Corvair Forum

I've been using Premium Unleaded in my '68 Monza since I bought it about a month ago and I've been hearing that using unleaded fuel will eventually gum up the works in the engine? Is this true? If so, what are good alternatives for fuel to use in Corvairs?

no - not true. unleaded fuel will not gum up the works in the engine.

-Scott V.

If it does you can use Gummout!

Unleaded Premium is fine -- I could be wrong but I think it's cleaner than leaded gas .

Many older cars were not supposed to use unleaded because of the valve seats but Corvairs already had hardened seat inserts .

I run premium unleaded in my car most of the time except at track events where I use that high dollar racing fuel .

It smells cool and the tailpipes burn white when at the track .

There are several issues with modern fuels and Corvairs, as described below.

UNLEADED FUEL Leaded fuel was phased-out to provide compatibility with catalytic converters, as they became the norm for emissions reduction in cars. Catalytic converters would be damaged by lead content in fuel. The lead also had some lubricating properties that helped to reduce valve wear. As the lead was phased out, hardened valves and valve seats became the norm in engine production. Because of the higher valve temperatures in air-cooled Corvairs, Corvairs were already manufactured with hardened valves and valve seat material, so the loss of leaded fuel had no negative impact on Corvair valve wear.

ETHANOL Of greater concern is the use of Ethanol (E10) in fuel. There are a number of negative impact issues related to Ethanol that can have a negative impact on Corvairs, including poor long-term storage of Ethanol fuels, as they decay faster and build up water contamination faster than non-ethanol fuels. This has less impact on daily driver Corvairs because the fuel is used rapidly, but Corvairs that are driven infrequently can suffer from "stale" fuel more quickly if it is Ethanol based. Higher percentages of the Ethanol alcohol content in fuel can actually damage older fuel systems and are not compatible with Corvairs.

You may find the following article informative with regard to the pros and cons of using Ethanol in older cars...

Tech 101 – Ethanol in gasoline and its effects on collector cars
http://blog.hemmings.com/index.php/2012 ... ctor-cars/

FUEL OCTANE RATING A number of factors affect how high the octane rating must be to be tolerated in a Corvair. Turbocharged Corvairs should always use high-octane Premium fuel to prevent detonation. When driving a lightly-loaded normally-aspirated Corvair in moderate ambient temperature conditions, many Corvairs can tolerate Regular fuel. But if you add more passengers and cargo, tow a trailer, drive in hilly terrain with lengthy uphill driving, or increase ambient temperatures, Regular low-octane fuel may not be enough -- especially in the 102, 110, and 140 hp engine configurations with higher compression ratios. If you are planning on taking the family on a long trip in your Corvair, and if the journey may include some hilly terrain, you will probably need Premium fuel to avoid that deadly pinging, rattling sound of detonation. (Taking the family, luggage and camping gear to Lake Tahoe in the Corvair for summer vacation, anyone?)

A question regarding fuel; I very occasionally get the faint jingling sound of detonation when climbing the mountain between my house and town.
If I back off the throttle, it immediately goes away, and it doesn't happen on the flat at all, so I figure it's a borderline case of pinging. I'm wondering if I need to double check the timing on my 64 Turbo, or what? I am planning on going to the Crane electronic ignition set-up soon to deliver a hotter spark then the old points and condenser setup.
Also, has anyone ever used the commercially available octane booster additive in their Corvair? I am running Premium fuel, but it is 10% Ethanol, as the only Ethanol free gas around here is mid-range Octane, not Premium.
Which would be better, the Premium Ethanol added gas, or the mid-range Ethanol free with octane booster added?
The car isn't exactly a daily driver, but I will go through a tank of fuel within a 2-3 week period, and it will be more during the summer when I can drive more as the weather improves.
I don't think the Ethanol in the gas will make a difference as far as "stale" gas in that short a period of time, but I'm not sure.

