Alfa Romeo Forums banner

21 - 32 of 32 Posts

·
Registered
Joined
·
256 Posts
Let me throw in another twist to this thread. Out here in the corn-belt, I can get 91 octane (PON I presume) nearly everywhere and it has no ethanol. However, some gas stations do sell 93 octane but it is mixed with up to 10% ethanol. My 86 GTV6, 91 Spider, and 74 GTV work fine with 91 octane. However, I have a 65 TI with high-compression 2 liter engine that knocks a bit with 91 octane. The engine was built in Illinois by Mike Basic and we used 93 octane while the car was in Illinois and it ran just fine. Since we moved it out to Nebraska, we have been using 91 octane and it knocks a bit at low RPMs. Should I retard the timing for 91 octane or use 93 octane with ethanol?
 

·
Premium Member
Joined
·
13,053 Posts
Some years ago I had a 2l motor with Motronic pistons and an un-shaved head that gave a measured compression ratio of 9.7 to 1. It had RJ cams and 40DCOE's and probably made over 150 HP. It ran fine on 91 octane and I was unable to make it ping. I later rebuilt it with 10.6 Venolia pistons, a better head and a bigger intake cam and it made 170 HP on a conservative dyno. That motor needed only 34 degrees total advance and it ran fine on 93 octane.
I believe that you need to get on a dyno and play with the ignition timing to find out how much you need and if you get some detonation. I recently crewed for a 215 HP GTV that only needs 28 degrees of advance so it is hard to say what any motor needs without putting it on a dyno.
 

·
Registered
Joined
·
945 Posts
Way back when Fiat 850's were still common I had one with a pretty much full race engine in it, as a daily driver commuter car.
I had to run 100LL fuel in it or it would break rings.
So long as I had 100LL available it was very reliable.
I don't remember what the octane of Supreme was back in the early 80's but it was never enough.
Avgas even smells better and ran super clean too.

For my Spiders I will be running alcohol free if the octane is high enough.
If not I will mix it with 100LL Avgas as the cheap way to gain octane.
We have a local station that sells what is claimed to be 100 Octane alky free fuel, but rumor has it that it is actually just the alky free fuel laced with octane booster rather true 100 octane.
At $7.00 Gal. I want to know it's 100 Octane from the refinery.
 

·
Registered
Joined
·
6,811 Posts
I always use 91 or 93 octane on my 92 Spider Veloce.

I only put gas once a month or every other month so it is not a big deal.
 

·
Registered
Joined
·
4,289 Posts
If you use 100LL (low lead) Avgas be aware that it’s kind of a misnomer. It has less lead than the old 100/130 green stuff but it still has a LOT of lead in it. So much so that aircraft spark plugs have deep wells to cope with the deposits that get cleaned out at every annual inspection but it also gets onto valve stems and often causes problems. Just an FYI...
 
21 - 32 of 32 Posts
Top