Fuel Question

The answer is "maybe" depending on several engine parameters. A performance cam can reduce piston pumping pressure at low rpms such that it allows slightly lower octane fuel to work at low rpms. Same for retarded ignition timing. Neither work at very high rpm and the danger is that sheer engine noise will mask detonation noise. Finally, there are several ways to rate gasoline octane. The US and Canada use the 'research' or 'R'  method while Europe & the far east use the 'M' or Motor Octane Number method that gives a higher number on the same fuel. Then there's the 'R+M' rating which is an average of the two. Google 'octane ratings'- WIKIpedia has a good description.

Without getting too technical, the simplest way to answer your question is simply to pump a few gallons in and go hammer the engine on a straight road. If a thoroughly warmed up engine rattles on acceleration, return and add more gallons of a higher octane to dilute the first one & raise the anti-knock rating of your combined fuels. If you fill up, you have no room in the tank to do this.  Do not waste your time with 'octane boosters'. Some work but most don't and weeding out the useless ones is an expensive task. And if you do find one that seems to help today, there's no guarantee the usually small additive company will make the same product next week.

If you have an expensive modified engine and you get it professionally tuned, they will probably use 102 or even 110 octane racing fuel while tuning, as a safeguard. VPI in the U.S. has about 50 different blends, none of which are cheap or available at any corner gas station. I used to drive another guy's race Pantera with such an engine and the owner ran low one day and added a cheaper 15% blend of gas/alcohol advertised at around 100 octane. We had to bump-start the thing in the gas station- it wouldn't start on the starter. It detonated at idle- you could hear it knocking 20 feet away. He limped it home a few blocks and drained the tank. That fuel had a slightly higher density and his highly tuned Holley couldn't flow enough of it thru the carb jets to work safely. It would have taken a full re-jetting the carb & adjusting the timing on a dyno- again- to allow that 'cheap' fuel to work. Fortunately the adventure did not result in cracking a piston.

Thanks Boss,

In my area there are two Fuel choices:

93 with 10% Ethanol or

90 with 0 Ethanol

Which would be better suited to:

The Engine is highly modified with FAST EFI,Comp Cams Solid Lifters Aeromotive Fuel Pump and Controller 6AL etc.etc built by an now long gone Dirt Track Racing Shop.500 + HP 10.5 Compression.

I'm more interested in reliability now that it has been modified with enough HP for me.

The retail fuel companies know what they are doing. Use the highest rating you can find.

The only way that you can now compensate for your static compression ratio is to use a custom cam. It will be leaving the exhausts open for so long, you will be throwing flames out of the exhausts.

Now bear in mind that you need to be talking about actual measured static compression ratio, not "advertised" compression ratio.

Most Ford engines that were advertised as around 10.5:1 actually measure out at closer to 9.5:1.

About the highest static ratio you can run is just under 10:1 with 92-93 pump gas. The ethanol doesn't hurt anything. Don't worry about it.

Sorry to say at actual 10.5 you are going to need the old 103 and it's going to be leaded. That's now Sunoco racing gas and the last time I was on the track was $7.50 a gallon, and left freakin' lead deposits on the plugs that you can't believe.

It also IMMEDIATELY drops your idle rpm down from say 900 with street pump gas to somewhere around 750rpm.

Now the ONLY reason you should even want to run it is for detonation reasons. Higher octane gas produces less heat calories and therefore less horsepower then even regular does.

Don't create a problem that you don't really have.

We put C12 in every car that leaves Pantera Miami.  No need to run it straight.

What about the Ethanol factor....

RON 93 with 10% or

RON 90 with no Ethanol ?

I am in Canada and locally I have access to Petro Canada Ultra 94 with Ethanol and Shell V-Power 91 without. I haven't had problems with either, but am loyal to Shell and know of quite a few strong motors that don't have an issue on it. A couple years ago I was reading a few forums on which was better of the two. Of course there is lots written on the ethanol vs non and I came to find the story of a small time independent circle track racer (I can't remember if it was dirt track or pavement) that was in a class that couldn't run race fuel. He was quite competitive that year and was fighting for sponsorship. He said being an independent at the time and having to watch every dollar and make every race point count he had quite a few things broken down stat wise. In regards to fuel he said he was consistently getting a lap to a lap and a half more out of the Shell 91 vs the Petro Canada 94. He wouldn't have been pushing high horsepower in his class, but I thought it was an interesting statement.

