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oil gauge flutter and fuel question

Started by raueda1, 04 September 2023, 08:12 AM

raueda1

Since I don't have enough to worry about I figured I'd start worrying about this. The car has done this from day one as far as I can remember.  It's not much, just a very small needle flutter at idle when engine is hot.  I hope it's normal, cause I'm not inclined to rebuild the motor.  Pressure at hot idle is typically 1.5 bar.  I've never seen it below 1 bar except once or twice when hot and at abnormally low idle speed, such as when messing with WUR or something like that.

Now the fuel question.  US cars have 8:1 compression.  Is this low enough that 87 octane (~91 RON) is OK?  Here's why I ask.  My car got +1 pistons during a rebuild.  Those particular pistons reduced the car to 8.6:1 or 8.4:1, can't recall offhand.  Of interest is that there are a lot of people out there saying that 87 octane is usually OK until you get over 9:1 or more.  IOW, 8.8:1 is only borderline high compression to begin with and quite low compared to the muscle cars of the era. This suggests that regular gas would be OK and would certainly be fine in a US spec car.  But I suspect that this idea is heresy.  I think I'm going to go out and advance my time some more.   ::)    Any thoughts?  Cheers,
-Dave
Now:  1976 6.9 Euro, 2015 GL550
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

ramiro

I noticed the same thing on my 6.9 , and actually changed the oil hoses because i suspected that maybe something is leaking there and the pump pulls some air.

But after changing them the oil gauge still flutters sometimes but not always same as before, it is most visible when i let off the throttle while driving slowly in town and the oil pressure is about 2 bar.

About fuel i can only say that i mostly use 95 ron but with stock ignition timing , i tried advancing but i am sure that i heard pinging on accelaration so i put it back to stock , with my engine that runs at and above 100C when i push it to the limit i also like to have some headroom.