65ZO1,

Remember as you raise the pressure your actually reducing the duty cycle as well.

That 85% duty cycle has NEVER been substantiated as being a threshold that once crossed causes any sort of damage.

But it seems that your getting the jist of what I have been talking about :cheers: :D :thumbs:

 

Hey Ski can you provide some clarity for me on this?

Paraphrased from Holley:
Their 24lb injectors supports a maximum of 385* horsepower.
* A BSFC of 0.45 and 90% duty cycle is used for the maximum horsepower recommendation

How does this relate to what you are saying? Im feeling pretty stoopid right now.

If Im reading this thread correctly, either they are severly under-rating their injectors, or their 24lb injectors are essentially smaller injectors being pushed a little harder?


[Modified by VetteNoob, 3:59 PM 9/5/2003]

 

hey vettenoob let me tell when i went to holly for a tour last year i told them about my car and the injectors and the pressure i was running and they two were dumb founded and they were there number 1 and 2 engineers there so who really knows :cheers:

 

VetteNoob, acutally it looks like they are using the equation to rate their injectors: BSHP=24 * 8 * .90 / .45 = 384 hp.

If they rate their injectors at 44spi and you raise the fuel pressure to say 55psi they would support up to 429 hp (fuel flow increase goes as the SQRT of the fuel pressure increase).

Now, from what we've seen here, if you design you engine so as to reduce the BSFC those injectors will support even more hp.

 

That is exactly right 6ZO1. The next problem is what the hell BSFC are you? I believe the motors of today can not be compared to the BSFC of yester-years.

 

Well I'm not so sure how much BSFCs have changed over the past 20yrs though I'm sure today's engines are more hi-tech and advanced.

As mentioned, testing has shown me that my current BSFC is very close to 0.50. So I feel that when I do heads & cam I will need to do further tuning to determine where efficiency is and what injectors are required for best results.

So, I guess the way out of the woods is tuning and testing along with a well thought out plan for major engine mods. As always, the dyno and the time sheets will tell the story.

 

Is just me or is the whole BSFC rating a bit arbitrary? What test? Is there any test to actually test BSFC? The only way I can see to determine your true BSFC is by using a backward formula for instance if a 500+hp motor can run on 22 lb injectors then the BSFC is .35 or close to it. What I don’t get or fully believe is that if a 300 hp motor runs on the same injectors that it's BSFC would have to be .59. Wouldn't you have to perform an exhaust analysis to determine the efficacy at which the fuel was being burned? And what effect does load have on the BSFC rating? The only thing I believe rite now are the HP numbers that Jesse and corky are putting down. I just cant buy the argument of I have 30 pound injectors in a 330 RWHP car so there for you must need 30pound injectors unless they ran the smaller injectors and tuned the fuel pressure and still couldn’t get the same HP numbers. If that’s the case then if I increase to bigger injectors then it decreases the BSFC of my motor because if I make the same HP numbers with larger injectors then the only variable in the formula is the BSFC number. My motor is not going to produce nearly 500 HP so I feel if I go with the 25# injectors I should have another 100 or so HP before I will need to increase to a bigger injector.


[Modified by ejfagala, 9:05 PM 9/5/2003]

 

I am certainly no expert on this. But I'll throw in an objective other opinion. Just because somebody gets their engine to run well with a certain size injector does not mean it's necessarily the best sized injector for that engine. For instance, there may be some guy out there who always uses 1 5/8" headers on every engine he builds. He always tunes everything else on the engine, but always uses the same size headers. He argues "I get great power out of my 1 5/8" header". Well, that doesn't mean those headers are ideal for that engine.

Again, I'm no expert on this. I would wonder, as a benchmark, what injector size and fuel rail pressure is used on the new Z06? It makes 405hp and I'm sure GM did a lot of engineering analysis to determine the ideal injector size and fuel rail pressure. I don't know the answer to that question. So, it'd be interesting to finish filling in this table:

ENGINE hp injector size fuel Pressure
L-98 245 19lb/hr ~39psi
Z06 405 ? ?

Do any of you guys know?
:seeya

 

Yes it's true that I've done the reverse calculation to verify that the BSFC for my engine is now very close to .50.

What I've gathered from this discussion is that before I change injectors after an air flow increasing mod I will do enough tuning to see if the current injectors will get the job done and, if not, I can roughly calculate what size injectors I will need.

Regardless of which injectors you go with, please come back with results.

