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Smaller Carb or bigger one or smaller jets

Posted By Tim Quinn Last Month
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Tim Quinn
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Thanks for your info
Tim
Saturday AM
Florida
Tim Quinn
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Like your plan
Thanks,
Florida's Tim
Tim Quinn
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With the higher cost of corn free gas, would it pay
to burn it for better mileage ?
Let "us" know,
Tim
8:05 AM Saturday
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Thanks for your input.
Trying to find out if it pays to burn 'corn free' fuel.
Tim---- Saturday AM
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Have electronic ignition, not Pertronic but full distributor that is electronic.
Almost ready to grin and bear it, but might see if ethnology free fuel is worthwhile .
What da ya think ?
Thnaks,
Tim
Saturday 11May19
Ted
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As mentioned, ethanol in the gasoline will cause the fuel mileage to drop.  This has to do with the BTU’s per pound for ethanol being less than that of gasoline.  Said another way, it takes a higher volume of ethanol to equal the same energy output of gasoline.  As the ethanol percentage goes up, the fuel mileage goes down.  In my part of the country, the 91-93 octane gasoline has 3-5% ethanol versus the 10% in the 87-89 octane grades.  For that reason, I use the premium fuel in all my carbureted vehicles.
 
The Summit carburetors are jetted reasonably close as delivered.  Most of them need no jet changes and only a very small number of them get a two number change.  Camming and head work usually dictates if the fuel mixture change is richer or leaner from what’s in the carb as delivered.  There are cases where only the secondary jets are changed and the primary jets remain as delivered.  Keep in mind that leaning the primary mixture can actually have the reverse effect on fuel mileage in that the engine may be requiring more fuel and as a result, you are having to drive deeper into the throttle to maintain the same speed.  Without a wide band sensor, spark plug readings will let you know if you’re grossly rich or lean but may not be the best option for fine tuning.
 
You already have the 600 cfm model which is adequate for most warmed over Y’s.  I lean heavily towards the 750 cfm versions as the vacuum secondary function simply insures that the engine only receives only the amount it requires.  With the 750 version, most Y’s will never be under-carburetted.  I have the 500 cfm Summit carb on my own 272 and it is on the small side but it is a good driver.  There’s very few times that engine exceeds 4500 rpms so it’s not on the top of my list to get a larger carb for that particular engine.


Lorena, Texas (South of Waco)
Tim Quinn
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Ted, thanks.
I'm going to leave the jets alone and try "corn" free gas and see if the mileage improves.
Again, thanks
Tim 
Hot 'n Humid, FL
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Hey Tted,
I found this report about ETHANOL from THE MINNESOTA BIO-FUELS ASS.
So are our old Y-blocks going to be more efficient  (better mileage) with 93 octane or will they just run better ?
Tim
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This is where ethanol comes in.In terms of its octane rating, ethanol has a rating of 113. As mentioned above, fuels with a higher octane rating reduce engine knocking and perform better. Also, almost all gasoline in the US contains 10 percent ethanol. When you mix 10 percent 113 octane ethanol with 85 octane gasoline it increases the octane two points to the normal 87 octane most consumers use. So the higher the ethanol content, the higher the octane. The octane rating for E15 (15% ethanol) is 88 octane and E85 (85% ethanol) is 108 octane.In addition, as Argonne National Laboratory states, ethanol reduces greenhouse gas emissions between 34 to 44 percent compared to gasoline.Moreover, since ethanol is cheaper than those synthetic aromatics, gasoline blended with ethanol reduces the price at the pump. As detailed in a study released earlier this year by the University of Illinois, ethanol is 35 cents to $1 cheaper than benzene, toluene and xylene.In other words, consumers not only get to save at the pump, they get to ensure their vehicles run smoothly while reducing harmful greenhouse gas emissions. Talk about a win-win-win solution. Moving forward, as car manufacturers increase the number of models equipped with high compression engines to maximize performance and efficiency, higher octane fuels will be required and ethanol is set to play a crucial rol
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Everything equal and where a typical pump gas octane works just fine, ethanol blended fuel is less efficient and produces less power.  Where ethanol (E85) can be a benefit is in custom built performance vehicles that require higher octane than is typical from pump gas and the engine has been built to take advantage of it.

A problem with ethanol free is, every time I've seen it, it's more expensive so you might get better mpg but at a higher cost per g.    You also have to plan the entire trip around the availability of ethanol free gas which can mean driving farther out of the way for gas and using more expensive gas to do so.  So, is it actually more cost efficient?





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Tim Quinn (5/12/2019)
Hey Ted,
I found this report about ETHANOL from THE MINNESOTA BIO-FUELS ASS.
So are our old Y-blocks going to be more efficient  (better mileage) with 93 octane or will they just run better ?
Tim
Florida 
'56 Crown
This is where ethanol comes in.In terms of its octane rating, ethanol has a rating of 113. As mentioned above, fuels with a higher octane rating reduce engine knocking and perform better. Also, almost all gasoline in the US contains 10 percent ethanol. When you mix 10 percent 113 octane ethanol with 85 octane gasoline it increases the octane two points to the normal 87 octane most consumers use. So the higher the ethanol content, the higher the octane. The octane rating for E15 (15% ethanol) is 88 octane and E85 (85% ethanol) is 108 octane.In addition, as Argonne National Laboratory states, ethanol reduces greenhouse gas emissions between 34 to 44 percent compared to gasoline.Moreover, since ethanol is cheaper than those synthetic aromatics, gasoline blended with ethanol reduces the price at the pump. As detailed in a study released earlier this year by the University of Illinois, ethanol is 35 cents to $1 cheaper than benzene, toluene and xylene.In other words, consumers not only get to save at the pump, they get to ensure their vehicles run smoothly while reducing harmful greenhouse gas emissions. Talk about a win-win-win solution. Moving forward, as car manufacturers increase the number of models equipped with high compression engines to maximize performance and efficiency, higher octane fuels will be required and ethanol is set to play a crucial rol

The Pro-Ethanol groups will tend to put their own spin on their marketing in promote ethanol use.  What’s not mentioned very often when discussing ethanol laden fuels is the increase in engine wear that goes along with that increase in ethanol.

If an engine does not require a higher octane fuel to prevent detonation, then using an increased octane fuel will have no benefit in increasing the fuel mileage.  If you have an engine that runs fine on 87 octane gasoline, then going with a higher octane fuel will have a zero effect on the fuel mileage assuming the fuels in question do have the same density.  What does have a direct increase on the fuel mileage is the density of the fuel.  The higher the density, then the smaller the jets in the carburetor must be in which to properly meter the appropriate amount of fuel to the engine.  This goes back to the energy content of the fuel per pound or BTU’s.  While I don’t check pump gasoline for density very often, I do check the race fuel density and when changing from one fuel to another that has a density change, the jet size can be accurately predicted based on that density change.


Lorena, Texas (South of Waco)


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