re: 93 Octane

[TJCallahan@domain.elided]

In AD v8n665, Fred wrote:

>I got that from the man who wrote the manuals!  Ian say 87 
>works well and so do I.  So, start saving and don't buy more 
>octane tha you really need.  High octane does not produce 
>more power at certain ignition timing settings.  Fred

I don't doubt Fred (or Ian) in the use of 87 octane for the 164. I do have a question (or twelve) for Fred and the collective group, however.

Does the 164 self-adjust the ignition timing on a real-time basis? That is, will the engine management system on the 164 adjust the timing so as to keep the advance just below the knock level? If so, won't you get more advanced timing with a higher octane fuel? More advanced timing corresponds to better performance, generally speaking, doesn't it?

I have no working knowledge of the 164 or the sophistication of the engine management system it uses. I do know, however, that my '99 Volvo has a fairly sophisticated engine management system that self adjusts the timing based on knock sensors (and others) to get the timing as far advanced as possible without damaging the engine. I know I can put any octane grade of fuel in it and it will have, by the end of the tank, adjusted the timing (and other engine parameters) to the driving conditions. My '88 Jaguar, however, had a less sophisticated system (timing off the crank, through a distributor and coil, into the plug wires and plugs).

I noticed a minor, but noticeably improved, change in performance when switching from "Regular" to "Premium" octane grades in the Volvo. This was due, I believe, to the engine re-adjusting for a less-knock-sensitive fuel grade (no other changes were made to the car during this time).  I'm certainly not claiming that a tank full of premium fuel, by itself, will add 400 horsepower to your 800cc engine, but in performance based machinery (into which category I would place the 164) it will allow the sophisticated engine management system to operate at a higher efficiency. Higher efficiency turns into higher performance.

To measure the performance change for my Volvo, I used the precision performance tool at my house - my wife's opinion. The car is her daily driver and, after 30k miles, she was complaining about it being 'a dog' in performance. When I asked her, she advised she was putting regular into it for economy reasons (the owner's manual recommends a higher octane but further advises the car will run fine on less). I suggested she should use premium fuel, which she did. After a couple of tanks full of premium (and no other change), she was much happier with the way the car responded to her right foot inputs.

Eric - do you have any insight (or better explanations) to offer about engine management? I know there's a LOT more than the tiny bit I described here, the engine management systems are incredible in their complexity. As an ex-engineer, I'm in awe at what they do and how they do it.

As always, use what works best for you.

Tom
Seattle
10123
11615
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