Recommended fuel for 308 with 10.2:1 and P6 cams

Please do not take this as definitive information for a 308, but I have two non Ferrari engines with aluminum heads that run over 10:1 (10.3 and 12.5) and both run fine with 92 octane pump gas. The 12.5 engine does have a modern engine management system, but the 10.3 engine is old school with (tweaked) mechanical advance.

 

I have oversized 10.5 pistons in my 308GT4, if used 93 octane with ethanol I'm ok, but I use ethanol free 91 octane and I ping ever so slightly under hard load. For that I use Torco octane boost which works well.
https://www.summitracing.com/parts/tic-f500010te?seid=srese1&gclid=Cj0KCQjwqpSwBhClARIsADlZ_TkrWZrDQLCaoiVBQ29Q4iqANVko8C-51zCK2TDqWf6FH2EUV1wujq0aAl1NEALw_wcB
In my '67 Alfa GTV with 11.5 compression 2L, I use a higher concentration of the same on the street. On the track I'll put in 50/50 112 race fuel.
I followed that 308 ale, looks like you got an awesome car. Have a great time with it. Pete.

 

fyi, always used 93 without issue

 

Did you cc everything to conclude that is the actual ratio?

edit....I just read you dont know the bore size so you are guessing on the ratio. You can never trust a piston manufacturer. If the shop that built it kept the build specs that would nail it down.

 

91 octane is fine with 2v carbureted 308s even with bumped compression and P6 cams. The volumetric efficiency of the 2v 308 heads (not great) is such that the static compression ratio, likely even up to 11:1 or so, is likely never dynamically reached. I'd say it reaches maybe 95% volumetric efficiency tops with most hot street builds, which in your case with 10.2:1 static cpr means you're fine. 2v 308s are a wonderful thing but the heads just don't flow enough to really get you into trouble with fuel octane unless you're running really high static cpr, I'd guess 11.5:1 or so, or if the heads have been ported to some magical to-date unseen amount of flow.

 

I use 101 at the VP pump in my 328 and my car is stock. Thats the easiest and best way to go in my estimation. I also use it in my Hyabusa. I use it in my 328 whenever I remember to go to that station which is right down the street from me. The gas in Cali sucks for sure, so I treat my car to a tankful when I can.

G

 

I notice a difference in the way my car runs on the 101. It pulls a little harder , slightly even. What is noticeable , when Im just about at red line in 4th gear, I can reach 125 MPH on the freeway, when Im on that disgusting 91 crap, I can barely get to 120 MPH in 4th gear.

My 328 loves the 101, and like I said, I fill up with it whenever I can. Its to bad it doesnt have lead in it, it would be even better. I dont run a cat converter in my 89, and with the 101 the car runs even better.

G

 

Oddly it's not the octane but that 101 race fuel is cleaner then the others. The 3x8 series engines just don't have enough CR to warrant octane that high.
Please note, the higher the octane the harder it is to ignite. So at a certain point the fuel is wasted as the full energy isn't released. Too low of an octane for high CR is where detonation occurs as the compression temperatures of the air will ignite the fuel before the spark.. that's BAD. 308 & 328 Don't have high enough CR to do that on basic pump gas.
Static and dynamic are two different CR's and dynamic is where it matters. Factory dynamic CR is low, under 8:1 if I recall correctly.

91 non ethanol fuel would be the sweet spot. And non existent here in socal.

 

The old shade tree way of "adjusting" for octane was to advance the timing until it pinged and back off two degrees.

FWIW, on conventional (non-computer-controlled) engines we never saw any difference in power on the dyno by increasing the octane above whatever was specified for the engine UNLESS timing was advanced to take advantage of the increased octane. IOW, if 89 Octane/whatever timing setting produced power with no pinging, going to 93 octane did not increase power. BUT going to 93 allowed the timing to be advanced and THEN produce more power.

I don't know if the Microplex can make appropriate timing/fueling adjustments. If it can, then higher octane fuel could increase engine power up to some point depending on whatever parameters are in the timing/fueling curve. But if the proper octane fuel is used, going to higher octane fuel won't increase power on its own. One would ASSume that the octane rating specified by Ferrari would produce the maximum power the engine is capable of. But Gino's input suggests otherwise...

Somewhat related... it is a simple, one wire change to convert the Mircoplex timing curve from USA to Euro. Doing so advances the timing at low/midrange and makes a noticeable difference in acceleration in a 5 mph roll-on in first gear. I've been running Euro timing since around 2010 when I read about it on this site when RifleDriver posted about it and I did many such "roll-on" tests with a temporary switch that could instantly shift the timing from US to Euro.

 

Don't forget the lower crossover tube rubber connectors. When I took delivery of my car in '22, mine were rock hard and beginning to crack.

 

Yes. Easy to overlook. Also 23, 24, and 27 in the diagram, though those just generally handle fuel vapor, leaking there is not good. These vent hoses are 5/8" (or16mm) ID IIRC. Pegasusautoracing.com is a good source for fuel rated line in various diameters and short lengths, as well as the Ferrari regulars. When replacing the lower crossover hoses, after you have drained the fuel from the drain plug on the cross tube, which is after you have pumped all the fuel you can via the fuel pump and a piece of hose into a gas can or three, its easier to just cut them off, either by slicing clean through the middle, or by slicing lengthwise. I have a hose/pvc slicing pliers-like tool that can do up to 2". Available at Home Depot and similar in the plumbing aisle. There will still be some fuel present, so do this all outdoors if you can, and be ready to mop up a half pint or so.

 

Someone here in Omaha besides me?
One mile straight west of Millard North HS.