re: 93 Octane

[Ian Lomax <sfalfisto@domain.elided>]

let me clarify one thing i said to fred offline.  i
said that for cars designed to run 87 octane gas, it
works as well if not better than 91.  

in particular i was referring to the diamondstar 2.5l
v6 that i spent three years developing.  since i
worked on the OBDII side i had to calibrate the
misfire sensor, and we used strange fuel mixtures to
induce misfire and other strange driving behaviours. 
i found that 91 octane induced misfires ot one point
during the calibration cycle (which i think was later
improved... i think...)

i have yet to try 89 or 87 octane on my test bed (94
164LS 24V) and i'm not sure if this advice also
applies to the 24V versions.  but i'm certainly
curious.  i also have the perfect testbed for inducing
knock, san francisco's infamous hills!  i'll let yinz
know.

cheers,
ian lomax
71 spider (engineless)
94 164LS (lots o' engine)
sf, ca
--- TJCallahan@domain.elided wrote:
> 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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