The recommended timing setting of 24° BTDC is a recommended starting point. Since there are no sensors on the old Corvair to detect signs of detonation, and no computer to automatically make adjustments in the ignition timing to protect the engine, it is up to you. Your "sensor" is detecting (hearing) signs of detonation when you are climbing a long grade with your engine under boost. Your on-board computer (brain) responds appropriately. When you back off the throttle, the boost goes away, and so does the detonation. The fuel octane is a critical element in the design of the turbocharged Corvair engine. The octane rating of the fuel you are using is not quite up to the task with your current engine settings, so if you cannot increase the octane rating of the fuel, you need to adjust other variables to prevent detonation. The pressure retard device on the distributor works (hopefully) to retard the timing under boost. If that is not enough, your only option is to lower the static timing a little to further reduce the total timing advance that is in effect. A little trial and error with retarding the timing a degree or two will likely help to protect your engine and eliminate the detonation you are hearing. Lowering the initial timing setting a couple of degrees may produce a slight power loss at some engine operating speeds and normally-aspirated operating conditions, but all settings are a rough predicted compromise since engine sensors and computer control was not an option back in the 1960s. Power loss when detonation is occurring can be much-more significant, and the physical damage that can result in a engine combustion chamber under detonation conditions simply cannot be tolerated! Ultimately you are tuning for maximum performance under full boost conditions. The design limitations in the Corvair may not permit fine tuning at all power settings for maximum power throughout the operating range of the engine.

Just remember that your turbocharged Corvair was one of the first turbocharged engines ever mass produced, and it has some pretty antiquated designs with minimal technological protection built in. A long, sustained period of operation under boost on a warm day while climbing a long hill is a pretty rough go for your engine — probably one of the most difficult things your street turbocharged Spyder or Corsa has to endure. Short periods of boost while accelerating up to the desired speed is usually OK. A lengthy, sustained hill climb under continual boost is perhaps too much to ask! I found that out one hot summer day in 1971 when I was driving my turbocharged Corsa in southern California from Camarillo to Thousand Oaks on the Ventura Freeway — a lengthy section called the "Conejo Grade". As I neared the crest at about 70 mph, one of my pistons decided to vent its frustration!

My poor piston!!

You might try non-Ethanol Premium if you can find a gas station in your area that sells it. It produces more energy per gallon and the change might improve your gas mileage a bit, and perhaps produce a little more normally-aspirated power for that hill climb.

Ethanol creates 34 percent less energy than unadulterated gasoline per gallon. This equals a loss in fuel economy of up to 3 miles per gallon for E10 fuels. In terms of heat, ethanol produces 76,330 BTU per gallon, whereas diesel fuel produces 128,450 BTU per gallon, gasoline 116,090 BTU per gallon and LP gas 84,950 BTU per gallon. The fuel economy gets even worse with E85, a loss of 7 to 8 miles per gallon with its higher ethanol content. Consumer Reports, testing in 2006, verified a loss in fuel economy of up to 30 percent in a Chevy Tahoe designed to run on flex fuel when it was tested with both unleaded gas and E85. Poor fuel economy can also be attributed to improper fuel system calibration based on computer feedback from oxygen sensors because of the temperatures needed to burn Ethanol.

Ethanol is hygroscopic, which means it absorbs water more easily than gasoline. That leads to water condensation inside fuel tanks, carburetor fuel bowls and fuel lines where air spaces are present. Water content in fuel will also swell up the paper filter media inside fuel filters not specifically designed for flex fuels and can thus restrict fuel flow at the filter.

http://blog.hemmings.com/index.php/2012 ... ctor-cars/

E10 and E15


Label required on pumps that dispense E15. Label reads as follows: ATTENTION. E15, up to 15% ethanol. Use only in 2001 and newer passenger vehicles Flex-fuel vehicles. Don't use in other vehicles, boats or gasoline-powered equipment. It may cause damage and is prohibited by Federal law.

E10 and E15 are blends of ethanol and gasoline—the number after the "E" indicates the percentage of ethanol.

Most of the gasoline sold in the U.S. contains up to 10% ethanol—the amount varies by region—and all auto manufacturers approve blends up to E10 in their gasoline vehicles.

As of 2011, EPA began allowing the use of E15 in model year 2001 and newer gasoline vehicles. Pumps dispensing E15 must be labeled (see example). The vehicle owner's manual may indicate the manufacturer's maximum recommended ethanol content.

Vehicles will typically go 3% to 4% fewer miles per gallon on E10 and 4% to 5% fewer on E15 than on 100% gasoline.

If I run anything less than 91 octane, my Vair is not happy.

Any national brands that sell 91 octane? I get the best gas I can find in my little town, but I think it's 89.