Luna,
You make some exelent points and I have seen Ski and Cork running those times withthe 24's for a long time so I beleive they do it.Now ith that said I still feel that a little bigger injector with a lower DC is still a better way to go as long as it can be tuned properly. I could have stayed with the 24's no problem and even considered it but felt the 36's would be a more moderate solution for my application. I run 13.1 AFR across the board thanks to some decent tuning from both MADZ28 and CAM. My Mail order tune was lean across the board with the 36's but once CAM got it on the wide band and we added a bit of fuel and timing all waws well. I am shure Ion could have tuned it just as well but he is a long ways away so I just use him for all of my mail order stuff (Break in tune). Again I don't think either side of this is wrong but I do think Ski has a habbit of pissing people off with his "You dont run 10's so shut up" attitude. Your aproach is refreshing and thanks for the input.

 

What were your duty cycles.
Tuning a Speed density/MAF is a science. Just like jets etc on carbs. But once you get a few under your belt, it starts to really become easy.

 

I never had the 24's with the 383 but the 36's are around 80% if I remember right. I can look at the datalogs later on tonight and post. Again I am a conservative person and if I can achieve the same results with and be a bit safer then I will. I still feel that smaller injectors can go a lot further then most would suspect. The problem for me is BSFC. I think knowing what the BSFC is on a modified motor is a crap shoot, we know a motor becomes more efficient as we get better heads, better Squish, and bigger cams but how much ????????? I am making over 400RWHP and 400 RWTQ and still getting 17 MPG in town and 24 HWY so I am shure it is more efficient but how much so that is the real key.

 

Get out your formulas and figure it up. The evidence is in the formulas they use every day to determine these things. It is possible to fire an injector 2 times per cyl firing revolution=1cyl firing cycle.
A FMU is a different story,never seen one used on N/A set up and as I said BIG pump=2 small or 1 large.Boosters supply pressure but do they supply the necessary volume??

Soooooo I think I will stay with the formulas instead of OPINION's as to what will work and what won't.
BTW static is full open and never closing. and ya run into the problem of not closing when it's time and with the high FP ya have opening and closing issues.

Do the math and there is your empirical evidence. The people that do F-1 use these and they don't seem to have a big problem (formula's)

If ya can make 116# idle ya can make 30# idle,that's the reason for that statement.
Read the posts.

"O" figure out the BSFC without puting the engine on a dyno-- Sounds like another OPINION or guess to me,instead of using the accepted norm for a N/A engine=.5

EDIT: Do you know how Hilborns work? If ya do ya should be able to figure out how they double fire the injectors.

 

I'd prefer to run 42s at a stock FP compared to 24s and a jacked up FP(think moderate blown setup). There is more possibility for problems at a higher fuel pressure and fuels starvation. I guess it depends on how borderline the DC is. If running at 95% DC, I would go ahead and jack the FP up a little bit.

It is hard to argue with the safty afforded by a lower DC but if an injector is rated at 24#s don't you think it can deliver? I doubt FMS,Bosch, lucas, etc are rating an injector when in fact it cannot sustain it.

I'm not arguing the wisdom in doing a 24# setup for a car running 10s but if it works and has some safety margin, what is to argue about ? He is running 44# or so of pressure IIRC and <100%DC. My choice would be going to at least 30s in just for a little more margin. The Gen7 should be able to tune 30# with a low idle with no problem at all, I don't know why they cannot resolve that. It is trivial with LT1edit.

 

LOFLMAO Who said ANYTHING about emissions. I am talking engines and what they do.Those 116 were in an 8 second trailer queen.
The CAM made it necessary to idle at 1800 not the injectors.

 

I've seen the guy in that post with the white Vette run well into the 10's when it was a 406 with 24# injectors on a 165 computer and a restricted old TPI MAF. The car does have full interior. It is impressive to watch and really had me scratching my head. He's still running IRS also. I had the injector size discussion with him 2 years ago and was kinda left in questioning my thinking. Seeing was believing, No BS from him, it's the real deal.

 

The guy on the corvetreforum, Jesse (SKI) is using 30#'s in his 10 second car, and swears that all you need is 24#'s and he says he isnt running more than 45psi and is not saturating the injectors.

 

What you are missing is that is only possible if you are at 50% or less duty cycle. If an injector is already at a 100%DC, you have them open ALL THE TIME. Remember that is the issue.


Yes they provide some volume but remember, this is not an issure of the fuel lines and fuelpump, rather can 24# injectors power a car to 10s.

Remember that a std FPR is actually a FMU. Why do you think there is a vacuum reference from the intake going to it?



Do you really think that someone that has run a 5176 kit wouldn't know what 'going static' is? :rollseyes: This isn't an issue with FMS/SVOs like it is with the stockers. Why does it matter in this conversation, the fellow is running on 44psi. Static lockup is more in the 90+ range. You can still have a fuel inj at 100%DC (fully open all the time) and not be 'static'. If the PW is commanded lower and it complies, you aren't static



If you can find any techical info on F1 let me know. Most is guarded with security on par with FortKnox

Seriously, the formulas are fine. However, people sometimes misuse them. You are assuming certain things that skew the formulas result so that it fits your argument.

Answer the question, how many H/C LT1s make 400RWHP with 24#? You are basically saying it is not possible with your application of the formulas



I read all the posts. The issue is not 'making it idle'. The issue is making it idle and not burn your eyes with gas coming from the exhaust. Also note I said he should be able to make 30# work fine, I have no problem doing so on an Lt1.


