Here's some interesting data.

http://turbobuicks.com/forums/showth...threadid=20689

Some of the conclusions, are interesting. If you look at the data, the injector is rather stable, then starts going rich, then lean, and then continues going richer. IMO, this constitutes erratic behaviour, I'll let the reader draw their own opinions about that as well as the testing. Not to mention the test was done with one size of injector.

FWIW, if anyone downloads the .exe from www.chuengineering.com and then follows the links from scan tools at Turbobuick.com, to BM Computers, and down loads the file Cat3-6, it's an interesting read. In scope mode you can see the PW approach 100%, the O2 voltage drops, and Knock Retard begins, all at about the start time. If you want to hunt around there are more datalogs showing the same series of events.

You can also poke around and find some logs showing what happens at tip in. If the injector is too small, then you have to use a LONG PERIOD of PW for fuel, the longer, this PW, the more likely you are to approach the min off period, and can get the injector erratic. The issue with DC is really about the off time, and the injectors ability to handle that. It's just a much easier concept to deal with when you work with DC, rather then off times per injector.

 

Funny how some people grasp for straws to convince themselves that what they already have (smallish injectors, in this case) is the "best."

I guess the point of having some extra injector on hand, to do AE fuel with, went over a few heads, too.

Oh well, it's a free country.

(New set of 60 pph'ers, sitting on the desk at the moment. Looking forward to trying 'em out )

 

Yep.

Lemme and the list know how the 60s work out for you. I've been really happy with mine.

 

Geeess...I almost missed this. Thanks for the link to a *very informative* thread. It sure dispelled a lot of misconceptions I had about fuel injectors. Highly technical info like that comes along once in a blue moon. Again, thanks for pointing out the difinitive answer to injector duty cycle testing.

Nick

 

Just starting to learn all this stuff and not sure if I grasp any of it yet. But what is the best way to know what is the best size injectors for an application?

my car runs like crap, have little money and know even less....just need some guidance as to the best method to determine what is the best way and what some of the critical parameters to know are.

 

I believe the best way is to look at the stock HP, and injector size, and then at the projected HP. If you want to double the HP level of the oem engine, then double the injector size.

Another train of thought is that for every pound of fuel you can get 2 HP. Then figure 90% of that, since you don't want to run the injectors static.

 

While for turbo v6s, the weight, ET, etc., you can manipulate the injector size for what you'd need for a v8.

http://www.gnttype.org/techarea/misc/lubrant.html

 

Boy am I ever confused now. Through reading through all those posts on that forum, (and I do not know alot), it seems that he's stating that you can get more than you expect out of an injector? Or am I missreading the information?

And the other guy running the 406 is agreeing with him. Grumpy based off your charts you just showed, 406 dude should have only been able to run in the mid to high 13s? or is it cause of the turbo site dealing with turbo equipped cars? But Hp is hp right?

I just do not want to get the wrong stuff, my car is a POS and I need to spend my money wisely...thanks for the help.

 

That often happens, ie confusion, that is.
And here's another site with another computation.

http://www.bgsoflex.com/auto.html

Some times you have to just bite the bullet and go with what makes sense to you.

Like I said earlier, if you want to use GM electronics, then it seems to make sense at least to me that if you double the HP double the injector size. GM has teams of guys that have spent life times studying this stuff.
There are some that just insist that they're opinion is the only valid option. Or they have some point to prove.

I'd rather have a touch too much injector then not enough. Shopping around might pay off with finding a used set cheap. The first several sets I had in my car were used ones, that I played with to see what gave the best results, and showed me what I needed to do.

 

Interesting stuff.

 

Especially if you stick to just the data.
The graphs are priceless.

 

I am still confused....the two boards together there seems to be a dividing line between the two.

Turbo-board - the guy seems to have posted pretty concrete data that conflicts with most of the searches I have done here, and on other boards regarding the subject. But I guess that is expected on board where many people chime in.

At this point in time, it seems to me that there is a bunch of misconceptions surrounding the subject, most of which is just theory.

Guess we will have to wait to see how gnjone's theory holds up. Right now it seems pretty solid, and very much to the contrary to what I have been reading while trying to find my injectors.

 

If you stick to the graphs, there is no theory involved.

As the duty cycles go high, the injector flow gets erratic. They go rich, then lean, then rich again, all in the last 10% or so of duty cycle.

And you have to recognize this testing was done under steady state conditions. Look at the DS file and software I mentioned, earlier, and you can see for yourself in plain view how it all correlates. No conclusions need to be draw when the data is in plain view. It's all plain as day, just looking at the data.

