REC-90 Gasoline

[Jeff B.]

Requesting comments/opinions on a new (?) gasoline (REC-90) that has recently become available in my area. Supposedly an ethanol-free unleaded gasoline of 90 octane (RON or MON?). Marketed primarily for marine engines and others that perform better with non-ethanol laced fuel. I have not tried any yet, as I wonder if the octane is sufficient for my bone stock 67 390hp with 10.25CR?
Thanks for any thoughts.

[Duke W.]

Re: REC-90 Gasoline

Posted octane number, sometimes known as pump octane number (PON) is the arithmetic average of RON and MON, (ROM +MON)/2. So it's less than "premium" 91-93, depending on state, but greater than regular 87 or "mid-grade" 89.

10.25:1 is the advertised CR of the 427/390, but it probably left the factory a few tenths low due to high decks, and how do you know what it is today, especially if the engine has ever been rebuilt with typical lower compression pistons and thicker head gaskets?

The only way to know if YOUR ENGINE will tolerate 90 PON is to test. No one else can tell you one way or another, due to differences in individual engines (even of the same configuration) and differences in ambient air conditions (altitude and ambient temperature/pressure range) where you live from other parts of the country.

Let the fuel get close to empty and add 2-3 gallons of the 90 PON. Then test for detonation. Load up the engine at low revs on a hot day. If it detonates you might be able to eliminate it with a bit less initial timing, but I don't recommend going below 4, which should yield 36 total WOT advance at 5000 assuming you have an OE centrifugal curve.

If it doesn't detonate run the test at least two more times, and if it doesn't detonate, you're good to go, and you might be able to advance the timing a couple of degrees.

You'll find more details in my tuning seminar which is attached to the restoration documents thread near the bottom of the sticky section.

Duke

[Larry E.]

Re: REC-90 Gasoline

Requesting comments/opinions on a new (?) gasoline (REC-90) that has recently become available in my area. Supposedly an ethanol-free unleaded gasoline of 90 octane (RON or MON?). Marketed primarily for marine engines and others that perform better with non-ethanol laced fuel. I have not tried any yet, as I wonder if the octane is sufficient for my bone stock 67 390hp with 10.25CR?
Thanks for any thoughts.

Jeff: Just curious what is the cost/gallon of the above(REC-90)? I use straight 100LL Av. Gas which is $5.50/gal
at my local airport for my 66 L72. Larry

[Jeffrey S.]

Re: REC-90 Gasoline

Jeff,
I have been using 90 octane rec fuel for 2 driving seasons on my 69 small block which was rebuilt to have a true 10.25:1 CR and has never detonated at 36* full advance. However, it did, on occasion run on when shut off so I went back to adding a few gallons of 100LL from the airport near me. That must have raised the octane a few points and it solved the problem. It's just very inconvenient to have to fill a gas can and then transfer it to the car.
Jeff

[Mark E.]

Re: REC-90 Gasoline

Test driving fuels basically as Duke suggests, my 1970 LS5 (the 454 version of your engine...same heads, cam, CR) will run on 87 octane ethonal-free with minimal pinging IF timing is significantly retarded. Performance is noticably affected. It runs much better with timing close to optimal and using this fuel mixed 25% with 93 octane that has 10% ethanol.

To minimize exposure to ethanol, I drive the car with this mix, but store the car filled with ethanol free fuel. After several years of this, so far no corrosion noticed in the tank or carburetor.

[Gary C.]

Re: REC-90 Gasoline

Mark,

Problem caused by ethanol in classic Corvettes, is not only corrosion, but it melts the rubber hoses and gasket material.

Found out about ethanol the hardway when we moved to Nebraska in 1970, which along with Iowa mandates ethanol in their pump gas to support corn growers in their States.

Gary
....

[Duke W.]

Re: REC-90 Gasoline

Since so-called "gasohol" has been available in some areas since sometime in the seventies, automotive elastomers have been reformulated to tolerate 10 percent by volume ethanol.

So the question all should ask is how old are the rubber fuel hoses on your vintage Corvette, and remember that on C2 and C3 models if the hose from the frame pipe to the fuel pump nipple ruptures, the entire content of the fuel tank will drain out and this hose is subject to relatively high operating temperatures that will shorten material life.

Duke

[Joe L.]

Re: REC-90 Gasoline

.... and this hose is subject to relatively high operating temperatures that will shorten material life.

Duke

Duke------


....and especially so for big blocks!

[Jeff B.]

Re: REC-90 Gasoline

Jeff: Just curious what is the cost/gallon of the above(REC-90)? I use straight 100LL Av. Gas which is $5.50/gal
at my local airport for my 66 L72. Larry

Larry:
The REC-90 is sold thru a separate pump isolated from the typical pump islands that offer the three grades of unleaded. Price for the REC-90 is $4.999 per gallon.

[Jeff B.]

Re: REC-90 Gasoline

Posted octane number, sometimes known as pump octane number (PON) is the arithmetic average of RON and MON, (ROM +MON)/2. So it's less than "premium" 91-93, depending on state, but greater than regular 87 or "mid-grade" 89.

Duke

Duke:
Out of curiosity, what would you estimate the research octane (RON) of this REC-90 be?
Having been a distributor for Gulf Oil from 1966 until the BP merger in 1986, I remember our Gulf NoNox (premium) was rated at about 103 RON, and our Good Gulf (regular) was about 97-98 RON. Since this REC-90 is supposedly 90 PON, I think this might translate into a RON of around 99-100. What would be your guesstimate?
Jeff

[Duke W.]

Re: REC-90 Gasoline

The difference between RON and MON is called sensitivity and is usually in the range of 8-10. So 90 PON would likely test between 94 and 95 RON and 85-86 MON. And the Aviation Method would test about the same as MON.

Back in the sixties "premium" fuels were usually in the range of 97-100 and "regular" about 94. On the West coast Chevron had their "white pump" which was supposed to be 103 RON. True octane ratings were not required to be posted, which gave blenders considerable latitude. For example for a given grade blenders could get away with lower octane numbers in cold winter temperatures and higher altitudes than in summer temperatures and low altitudes.

More info on this subject is in my tuning seminar that is in the restoration documents thread, next to the last thread in the sticky section like how octane numbers over 100 are determined.

Duke