First of all how much difference do bigger injectors make? Are there any major pros/cons to take into consideration? And finaly who makes the best ones for the Z? Right now I'm running NA with a few mods, but I think I'm going with the Vortech SC at some point...any advice?

 

To add to the question, would it be a benefit to have the stock injectors spec? Cleaned and balanced for flow?

 

What kind of injectors do we have ? saturated? side feed?

On RC Engineering site they have RC 440's in side or top for like 80 bucks a piece? PE's 380cc injectors are over 800 bucks for six? I'm curious as to how much different the RC 440's on their site are form the RC 440's offered in the Greddy kit...

 

there is absolutely nothing to be gained unless your motor has the need for them...ie heavy NA mods, lots of juice, or some form of forced induction.

cleaning or balancing the stock injectors would also be a serious waste of time and money, until the car has accumulated significant miles....the injectors are all tested by Nissan to be within certain min/max specs before installing.

 

thanks!

 

good question though.

 

Yeah thanks for the reply. I had found a set of stock injectors for $50 and was gonna have them changed.

 

There are two ways to get more fuel into your engine. Bigger injectors, or increasing the fuel pressure of you stock injectors. Ideally, you dont want to exceed 80% duty cycle on your injectors. There is a calculator on the RC website that can help you calculate what size injector you should get, given your WHP assumptions. Like Z1 said, however, you dont need bigger injectors until you go F/I, or increase hp beyond the fueling capability of the stock 280cc injectors.

Also, the RC 440cc injectors that RC sells on the website are identical to the Greddy 440cc injector included in the Greddy TT kit.

 

Here's another dumb question. What does the cc number refer to? Is it cc/minute or what?

Why do the PE 380s (with a lower cc number) cost so much more than the RC ones at 440 cc? Are they somehow "better"?

Thanks

 

Selecting the Proper Injector

In order to select the correct size injector for your application, you might wish to use one of the following formulas.
In most cases a naturally aspirated engine will have a B.S.F.C of .50. This means that the engine will use .50 lbs. of fuel per hour for each horsepower it produces. Turbocharged engines will want to be at .60 lbs. per hour or higher.

Using these numbers as a guideline, you can select the approximate injector size in the following formula for a four cylinder, naturally aspirated engine at 200 bhp.

Most injectors will max out at 80% duty cycle and this is the accepted industry standard.

B.S.F.C is brake specific fuel consumption - How much fuel you are using per horsepower per hour

The proper injector for this application would be 31 lbs. / hr. or 330 cc / min
To find the HP value of the of the above mentioned injectors use this formula:


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To convert cc / min to lbs. / hr. - Divide by 10.5

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To convert lbs. / hr to gal. / hr - Divide by 6

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To convert cc / min to gal. / hr. - Multiply by .015873

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To find the new FUEL FLOW rate after a fuel pressure change:



Example 1:

If a 240 CC injector tested at 43.5 PSI is run at 50 PSI. The result would be:



Example 2:

The horsepower value of this injector would increase by the same rate
(X 1.0721), if all other engine management systems remain unchanged.

Flow rate at old pressure
240 cc/Min divided by 10.5 = 22.86 Lb/Hr Flow rate at new pressure
257 cc/Min divided by 10.5 = 24.48 Lb/Hr




240 cc/Min X 1.0721 = 257 cc/Min 22.86 Lb/Hr X 1.0721 = 24.51 Lb/Hr
36.58 Hp X 1.0721 = 39.22 Hp

 

The cc number is the flow of the injector, usually rated at 43.5psi. It is cc/min of flow. Some manufactuers will rate their injectors at a higher fuel pressure. It is my understanding that PE does this...they rate their 380cc injectors at 52psi...or something of that nature.

It's just important to compare apples to apples, and compare the injectors at a fixed fuel pressure. From what I understand, the PE injectors are are based on an injector with a different nozzle pattern..or more nozzles..whatever. They are just considered to be superior to the typical RC injector, but they are more expensive.

 

Thanks!

 

Some fuel injectors are rated in volumetric flow rate, and others are rated in mass flow rate. Why is this?

Is the reason for bigger injectors in FI apps to enrich the AFR to compensate for the extra boost? I believe a lean AFR, combined with FI, will make it easier for the engine to detonate.