 

The big question for me when I do injector sizing is what is the BSFC ratio to use, along with the FP... I have been using .45 and 43 psi, respectively. This is on my N/A 406.

Any thoughts on the BSFC # to be using?

 

Grumpy.

I think you should refute your point on the Turbo-board and see how it fairs. Registration is pretty easy.

I do not pretend to be an expert, more of an idiot. But from the graphs,



it appears to me that the injectors over 80% get extremely consistant. Contrary to popular belief that one should not exceed the magic 80% DC mark. No?

88tpi406,

What injectors are you currently running with your setup? You seem to be in the same boat as I am.

 

Browse thru their forums a bit more closely, and ask me that, again.

But at over 90% the go rich, then lean, then rich. That is being erratic. The larger the injector, the closer the tune, the more critical it becomes. Again, remember the test was done on a steady state conditon. Please get the file I posted, and .exe and just look at what happens in an acutual car. Where the 80% came from is anyone's guess.

I'm running 60 PPH injectors in my lil 231, idles just fine, makes plenty of power. It also ran well with 55s.

There is no point to be made for running small injectors, other then possibly saving a few bucks short term. Launch a set of headgaskets or knock a corner off a piston, and your injector savings, is gonna get costly. Since you get to repair the engine, and then eventually get the injectors anyway. Or go for running them static, or race fuel, add some Toluene, Zylene, or some other chem., and cross your fingers.

 

I have 30# SVOs...but I don't yet have my car on the road...and that is when I thought the the SVO's were more like 33# Accel type injectors...

The long and short is that I will have to wait and see how the engine likes them...the only reason I didn't go bigger was $$$...but that may change.

As Grumpy stated a while ago in a different thread...I just don't want to go too large so idle is impacted by not attaining a short enough DC...so maybe 42# for my application and future growth...

 

Grumpy should refute his own point? You want him to argue with himself? Maybe he should present it, and let other people try to refute it.

The guy who ran his car w/ no coolant...twice...and shoved a wooden dowel pin into the knock sensor hole...now taking shots at Grumpy using other peoples' data.

That's some of the best humor available on the Internet! At least your last sentence quoted above is accurate.

 

Me and a friend at work have been searching the internet for some info on this duty cycle thing. There just isn't any data to support the erratric operation theory. We did find reference to some bozo who claimed he could put an injector on a bench and just *listen* to it and determine that it is erratic. We had a good laugh over that one! We did find some injector flow graphs that all pretty much looked the same. There are some here...

http://www.gnttype.org/techarea/fuel...lowcharts.html

I wonder how this compares to the data of that guy from turbobuicks.com, although it's not published. Does anyone know if this flow data is accurate? Bruce? Anyone?

Nick

 

LOL
You, and your friend, are just continually ignoring the data and then say there isn't any.
Look at the RC Engineering Web site, check the DIY-EFI archives.

Not to mention that if you go to the opening URL, you see the injectors run at constant flow, then spike upward, which is RICH, and then from that Rich upward spike, they SPIKE DOWNWARD, which is LEAN, and then Spike UPWARD again. What do you call that?. Steady state, then going richer, then leaner, then richer again, sure sounds like erratic behaviour to me.

 

Dunno if you'd believe some Bozo, but IMO, it misses the issues. Injectors need a min ON time, and a min OFF time to guarantee reliable and stable operation.

If you look at the RPM test points, it's at 600, then 2,500, and then 5,000 RPM. The steps are so large that even at the 12 msec PW when it would be going erratic, the test just jumps past that all together.

 

why are you attacking me? I was merely suggesting that Grumpy refute his point, as he seems to have a good theory, except it contradicts what those guys over there have been saying. That is all. I was NOT taking any pot shots at Grumpy.

As I said before, I am trying to learn here and sorry if once in awhile I do something not 100% right. At least I am trying.

if you read both threads you will see there are some guys that are running extremely fast and clearly know what they are doing to get that fast that are saying the opposite of Grumpy. I have been reading on some other boards as well, and these same people are doing some amazing things.

The guys that were mentioned just built/tuned a 383/SR that went to the track the first time with 24# injectors and went 121MPH on a track that clearly goes uphill from what the people were saying.

