Controversial Topic

[Richard S.]

I know that some members will take exception to my post however, this has been my experience and I wanted to share it. Yesterday I took a 2 plus hour drive in my 60' with the temp. at 95 and a heat index of 105. Each leg of the trip was just over 50 miles and the gas mileage was just under 10 mpg. For the past year I have been using only 110 octane VP fuel. Percolation has never occured since I made the change and for the first time I can take a long trip on a hot day and not worry about the engine quitting or failing to restart. Again this is my experience in the hot, humid midwest summers. I did expect a little better mpg but at least it runs great on a hot day.

[Leif A.]

Re: Controversial Topic

Richard,
I think that 110 octane is a bit of overkill for you car...by about 20 points. That being said, there is definitely a solid camp out there that believe "pure" gas is more heat tolerant than "ethanol" based gasoline.

[Mark E.]

Re: Controversial Topic

Yesterday I took a 2 plus hour drive in my 60' with the temp. at 95 and a heat index of 105.

A 1960 Corvette is very cool, and I commend you with actually taking it on a road trip. I can't remember the last time I saw a C1, or even C2, on the road when it wasn't part of a show or event. And I'm really impressed you (presumably) enjoy riding for hours with no air conditioning in 95 degree heat. Did you also have the top down to complete the experience? I avoid that kind of weather even in my air conditioned '70...

EDIT: I'm curious- why do you think this topic is controversial? "Which oil is best?" and "Which Corvette is best looking?"- now those are controversial topics.

[King M.]

Re: Controversial Topic

Was it leaded? That is even better. That's what I run in my l-79

[Gary R.]

Re: Controversial Topic

What do you have for an engine that would require that gas?

[Richard S.]

Re: Controversial Topic

Yes, it is leaded. I had the FI unit adjusted by Tim Mickey to run on both 110 octane as well as ethanol blend should that event ever happen. At 10 mpg and an extra 5 gal. in the trunk there is only so that you can go before the need arises to fill up with ethanol. A few years back my wife and I did make the 600 mile round trip to Bloomington Gold however, there were problems with percolation so this year we took the SUV to Indy. There seem to be two camps of thought on this forum, those that feel non-ethanol fuel prevents percolation and those that run ethanol and never have percolation problems. I only tried 110 octane as a last resort after being stranded for hours in remote locations on hot days. If you view the archives you will see that some members have very strong opinions regarding ethanol.

[Frank D.]

Re: Controversial Topic

I drive my '61 original Corvette 270hp, solid lifter, dual quad car in Orlando summer heat for hours some days running 87 octane, ethanol laced gas with zero issues. I put fuel injection gaskets on the intake to block off the exhaust gas intake runners, wired open the passenger side exhaust heat riser and put 1/4" phenolic spacers under each carb. There is no need to run racing gas, or even hi test, if your compression is low enough and you make some sensible mods... With my 5 speed Tremec overdrive and keeping my foot out of the car I can get 22 miles/gallon...

Of course, a fuel injection setup changes the game entirely...

[Bob W.]

Re: Controversial Topic

Frank what are phenolic spacers ? and were did you buy them?
Bob

[Steve G.]

Re: Controversial Topic

How did you determine it was the fuel percing when you had problems previously?
Steve

[Frank D.]

Re: Controversial Topic

Fuel perc on a carbureated car is pretty easy to determine....often you can hear the fuel boiling in the carb. A typical scenario is hard starting after the car has been sitting for 20 minutes to an hour after a long, hot run. The symptoms are similar to a flooded engine. Flooring the gas and cranking will usually get the car going.

Phenolic spacers are an excellent insulation product that is laminated and used like the wooden spacers that racers made themselves years ago.
Here is an example for a 250 hp WCFB carb or a C1 dual quad WCFB: http://dashman.net/search.html?q=wcfbpk&submit=Search

[Ed S.]

Re: Controversial Topic

I use ethanol free 93 octane as often as possible in my 64 L76 and I wired the heat riser open. The combination of the two has completely eliminated percolation. Even if I use E10 93 octane I only experience a little percolation on extremely warm days (90 or higher).

Richard - if you haven't done so already, you might consider downloading a free smart phone app called "Pure Gas" - it will display ethanol free gas stations near you - where ever you are - because it is GPS based. Great app, user friendly and pretty accurate.

[Loren L.]

Re: Controversial Topic

I have to ask - does your car run 4.56 or higher rear gears, or did you complete the 50 mile legs in less than 30 minutes? Or do you have a
hole in the gas tank? 10 mpg would be simply unacceptable, especially when paying a premium for fuel. Something is wrong.

[Steve G.]

Re: Controversial Topic

What makes "perc" a controversial topic is the fact that it has been, and continues to be, misdiagnosed. This is probably one of the best examples of that.

While I am no expert on these fuel injection systems, I am well qualified when it comes to carbs. I have held a journeyman's ticket for almost 40 years and stared down the throat of carbs when there was nothing but carbs in the 70's and 80's. After a time away from the trade, I find myself back in the thick of it. There are 2 carbs on my bench as we speak.

I have yet to see, on this board, a correct diagnosis of "perc". Every time I have seen that diagnosis made it has turned out to be something else. Regular run of the mill, everyday, seen it a thousand times, carb issues. Everytime someone runs into a hot engine hard start with fuel drip it is mis-diagnosed as perc.

Percing fuel does not cause a drip of raw fuel down the throat. Boiling fuel causes excess amounts of fuel vapour (steam if you will) to enter the air stream through the bowl vent. That's how the diagnosis of perc is made. Look for the steam. If it's dripping down the throat from the main nozzles it's not percing.

I believe where this thing fell of the rails is the association between the drip and the hot engine. Because the drip was only seen after the engine was hot then shut off it was presumed the heat must be making the fuel boil. The experts forgot to consider that heat also causes expansion. And a carb has a spillover point. If the fuel level in the bowl rises above the height of the discharge nozzles it will flow of it's own accord. The designers knew about this and there is a cushion area between proper fuel level and spillover level. However, if the fuel level is too high (close to spillover) the expansion at shut down when the temp rises is enough push it over the top.

So you can wire back your heat riser and block your crossover and reduce the heat so the fuel doesn't expand as much, or you could simply correct the high fuel level.

According to the fuel industry, the instances of vapour lock and perc peaked in the 80's and the current fuel composition is far less likely to produce those issues. The fact that, other than a handful of people reporting issues, the rest of the continent runs the same fuels in the same temps without problem supports that assertion.

This FI engine having perc issues defies all logic. They have no heat riser and no exhaust crossover. They have already reduced the underhood temp significantly compared to what the rest of the world sees running pump gas. And it's still boiling? FI takes fuel from a reservoir and pressurizes it. Fuel under pressure is even less likely to boil. This setup most resembles what we have today, fuel delivery under pressure. Today's car's don't experience this "percing" phenomena.

And as Loren points out, 10 mpg? This problem hasn't been solved.
Steve

[Chris S.]

Re: Controversial Topic

Here is Jerrys advice.....http://www.jerrybramlett.net/faq.html#gas

[Richard S.]

Re: Controversial Topic

Loren, I agree. The rear is 3.70 and the trip was 50 miles each way at 70 mph. For the 1st 38 miles the fuel gauge registered full then dropped to 1/2 over the last 12 miles. I topped the tank off before I left and elected to add another 5 gal. when the gauge showed only 1/2 tank. I brought along an extra 5 gal just in case and was surprised when the tank took the whole can of fuel. The tank has a new sending unit and the fuel gauge has always been a little funky however, this mileage did shock me. Perhaps the set up is too rich but it starts and run perfect and I am reluctant to make any changes.