Fuel FAQ/Article
This FAQ covers injector related topics, octane, boosting octane levels, and other fuel related things!
Q: What is Octane? How does it affect my turbocharged vehicle?
A: Octane is the measure of a fuel’s resistance to detonation. Higher octane means a fuel is likely to suffer from detonation under certain circumstances (ex: high compression, boost, timing advance, lean A/F mixture, or any combination of the above).
Q: Can I benefit from higher octane?
A: If your specific application does not utilize the high octane properly, you will see no benefit to using a high octane fuel. For example, an ’87 Civic DX is not going to see additional horsepower gains from using 100 octane race gas over 91 octane premium, or even 87 octane regular for that matter.
Q: When DO I get a benefit from high octane fuel?
A: Some examples of ways to gain power with racing fuel include advancing ignition timing, running more boost, running leaner, or running more compression. All of these things can yield more horsepower when done properly.
Q: California gasoline sucks, I can only get 91 octane at the pump! What can I do?
A: There are a number of things you can do to get more octane into your car such as: Alcohol injection, propane injection, race fuel from the track or some 76 Gas Stations, crappy parts store octane boosters, or homemade octane boosters. All of these things can increase your available octane in varying degrees.
Q: I heard higher octane gasoline has a lower specific output than low octane gas. Is this true, and wouldn’t it make me lose power to use a higher octane gas?
A: Yes, it is true, however, in many cases (especially turbo’d cars) the gains from higher octane outweigh the loss of specific output.
Q: What is Xylene, and is it safe to use in my car?
A: Xylene, or Xylol is sold as a paint thinner that can be found at nearly any hardware or paint store. It can also be found as the major octane boosting chemical in the gasoline we use everyday as well as off the shelf octane boosters and carb cleaners. While it is safe, caution should be used when mixing it with gasoline, no more than a 30% mixture of Xylene to gasoline should be used as it may damage seals. The octane rating of Xylene is 117.
Q: How do I convert Lb/Hr into CC/Min?
A: Simply multiply the Lb/Hr by 10.5. Ex: 50 lb/hr = 525 cc/min.
Q: What is BSFC?
A: BSFC stands for Brake Specific Fuel Consumption.
Q: What does Brake Specific Fuel Consumption mean?
A: BSFC is how many lbs of fuel per hour an engine will need for each horsepower it produces.
Q: What kind of BSFC is my car running?
A: Well, according to RC Engineering, BSFC should be .45 to .50 for naturally aspirated engines, .55 to .60 for supercharged engines, and .60 to .65 for turbocharged engines.
Q: Most injectors are tested at 43.5 PSI, how do I find out how much my injectors flow with more fuel pressure?
A: Follow these steps to calculate new flow with additional fuel pressure:
Step One: Divide the New Fuel Pressure (x) by the Old Fuel Pressure (y). For Example: 48/43.5 = 1.103.
Step Two: Calculate the square root of the result of step one. For example: square root of 1.103 = ~1.0502.
Step Three: Multiply the answer from step two by the old flow rate (c) to get the Corrected Flow Rate or . For Example: 1.0502*450(c)= 472
So this is what it looks like:
[√ ( x / y)]c = Corrected Flow Rate
To sum things up, a DSM 450cc/min (42.8 lb/hr) injector would make 472cc/min (45 lb/hr) if the static fuel pressure was raised to 48 psi.
Q: How much horsepower are my injectors good for?
A: Follow these steps to calculate how much horsepower a set of injectors is good for:
Step One: Multiply injector size (in lb / hr) (a) by your max desired duty cycle (b). For example, 43(a)* .80(b) = 34.4
Step Two: Divide your result from step one by your BSFC (c). For Example: 34.4 / .60(c) = 57.3 horsepower per injector .
Step Three: Multiply your horsepower per injector by the desired number of injectors (d) to get your max horsepower for the desired injectors. For Example: 57.3* 4(d) = 229.3 HP
It ends up looking like this:
Q: If I max out my 450cc/min stock DSM injectors, how much power can I make?
A: Using the above described calculations, it might be possible to make 285 horsepower on race gas with 43.5psi of fuel pressure.
Q: How much does the stock fuel pump flow in my Turbo DSM?
A: About 100LPH @ 43psi and 12 volts. When re-wired, the stock pump may flow up to 140LPH @ 43psi and 14 volts.
Q: How much boost does the stock pump limit me to?
A: If the pump has not be re-wired I would not run more that 13psi on 91 octane gas, and up to 15psi on a re-wired pump.
I hope this FAQ helps!
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