BSFC and injector sizing

87GN_70GS

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From what I can gather, it looks like the BSFC of E85 is .60 - .65 (compared to .50 for gasoline). That would say that the calculations for the maximum hp supported by the injectors, derived from max flow rate, would decrease the hp number by ~20 - 30% compared to gasoline: Hp = 6 x Inj_flow_rate / BSFC.

Or for the required injector flow rate, derived from max hp, it would increase the injector size by ~20 - 30% over that of gasoline:

Inj_flow_rate = Hp x BSFC / 6
 

87GN_70GS

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Yes, that should leave you with about 15-20% duty cycle headroom.

The above formula is for the ideal case with the injectors runing static (100% duty cyle). In the real world, it might not be a bad idea to factor in 15% headroom to allow for varying conditions, tuning, etc., so add 15% to the injector size:

Inj_flow_rate x 1.15
 

Chuck Leeper

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"compared to .50 for gasoline".
I think that number is for a n/a engine. Forced induction engines are usually higher. Closer to .6- .65, depending on how well it's designed.
 

Quik

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also remember you need the room in your pump and fuel lines to support it.


now i run a mix of E85. i run 40% E85 and 60% 93. they say anything more the 30% you need to tune for. I happend to not need to tune for it. i noticed cooler temps, i noticed off boost how snappier it was, also it spooled turbo faster and hit much harder. If you want to first try it out before you go full bore E85, try a mix of it.

my exhaust smells like rum
 

Hot Air

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BSFC = Fuel Consumption / Power Produced

While E85 will require more fuel due to it's low BTU/Gal, it will make more HP. I wouldn't think the BSFC would change for different fuels.

Hot Air
 

forcefed86

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Figure your standard gas BSFC first. Boosted engines closer to .60-.65 on GASOLINE. Once you get your injector sizing calculated, multiply your injector size by 1.47.

IE 42 if you needed 42# injectors to support your HP rating on gas take that and multiply it by 1.47.

42 X 1.47 = 62lb Injector for E85.

This information is taken from Injector-Rehab.com
E85 Injector Sizing


What Size injectors when running E85?
This is becoming a very common question. The answer is not as easy as straight forward as I wish it was. I will try to explain a simple calculation to get an idea to guide you in the right direction.
First things first. You will need to determine your base injector size. This is the size that you should be running on gasoline. To find this size, simply use the calculator on our site located here. Now that you have determined your base injector size you will need to determine the difference in size to run E85 Fuel. The way to do this is to do some simple math. You are going to use the multiplying factor of 1.47 to get your size. The 1.47 number represents the difference between the stoiciometric fuel ratio of gasoline and E85. Gasoline is 14.7 and E85 is 10.0
Now that you have the "magical" factor and your base injector size, do the math. I will do one with you just to show an example.
Let's say that in the Injector size selection guide size calculator, you came up with a size of 42lb injector needed to reach your HP goals. Simply take the number 42 and multiply this by 1.47.

42 X 1.47 = 62lb Injector
*Note that this is not THE absolute number, but rather a GUIDE to help you determine the size of the injector. Good luck on your mission to use a renwable fuel!
 

Hot Air

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I would caution you to think BIG. Since E85 will cool the charge so you can run more boost...don't scrimp on the injectors. Also, since E85 likes to run rich...don't skinp on the injectors. Also, be sure you have a capable fuel pump(2)!
Conrad
 

Alky V6

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BSFC = Fuel Consumption / Power Produced

While E85 will require more fuel due to it's low BTU/Gal, it will make more HP. I wouldn't think the BSFC would change for different fuels.

Hot Air
BSFC is a unique number range associated with each unique type of fuel. It is a very important number in the determination of how much fuel of a certain type must be burned to create a specific amount of horsepower. The BSFC number for one specific type of fuel will fit within a range depending on the efficiency of the engine and whether you are looking at a lean burn ratio, a stoich ratio or a rich burn limit ratio to create the HP you are calculating for. That's why you may see a BSFC range of .45-.65 for gasoline. The lower end of the range would be for lean burning, and/or an engine that makes efficient use of the fuel. The higher end of the scale would represent inefficient use of the fuel, or cases where extra fuel is being used to cool the combustion process, such as in supercharging or turbocharging.

target horsepower x BSFC = total lb/hr fuel requirement for the engine.
example: 1,500 HP x 1.35 BSFC = 2,025 lb/hr
1.35 being on the higher end of the BSFC range for methanol.

total lb/hr fuel requirement / number of injectors being used = lb/hr fuel requirement per injector (uncorrected).
example: 2,025 lb/hr / 18 injectors = 112.5 lb/hr per injector (uncorrected)

60000 / peak engine rpm = available injector time (ms) per crankshaft revolution.
60000 / 9000 rpm = 6.67ms

(available injector time per crankshaft revolution - injector recovery time in ms) / available injector time per crankshaft revolution = maximum injector duty cycle.
example: (6.67ms - 1.3ms) / 6.67ms = 80.5% duty cycle

lb/hr fuel requirement per injector (uncorrected) / maximum injector duty cycle = required injector size.
example: 112.5 lb/hr / .805 (80.5%) duty cylce = 139.75 lb/hr injector

If you want to be safe about sizing the injector, pick a BSFC number that is on the higher end of the range for the fuel you're doing the calculation for.
 

Alky V6

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The BSFC range for E85 is .63- .70. This would be an efficient stoich burn. For a boosted application this number would be higher, .84-.91.
For instance, The BSFC range for methanol is .9-1.00 for an efficient stoich burn. In a turbocharged application, it is not uncommon to use 1.35, or even higher, up to 2.0 in high boost, high HP applications. My Stage I project worked with a BSFC number of around 1.18.
 
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BEATAV8

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.65 BSFC seems really low for E85.

If a typical gasoline forced induction is around .65, and E85 requires 30% more flow compared to gasoline, then the E85 BSFC is more like .85

.85 BSFC would put 120lb injectors just under 850HP @ 100%
 

Alky V6

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.65 BSFC seems really low for E85.

If a typical gasoline forced induction is around .65, and E85 requires 30% more flow compared to gasoline, then the E85 BSFC is more like .85

.85 BSFC would put 120lb injectors just under 850HP @ 100%
.65 BSFC with E85 would be for a cruise, stoich burn.
.85 BSFC would be minimum for a boosted, max horsepower pull.
 
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norbs

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Can someone explain why a turbo engine requires more fuel pr hp than a NA engine........that would mean a turbo engine is less efficient than a NA engine?? Here is some data from a dyno manufacturer.

http://www.land-and-sea.com/dyno-tech-talk/using_bsfc.htm

.........................................................................................Engine @ 1,000 @ Peak TQ@ Peak HP
Type RPM Torque Hp 4-stroke (low compression, carburetor) .........0.62 0.47 0.52
4-stroke (high compression, carburetor) ..........................................0.60 0.42 0.47
4-stroke (high compression, closed loop) ........................................0.52 0.35 0.42
4-stroke (supercharged, carburetor)............................................... 0.75 0.50 0.55
4-stroke (turbocharged, closed loop).............................................. 0.57 0.45 0.50
2-stroke (low compression, carburetor) ..........................................0.85 0.55 0.60
2-stroke (high compression, carburetor) 0.80 0.50 0.55
Diesel 4-stroke 0.35 0.25 0.30
Diesel 2-stroke 0.40 0.29 0.34
 
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