[IceMan408]

I am about to finish the parts list for an upcoming project that I got tapped to do the engine for. In the past 55 years or so I have built a fair number of performance engines in various sizes from several manufacturers, but they have all been carbureted – I have no real-world experience with fuel injection. Engines are easy, but fuel injection and computers are a horse of a different color. I hope you folks with real world experience can enlighten me.

Injector Sizing and brand are more complicated than it may seem. Factory stock engine was 240HP with 19#/Hr. injectors – the Injector Calculators call for 19#/Hr. @ 39.5I PSI (Ford). The Calculator and Ford agree. If we modify the engine to 450 HP the Calculator calls for 35#/Hr. and that would be at 43.5 PSI which is the pressure the injectors were rated at. Easy, right?

A lot of folks on this and other forums are running injectors larger than what the Calculators would call for, and almost none of them will mention what Fuel Rail pressure they are running. An exception to this is Michael Ponthieux who states in his Pre-Tune Information article “I highly recommend using no less that Siemens Deka High Impedance 80lb injectors in ALL ENGINES (excluding split port).” On fuel rail pressure he writes “Decipha recommends 65 PSI of base fuel pressure for injectors smaller than 80lb.” In the injector sizing chart in his article, it shows a 36#/Hr. injector for a NA, 8-cylinder engine supports up to 460 HP. That 36#/Hr. was taken at 43.5 PSI.

OK, let’s talk about Siemens Deka injectors a little as that appears what a lot of folks are running. I have found getting any good information on Siemens Deka injectors is a real challenge. TRE (The Racers Edge) states that the Siemens Deka 60# and 80# have an operating pressure range of 30 PSI to 100 PSI. They claim a 60#/Hr. injector operating at 80 PSI will deliver 80#/Hr. Siemens Deka 60#/Hr. injectors can be had with either a Cone or Pencil spray pattern. I can find nothing written about spray patterns and if it really matters.

So, the book (Calculator) answer is to use a 35#/Hr. injector at 43.5 PSI. for 450 HP, but the Real World appears to have a better answer than the Book. And we have not even discussed if a Cone Spray is better than a Pencil Spray for our use, or does a Siemens Deka, or any injector for that matter, have a “Sweet Spot “within its operating pressure range that it operates better? Is operating at a higher pressure actually better? Will the injector last longer if operated at a lower pressure?

And finally, we have to sort through the marketing BS to buy what we THINK we need. Is the Siemens Deka injector set you bought the real thing or is it a fake copy? I have seen Siemens Deka sets online for $89.00 – do you really think they are the real thing? I was told by a Trick Flow Tech support person that the Trick Flow FS-89036 injector is the same as the ACCEL 150836 injector. The printed specs are identical – but the price varies a bunch.

Your thoughts would be appreciated.

[jsa]

Generally higher pressure improves atomisation. Generally higher pressure slows injector response and changes the hi and lo slopes disproportionately. Higher pressure makes the pump and electical system work harder.

It's reasonable to expect that higher pressure to the extreme shortens service life.

[JuiceSC]

Fuel injector sizing comes down to how much 'safety margin' you are comfortable with.
450 HP N/A, 42lb injectors are plenty. No less than 36lb'ers. So the 35's are spot on, but they are the minimum.
Mine makes over 400 at the wheels, 42's work fine, but they are maxxed out.

Not having actual injector data is not a deal breaker, but increases the tuning time drastically. If there is data available, run the rated pressure so the data is accurate.

[cgrey8]

A lot of folks on this and other forums are running injectors larger than what the Calculators would call for, and almost none of them will mention what Fuel Rail pressure they are running. An exception to this is Michael Ponthieux who states in his Pre-Tune Information article “I highly recommend using no less that Siemens Deka High Impedance 80lb injectors in ALL ENGINES (excluding split port).” On fuel rail pressure he writes “Decipha recommends 65 PSI of base fuel pressure for injectors smaller than 80lb.”

He's been a fan of those Deka injectors since they first released a decade or so ago. And I have to agree that the engineering that went into them is impressive. I also have to admit that if I were going to buy NEW injectors, they would be high, if not right at the top, of my list for all the same reasons. However that said, I've never bought an injector new. My builds have not been budget builds, but they've been about maximizing budget. So when faced with either buying NEW for $300+ or buying used off eBay for $50-75 for a set, I tended toward used.

When I was planning my 331 build, I came across an eBay find for a set of Bosch 36lb (ivory) injectors that were the newer EV6/USCAR style body but with the older EV1 connectors to work with my existing wiring harness. I bartered with FIC (the one here in Atlanta, not the "big name" FIC) to flow them on the bench to make sure they were good. The guy that flowed them recognized them as injectors from Pontiac Supercharged 3.8L V6s. I traded him some old 19 and 24lb injectors as payment. At the time, they were redrilling & refurbing used injector cores to be higher flowing flow-matched sets that they then resold. They needed cores, I needed flow-testing. So we worked something out.

Moving on...

...Siemens Deka 60#/Hr. injectors can be had with either a Cone or Pencil spray pattern. I can find nothing written about spray patterns and if it really matters...