So YES i am confused as to what would be best for me still. If i can get over 100mph in the 1/4 I would be thrilled. 20+ more MPH would be spectacular.:hail:

 

Nope, that falls with in the realm of possible. Try it enough though and you will have problems. The SBC has 5 bolts per cylinder to clamp the heads down, so what other cars such as Buicks pop headgaskets as the fuse, the SBC knock the edges off the piston domes, or kill the lower ends. While severe detonation will quickly kill an engine, tip-in preignition takes longer but has the same final results, ie shorter engine life, or component failure.

You can go fast with all sorts of odd combinations, but that's more luck then anything. Some folks are rich enough to afford to be lucky, and swap engines out and play a richer man's game then some of us. But, to use the results of an engine that lasts one season atta time, is hardly comparible to one that goes 10's of thousands of miles.

And don't forget that what's always claimed to might not be the full truth. Little details about the type gas or custom brewing are often ignored, or left out of some postings. Not to mention there's things out there, that are much better then Toluene or Zylene for boosting octane. And if you threshold tuning for detonation, then they make all the difference in the results.

 

Good thread. I posted a response over there.

I think two key things are being overlooked:

(1) duty cycle alone is not enough to judge what an injector is doing, you also have to state what frequency (analogous to RPM). a 95% duty cycle applied to a 1 second time interval is 950ms on / 50ms off (no big deal), but 95% applied to a 10ms interval is 9.5ms/0.5ms. big difference. so you have ot take into account both rpm (frequency) AND duty cycle..

also eraticness can't be measured by taking a sample of a large number of injector cycles, you'd have to measure individual pulses.

for ex. if you were expecting 1.00g of fuel with each pulse, but what you actually got was a random amount between 0.90g and 1.10g per purlse, you'd still average 1.00g of fuel (makes the injector look dead on), but with 10% error margin (10% AFR error margin). have to look at each individual pulse to determine if the amount of fuel being sprayed is erratic or not.

 

I believe that anytime you put your car on the track, you better expect the worse and hope for the best. That is just the name of the game, and the reason mine has not seen a track yet. I can't afford the chance of it breaking.

I am assuming threshold tuning is referring to pushing the limits of the motor. Isn't that what you do in tuning if your trying to get the most out of the setup?

Also I do not believe these guys are ruining anything, they seem to race nearly EVERY weekend and make several hundred passes a year. This leads me to believe they may just know what they are doing, and the rest of us just do not understand.

Why would octane boosting matter. From reading these guys built higher compression motors, and fully intended on running some octane on the strip. Correct me if I am wrong, octane on a motor that is not tuned to use it will only hurt performance. Right?

 

Wrong. Octane is simply a measure of a fuel's resistance to pre-ignition or detonation. It will only hurt performance if the octane rating is too low for your engine. Do a Google on "octane rating" and you'll find out more than you want to know.

 

What I think is really missing is the consistency of each shot for an injector at each duty cycle chosen. As far as I can tell, the test on the other board are averages over many shots so that a decent amount of fuel can be collected. I would expect that if an injector single shot volume was within 2% at low DC then the number would grow to something much worse at high DC. Its those shots on the low side that will harm your engine.

Unless those tests can measure single shot volumes they are not too meaningful.

 

No I think your mistaken. Your right it resists detonation, but the flame kernal will not propigate as fast with higher octanes, therefore if a motor is optimally tuned on 92 octane and someone thinks adding 105 octane will not effect the performance they are mistaken.

It WILL since the cumbustion pressures are not going to occure at the same time as with the 92 octane since the flame kernal will not fully burn all the fuel at the same rate as with the 92octane. Therefor ones timing will be messed up.

Been reading on this stuff a little lately since this topic came up.

So again, simply adding arbitrarily octane to a motor that was not designed/tuned to run it will not yield results.

I have been searching the other forums around and that 121 MPH out of a 383/sr/195 AFR motor is the fastest one I have found so far. So octane or not, these guys are blowing the rest of the similiar combos out of the water.

I will have to keep an eye out to see what they do next.

 

ghost _man's quote didn't make it into this post somehow, but:

According to the research I've done, if you have an engine that will run fine on 87 octane fuel but you use 93 instead it will not negatively affect the engine's performance, only lighten your wallet unnecessarily. Now, I don't know about how the octane boosters that you can add to the fuel affect the combustion process, but I would guess that the net effect would be the same. Also, by running higher octane fuel than necessary in the above mentioned engine, more aggressive timing could be run to take advantage of that. In that respect maybe we can say that there is power being left on the table, and thus a negative effect on the power............

I think you and I are more in agreement than we think.

 

Sure...... Just because you turn the times.. doens't mean you know know why you did.. I've wasted to much time with the parties involved explaining the realities..

