and feeling 6 or more hp. Not out of the realm of possibilities at all.

You see, I'm running an EXTREME amount of boost for an M62. In the right conditions, WITHOUT water/methanol injection running, I produce 12PSI with a roots blower. That'* some serious compression heat, which is a direct lead-in to KR. Octane has a big effect on curing it.

I'm of the old-school (much to DrJay'* chagrin) and still firmly believe that knock leads to inefficient burn. Inefficient burn causes deposits in the cylinders and on the valves. Deposits act like little glow-plug-dudes....and you end up getting worse over time. If knock wasn't bad for our engines, why would the PCM retard timing to prevent it? And why is 91 octane fuel REQUIRED by the manufacturer? Why does higher octane help prevent KR?



The days of dieseling carbureted motors are not forgotten for me.

I will buy what you say then, but I understand the topic is seat of the pants feel from a "stock" vehicle by the average person. You and your car my friend don't fit the bill here.

I believe doc is relying on the fact that most cars are over enginered and there'* probly a lot of them that can survive this. I personally don't believe it'* worth the risk unless you like swapping motors. The more efficient the engine burns the fuel the better all the way around. Pre-ignition is inefficient enough to cost you economy so I really don't see where it would be all that cost effective even without the risk anyway.

Yeah I think you were a little mixed on your numbers ...From what I've heard 1deg = 2hp and 10hp = recognized as the edge of "felt".

But I want to focus on this statement:

I think this is why this debate is getting nowhere. You're not even on the same page. NOBODY SAYS DETONATION IS GOOD!!!!!!! NOBODY SAYS DETONATION IS OK!!!!!!
Please read that several times if need be. I keep saying this isn't about performance, gas mileage, or if detonation is a good thing.

DETONATION IS BAD!!!
Bad bad bad

That out of the way, for the 400th time...

The neat thing is our cars are equipped with whats called a "Knock sensor" which can detect and with the PCM retard the timing in an EXTREMELY short time. This saves our cars from potential damage. Thus you have NO MORE detonation and no more foul effects from detonation. No detonation = No damage ...see where I'm going?
What you ARE left with is lower performance and gas mileage but it will not damage your engine.


The second sentence was answered like 40 posts ago..here:

GreenMachine - "I agree with DrJay on this one. I have the original owners manual, and it states that 91 or above is recommended, but that 87 can be used, but it will affect acceleration. It also says that a light pinging when under heavy load is normal, but a heavy knocking is bad. This is right out of the owners manual. "

It seems like I've read the same thing before in mine but its MIA right now...Maybe you can read it in yours and tell us what it says?

3rd sentence - Now you're just backtracking...I get why you're asking this but I believe we're all past the point of needing to answer it.

Oh and on a side note ZZperformance seems to think the PCM is capable of retarding timing as much as 25.5degrees. So with our little experiment earlier you could run 24deg at idle and 11deg at WOT on 92. The PCM is capable of taking 59.5deg from the idle and 36.5deg from WOT....Have any of you changed the timing on a distributor based engine? You know how much even 2-3degrees makes. This simply illustrates that the PCM is MORE than capable of dealing with detonation before its a problem.

I don't get how this is even a debate? All anyone keeps saying is how it affects performance, gas mileage, and "you should buy it because you bought the car."

Meanwhile back in the real world the computer can pull up to nearly 60degrees of timing in efforts to combat detonation. If you have detonation after that you've got a tank full of 5octane fuel.

You seem like you know a little something on the matter
Could you explain to me, in detail, how detonation in a knock sensor equipped car (fully operational) is a "risk"?

Sure thing Doc. For a knock sensor to work it has to see detonation. Since you stated 400 times already that detonation is bad I will say we all agree with you on the point. Not until after the sensor sees detonation does it goto work so there is the first part of the problem. Once it sees it it signals the pcm and the pcm retards the timing. Octane is the easiest way for the owner to avoid detonation. By choosing to run the lower octane you are actually asking the engine to detonate and hoping it will survive by the pcm pulling enough timing. The next problem is what exactly does retarding the timing do? A little retarding will cause some power loss, but retarding the engine is like lugging it. It creates heat which in turn creates sludge, deposits, and can even lead to more knocking which means more timing pulled and so on. The fact of the matter is the knock sensor and retarding of the timing is only meant to happen for short periods of time to save the engine from instant destruction. The is nothing the system can do to protect itself from the long term abuse by someone too damn cheap to run the fuel that the manufacturer recommends or requires. Does this mean you are guaranteed to destroy your engine running low octane fuel? Nope, just like rotating the cylinder with one round in the chamber doesn't guarantee your brains on the wall. The question is how many times are you willing to try it? If you still don't buy it I will ask Dustin Whipple for his explanation. Maybe someone who designs and manufacturers blowers will have more clout in your eyes the ours. Until then.....