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I’ve got an 84 S3 and was just curious about what octane rated fuel you guys and gals are running? Stock engine
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with no mods. Usually I use 91 but I’m wondering if it’s overkill. Should I be using 89 octane? Thanks
 

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Does your manual or gas flap sticker tell you which?
I do know that higher octane than is required by the engine does absolutely nothing, except to your wallet. You don't get better mileage, you don't get more power.
 

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In the USA 'regular' grade ("87") is all your stock Series 3 engine needs. If driven regularly, up to 10% ethanol seems to cause no problems. For storage I advise searching for ethanol free gas (see: Pure-gas.org - ethanol-free gasoline in the U.S. and Canada)

Note that the US & European methods of rating octane differ slightly. In the US we use PON (Pump Octane Number). In most of everywhere else they use RON (Research Octane Number). RON 91 is about the same as 86 PON. Thus if you read a European owners manual it will advise 91 octane. But that means RON.

Font Number Parallel Document Publication
 

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87 Alfa Spider Quad
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He just said "you should see some of the engines that come in here". I didn't bother to dig deeper. He's been working on Alfas and Fiats for about 100 years, so I just accepted it. Plus, I don't buy tanker loads of gas for it. If it were a daily driver, I would have questioned it more.
 

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In German we can buy Aral Ultimate 102. It is of course expensive, but, I learned a lesson what happened, when your Spider stands still for years with "bad" gasoline. I will not drive very often and not during winter.

However ist is not the octane value, this gaz is ethanol free (!!!) and has cleaning additives, which have been tested. I also add stabilizer (Liqui Moly) and it should be fully full most of the time.

WHY? This year I had to derust my gaz tank... :rolleyes:
 

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1974 Giulia Nuova 1300 , 1988 Spider 1600
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@ celeste Spider I am sorry to tell you that the Aral 102 also has ethanol ( 5 % ) "included". The good thing is the 102 Octane .. should be around 95 US octane.. But for a Alfa Romeo with stock or even mildly tuned this stuff is overkill.
98 Super + from a leading brand like EXXON , Aral, Total. .. is fine .

@ferrasm1 I would use the 91 octane gas... the Spider will love this stuff. 89 octane is a little low (my opinion )
 

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2015 Chevy (Holden) SS, 1989 Milano (Shankle Sport), 1991 164S
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If you hear no knocking or pinging when driving up a steep hill, the lower octane, as probably called for, is adequate. Higher octane fuel, if not called for, is a waste of money. Our 2.5 Milano called for the low grade, 87, in the US, but we found that it would ping just a little going up certain hills, otherwise fine. So, we switched to the medium grade, 89, now and then, and all is fine. Premium would be a waste.

In our 91 164S, I've found that it runs just fine on medium grade instead of the premium called for, but I do run a tank of premium once in a while, just because. Have detected no pinging or knocking at all on the medium grade. Of course, I'm not on the race track, just mild sporty driving around. Still, it does see high revs now and then, lol.

As Peter recommends, always make sure you do use tier 1 gasoline with the FI additives, or use Techron now and then in order to keep the injectors clean. The stuff works. Have never ever had an injector problem with any of my FI Alfas through the decades. Neither the 89 Milano nor the 91 164S have needed their injectors touched, for example. My mechanic Carlo was always pleased about that.
 

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It appears that S3 Spiders do not have a built in knock sensor and have no way to adjust the timing advance to prevent knock if octane is too low for the condition of the engine, or strain put on the engine in certain circumstances. Since the S3 engine is not a particularly quiet running engine it would be unlikely to hear light knocking which can be very damaging to the engine. Running a "lower octane" premium (90 or 91) is good insurance and won't break the bank. I would never run or recommend 87 or 89 octane for this engine or any other with a 9.0:1 compression ratio and no knock sensor.
 

