In most cases, a fuel’s octane value is the performance enthusiast’s primary focus. But I must be absolutely clear here: There is no performance value in a high-octane fuel unless the engine’s compression ratio and thermal-operating conditions dictate its need to stave off detonation. An 8.5:1 compression ratio engine will, as often as not, produce a better output on a quality 87-octane fuel than a costly 110-octane race fuel. Today, various sanctioning bodies allow a wide range of fuel specs. Some allow only gas-station pump fuel while others specify a certain brand of race-grade gasoline, oxygenated gasoline, methanol, or ethanol/ gasoline mixes such as E85. At the end of the day, you need to understand that an optimal result depends on knowing the best air/fuel ratio required for that particular fuel, so you can successfully increase output. In some cases, such as with methanol and E85, mixture quality is also important. A simple thing, such as a really effective booster, can easily be 30 hp and 30 ft-lbs on a typical 350- inch racer over one that is not.
This Tech Tip is From the Full Book, DAVID VIZARD’S HOW TO SUPER TUNE AND MODIFY HOLLEY CARBURETORS. For a comprehensive guide on this entire subject you can visit this link:
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Almost everything covered so far about the selecting, modifying, building, and calibrating your Holley has been for the use of a conventional non-oxygenated gasoline. This chapter focuses on some of the needto-know factors of other fuels you might want to use.
Probably more than 99 percent of those reading this book have used oxygenated fuels in their daily driver. Next time you fi ll up, check the labels on the pump. Many have a notice stating that the fuel could have up to 10-percent ethanol blended into it. Ethanol is an oxygen-bearing compound, which calls for a much greater amount of fuel per pound of air to achieve the stoichiometric air/fuel ratio. An engine equipped with an oxygen sensor feedback fuelinjection system compensates for the fact that a gasoline may contain up to 10-percent ethanol.
That, however, is not true for a carbureted engine. For complete use during combustion of both air and ethanol, the mixture ratio has to be exactly 9:1. (For methanol, the ratio is 6.5:1.) To get to the stoichiometric ratio for station pump fuel with a 10-percent ethanol mix requires a jet area increase is necessary, as shown in Figure 13.5. If you are blending gasoline with methanol, the jetting increase needed is greater. Figure 13.6 gives you the details. When using the numbers in Figure 13.5 or Figure 13.6 for a jet size increase, there are a couple of factors you should be aware of. One is that the percentage of jet increase refers to the total increase in jet area. Remember, at WOT about 25 to 30 percent of the fuel goes through the power valve jetting, so if you are going to calibrate solely with the carb’s main jet, it has to be a proportionally bigger increase than shown.
I prefer to rejet the powervalve restriction channel, because when going from mid to wide-open throttle, the response is usually cleaner and sharper. The difference is not very signifi cant with small amounts of alcohol in the fuel; you get a more signifi cant difference when E85 or near-100-percent alcohol is used. The improved transitional throttle response may not be important for the drag racer, but it is important for a circle track racer on a short track. Another factor to consider is the cooling effect due to a high latent heat of evaporation. Also, the best power with alcohol-type fuels happens at a much richer mixture than stoichiometric. Therefore, all the jetting increases in Figure 13.5 and Figure 13.6 are the minimum increase you should use. Among all that has been said so far, there has been no mention of how you would know just what percentage of ethanol is in the gas-station pump fuel you bought. It is far from a consistent amount. This is yet one more example of why the installation of a wide-band oxygen mixture ratio gauge makes so much sense.
Now let’s address the subject of potential power increase with a fuel mixed with up to, say, 10-percent ethanol or methanol. By weight, ethanol is 35-percent oxygen and methanol is 50-percent oxygen, which makes them appealing as means of power enhancement. But this simplistic viewpoint is somewhat misleading. By the time you take into account all the other factors involved the theoretical power improvement at stoichiometric between straight gasoline and a gasoline/alcohol mix is very small. In fact, the difference is usually in favor of the straight gasoline. So why use an alcohol/gasoline mix? Well, small power gains are realized mostly because the latent heat of evaporation of alcohols is considerably higher than that with straight gasoline.
Also, ethanol and methanol produce the best power when they are richer than straight gasoline. This means the jetting changes indicated in Figure 13.5 and Figure 13.6 need to be bigger than shown. Just how much bigger is a question of trial-and-error testing; a job to do at the track.
While attempting to get the best trap speed be sure to take note of the air temperature, humidity, and barometric pressure. When the weather is very hot or cold the use of an alcohol additive produces very little improvement over a straight, nonadditized gasoline. This is because at high ambient temperatures the alcohol evaporates and uses up intake manifold volume, thus reducing the volumetric efficiency by more than the cooling effect increases it. At low temperatures the ignitability of the alcohol is compromised and offsets the possible gains from other aspects.
A low-percentage alcohol blend works best when ambient temperatures are between about 70 and 90 degrees F. This is true even though this blend is also dependent on the engine’s underhood and coolant temperatures. Note that the potential to increase the octane value of a straight gasoline is reduced as the temperature increases where the mixture enters the cylinder. So in practice, high air and coolant temperatures nearly nullify any octane benefi ts you get from alcohol additives. At the end of the day only fi ne tuning of the system can show benefi ts at the track.
Oxygenated Race Gasoline
For many years, sanctioning bodies banned oxygenated fuels, but beginning about 2000, oxygenated fuels began gaining in popularity as a means of increased output. Although race fuel blenders don’t talk about the contents of their fuel, you can assume that for the most part, oxygenated fuels contain compounds such as propylene oxide (up to 2 percent) and nitro paraffi n (including nitro methane).