It often depends on the application as to which pattern is going to work best. You'd think cone would ALWAYS be the best, but if you have tall/narrow ports, you may wind up just washing the walls with a wide cone. And if you are going to be wetting the metal, it's probably best to wet the intake valve, which gets significantly hotter than the ports get. In daily driver kind of cruising conditions, the intake valve's heat will boil the fuel off quicker than the walls will, the fuel will cool the valve, and getting the fuel (with its detergents) on the valve helps keep them cleaner. However if this is a straight race-build where fuel economy, longevity, and emissions are not important, then a cone might make more sense? The exceptionally high flow of air at WOT is going to have so much turbulence in the ports that any side-spray while the intake valve is closed isn't going to matter much. But the better atomization of the cone along with the significantly shorter time period between injector fires at high RPMs may result in better performance...again may, not will.

And then of course if you have LARGE ports like the cathedrals or round ports, then the cone might make more sense, even for applications targeting daily driving. So it all just depends on what the application is and your intentions for it as to which pattern is best. MOST people will guess and not really know which pattern would've been better. But when you have a shop where you can afford to buy both sets and test which injectors work best on different engine builds, having that choice is nice. Now how much fuel economy or performance difference could it possibly make? I have no clue. I'd be curious to hear from those that have tested the difference and would be willing to share their build characteristics and the results of the tests.

Is operating at a higher pressure actually better? Will the injector last longer if operated at a lower pressure?...

As already mentioned, higher pressure generally gets you better atomization. Higher pressure USUALLY increases the amount of force it takes to open the injectors AND affects how quickly the internal spring gets the injector closed. But in the early days of fuel injector design, this also caused fuel control issues. Different injectors of the same part number would have different response times. Hell even the same injector could have consistency-tolerances that result in slightly different fuel delivery from fire-to-fire creating an inconsistent fuel delivery and thus impossible to accurately control and tune for. With lower injector flowrates, this "slop" is generally tolerable and often not even noticeable. But as the flowrate of the injector is increased, so does the affects of the slop. This was no good for getting precision control of fuel in racing applications. You just had to accept that fuel control at idle and cruising might be a mess. It was also a problem for production vehicles having to meet ever-increasing emissions & fuel economy standards. So while you didn't notice a problem, the EPA did.

This is why a good set of flow-matched injectors from a reputable seller was so valuable back in the day. This is also the reason race applications which REQUIRED exceptionally high flow injectors would opt for low impedance (1-3Ω) injectors instead of standard high impedance (11-15Ω) injectors. The lower impedance increased the current going through the injector which gave the open-actuation more umph to make the open-event much shorter, more consistent, and less dependent on fuel pressure with the injector designs of the day. But low impedance injectors require special injector circuitry to avoid burning up the injector and the controller. So they don't tend to be as popular in hobbyist applications where reuse of the existing EEC and wiring is desired.

Injector design has improved a lot since the 80s when electronic fuel injection became the standard. The injector design is what dictates how affected by fuel pressure the open/close events will be. I believe what makes Deka injectors so good is a mechanical design that not only makes their fire-to-fire fuel delivery more consistent, but also more consistent compared to every other Deka of the same model all while giving a quality spray pattern, even at lower pressures. And this becomes even more important for fuel delivery systems that, from the factory, want to vary the fuel pressure at runtime. I wouldn't be surprised if their design effectively eliminates the affects of fuel pressure on intake open/close events. I have not done testing or read papers on testing so I can't say this is the case, but I'm sure work was done in this area. Even my used set of EV6 era Bosch 36lb injectors were so close in performance (with a fixed pressure) that the guy at FIC said they could be sold as-is as flow-matched from a fuel delivery precision standpoint. But that wasn't surprising being a a relatively low 36lb/hr injector.

The thing that made the Dekas so popular is their precision fuel control across a wide range of pressures, great atomization, & high flow rate (well above 42lb/hr @ typical stock pressures) while still being a high impedance injector and thus electrically compatible with stock EECs.

...Is the Siemens Deka injector set you bought the real thing or is it a fake copy? I have seen Siemens Deka sets online for $89.00 – do you really think they are the real thing?...

Unfortunately in the past decade, eBay has become littered with counterfeits of whatever is valuable. Bottom line is if something is expensive, someone will find a way to cut some corners and sell a version of it cheaper, either under a different name or as counterfeits. But MOST of the time, that's only going to exist for NEW stuff. I'm not going to say it can't happen with used stuff. Anything's possible and part of why people pay the premiums for things is essentially paying for the insurance they are getting what they expect.

...I was told by a Trick Flow Tech support person that the Trick Flow FS-89036 injector is the same as the ACCEL 150836 injector...

That may be true. It's not uncommon for a reputable company to use their brand recognition to resell parts.

In certain cases, the reseller is adding value. It could be they are procuring the same ACCEL parts you could get, but then they do additional testing or inspection of them and possibly group them so the sets you get from them are more matched than what you'd get from ACCEL. Or they may be literally selling you exactly what you could get direct from ACCEL. I don't know. You'd have to talk to them and find out what value-add they are applying other than their brand name.

But the practice of reselling WITH a value-add exists. There's a famous machine shop in Utah that buys cylinder heads from the same mfg you could buy from. But what they are doing is completely tearing the heads down, performing SIGNIFICANT additional machine work to the heads, and doing additional valve work to them to produce a far superior product (in their opinion) than what they received...and that is what they are reselling with their name on the product. But they are VERY up front about where their engine parts originally came from, what exactly they are doing to them to improve them, AND WHY they do it to justify their price.