Availability of racing gasoline

[Mark G.]

Re: Availability of racing gasoline

I use Sunoco gt unleaded 98 in my 69 L71. If you need leaded fuel, try a local race track, although it won't be cheap.

[G B.]

And... we're OFF!

I really hesitated to mention Rochester FI spider percolation again. It always causes confusion. Spider percolation is not caused by ethanol content or lack of lead additive. It is not pre-ignition, vapor lock, or detonation.

A stock Rochester FI unit fuel bowl reaches a steady-state temperature of about 130 degrees in normal operation after driving for about 20 minutes. The fuel inside gets hotter in warm weather and after a heat soak during a brief stop. The gas in the spider gets even hotter through conduction heat from the nozzles. Depending on the particular fuel you're using, this heat can cause some of the gas in the spider to boil during idle... especially immediately after a heat soak period. The engine will idle roughly or not at all when this happens.

The gasoline pressure in a Rochester FI nozzle at a 750 rpm idle speed is about .3 psi. If you up that pressure significantly without upping the idle speed, the idle A/F ratio will be too rich for a smooth idle. However, you can up the gas pressure by just increasing the idle speed (a whole lot) and prevent percolation that way.

There are many other ways to limit percolation. You can restrict driving to short distances or just in cool weather. You can keep your foot on the gas when idling. You can remove the hood. You can cool off the gas going to the unit by rerouting the fuel tubing from the tank and by-passing the engine mounted fuel pump. You can also direct a stream of cooling air at the spider from an auxiliary fan set-up. You can even install heat insulating materials to connect the spider to the FI unit. Jim Lockwood has discussed this as well as re-plumbing '57 - '62 spider feed tubing to recirculate fuel from the bowl like a '63 - '65 unit. All of these methods help reduce percolation events.

Per ASTM specs, 100 LL aviation gasoline has a higher 10% boiling temp than pump gas (167 degrees vs. ~158 degrees for summer pump gas). However, I still had some percolation on hot restarts when using av gas the last time I experimented (2012). The VP110 spec sheet states a 10% boiling temp of 184 degrees. The Sunoco 110 gas 10% boiling temp is 174 degrees. I've never tried the magic cures such as Jet A (high grade kerosene), octane boosters, diesel fuel, or Marvel Mystery Oil as gasoline additives. But, for the life of me, I can't imagine how they could possibly affect the 10% boiling temp of pump gas significantly.

Personally, I choose the path of least resistance. I use undiluted racing gas. It has eliminated spider percolation in my life. It's not cheap, and never will be, so that is not my complaint or question. My question was about availability in other parts of the country, and why scarcity might be in the future.

Thank you all for your responses. It sounds like racing gas is still commonly available, and that it can be found at a "reasonable" $10 a gallon.

[James G.]

Re: Availability of racing gasoline

I use Sunoco gt unleaded 98 in my 69 L71. If you need leaded fuel, try a local race track, although it won't be cheap.

What is the charge pergal ob tge 98 unleaded?
I have been using SONOCO 110 leaded available locally on the pump at $11.99 a gal last time I bought it, about a month ago.
I am switching to 100LL as I can buy it for $5.72 a gal when I checked last week. I have another customer who runs 100LL in all of his 11:1 big blocks, he swears by it.
FWIW the RVP of Sonoco 110 and 100LL are both mid 6's. Reid Vapor Pressure

[Mark E.]

Re: Availability of racing gasoline

Mike, I've found that av gas, marine gas, and pump premium don't work well for me in '57 - '62 units at idle on a 95 degree day in heavy stop-and-go traffic.

It's impressive that a guy still commutes in heavy traffic with his C1 fuelie.

[G B.]

I yam what I yam.

It's impressive that a guy still commutes in heavy traffic with his C1 fuelie.

But I'm not able to impress anyone. I just drive an old Corvette at every opportunity: getting a haircut, going the post office, eating out, runs to the parts store... whatever.

Driving is one of the fun things my wrinkledy ass can still do. I don't drive on freeways much or at night, however. Actually, I don't go anywhere after dark except to bed. I'm not exactly what you young people would call a "hepcat".

[Michael G.]

[Mark F.]

Re: Availability of racing gasoline

Hi Mike,

Interesting - and yes, good luck!

Couldn't you deduce the same relationships just by looking up the vapor pressures of each component you're interested in?
They should be listed as part of the ingredients on the Safety Data Sheet (SDS) and should roughly follow an inverse relationship to their respective boiling points (distillation temps). Higher VPs correlating with Lower BPs... FYI - BPs are probably also listed on the SDSs.

Finally, please be careful!
MANY years ago in Organic Chemistry, I remember fellow students across the lab bench from mine failed to properly grease the connection between their flask and the distillation column. Of course, they had the gas flame too high (no, we weren't using electric heating mantles), which ignited whatever it was we were distilling (can't remember what the mixture was). They panicked and backed off w/o shutting off the gas. Fearing the whole thing might explode, I reached over from my side and shut their gas off...Never forgot that lesson - always grease your fittings!

If you go the lab experimental route, let us know what you find out and what your conclusions are!

hmmmm...just looked up several gasoline SDSs on the web. They were not listing individual component VPs/BPs, etc. I guess you'd have use the CAS# to look up those values. Back in the day, I seem to recall more Physical Property data was listed on MSDSs...Oh well...

[James G.]

Re: Availability of racing gasoline

Watch them do RVP tests on you tube... pretty neat.

After (3) 100 degree heat cycles, releasing the vapor pressure after each, the most the 87 OCTANE sample could muster on the 4th 100 degree CYCLE was mid 3's RVP.

[Joseph S.]

Re: And... we're OFF!

I have been following this thread in anticipation of solving my own percolation problem, after restart, on my carbureted '63 L75. Good information on avgas, however I had inconsistent results with vapor lock when using 100LL in an aircraft, from different suppliers. In any case avgas as we know it may be short lived. (already some airports refuse to offer 100LL).

I was hoping for one of those magic cures to raise the boiling point on 91 ethanol free or avgas. Racing fuel is not practical for me since I want to use the car for road tours. I have always thought the higher the ethanol content the lower the boiling point, thus I try to stay away from standard pump gas premiums.

Interested in seeing any results of the fuel or fuel mixture that has the highest boiling temp. Joe

[G B.]

Ethanol isn't a factor

Pure ethanol boils uniformly at 173 degrees F. It does not lower boiling temps when added to pump gas. But, with only a 10% concentration, it doesn't raise boiling temps much either.

[Michael G.]