KILRWAIL

My engine is a 3.2 litre based on a 3.0 case with 98 mm pistons and PMO carburetors. Compression is about 9.3:1 and the carb’s are jetted conservatively to run rich at an AFR of about 12.5 at 6000 rpm WOT. I have an Innovate AFR gauge with 2 oxygen sensors. Timing is set to peak at 30 BTDC and I have colder than normal NGK BP7ES plugs with an MSD system.

I want to use a higher octane fuel than Shell 91 V-Power and I don’t want any ethanol that I would get from Sunoco/Petrocan 94. I can buy leaded 110 race fuel or unleaded 110, 114 or 120. I can either mix a race fuel with 91 unleaded or use it straight, since the car is almost never driven on the street.

I’d be interested in any and all opinions/facts about the different choices of fuel.

Makmov

Why do you want to use a higher octane fuel? Does it pre-detonate?

Here is the truth about fuels. Octane is an anti-knock additive period, and has nothing to do with fuel performance.

Fuel density is everything. You can have a high octane fuel with low density = low performance or a high density low octane fuel with high performance.

You need a hydrometer and check the specific gravity of the fuel you are using to know for sure what the density of it is. 0.71–0.77 (0.026 lb/in3; 719.7 kg/m3; 6.073 lb/US gal; 7.29 lb/imp gal)

BTW US Shell V-Power is 10% ethanol.

Amber Gramps

You are going to find dozens of opinions on the subject by doing a search of "100 octane".

What I typically do is spend $50 at Chevron on 91 octane, then drive across the street to VPRacing and spend $50 on 100 octane. It makes a nice potent 95 octane blend that combined with the chip (I'm not allowed to talk about here) makes for one insanely neck snapping ride. Seriously don't try this at home.


https://rennlist.com/forums/911-foru...ml#post4296220

Steve Weiner-Rennsport Systems

Peter,

Currently, your timing is conservative and looks like its set for 91 octane pump gas. This permits safe running with that fuel, but sure leaves a bunch of performance on table that you can take advantage of by using better gasolines.

You can use 104 octane unleaded or 110 octane leaded race gas to permit more timing and better acceleration and power. Any more octane is simply a waste and in fact, can cost performance. There is a LOT more about race gas than simply comparing octane numbers and specific gravities so you need to know more about whats available in your area.

FWIW, ethanol has a RON rating of 116 so that in itself not a liability. Its BTU content is the main issue and that can be compensated with by jetting. Your 91 octane, E10 pump gas simply lacks sufficient octane in its blended state to support much timing with these engines at your CR.

g-50cab

If you car sits for more than 90 days at a time I would do whatever you can to either put zero ethanol gas in E0 or use marine version of sta-bil.

Beyond that - and with that engine - if it's rarely driven on the street I might be inclined to push the timing up for 110 and unleash that snarling beast. - That sounds like more fun!

KILRWAIL

Thanks for the feedback guys. I'm surprised no one mentioned the destructive effect of leaded fuel on the O2 sensors. Given all of that and the reading I've done, I plan to start with a 50/50 blend of 91 and 110 unleaded and experiment with slightly more timing advance (31-33), while monitoring cylinder head temps.

theiceman

leaded fuel ? i didn't think you could even get that for the last 30 years