^^^^^ Sorry to say bro, But here is what you need to look at when selecting Injector sizes, As I am a builder and a EFI tuner and have been so for over 5yrs,

80% is were you would want to limit your injector duty cycle, not 100%. Over working an injector will cause overheating issues(the injector) as well as poor spray patterns, with spray patterns bieng VERY important when trying to burn that fuel and in a manner that makes more power for you. I always tell customers to buy and injector that leaves you room to grow, now yes in a situation were you never plan on making more than 400WHP, 1000CC injectors is a bit much and not needed, but in this situation 440-525's are no were near a OVERKILL like stated. The only time larger injectors will cause issues with a tune if they are to big, is down low(idle) due to the lag they carry while running a honda resistor box, now this can even be fixed with the new injector drivers out(FJO Ect Ect). With the correct tuning and hell even a good FPR, injectors are the last thing that would create a low power output unless the injector is not closing all the way or leaking, but this would be seen in the A/F if it was the case.

Bottom line, over working an injector is a BAD thing. The lower duty cycle you attain the better(to a point) with a lower duty rate you increase the way the injector works and sprays, an injector working at 60% in most cases will peoform better than and injector working at 75% its just how it works

 

Please read the posts and the thread carefully before commenting. Thus far no one has recommended running injectors at 100 percent duty cycle.

To recap, 440cc injectors will support 300 hp at 100 percent duty cycle. Do the math. At 80 percent duty cycle, 440cc can flow 275 hp. You may recall our boy is putting down 175 hp and hopes for 200hp or so. If he needs head room for another 100 hp in his N/A 1.8 motor, he and his tuners are dreaming and dreaming big. If he has 525cc injectors, he has "head room" for another 125 - 130 hp (325 hp N/A B18, sign me up).

Buying oversized injectors is something anyone "can" do but buying properly sized injectors also is something anyone can do, and indeed "should" do.

The injector sizing formula has been around for about 45 years longer than you have been tuning. Here it is:

Horsepower (200) * B.S.F.C. (Brake Specific Fuel Consumption. with .50 commonly assumed) = 100
Divide the number of injectors (4) * .80 (duty cycle) = 3.2
Divide 100 by 3.2 = 31.25 lbs of fuel per hr.
31.25 * 10.5 = 328cc

This means 310cc would be running at no more than about 83 percent duty cycle, leaving you plenty in reserve for any street application. Remember, the 80 percent duty cycle guideline were developed to accommodate engines running at high rpm continuously for long periods, such as in race engines. The figure also is normally used for aircraft applications in which motors run near maximum output for long periods.

As stated earlier, Honda engineers saw fit to outfit ITR 1.8 engines rated at 200 hp with 240cc injectors. This illustrates the gap between street applications and high performance/demand driving. Our boy has a street engine with about the same output and I am recommending injectors a full 70cc - 80cc larger than what Honda recommends. That's plenty and then some.

 

LOL thats funny stuff, U keep stating the 100% duty cycle, not me and 80% is more than a guidline it is a standard, have you seen what happens to a motor that looses and injector at 8000RPM due to overworking it?, I have, its not pretty, I have seen injectors loose it at 90% and some have gone up to 105%,Overworking and injector is a dumb thing to do and can be avoided by giving youself room, why run and injector at 80% when you can run it a 70% or even.... Ehh fuck it im not going through it again.... you can do your math all day long, but doing it and adding it up is two diffrent things, I am not going to sit here and argue about BSFC, its dumb, I am going to say that what I wrote stands, the injector he is using has NO affect on power, so saying something like, "well man 1st off why are you using such a big injector?" is pointless to the topic at hand, you need to read. My whole point above which you failed to notice is that the lower duty cycle will net a better working environment for the injector and less heat. dont take me on some mathmatical trip back to basic EFI understanding, I have been to EFI101 and the EFI advanced course, so im not a dumb shit. And Im also not going to have a pissing contest with you, so lets end it at that.

 

Sorry 1 more thing, im not trying to start ANYTHING here I swear, so dont take this the wrong way, But were do you go for your tuning, part throttle headaches??? Why why why?? I have taking quite a few setups that needed to be broken in that were running 1600CC injectors(yea I know to big) and set the car up for off boost driving until proper breakin and I have NO problems getting the car to idle at 900RPM's and get damn good if not bad ass MPG at the same time as well as stock or better part throttle driving. Im not sure if you are talking about using AFC's or ECU hacks but reaching the ECU's limits? the stock honda ECU is capable of supporting 800+WHP cars all day long, and hell some of them are driven daily and get great MPG, I run 880CC injectors on ,my personal car and net 300 mile to a tank!(10gal tank).. ok that all

 

I can appreciate you are offering your advice based on your experience.
My point is that no one in the fuel injection/engineering business agrees with you. That fact really is more important than whether I agree with you, so we would do well to put the debate in that perspective. Believe me, I take no offense in you disagreeing with me.