Good luck with your mods.

 

still not quite satisfied by this just run more pressure theory, because as we all should know high engine oil pressure is great up to a point but at a point it just becomes pressure and no volume in other words no matter how much pressure you put behind the fuel only so much can flow through the injector orifice just so fast and all else will be bypased ....its like taking a 1" garden hose and running lets say hypathetically 60# of pressure through it you may get lets say 10 gallons per minute now lets restrict the hose down to 1/4" with the same pressure i am shure the actual flow volume would go down but the extra restriction would cause the 60 pound pressure to measure artifically higher so just where is the limit? under any pressure only so much fuel can go through a syrenge needle size hole so fast till you have to change the hole size to flow more because lets remember the injector pulse width is precise and you only will have so much time to get all the fuel through it that you need till you start overlapping with the next pulse .....right ??? i thought i had it sorta figured out now i think i am loosing it :crazy:

 

but i do not think 60 is even close to maxing it out those big turbo buicks and the outlaw mustangs are pushing 70-110 psi through theres my buddies gn pushes 75 through his :cheers:

 

once again my question remains unanswered corkvette1 and that is why all the pissing around with the pressure even running a risk of running too lean and or abusing the injectors not to mention the wear and tear on the pump why not just go up to some injectors ment for the intended application? and as far as the outlaw mustangs and such i dont see how they even fit into this topic as we know they tear that stuff down after just a few races and do not have to be as long lasting as price is no object plus it probably takes that much pressure to push the kind of fuel volume there huge injectors flow. but as far as this bump the pressure up to increase the flow it only should be used to a extent than one should just go up to bigger injectors leaving as many things running at there intended specs eliminating more variables than needed and overcomplicating matters..... bumping pressure in a small injector is like trying to force a tennis ball into a golf hole by using more pressure, ya it might work but why not save all the hastle and just get a bigger hole.....
---------------------------------------------------

 

LADYSTOY69 do you think mine and jesses injectors are too small at 24lbs

 

LADYSTOY69 do you think mine and jesses injectors are too small at 24lbs
first to answer some of the above questions :
BSFC or brake specific fuel consumtion can be measured as some dynos are equiped with fuel flow instermentation but if not yes it is true it is just estimated on modern, efficent n/a engines such as tpi at .50 or slightly less at the torque peak which seems generally pretty close but as mods are made it does change some and should be estimated from there.

secondly i went to iowa injection services and they have a injection dyno test bench and i asked them about this delema (keep in mind they do not sell injectors) and they showed me how you can see different behavior of injectors at different pressures, duty cycles, and pulse widths. they showed me that even at as little as a 85% duty cycle many injectors will freeze in between opening and closing they just sort of flutter and they said that can reduce flow by as much as 50% which will lead to a lean condition at wot higher rpm's not to mention that the higher fuel pressure slows the injectors reaction time which should be 1.5 to 2.0 milliseconds just remember this is a very small solinoid opening the injector the more pressure fighting it the less efficient the injector will work..

and now for your answer cokvette do i think you and ski-downs injectors are too small?? well thats not the true question i belive the true question is are they the most benificial and efficient to do the given job rather than can they be forced to handle the task. right?

well there are a few variables in each of your cars that would be nice to know that are missing in your descriptions like fuel pressure (base) but i will give my opinion anyhow.......

as i calculate it
ski down is putting out a claimed 437rwh so his ideal injector would be 34# at stock fuel pressure settings.
using this formula: (bhp x bsfc)
--------------------------------- = injector size
no. of cylinders x 0.8

becase a 24# injector at stock pressure and a 80% duty cycle should only handle 307.2hp.
using this formula: (flow rate x no. of injectors x 0.8)
----------------------------------------------- = hp
bsfc

if you dont like using the bsfc you can use this formula for a injector size estimate
cfm X 0.44298
-----------------------= injector size
no. of cylinders
as i figure it to even limp these 24# injectors along it should take about 61psi of fuel pressure to flow like a 34# injector so obviously a bigger injector would make the job of flowing enough fuel at a ideal fuel pressure with the least wear and tear and injector flutter not to mention the risk of going lean much easyer..right? not saying it is impossible to flow a 24# inj. that high as i am not shure how much a 24# could flow left wide open i would have to know the orifice size in the injector and i dont...