Absolutely. A dyno is needed to be sure, plus BSFC varies with rpm. .5 is a rule of thumb, not a universal constant The norm range is .4-.5 for NA. Just because you don't know doen't mean it is not less than .5. This is why you have to take diffeq if you want to be an engineer. You need to be able to solve equations with multiple unknowns if for any other reason than to esablish extrema.

It has nothing to do with that but rather, as presented above, you can only double fire when the injector dc is less than 100%. If it is already open all the time, you can't do it. We are talking about a car that you question the ability to do what it does with 24#inj. If you are asserting the injectors are underrated for the task, how do you suppose there is enough headroom to double fire.

 

A couple of things to think about.....

-running a higher rail pressure not only increases the flow capability of the injector, it reduces the variation in injector flow due to small variations in pressure.

-keeping the injector duty cycle low offers the advantage of maximizing the portion of the fuel that is sprayed while there is actually air flow into the runner.

-I can't understand why the guys on that forum are reporting an inability to avoid running rich with larger injectors. Seems like it should be easy to resolve.

-I agree that 0.50 BSFC is VERY conservative, but might not be that far off for a sloppy, inefficient tune. My engine was tuned first on an engine dyno, and achieved an 0.430 BSFC running an n-alpha mode (looks only at TPS and RPM). As ill equipped as n-alpha is supposed to be for "street" driving, the car got 20mpg on the highway. I think when people start talking about sub- 0.400 BSFC's, they are talking about race engines tuned for a very narrow power band. With nitrous, my BSFC increased to almost 0.540 #/HR/HP.

-The article by Russ Collins of RC Injectors, that used to be on the net on a "supra" page has disappeared, but it had some excellent real world observations on what happened to injector flow and spray patterns as the duty cycle went over 80%. Russ acknowledged that drag racers tended to ignore the suggested limit of 80% DC, because the period over which that occured was a matter of a few seconds in a complete pass. The guy was the "god" of fuel injection in the motorcycle community. You can find support for the idea of limiting injector DC at sources like Kinsler and MoTeC. They aren't amateurs.

My preference is BIG. I run 64# Bosch injectors at 58psi (=78#/HR). The engine has a good BSFC, makes decent power, and idles smoothly at 800rpm. In all fairness, the injectors are being driven by a high-end ECU, with high quality peak and hold drivers. But the same injectors are able to support a 300-shot of dry nitrous, for a total of 800HP through the injectors, with a shade under 70% DC. Limiting the DC offers the advantage of having enough "closed" time that you are able to start moving the injector firing time (end of event) relative to TDC, and the ECU will also allow you to program that as a function of load and RPM.

Its hard to argue with someone who claims they run 10's all day long, with a 24# injector, particularly when you don't know the actual engine flywheel HP, the BSFC or the fuel pressure. It seems odd that they feel that fuel pressure is the way to tune.

But its also hard to argue with simple facts. If an injector is rated at 24#/HR at 2.7bar, and operated at 3bar (43.5psi), there is a limit to how much power you can make with it. If you assume they have a super tune and can run 0.400 BSFC, and the injectors can operate at 100% DC for a few seconds, it is possible to make 500flywheelHP, and that is enough power to run 10's, particularly in a light weight chassis (something closer to 3,000#). But the question is, are you limiting the engine's power with a poor spray pattern, or unstable flow at the point of peak fuel consumption? That's not something that would necessarily show up as a lean condition on a wide-band. Could you make a few more HP by running a 30# injector at a lower DC?

Different strokes for different folks.....

 

He isn't running a trailer queen. That is the issue that we are discussing right? His assertion of making 30# idle w/o unburned fuel coming out of the pipe. He could make it idle, just not cleanly.

FWIW,I don't know why he can't make it happen.

 

I think something that i interesting to note i that none of these cars have made it on the dyno. While rich cars make way less hp, lean cars typically make decently good hp but with durablity at stake.

I suspect if they ever got these cars on a dyno they would find the afrs in the 14+ range.


Also, something else important to note is him saying that hes able to do 10's with 24's and 40psi rail pressure. I've witnessed countless times cars max out 24's at around 360rwhp with stock fuel pressure.. by max out I don't mean they won't make more power but they will not continue to hold safe afr's at higher rpm.

It takes quite a bit more than 360rwhp to run 10's.

 

Ya can double fire them and ya don't have to be at 1000% ya can set duty cycle at 80% and fire them twice(insert fuel in the port) during all the time the intake valve is closed and during the intake stroke. Which is 3/4 the cycle of one piston.( all movement except the exhaust stroke) The same way Hilborn MFI works and ya don't understand that obviously.
Don't tell me about puddled fuel,the sprint cars don't seem to have a problem.

Soooooo ya do it your way and I'll do it mine, without OPINION's and use the formulas that are known to work.
At our race shop SIZE MATTER'S including injectors.

 

Heres a good thought,

Why not use properly sized injectors? Hell 30's cover just about everything NA and they are less than $200 bucks!! They said they where having problems getting a 30 to idle which is crazy because i've got injectors 3 times that big idling in some blower cars.

 

Although he may not have any dyno time, he does have an onboard wide band that the DFI Gen 7 uses to control WOT fueling and it is reporting 12.8. It sure doesn't look like it's running lean.