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Selecting perfect size of injector

EFI Tuning Fundamentals

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How to calculate the correct size of injector for ic engines

Do you want to know the entire formula or just the final figure? For final figure you can google Fuel injectors calculator.

As implied by Shota, it's a rather open ended question.

If you could provide comprehensive details of the application - fuel type, N/A or forced induction and boost level expected, number of cylinders, and peak torque and power anticipated, would be good starting points.

Everything you need inc the calculator is on injector dynamics website buddy. They use a much better system based on air flow rather than the brake specific fuel consumption method on most calculators found on google.

Sure it is a better system as long as you know exact engine real VE at every single RPM break point which is not the case in 99 percent of deals - people just using their best estimation just like with BSFC...

Think I've typed out about 4 different reply's to this but I'm just going to laugh and say "if you say so pal"

I thought you said that you have 0 time for me)) It seems to be a habit of yours to turn technical conversation into something less technical but personal))

Don't flatter yourself! What exactly about you is professional? You blagg almost every comment to come across like your all knowing but all your doing is regurgitating your google education! You have offered 0 advice or comment from you own experiences or knowledge but rather from what you've read and try to belittle or make those who actually do this stuff in practice look wrong or don't know what they are doing. Your now here jumping on a comment I've made banging on about VE & RPM brake points (blah blah yet more shite coming from you) Have you even looked at injector dynamics calculator? NOTHING about VE or RPM brake points are required in their calculator! Engine size, number of cylinders, number of valves, estimated lambda, fuel pressure.........

I directed the OP to a very reputable company who have put a lot of effort into proving a calculator that stands above the rest to make things easy for him. Many many people use injector dynamics who are waaay above the likes of me and you in building/tuning/racing so why wouldn't you use them? Especially when those who ACTUALLY know what they are talking about know how flawed the BSFC can be for you to then pipe up with utter irrelevance and playing them down saying there guessing. I for 1 wouldn't embarrass myself to that extent! I'm sure I'll have some sort of reply because that's your level of maturity, you have to be right and have to have the last word. I may reply but I have a life so may not! Hope you have a good day.

Wow... I need a little bit of time to put a good reply together but i will definitely answer it with good explanation of this matter. You seem to be misinterpreting what i'm doing here just because I cought you once not being correct.

Case and point, does a google search and knows it all, claims he's right and apparently caught me out being wrong. I'll point out again I was talking from EXPERANCE not what I have read! Yes AEM advised that way but there's more than 1 to skin and cat buddy! That's the way AEM recommend to cover all abilities and preventative of issues falling back on them. Tell me, how many water meth kids have YOU installed and ran exactly? So yes, please by all means come out with whatever reply that makes you feel superior in an attempt to belittle me again. There's those who talk and those who do and your doing a lot of shit talking buddy!

1) I have been involved in tuning since 2005 improving my skills from very beginner to someone who understands the engine work not so bad. I have been doing my little project that used to run 15.11ET quarter and now runs 9.5ET. All improvement was possible only because i was gathering useful information over the years and been able to apply it on my car - so i have quite a good understanding what's working and what's not. I came here to get even more information but at the same time to share my knowledge and experience. And that is what I do - if i tell someone he can google specific information i already know that it is good enough and it works, i tried it on my project and it proved itself to be OK. That is the only reason why i can refer to Google in some cases - just to help people to save time and quickly find something that is good enough to deliver what they want. If i feel like that is not good enough i will go a step further and advise something more advanced ( whenever i feel it is necessary). If i do not know the answer i just ignore the topic.

2)Now about the subject. First of all ID is of course very professional company and they know what they are doing when calculating fuel flow based on air flow. But so are Deatchwerks and Injectors Clinic and other companies that use the fuel flow based on BSFC. So it does not realy mean anything as both systems have room for errors. I use ID1700 on my project but when they use boost level as the point of reference for fuel flow calculation my first question is why. I can have absolutely different ( as much as 15 percent ) air mass flow on the same displacement engine with the same boost. It means that fuel requirement can be different to the same amount that yields in 15 percent more fuel injectors size requirement. So why then it would be better than using BSFC as reference point that can bring about the same percentage error ?

