Corvette Action Center Deep Dive Series: Gasoline for your Corvette - Page 4 of 8

Page 4 of 8
© 2009 by Hib Halverson
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Flexfuel Vette?

"E85" is a blend of gasoline and approximately 85% ethanol. Four years ago, the spin from environmentalists, politicians and GM had some thinking E85 was going to rescue us from rising gas prices and dependence on foreign oil.

It didn't happen. Reality is that E85 is slow, at best, to catch on, has economics that don't match the hype and, because it's mostly ethanol, has a detrimental effect on food prices world-wide. E85 is intended for use by "flexible-fuel vehicles" (FFV), which, through the technology of electronic engine controls, can run on any mix of gasoline and ethanol with up to 85% ethanol by volume. GM markets several FFVs, mainly trucks along with the Buick Lucerne, but, right now, no production Corvette can use E85. "We continue to believe that biofuels, specifically E85, are the most feasible and perhaps least appreciated pathway to reducing our oil dependence and greenhouse gas emissions," said Mike Robinson, Vice President of Environment, Energy and Safety Policy. "We are on target and committed to make 50 percent of our production flex-fuel capable by 2012,"

FFV fuel systems have significant differences. They have no magnesium, aluminum or rubber parts exposed to fuel. Stainless steel fuel lines, sometimes lined with plastic, and stainless steel fuel tanks, instead of tin coated steel, or plastic tanks are used. Fuel pumps must be safe with ethanol which is conductive rather than dielectric like gasoline. Tank-mounted pumps are designed to prevent arcing and filler neck flame arrestors are sometimes used. FFV engine controls support special sensors to measure the percentage of ethanol in the fuel and a greater range of injector pulse widths needed to deliver up to 40% more fuel.

While consumers believe E85 is always 85% ethanol, it's not. Federal regulations mandate 70% to 85% ethanol, however, the Government does not police that so quality control is lax. We've seen test data of samples from a few retail E85 sources n the Midwest which show as low as 64% ethanol. Also, there is no requirement for the octane of the gasoline used to make it, so E85 is typically between 95 MON and a widely-claimed-but-seldom-achieved 105 MON. The best quality E85s available to consumer, which are rare, when rated by the (R+M)/2 method consumers understand, are 95-97-oct.

>Because of its higher antiknock rating, E85 could be used in engines with somewhat higher compression which have higher specific outputs, however, burning pump gas in an engine with high enough compression for best use of E85 results in detonation, so to avoid that, FFV engines have no higher compression than engines using conventional gasoline. Using E85 in an engine with low enough compression to run detonation-free on gas results in less power, compared with an equal mass of gasoline. E85 requires an air/fuel ratio which is much richer and has a lower heating value. A FFV on E85 consumes more fuel because of its low compression, rich AFR and lower heating value and that results in poor fuel economy. In one test, a flex-fuel Chevy Tahoe averaged 18 MPG on gas, but barely made 13 MPG, or 28% less mileage, burning E85. At the time, gas averaged $3.42 and E85 averaged $3.09, or 90% the cost of gasoline. In another FFV Tahoe test, this time by Consumer Reports, the truck got 14-mpg on gas and a horrid 10-mpg on E85-29% lower mileage.

To save money with current FFVs, E85 must cost at least 25% less than gasoline notwithstanding the additional cost of the FFV engine. A CAC survey of September '08 prices in 44 states shows it averaged only 18.4% less. In very few places can it be had for the 25% less it needs to be to save consumers money after they recover the additional cost of the flex-fuel hardware. Unfortunately, it's hard to find at any price. Less than 0.01% of gas stations in the country sell it. Even worse, it's a net energy-loser. Ethanol contains about 76,000 BTUs of energy per gallon, but producing it from corn takes about 98,000 BTUs per gal. A gallon of gas has about 116,000 BTUs, but making that gallon of gas requires only around 22,000 BTUs.

C6.R race engines have been using E85 for a while, however, the fuel used by Corvette Racing is a special blend of E85 for motorsports, which is consistently high-octane and blended with cellulosic ethanol and not the inconsistently-blended, corn-derived product available to consumers, so, in a practical sense, the fact that GM is racing their Corvettes on E85 is an irrelevant PR ploy.

Last year, GM built a near-production Z06 concept powered by an E85-fueled (but not flex-fuel) LS7 as the pace car for the 2008 Indianapolis 500, Detroit Sports Car Challenge and Woodward Avenue Dream Cruise. While the E85 used in that Z06 concept, also, bared little resemblance to the E85 regular folks pump into their flex-fuel Tahoes, clearly, there has been some thought about a flex-fuel Corvette. Since it would produce less performance and less gas mileage, won't help the environment nor contribute to energy "independence," all we can ask is: "Why?".

We'll close-out this E85 discussion by saying there is a group of enthusiasts who've drunk GM's corn-ethanol coolaid and believe E85, because of its advertised 105-oct is a solution to detonation for pre-'71 Corvettes and other '60s/'70s muscle cars with high compression engines. Reality is, there are three problems with trying to use E85 for this purpose: 1) because of a flexfuel vehicle's ability to sense fuel quality and the relatively low compression of FFV engines, the octane of pump E85 is pretty inconsistent, varying from 95 MON to a widely-claimed but seldom-achieved 105 MON. This inconsistency is livable with FFV engine controls but could be disastrous in a non-computer, musclecar era Big-Block needing 98+ MON, 2) an 85% ethanol/15% gasoline mix would require a significant change in carburetor calibration which, in cases other than Holleys, might be so great you couldn't find jets big enough or air bleeds small enough and 3) because of the highly-corrosive nature of E85, fuel systems on 40+year old cars would require a new or greatly modified fuel system, from the tank to the carburetor, and that's a challenge most owners of old Vettes probably would be unwilling or unable to meet. Your best bet, if you have something like a '65 fuelie, an old LT1, a 427/435 or an L88, is a 100-octane unleaded along with a pour-in additive to prevent valve seat recession, such as Red Line "Lead Substitute", or leaded racing gas.