These compounds may also be used with methanol and ethanol. The alcohol content added to a mixture tames the combustion process, reduces peak temperatures, and adds some octane value. As a result, the fuel is more “compression friendly.” The fi rst question that most hot rod skeptics ask is, “Does oxygenated fuel work?” The answer is “Yes,” as long as you know what you are doing. Because part of the content of the fuel fl owing through the jets is oxygen, it is necessary to increase jet size. The stoichiometric ratio of a typical oxygenated fuel is a couple of ratio numbers richer than a nonVizard/Walters oxygenated fuel. To bring the mixture up to what is required usually takes jetting 4 to 7 numbers up from what is already being used either in the main jet or the power valve restriction channel.
Also, the ignition timing may need some attention, depending on what was used prior to the fuel changeover. Usually flame speed is higher with oxy fuels so the timing may need to be retarded by a degree or two.
E85 is theoretically defined as a blend of 85-percent ethanol and 15-percent gasoline with a great potential to be a very cost effective power-producing race fuel. In practice, the label E85 encompasses a mix of ethanol and gasoline ranging from 51- to 87-percent ethanol. This wide range is to ensure good startup characteristics from summer to winter. The more ethanol there is in a blend, the harder it is to start under cold conditions. The problem for the racer is that this big variation means that jetting must suit the blend of the day.
Vehicles made to run either gasoline or E85 are designed around the output of an oxygen sensor, which corrects the injector open time to produce the correct air/fuel ratio. With a Holley carb, you don’t have that luxury. So, while running E85 promises performance similar to a high-dollar oxygenated race gas, it is not without problems.
As long as it is not too cold, running a true E85 (85-percent ethanol, 15-percent gasoline) is about your best bet for output. To ensure that this is what you are actually feeding your engine, you need an Echecker from Quick Fuel Technology. This ingeniously simple device allows you to measure, within close limits, the ethanol/gasoline ratio. Most E85 contains 87-percent ethanol. But you may need to buy some straight ethanol to boost an ethanol-shy E85 mix to the 87-percent mark.
Another option is to brew your own E85. I have found that a mix of good 87-octane fuel and acetone or methyl ethyl ketone (MEK), plus ethanol in a ratio of 13/2/85 produces good results. You may be asking yourself if using 93-octane would be better in your home brew. The answer is that you could barely notice a difference, so 87 is as good as any—and cheaper. Also be aware that tetraethyl lead as used in race gas does little for increasing the octane value of alcohols. This usually means that mixing ethanol or methanol with leaded race fuel is a waste of money
If you want to hop up your E85 blend for a power/torque increase of at least 1 percent (but usually nearer 1.5 percent), try this: Add the appropriate dose of ACES IV-A Alcohol Formula from American Clean Energy Systems. I have personally run dyno and wear tests on this product over many years. Many top racers who know about it absolutely do not want me to tell you about it because they do not want to lose the edge it gives them over those who are not using it.
So what does ACES IV-A do? First, it totally counters an alcohol-based fuel’s lubrication stripping bore wash effect. From my own tests I can say that bore and ring wear are reduced by a minimum (not “up to”) of 300 percent. That means if the bores wore 0.003 before then it would be a maximum of 0.001 after ACES IV-A is used. Second, the typical top ring ridge is not seen even with a full season’s circle track racing. The upper cylinder lubrication decreases friction and increases power.
Third, ACES IV-A includes an ignition enhancer. This helps toward a cleaner burn and usually less of a need to run quite as rich a mixture. Last, there are corrosion inhibitors in the formula. Ethanol and substantially more so methanol attack many of the component materials of a fuel system made for straight gasoline. Those corrosion inhibitors also act as a lube for fuel pumps, considerably extending their lives. For all practical purposes, using ACES IV-A totally eliminates fuel system corrosion of an alcohol-fueled engine. An effective dosage amount can be as little as 1/2 ounce per gallon. If your regular street driver is a flex-fuel vehicle, you can save yourself some dirty varnished injector problems down the road by running regular gasoline/alcohol fuels blended with ACES IV-A.
Legislation cutting the amount of sulphur allowed in gasoline and Diesel fuels for the road has been introduced. This means that in the near future we will see the number of problems with varnished injectors and in-tank pumps continue to increase. The use of ACES IV-A is a 100-percent corrective fix!
If your intent is to use ethanol or methanol, the design of the metering blocks needs to be drastically revised as to fuel volume handling capability. It is possible to modify gasoline metering blocks to get the job done. Heck, back when, if you wanted to run alcohol fuels, there were no real options other than using highly modified production metering blocks. These days things are a lot different. Holley and many aftermarket Holley specialists offer metering blocks specifically for ethanol- and methanol-based fuels. If you have the budget this is the painless way to go.
Flowing enough alcohol fuel into the induction system means not only having jets with 60 percent more area (ethanol) or 260 percent more area (methanol), but also having the relevant passages suitably enlarged. Another consideration is the volume of the accelerator pump system.
At first, you would think that this also needs to be enlarged in the same proportions as the jets but this proves not to be so. In fact, the system runs very rich for best results with alcohol-based fuels, and the amount of vaporized fuel in the intake manifold is substantially less. In turn, the demands on the accelerator pump system are not proportionally greater, but they do, nonetheless, need to be enlarged.
When you make the swap from gasoline to alcohol be sure to get alcohol-resistant pump diaphragms, fuel bowl needles, check valves, etc. Also be aware that at high power levels the amount of fuel that is required to pass through the booster passage becomes limited by the size of that hole. Make sure this is not a limitation, as running into a lean mixture with either ethanol or methanol is bad news for pistons.
Written by David Vizard and Posted with Permission of CarTechBooks