This simple question has the simple answer - in order to get correct fuel injectors size you need to know VE of your engine, at least at maximum power RPM.

Returning to the original post, there is no such thing as a "perfect" injector unless one is extraordinary lucky in matching need to what's available, for the most part it's 'close enough' :-D

Shota, you should be well aware of my view on the BS that "VE" is when referring to force induction ;-), it has nothing to do with actual engine efficiency and it should be using something like Volume Ratio - the actual volume of the air entering the engine Vs the nominal volume of air the engine would consume - it is effectively the same thing but avoids confusion with the internal pumping efficiency of the engine.

I consider this differentiation to be VERY important as you can have two engines, same displacement, same air being taken into the engine, but the engine with best (internal) volumetric efficiency will have more power; less boost and less heating of the charge air as there will be less resistance, lower EGT because there is less restistance from the turbine having less impellor restriction to overcome, etc. It also means the same "boost" can have a significantly different air mass, and hence fueling requirement - Shota has direct experience of this, as he noted :-)

In fact, you could have the second engine actually having less "VE" (mass ratio) but producing more torque/power because the internal "VE" is better, and the air mass is used more effectively.

Anyway, back on topic. At best, the fuel demand of the engine is going to depend on the incoming air mass and the desired fuel ratio for the fuel being used.

As this is an estimate, there are different ways of getting that approximation - the easiest is to use what others are using :-) Failing that, there are multiple ways of estimating the engine's fuel demand, in no(!) particular order.

From the power expected from "a" cylinder and the expected efficiency of the engine - how much fuel is used to produce that power, which can vary considerably depending on the power unit and the rest of the power train. This would be the BSFC version.

If one knows the engine capacity, the number of cylinders, the engine's actual VE (usually around 85-95%), and the expected air volume to be injested by the forced induction (the BS "VE"), one can make an estimate that way.

If one has a specific "boost" target in mind, one could estimate the fuel usage from that, the anticipated intake temperatures and the cylinder volume.

Of course, one also has to have a good idea of what the fuel line pressures are going to be, and how that relates to the supplied flow numbers, and what the relative volume/mass of the final fuel will be.

One will also have to endure the entire fuel system is capable of not only supplying the fule volume, with a reserve capacity, but will work with the fuel type used, if high levels of alcohol are present.

My, personal, preference would be the first, but failing that I'd use the various formulae available and see how they corrolated - for the fuel and expected line pressure - then add 10% to the average... more if I thought I'd get greedy ;-).

Remember, every engine combination can be expected to be a little different - sometimes to a surprising degree - so at best we can hope for a close estimate.

So, ladies, if you can put your handbags away, what works for you works for you - if you're happy with that method, go for it.

Gord, I am well aware of your view on VE - we already talked about it once - my view is exactly the same. My engine was boosted with 2.3 Bar at 7300 RPM on the stock head and after heavy porting of that head and installing aggressive camshafts the boost dropped down to 2 Bar as turbo was maxed out. I installed bigger turbo and on the same boost 2.3 Bar the engine was consuming about 15 percent more air at the same RPM. I had ID1700 fuel injectors that at the first glance might seem to be too big for my level of boost but that additional margine allowed the engine to inhale more air without changing them when new turbo was installed although the boost level was exactly the same. If I were to use the boost level as the only reference point I would have to buy new set of injectors))))

Yup, I know - not a dig :-), more a nudge of agreement, as we've had those discussions :-D

That's what I was trying to point out to others, there are many factors involved and, in the end, it's going to depend on the air mass entering the engine and the AFR of the fuel - everything else is just trying to figure out where that fuelling level is going to be, or rather best guess because a single variation can make a big difference, then selecting injectors, pumps, etc. that have a bit of margin over that so when the actual mapping is done they don't run out of capacity.

I expect there are several other ways of doing this sizing proceedure none of us have even heard of, that others will swear by.

I suspect part of Martin's response may have been in reaction to the "google it" suggestion - to be honest, I do have a tendency to be rather more cutting than that when asked open-ended questions with no actual information whatsoever - the milder versions being variations of "how long is a piece of string" :-D

We cool?


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