As noted..when your pulse width exceeds the time available to inject.. your static.. period.

Adding a ton of tolune to your gas.. helps to cover your lack of fuel as tolune has more BTU's than plain gas. Hense more power from less fuel, so if your running static, you can "cover" your lack of fuel.. to a point. Also..

theres the whole MAF 255 grams thing.. but thats another arguement..

 

heres the plain and simple as i see it :-)

Look at the chart of inj flow vs. duty cycle and see the spike at 85% and then follow to 90% and above ..


Starts getting a little wacky looking to me.... As i see it u never want a part on your car that u have to stress at 90-100% of its limits.. Most things just dont work well when they are pushed that hard for a long duration of time ....

Argue all u want , do u think that a static inj only magically spikes rich? Nope they can and do go both ways............... What about this test after an injector has 40-50k on it and still being run that hard? Bet after 85% it gets really screwy than..

Would u trust your car and tune to the point where u would be happy with something u know that is going erratic? I wouldnt be.

For me i can live real easy knowing that i have enough injector for the engine i have and keep the duty cycle in the 80% range and i will sleep alot better at nite too
later
Jeremy

 

Absolutly facinating thread! I dont know how I missed it when it was still up at the top.

One explanation that could account for why the injectors do this is pressure shock that forms behind any sort of flow control device that is suddenly closed. Since the fluid has momentum, it wants to keep going at a steady rate and suddenly stopping the flow gives rise to high pressure regions behind the valve, which can even lead to destructive shockwave formation that destroys piping. I guess what might be happening at high dudy cycle is that as the pintle touches down on its seat a region of high pressure forms behind it as the fuel is forced to stop and the pintle is then forced to immidiatly open again before the pressure region has moved off/disipated and the momentary increase in pressure causes the fuel flow to be slightly higher untill the pressure has returned to the normal fuel pressure in the system. Could possibly even generate enough pressure to stop the solenoid from being able to retract the pintle off its seat if the injector has to open as soon as it has closed.

 

Just a couple of notes,

While you might like to think your running .45 BSFC it's not likely to happen in a muffled street SBC. Figuring on at least .5 will keep you in the tuning area most mortals fall into. If your running boosted firgure on .55 as a min and probably closer to .6.

If folks want to continually ignore the AE stuff then well, just have fun, and wonder why the engine just never has the response you think it should. Yes, there are bandaids to get around this, but they are just bandaids. In a MAF car you can crank up the PE% vs RPM, and in the SD cars add alot of unnessary fuel in the VE tables. But, then at a steady load like staging the engine will start to load up. So then run a loser converter. Yep, it all plays dominos. There's a CORRECT tune, or not even close.

If you look at the way GM engineers things, you might do well to try and understand the logic. They have teams of guys that have spent life times figuring things out. Once you understand the hows and whys of the oem stuff them you can see how to manipulate it to your best use. There's an extreme amount of oem bashing by folks that are just clueless about what is really going on. And before any one jumps to any silly conclusions, no I'm not trying to infer I have all the answers.

Again, you want to double the HP, just double the injector size. until you're tried that, you really don't have any place to somment about it not working. This $10K for an engine and wanting to cut corners on buying injectors is just beyond me.

If all else escapes some one, think of this. The acclerator pump with EFI is TIME based. It lenghtens the PW to get the fuel. The longer the PW has to be the more likely the engine is to have Tip-In Pre Ignition. Which means the chamber temps go up, which means the engine is going to be more likely to detonate after having been in Pre-Ignition. IMO, I'd just as soon avoid all that.

And it's all really about injector off time, not Duty Cycle anyway.

Any given injector just needs a given amount of time to actuall turn off. And that off time is going to vary some because of the design of the injector.

Some injectors will run up to operating pressures of 120 PSI and be constant in actual flow vs calculated, while others will lock up as low as 70 PSI. In the Syty archives, is the report from Kinsler from 6-7 years ago where they ran the stock Syty injectors up to 120 PSI and they were fine. In the DIY archives are some results about some that locked up at 70 PSI.

Looking at some high speed injector photos will show they gradually close off, and they gradually open. This is shown by the fact that there are large droplets at opening, and closing. RC Engineering I beleive it was talked about this at one time on their web site.

But, that's all just a guess...........
Not that, I've actually run large injectors, or anything.

Oh, and at WOT with SEFI you drop to having 1/2 as many closing periods to deal with, so that'll gain you 5% more flow at a 90% Duty Cycle.