Selecting octane levell for new engine build[?]

[twas_brillig]

We'll probably be building a 1275 for a bugeye this summer and I got thinking about what octane level/fuel choice (i.e. compression ratio) that we should consider, and would appreciate thoughts.
1 - not a lot of annual mileage expected each year, which means cost differential isn't real critical
2 - ethanol is generally viewed as a Bad Thing for old vehicles not getting a lot of miles on them, and premium seems to be the only way to reliably avoid it
3 - if the engine can handle lower octane, should we burn premium in it?
4 - if we're going to burn premium anyway, why not go higher compression?
In some ways, this is a bit of a rabbit hole to disappear into. Comments appreciated on points I've missed and any other aspects. Thanks, Doug

 

[JPSmit]

For me the ethanol is the issue - I only run Shell gold - so, yeah, you might as well go higher compression.

OTOH - will you be ever running a turbo? which would need lower.

 

[dklawson]

I cannot speak about Canadian fuel blends but down here just because fuel is premium does NOT mean it is free of ethanol. Here ethanol is added to the fuel to lower emissions and it is typically in all grades.

My advice for a limited use vehicle is build for a compression ratio between 9 and 10:1. Run premium. Put a fuel stabilizer in each time you fill up. (Stabil "red" is for storage, "blue" is for ethanol protection).

With the tank of premium, drive the car under load (uphill in too high a gear, throttle floored). If you hear pinging and spark knock, retard the timing 2 degrees and repeat the load test. Stop turning the timing back when the bad noises disappear.

 

[Bayless]

Interesting Doug, your suggested method of setting the timing is exactly what the owners manual for my 1948 Prefect states.

Also, I guess we are lucky here in Oklahoma but there usually is no problem getting pure dinosaur fuel, usually in all grades. Used to be a 10 cent differential but now considerably more. Still I never use ethanol. Since retiring a few years ago I fill the Explorer once/month and the Saab (the turbo wants the highest octane it can get) more like every 3 months so the cost is not a major factor.

Oh, I generally agree with Doug's and JP's suggestions. It's a fun car so make it as much fun as you can.

 

[nomad]

Well, I've been arguing against this Ethanol paranoia for decades now. I run it all the time and have since it went on the market. Similarly, I've always viewed the gasoline stabilizers as "snake oil". I have stored my cars with ethanol blended fuel for at least a couple of years with no problems and no stabilizers. Longer if it was not blended fuel. The alcohol is volatile and doesn't last as long as gasoline. Also doesn't get the mileage since there just isn't as much energy in alcohol. The cost offsets that. The alcohol raises the octane and was put in as a substitute for a known carcinogen the gasoline people were using for that purpose after lead was taken out. We have a few blender pumps and they have been responsible for resurrecting a few old hot rod engines that have too high of compression for today's pump gas. I doubt the gasoline suppliers mind putting in dirt cheap alcohol since they can blend some pretty substandard gasoline with it. Alcohol is priced on the board of trade and usually sells for around a buck a gallon. Of course when it is blended at 85% with gasoline somehow it ends up about the same price as gasoline! Wonder how they do that.

My personal limit on compression is 9.5/1. I rebuilt a MGB in the 70's with high compression since back then that was the cheapest way to get power. Unfortunately, not long after the 105 Ethyl gasoline went away and I fought that car 20 years. Kept it till the 90's.

 

[nomad]

Should have mentioned also that if you have to back off the ignition timing to stop the rattle from too high of compression that you give up a LOT of power. My hot rod MGB turned into a slug after the high octane fuel went away.

 

[JPSmit]

Carrying on with the conversation - in Canada at least Shell Gold is ethanol free. Nomad, I understans your point. OTOH I have had all my gumming issues go away with ethanol free- particularly with my lawn mower.

What this conversation has reminded me of though is that there may be merit to sending your distributer to Jeff at Advanced Distributer to have it recurved for modern gas. I haven't for the Midget - but, did for the Vauxhall - which isn't on the road yet so I can't provide a difinitive review.

 

[nomad]

Well, I hope no one takes affront by my stand and I have pretty much given up on converting folks. Yes, I am, of course, biased since I have grown corn all my life.

The internal combustion engine wasn't developed for gasoline specifically and up to the days of prohibition alcohol as a fuel gave gasoline a pretty good run for its money. In fact there are those who claim that prohibition was caused by Standard oil wanting to get rid of the competition. I'm sure purveyors of gasoline gave the T-totalers plenty of help.

Anyway the two things I have found ethanol blended gasoline really good at is cleaning out a system of water especially. Dissolves lots of varnish as well.