How do injectors increase fuel mileage?

[HeavyHauler]

I'm probably gonna get a set of mild injectors soon - if anything, just to have when I really need them. I've been reading a lot about them and nearly everybody claims that they increase your fuel mileage, sometimes by 1-2 mpg.



How does this work, technically? Or do they really increase mileage?

 

[fox]

I tried the 275 injectors and mileage went up by about 2. Then tried stage 2 and there was no loss, if driven for mileage. This level was at risk of over heating the exhaust, so a bigger was turbo was needed.

So keep the power increase to 80 hp or less for best injectors.

Now to answer your question, the slightly larger injector will deliver the squirt quicker while the piston is at the top of its stroke . This is when it is more efficient. Actually like advanced timing.

 

[mhenon]

I thought it was more holes in the injector and/or a slightly different angle of injection.

 

[Hohn]

Larger injectors may or may not increase MPG.



Since they injector fuel with a faster rate-of-discharge, that means that they take less time to deliver X amount of fuel. That means that a higher percentage of the fuel is injected near TDC, when the intake charge is hottest. This can mean a more complete or faster burn.



The problem is that a lot of injectors atomize poorly as a result of the process that make them flow more. Usually, this is associated with extrude-honing, as you just don't have much control over where the metal is eroded from using an abrasive slurry.



The number of holes is important too, as it determines overall injector flow for a given size, obviously. But under certain conditions, multiple holes can be harmful to efficiency.



In the early days of Don M's EDM injectors, he experimented with different hole counts, as many as 14 holes (I've heard up to 22 holes). While they were VERY clean on the bottom end and made a LOT of torque, when boost came up, they would smoke like crazy. Why? Because the holes were so small that the fuel couldn't efficiently flow out of them under conditions of intense cylinder pressure.



They began to see "weird" things happen, like 8 hole injectors running cleaner than the 14 hole ones!



As far as I know, ALL Don's EDM injectors are now 8 hole. This design was just cleanest and most efficient overall.



Also, the Mach 1. 5s are the highest mpg injector he makes. It would seem that the mach 1 (smaller holes) might be more efficient, or maybe even the mach 2 (more of the "good" effects of a larger injector). But neither is true-- the 1. 5 is the "sweet spot".



The only proven mpg injectors I know of are the RV275s and the Mach 1. 5s, though I know of good results with a set of mach 1s I installed (22-24mpg empty on an '01. 5 ETH).



Injector efficiency isn't about larger or smaller necessarily- it's about the "right size". Call it the Goldilocks effect.



I personally think injectors between 70 and 90 hp are a good range for overall efficiency if well made. Unfortunately, there are huge difference from one brand injector to another brand, so that's a statement to take with a grain of salt.



In short, you want mpg-- go 275s or Mach 1. 5s. All others may help or hurt mileage.



JMHO

 

[KERMA]

Because the holes were so small that the fuel couldn't efficiently flow out of them under conditions of intense cylinder pressure.

It's called cylinder penetration. The fuel must penetrate the combustion chamber enough to effectively mix with the air, and still atomize enough for quick burning. It's a balancing act between a steady stream at one end of the spectrum, and perfect atomization with droplets so small they don't have enough momentum to mix with the air on the other hand.



If the atomization is too fine, and there is insufficient pressure to get the tiny drops moving, it creates "depletion zones" where all the O2 is used up within the fuel cloud. The unburned fuel makes -- SMOKE!! Obviously, the best results are achieved when all the air in the combustion chamber is utilized evenly.

 

[fox]

Very interesting, Thanks guys.

 

[Rotty]

Very interesting, nice post Hohn.

I would have guessed the if you could have an infinite/ maximum amount of holes would have been best, but obviously I was only bench race guessing... .

It is a good day, I have just learned something more today... .

 

[dacook]

Thanks for the info. I installed 275's this past weekend and love them. Oo. definitely noticed the power and, after a day of zipping around, I melloed on the pedal and have noticed a increase in milage. can hardly wait to pull the 5er for a camping trip

 

[KERMA]

Bigger holes get the fuel in quicker- it has more time to burn also.

 

[DBogo]

How much HP do the 275's add?

 

[Bob Wagner]

How much HP do the 275's add?

roughly 40

 

[DBogo]

im planning on getting some but i need a truck first

 

[Hohn]

About 33hp on an Standard output truck.

Figure maybe 40hp for an HO.

Justin