Technical Reducing octane requirement

When I built the SBC for my Austin gasser I wanted high compression, and didn't even consider the consequences. So I went with the smallest combustion chamber heads I could find, and ended up around 10.75:1 CR on it. It performs great, and I love the engine. But I drive it more on the street than the strip, and even with today's crap gas it doesn't like running on premium even. I add either some 108 octane gas to each tank, or keep a bottle of octane booster in the trunk to dump into each tank of gas. I really should pull it down, and work over the combustion chambers to add about 10cc's to them, which still would only put them at 69cc chambers, but would make it easier to run on premium.
My recently finished '39 Chev gasser I did an engine build specifically to work well with today's gas octane ratings, and it's worked extremely well. I started with a 1990 SBC 350 roller motor, fitted with flat top pistons. I then found some early 70's 487x heads with great flow characteristics and had them rebuilt with all the good stuff I could stuff in them,; like hardened seats, iron guides, screw in studs, stainless valves, roller rockers, and high lift springs. They have 74cc chambers, and my engine is 9:1 CR, and runs well on whatever gas I feed it; even regular gas! It still has plenty of power with the intake, cam, and heads I'm running, and starts and runs well hot or cold, and always fires off in a couple seconds. I couldn't be happier with an engine build than I am with this one.

 

That's not really true. Before the feds intervened around 1980, the vehicle manufacturers and oil companies used RON (research octane numbers) to identify fuel requirements. Typical RON values were 91-94 for 'regular', 96-99 for 'premium' and you wouldn't get over 100 RON unless you bought the 'super premiums' like Chevron White pump. These latter fuels were for the 11 to 1 and higher compression ratio motors that existed at the time. The ratings weren't displayed on the pumps. Actual RON could vary by region, and that's still true today with the R+M/2 numbers displayed.

In 1979, the feds mandated the R+M/2 rating, adding MON (motor octane number) as the second number for averaging purposes and phased that in. MON is generally about 6 to 8 numbers lower than RON, so displayed numbers dropped, even if RON didn't. There was also the transition from leaded to unleaded in the mid '70s that required new fuel blending that dropped octane a few more points, although that was improved as they got better at formulating the fuel. I'll also note that this rating method is only used in North America and a few other places, the rest of the world still uses RON ratings.

As to SBF compression ratios, the regular-fuel 2V motors were usually between 8:1 and 9:1, the 4V were 10:1, only the HiPos got above that; The Mustang II Organization .

It also helpful to understand the actual difference between octanes. As octane goes up, the actual energy contained in each pound of fuel goes down. It also burns slower, which is why it reduces knock, the increased power comes from the higher compression ratio used in motors that require higher octane. Knocking is a uncontrolled burn (burning too quickly). Using a too-high octane fuel will actually reduce power and fuel economy. As an example, a Japanese motorcycle site I'm on had owners all concerned because the recommended octane was 91 RON. So most switched to premium fuel, from looking at the R+M/2 pump numbers. They lost on average 2-3 MPG compared to 'regular'.

 

I originally wanted a slightly newer 302 just for this reason but could not pass up a 16,000 original mile 302 even though I had a feeling it might not like todays gas.

 

You guys have E85 fuel over there? Supposed to have a nice and high octane number, is relatively cheap (here anyway), and is available at any gas station in many areas. Granted, it isn't without issues but if the cost of high octane gas prevents you from running that converting to E85 may be a solution.

 

Lust lean it out a bunch. The compression will eventually drop on its own.

 

Wrong AF ratio, hole is off center

 

This is what I to not want to happen.

 

This article is the best on detonation and pre ignition
http://www.contactmagazine.com/Issue54/EngineBasics.html

 

I'm with G-son, my experience is that the E85 fuel has very high blending octane value. The closest source to me is 70 miles away, but I always pick up a jerry can or two when I find myself out that way.
It's cheaper than regular gas, but has less energy value so probably about the same cost per BTU.

Of course there's the whole gamut of issues with ethanol in fuel and I would not use it in a vehicle that is going to sit, but in a daily driver I've had no issues with it. A couple gallons in one of the cars that was knocking badly cleared it up completely, at basically no cost.
Be aware though, that adding E85 to the fuel tank will lean out the mixture which may be a problem if the carb is already calibrated a trifle lean (most carbs are calibrated slightly rich).

 

Water injection is one way to stop detonation. I use it on my supercharged flatty. I use regular gas. Boost only occurs with WOT. Water injection is activated by manifold pressure switch. I use windshield washer fluid with alcohol. Not only stops detonation but also increases HP.

 

I've always found that when I try to find a "shortcut" to fix a problem, it never works right and after a whole bunch of work I end up having to do the thing I should have done in the first place. Pull the heads and do whatever you have to do to lower the compression. In the long run it will work better and be less work.

 

I guess its time to find my books for timing specs instead of putting it where I think it should be,since I put the original valve covers back on one still had the spec sticker still on it so I put it close and it kind of fixed another issue. When cold this engine ran rough and one would think that having a bit more base timing would not had a effect but it did and now runs better when cold,instead of a jet change I am going to put in a different power valve and see how that does and with less base timing and more from vacumn its running better and yes its never going to like todays gas but I think it will be ok for now.

 

Speaking of octane, came across this today:



The following is an article by the British Society of Chemists, declassified in 2014:

It seems that the German and British aircraft both used 87 Octane Gasoline in the first two years of the war.

While that was fairly satisfactory in the German Daimler-Benz V-12 engine, It was marginal in the British Rolls-Royce Merlin XX engine in British aircraft.

It fouled the spark-plugs, caused valves to stick and made for frequent engine repair problems.

Then came lend- lease and American aircraft began to enter British service in great numbers. If British engines hated 87 Octane gasoline, American, General Motors Built Allison 1710 engines loathed and despised it.

Something had to be done!

Along came an American named Tim PALUCKA, a chemist for Sun Oil at their South East Texas Refinery.

Never heard of him?

Small wonder, as very few people have.

He took a French formula for enhancing the octane of Gasoline, invented the "Cracking Tower" and produced the first 100 octane aviation Gasoline.

This discovery led to great joy among our English Cousins and great distress among the Germans.

A Spitfire fueled with 100 Octane gasoline was 34 miles per hour faster at 10,000 feet.

The need to replace engines went from every 500 hours of operation to every 1,000 hours which reduced the cost of British aircraft by 300 Pounds Sterling.

And even more when used in 4 engine bombers.

The Germans couldn't believe it, when Spitfires that couldn't catch them a year ago, started shooting their ME-109 E and G models right out of the sky!

Of course, the matter had to be kept secret.

If the Germans found out that it was a French Invention, they'd simply copy the original French patents.

The American Allison engines improved remarkably with 100 Octane gasoline, but did even better when 130 octane gasoline came along in 1944.

130 Octane also improved the performance of the Radial Engine Bombers we produced.

The Germans and Japanese never snapped to the fact that we had reinvented gasoline. Neither did our "Friends" the Russians.

In all, 100,000 Americans died in the skies over Europe.

Lord only knows what that number would have been without "Super-Gasoline".

And it all was invented just a few miles west of Beaumont, Texas and we never knew a thing about it.

"A nation that forgets its past, has no future" - Winston Churchill