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1980 Eurospec S2 Spider
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It is interesting that the owner's manual for my car says:
"Für einwandfreien Motor betrieb ist Superkraftstoff (R.O.Z. 98) unbedingte Vorschrift" which roughly translates as "Premium fuel (R.O.N. 98) is an absolute requirement for trouble-free engine operation."
I second the recommendation for fuel stabilizer and a full tank for ethanol-containing gasolines during any winter or other lay-ups of more than 4 months.
 

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It appears that S3 Spiders do not have a built in knock sensor and have no way to adjust the timing advance to prevent knock if octane is too low for the condition of the engine, or strain put on the engine in certain circumstances. Since the S3 engine is not a particularly quiet running engine it would be unlikely to hear light knocking which can be very damaging to the engine. Running a "lower octane" premium (90 or 91) is good insurance and won't break the bank. I would never run or recommend 87 or 89 octane for this engine or any other with a 9.0:1 compression ratio and no knock sensor.
I will say that I run premium 91 or 93 fuel in my 4cyl and v6 Alfas, not 89, for both octane and detergents. A higher-mileage engine with carbon build-up (granted less common in an L-jet car that has had quality detergent fuels) can be more prone to detonation.
 

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2015 Chevy (Holden) SS, 1989 Milano (Shankle Sport), 1991 164S
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Our 2.5 Milano manual says the car is designed for 86 (87 here) pump octane as sold in the US. Works fine except for mild pinging on steep hills, so we use midgrade half the time; however, I've read that occasional mild pinging does no damage to an engine. Have used US 87 and 89 octane in our previous Alfetta Alfas,etc, for decades with zero effects, even at 160k miles or more. If Alfa recommends 86, they must believe that as well. These engines are far more durable than that.

BTW, if I buy Chevron gas, all the grades come with Techron.

Luckily, we are all able to buy the grade of our choice for our cars. Whatever pleases the owner.
 

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I put 93 octane in my Spider even though 87 would be fine.

I only fill up my tank once every few months so the cost is not that big of a deal.

If I was filling it up 1x a week that might be a different story.
 

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2015 Chevy (Holden) SS, 1989 Milano (Shankle Sport), 1991 164S
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LGB, did you advance the timing to take advantage of the slower buring of the higher octane gas, or just use the 93 because...

My Alfa mechanic did just that, per the book, with my 64 Giulia Sprint GT way back in the 60's and 70's when higher octane Chevron 'White Pump' Supreme gasoline was available where we lived, lol, at 28 cents per gallon. Told me to use that, or tell him if I didn't.

Here is a quote I found which explains a little:

"Fuel with an 87 octane rating burns more quickly while higher-octane fuels burn more slowly. In engines designed for standard unleaded fuel, efficiency and performance is optimized for 87 octane and could actually perform WORSE with higher-octane fuel since the burn rate is slower".

So, you might want to think about that.
 

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Did you advance the timing to take advantage of the slower buring of the higher octane gas, or just use the 93 because...

My Alfa mechanic did just that, per the book, with my 64 Giulia Sprint GT way back in the 60's and 70's when higher octane Chevron 'White Pump' Supreme gasoline was available where we lived, lol, at 28 cents per gallon. Told me to use that, or tell him if I didn't.

Here is a quote I found which explains a little:

"Fuel with an 87 octane rating burns more quickly while higher-octane fuels burn more slowly. In engines designed for standard unleaded fuel, efficiency and performance is optimized for 87 octane and could actually perform worse with higher-octane fuel since the burn rate is slower".

So, you might want to think about that.
Yes, usually bumped advance and on the new/old ‘74 spider cam timing adjusted as well (still has Bosch points distributor). I have not had a 4cylinder Alfa since 1987, until now so getting re-acquainted with things.

The Spider this winter will be getting the ported cylinder head/intake/carbs/cams that your former mechanic built for his Alfetta but put on mine way back when (all being R&R but his original porting). This time though I will save all the Spica stuff and the original head.
 
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