It also is conceivable that you know more than the recognized experts in the EFI industry, it's just that I believe you have failed to prove it here.

At best, you have established that you have been able to make oversized injectors serviceable, though that is far from making them desireable.

Pasted below are various links for calculating proper injector size. Interestingling, the RC Injectors page happens to use 200 hp N/A as a base for it's example calculation, which is essentially what we are talking about in this thread. As you will note, the calculation produces an injector size nearly identical to what I came up with. No big accomplishment on my part. I just used the same formula Russ Collins and everyone (with the obvious exception of yourself) uses.

As for the issue of how our boy's injector size affects his power output, I agree that it may not be the issue. But seeing he listed 525cc injectors was a red flag. Because they are well oversized and because he could have been running them for a time before tuning, it is conceivalbe that he rained out his cylinders and ended up with excessive bore/ring wear, leading to power-robbing compression loss. I am sure you would agree that 525cc in his application would be a disaster without some way to tame them, i.e. through tuning the fuel tables.

http://www.firebirdgt.com/formulas.h...njector_Sizing
http://autospeed.drive.com.au/cms/ar...ml?&A=0102&P=1
http://www.rceng.com/technical.htm
http://www.compsystems.com.au/TechTalk/EFI%20injector%20size.pdf#search='efi%20injector%2 0sizing'
http://www.hoon.tk/tech_tips/fuelinjector.html
http://www.msdignition.com/fuel_1.htm\
http://www.compsystems.com.au/TechTalk/TN010504.htm

 

I still dont see were my simple point was not taken? I never once said that a 525cc injector was the proper injector to use for that application, Yes if you do the math with all the BSFC numbers it will give you an injector that will fit your needs, with "YOUR NEEDS" being the biggest player in the whole point. OMG russ colins said so so it has to be. try and give Joe Krivickas, or even Patrick Rubio at PTE a call if you want to list names, and ask them if running a larger injector is a bad idea, Never in my statment did I say that bigger is best. But the way people are searching for more power each and evey day going with a larger injector and leaving room for more power is a good idea, plain and simple, please dont throw more math at me, we can dance all day, and use up needed bandwidth. My point was simple and over looked from the beginning, using larger injectors will not hinder you in any way unless your tuner is not capable of setting them up right. And in thise situation JohnVega is more than capable of doing so End point. Happy Easter All!!

BTW at 50PSI rail pressure a

310cc injector will support 52hp at 80%
400cc will support 68hp each
440cc will support 77hp each
525cc will support 90hp each
580cc will support 100hp each
680cc will support 117hp each
780cc will support 135hp each

Check the site for larger sizes and HP capabilitys

 

Clear enough, just trying to help the guy out. When someone has a problem and they used a reputable tuner, you start looking for what is missing or what doesn't belong and trying to figure out how it may be impacting the numbers.

Like I said, the oversized injectors caught my eye and I thought it was possible he had been running them and dumping unburnt fuel through his engine. His compression readings were even, but 270 is normal according to the Helms nominal spec for ITR/GSR. At 220 he's about 50 psi short and it could be worse, depending on how good his compression gauge is. He doesn't say what pistons he's runnig but I assumed ITR. He does say the head was milled, so he should be seeing some minor increase in compression over the spec.
Raw fuel continually dumped into the cylinders washes away the protective oil film and causes premature wear and blow-by. He asked if anyone had any ideas. I responded, which led to the discussion about selecting proper injector size.

Meanwhile, the injector sizing chart you posted illustrates well what I was saying should be followed when choosing injectors. Thanks for posting it up.

You have made it clear you routinely advise people to ignore that chart for the reasons you explained. To each his own.

 

^^^ I give up , I will tell you this, your are a very brite person, and are not tha average joe shmo that posts usless info, I enjoyed to battle of the wits with you, and hope to see you post more informative info on these boardes that need it.(in some cases ) My point got burried a long time ago. Oh well.

BTW the list I put up about the injectors, when its says 79HP that means if you need 77HP or even 79HP it would be more than wise to go larger to give breathing room, again this is a HOT TOPIC that could be discused for a LONG time,(agree? ) But yes, power output and compression need to be looked at, as Neal pointed out already compression is low.. GL with the setup bro...

 

Good exchanging with you. There are not that many with whom I would bother. You are worth it.

 

^^Likewise