Thriller,10% alky is OK IMHO and it does pick up the octane noticably. It's when the percent gets higher than 10% is when things tend to go sideways. FWIW, my 1990-build 351-C has SVO aluminum heads, an SVO hydraulic flat tappet cam, Rhodes fast bleed lifters and forged pistons with a measured 10.5:1 C/R . Ignition timing is at 29 degrees BTDC. It runs without knocking on 91 octane pump gas. I've used up to 1/3 tank of 89 octane when forced to on the road, but I also don't hammer the engine with that stuff, & i add 91 octane ASAP.

Caveat- I'm also at 4600 ft average altitude and my Bob Oliver-modded Holley is jetted for it. Years ago we got 22 mpg over the desert to 'Vegas- and back (1000 miles) on pump premium with precious little travel below 90 mph, so it CAN be done without race gas & higher compression.  Judy did an open-track day at Spring Mountain raceway without incident during that trip, too. You gotta pick your parts correctly & drive accordingly. NOT a race engine & way under 500 bhp!

@otis posted:

I am in Canada and locally I have access to Petro Canada Ultra 94 with Ethanol and Shell V-Power 91 without. I haven't had problems with either, but am loyal to Shell and know of quite a few strong motors that don't have an issue on it. A couple years ago I was reading a few forums on which was better of the two. Of course there is lots written on the ethanol vs non and I came to find the story of a small time independent circle track racer (I can't remember if it was dirt track or pavement) that was in a class that couldn't run race fuel. He was quite competitive that year and was fighting for sponsorship. He said being an independent at the time and having to watch every dollar and make every race point count he had quite a few things broken down stat wise. In regards to fuel he said he was consistently getting a lap to a lap and a half more out of the Shell 91 vs the Petro Canada 94. He wouldn't have been pushing high horsepower in his class, but I thought it was an interesting statement.

It may have just been a reference that he acknowledges that higher octane fuel produces less heat calories and as a result less total horsepower?

I'm surprised that anyone would notice the differences between a 91 and a 94 octane fuel.

The advantage to say 108 Sunoco leaded racing gas is that you can run higher static compression ratio but in order to take advantage of that, you need to alter the distributor advance curve and probably the cam timing events. You would gain horsepower and torque by doing so but to go back to 91 unleaded pump gas you would have to reverse that.

So to say that you make more power with racing gas, it isn't the gas that makes more power, it's the other mechanical changes it allows you to make.

A street car that puts 5 gallons of 108 in at the track is only likely to see the engine idling down from 900 to 750 or so.

If you set up your engine with 10% ethanol gas then you have already made the adjustments to it. That amount of alcohol won't hurt anything in the engine. At 20% you are going to have problems with any rubber based components like fuel lines exposed to it.

You would need to read the engineering specs of the product that you want to use like an "Aeroquip) -6 fuel line to see if it is certified for alcohol exposure.

Sorry, I don't believe it was a reference to the power, but more that he was getting better mileage a lap to a lap and a half between refills. The motor was performing the same while using less fuel.

Since the car was performing well on both fuels he was going to use the one that burned less for less pit stops.

Our county road grader operators often note similar things when counting how many hours putting on the machine they could operate more hours on Shell and Esso compared to Co-op and UFA diesel.

Petro chemicals is a very complicated field.

There is a gasoline commercial running here, I don't remember the brand at the moment, that claims it gives 50 miles more per tankful. Of course they don't define what a tankful is.

One of the shortcomings of ethanol as I recall, is that it is much less efficient then petroleum based fuel. So I'd look to the blend or additive for the answer to the better mileage claim.

Otis,

Shell Canada now has 93 octane with no ethanol. Also, Chevron self-serve stations, in Canada, have had 94 octane with no ethanol for years.

Good to know, David. Very few Chevron stations in Alberta. We are still limited to 91 Shell in the central region, but have never had an issue with it. I will have to check Calgary or Edmonton next time I am there.