Dumb Quesiton #2

[Anfanuts]

Back awhile ago, it was the "rule" to use Premium in stock Spica Alfa engines. This was when there was still lead in fuel and UnoCal was the benchmark then. I've always used that since (Premium). Probably a rumor by the oil companies! Recently, however, I was told by a reliable source that I could use Regular or Mid-Grade if needed. This is a stock 69 1750 Spica engine. Your experience and guidance is appreciated. I would probably not know "pinging" if I heard it as I've never heard it. (I am putting 4 oz of MMO in per 10 gal.). Thanks, Bruce

[bjfrantz@charte]

You'll need to retard your ignition, if you don't add octane enhancers. You will not get the performance or gas mileage for which your engine was designed. I don't think MMO improves octane rating. Any one know?

Barry

[Anfanuts]

Quote:

Originally Posted by bjfrantz@charte You'll need to retard your ignition, if you don't add octane enhancers. You will not get the performance or gas mileage for which your engine was designed. I don't think MMO improves octane rating. Any one know? Barry

[alfaparticle]

You should be fine with 89 octane. My Spider has 10:1 pistons, racing cams and an aggressive advance curve. It does not ping on 89. I can stomp on the gas pedal at any rpm above 2000 rpm in 5th gear with no problems.

[bjfrantz@charte]

Bruce, Alfaparticle,
I find this hard to believe, but I will try it out when I get my engine back together. I have always timed my engines according to their response to available octane.
Barry

[Anfanuts]

Thanks, if mid works for you it will certainly work for a spec engine. I say mid in quotes as it's not really midway between Regular at 87 and Premium at 93 but it is between. It does not seem unreasonable that Regular might work also. I also assume we should avoid ethanol insofar as possible? I'll do a search for ethanol.

[Anfanuts]

After two tanks of mid-grade (89 octane), I started to get some knock. Occurred in 5th pulling up a long steep grade at lower RPM (3000+). I dropped to 4th and upped the revs and it was OK. I run 5 deg BTDC instead of the spec 3 deg ATDC. Is this making the difference? I know I can use one grade gas less for every 5 deg less advance on my boat (Holly carb'd 305 Cvy). I also put 4 oz per 10 gal Marvel Mystery Oil in the gas (for the fuel pump), would that be making the difference?

Anyway, I've gone back to Supreme grade with no more problem. Getting 24-28 mpg so it's not a huge issue but adding up at $3.44/gal. Bruce

[bjfrantz@charte]

Stay with the high octane, unless you retard your ignition.

Barry

[conedriver]

The gospel according to Wes: avoid knock/ping at all costs; this is death to hemispherical combustion chamber engines. One of my favorite stories is Wes telling of Rita saying that he can't hear light ping anymore due to being around all of those drag racing engines in his early years.

Quote:

Originally Posted by Anfanuts After two tanks of mid-grade (89 octane), I started to get some knock. Occurred in 5th pulling up a long steep grade at lower RPM (3000+). I dropped to 4th and upped the revs and it was OK. I run 5 deg BTDC instead of the spec 3 deg ATDC. Is this making the difference? I know I can use one grade gas less for every 5 deg less advance on my boat (Holly carb'd 305 Cvy). I also put 4 oz per 10 gal Marvel Mystery Oil in the gas (for the fuel pump), would that be making the difference? Anyway, I've gone back to Supreme grade with no more problem. Getting 24-28 mpg so it's not a huge issue but adding up at $3.44/gal. Bruce

[lowmileage]

IMO (FWthatsW), anything of the classic era with 9.5 compression or above needs 93 with stock timing. We don't have 91 in my area and the drop to 89 is too much of a gap. Price difference here is irrevelant at 10 cents a gallon. And why would you want to retard timing and loose power?

[Gordon Raymond]

An interesting example is my '02 BMW M3. With all it's engine management wizzardry at work, I found (of necessity) it would run well on low octane regular. Problem was mileage dropped more than enough to offset any cost benefit. If it was designed as a premium fuel engine, it is cheaper to use premium fuel.

[Anfanuts]

That's now where I am back to - Premium. Some posts way above seemed to feel I could get by with less. Tried it. Not the case with a stock 1750 with ~8 deg more advance anyway. Lesson-learned. Thanks, Bruce

[FrencheGTV]

Wow I didn't realise you guys had such low octane levels. Over here in the land of Aus our 'regular' is 91 octane, 'premium' is 95 and what Shells calls V-Power (BP calls it Ultimate, Caltex calls it Boost98, etc etc) is 98. I run all my 1.8 and 2l engines on BP Ultimate and have no probs, except the price, around $1.68 Aus a litre last time i filled up. In the GTV6 I run premium, usually either BP or Mobil and have no worries, around 10l/100km with round town, freeway and a bit of 'spirited' driving thrown in.

[papajam]

The octane levels in the USA, Pump Octane Number (PON), are the average of Research Octane Number (RON) and Motor Octane Number (MON). I believe that the European octane numbers are RON, which is about 4 points higher than PON.

[Gordon Raymond]

Thanks Jim, I was looking this up this AM to post your very same reply! My research shows you got it dead on! We used to use RON until we switched to unleaded, is that right?
Gordon Raymond