Fuel Injectors: How to Determine your needs when purchasing Fuel Injectors
It can be challenging to determine the size and flow rate of your fuel injector. Here are some tips to help you make the right selection.
When choosing a fuel injector, you need to consider several things:
What is your Horsepower goal?
Which fuel type you want to run, gasoline, ethanol, race gasses and fuel additives such as MTBE or Oxygenators?
Injector harness plug style: for example, USCAR (ev6), Jetronic(ev1), Denso (Sumitomo) Multec (Mini-Delphi), etc?
Which intake and fuel rails you are going to use?
High impedance or Low impedance?
As you can see there’s a lot to consider when you are swapping intake/rails, using an aftermarket ECU, or considering racing the car. It can get confusing!
Don’t worry nearly any injector can be adapted or made to work. We’ll give you all the resources you need to make the determination.
Fuel Injector Flow
Fuel injector flow rate sizing is the first thing we consider when helping a customer determine what they need. While some manufacturers may choose a different rate, the industry standard is 43 psi/3 bar.
Injector flow is conveyed in two main ways: cc's per minute (cc/min) or pounds per hour (lb/hr). When someone says " a thousand cc injector" they mean 1000cc/min aka 96lb/hr. Likewise "I need 210's" means 210lb/hr aka 2200cc/min.
When sizing your injector for gasoline a very simple rule of thumb to follow is: 1cc/min flow for each horsepower. So, if you want to make 1000 crank horsepower on 93 octane gasoline, using a fuel pressure of 43psi you need a 1000cc injector.
This rule of thumb can be used for ethanol based fuels like e85. Just remember to add 30% since ethanol requires more fuel to make the same power.
If you’d like a little more accuracy, Here's a link to our online calculator
If you’d like to do the math manually, follow these steps:
First, estimate your brake specific fuel consumption (BSFC). Use the BSFC you estimated in other Blog posts or here’s the same standard numbers to choose from:
gasoline .45 - .50
e85 .63 - .70
Boosted (turbo, supercharger):
gasoline. .60 - .65
e85 .84 - .91
Keep in mind that higher boost and higher flowing cylinder heads will increase BSFC so don't choose the lowest BSFC if you are using things like power adders, ported or aftermarket heads.
Fuel Injector Flow
Let's say we are running a standard chevy truck engine from the "LS" family, adding a turbo that will run around 7lbs of boost and using ethanol-based fuel such as e85.
So, we'll choose a BSFC of .85.
Now, estimate a realistic and accurate horsepower goal and multiply it by the BSFC.
For 7lbs of boost, ethanol and a stock truck motor let's conservatively say 475WHP.
Our equation is: 475 x .85 = 403.75. This means we need 404 lbs/hr of fuel flow. Now for our 8-cylinder engine that uses 8 fuel injectors, we divide that by 8. and that gives us 50.5.
475(hp) x .85(bsfc) = 403.75
403.75 / 8 (amount of injectors) = 50.4
50lb/hr injectors required.
This accounts for a safe injector duty cycle.
Compared to our general rule of thumb “one CC per hp and drop 30% for ethanol” we’re close!
Fuel Injector Dimensions
Choosing fuel injector external dimensions or "body style" can be confusing. However, modern fuel injector manufacturers have solutions that can bring top technology to nearly every vehicle.
If you have difficulty making an injector fit, contact a fuel injector specialist. There are many ways to adapt injectors to get them to fit. Mostly all modern injectors fall into one of 3 main sizes: 34mm, 48mm or 60mm. Though there’s no industry standard, we at Snake Eater measure inside O-ring to inside O-ring.
Cutting edge fuel injectors are largely available only in the 34mm style. The Bosch ev14 compact is the standard for legendary motorsport injectors.
48mm is also known as ev14 medium or mid-length. At Snake Eater, we call this the LS2 length, since it is most famously found on the GM race based LS2.
60mm is highly popular because it’s easier to raise a fuel rail with a small shim and longer hardware than to fabricate custom mounts to use a shorter injector. This is most famously the Deka or LS1 and LS6 injectors.
There are many places to look when determining your fuel injector body style requirements. One of the best ones is to look directly at your OEM fuel injector. Chances are, there’s a direct swap or adapter option that will work.
If you’re using an aftermarket intake, many come with fuel rail kits. You can also re-use the OEM rails. The manufacturer should provide guidance on which body style injector you need.
If you can’t determine the style requirement, Snake Eater performance has a large library of vehicle fitments. Feel free to let us help you determine your needs. We also sell fuel injectors from the best manufacturers on the planet like Bosch and many more.
If you need help, send us an email firstname.lastname@example.org
Fuel Injector Plug Types
Over the years, fuel injectors have come in many plug types. However, there are several prominent styles that cover the majority of applications. With the simple adapters that are widely available, you won’t have much difficulty finding a good match.
Many plug types are known by their Bosch manufacturing generation such as ev1 or ev6. This can be confusing. It’s technically incorrect but has become the accepted naming convention.
Ev1 / Jetronic: found on earlier models, especially common on older low impedance injectors. They do not have an internal O-ring and are not considered water resistant.
Ev6 / USCAR: more modern, very common. They dominate new injector models. They have an O-ring on the male end of the plug and are considered water resistant. This connection aids in corrosion resistance.
Denso/Sumitomo: Similar benefits to USCAR, most common on imported vehicles.
Fuel Injectors: High Or Low Impedance
When searching for fuel injectors you might ask: "How do I determine if I need high or low impedance injectors?"
This depends on which ECU you are running. Your ECU will either be compatible with high or low impedance. If it's an aftermarket injector, it might be compatible with both.
The surest way to determine high or low impedance is to use an ohm meter across the injectors plug terminals. If the meter reads 1-4 ohms it is a low impedance injector. If it reads 8-16 ohms it is a high impedance injector.
There’s not as many options for modern low impedance, high flow injectors but there are a few! The highest flowing injectors available are low impedance. However, high impedance is best for most applications due to its lower electrical requirement to open, which means a cooler electrical system which may increase reliability.
Parts Dealer Links
GM/CHEVY Fuel Injectors
FORD Fuel Injectors
MOPAR Fuel Injectors
IMPORT Fuel Injectors
BOSCH Fuel Injectors
SEP Fuel Injectors
We're here to answer all your questions!
E-mail us at: Support@SnakeEaterPerformance.com
Give us a call at (808) 262-5928
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