and now for yours corkvette
corkvette is putting out a claimed 373rwhp so his ideal injector would be 29# at stock fuel pressure settings.
using this formula: (bhp x bsfc)
--------------------------------- = injector size
no. of cylinders x 0.8

becase a 24# injector at stock pressure and a 80% duty cycle should only handle 307.2hp.
using this formula: (flow rate x no. of injectors x 0.8)
----------------------------------------------- = hp
bsfc

if you dont like using the bsfc you can use this formula for a injector size estimate
cfm X 0.44298
-----------------------= injector size
no. of cylinders
as i figure it to even limp these 24# injectors along it should take about 52psi of fuel pressure to flow like a 29# injector so obviously a bigger injector would make the job of flowing enough fuel at a ideal fuel pressure with the least wear and tear and injector flutter not to mention the risk of going lean much easyer..right? not saying it is impossible to flow a 24# inj. that high as i am not shure how much a 24# could flow left wide open i would have to know the orifice size in the injector and i dont...

here is another formula for you :
injector flow rate will change as supply pressure is varied. the equation to convert static flow of a injector to that of a higher pressure is:
Q2= P2/P1XQ1
where :Q2=new fuel flow rate
Q1=original flow rate
P2=new pressure
P1=original intended pressure
keep in mind different injectors have different fuel pressures they are rated to flow at stock pressure for instance is 34psi but i have seen some injectors flow rated at 43psi.....just a note....
also a good rule of thumb is if you have to raise your fuel pressure more than 10%-15% you would probable be better off with larger injectors but dont get me wrong i do agree a little smaller than needed is better than a little bigger as it leads to tunning problems both ways notice i said little smaller not alot smaller..
like i could argue that a 24# injector will flow at 41# with 75psi of fuel behind it as on papper it will but it is limited by alot of factors like the oriface size
lets take for example the oriface size i dont know the size right off but looks pretty small right well lets just imagine leaving it wide open thus giving max flow at 100% duty cycle hmmm ok if thats all the fuel my motor can use maximum than lets take that oriface size and multiply it by 8 now that probably gets us up to about a 1/4" so i guess all we will need to supply this motor will be 1/4" fuel line right LOL i think not as pressure go's up and up and up you will eventially get to this point that no matter how much more pressure you put behind it the oriface simply just cant flow anymore fuel it has reached a limit not to mention that nice funnle shaped attamizing injector flow changes from a ideal pattern to just a mess that is why i say ideal operation not will it work as some of you guys are saying .........it may work and it may be possible but that dosnt make it ideal or efficiant it just means it works....

so simply put corkvette by telling me that you and ski-down have raised your fuel pressures alot (over 15% max) to make these injectors work with your engines tells me you also know they are too small because you are having to raise your fuel pressure to make them do the work of a bigger injector.....
so you yorself already answered your own question it is not yes they are too small but rather bigger injectors would proform better yes....

 

to ladystoy69 on the contrary we do not know the bsfc numbers but can only guess but me and jesse run between 38-42 psi and jesse can not turn his down below 42 psi and he is still running pig rich at 11to1 air fuelmeter on a wide band and i am right in the ball park at 38-42 psi all day long and thats on 24 lb injectors running my times which are in the sig the car weighs 3300 with me in it you do the math and tell me 24s are to small still :cheers:

 

This is funny...No matter what injector you use, how are people thinking the duty cycle changes??Its still the same pulse width and timing from the ecm..Turn the pressure wherever, duty cycle stays the same and the computer dosent know it.And i do this all the time.The only time a bigger injector is a good idea is a serious bump in displacement (like a 500ci BB) or a forced induction..Thats it..I make gobs of power with fuel injection, and even in my 383 ive barely even had to turn the pressure up to feed the motor......
Another thing the injector people dont tell you is besides better atomization, a higher fuel pressure is actually better for the injector..Better spray patterns and also the fact that they stay cleaner is also a benefit...
Someone tell us a story about how there engine blew up due to leaning out problems.....So far in 9 years ive seen 5 or so...And they ALL had an injector failure...So bottom line is save the cash for a mod that works.
:yawn:

 

where have you been hiding fosterperformance yes you are on our bandwagon :cheers:

 

well i guess if its trial and error you want than maybe this tool would be usefull http://tazzo.com/tazzo/efi.HTM

 

Wow, miss some replies....

OK. ladystoy69. Corky is exactly right. Saturday I was running PIG PIG rich with a 11.6-11.9 AFR. I have a POS regulator and I could not turn the pressure down any lower than 42psi, WITH THE VAC LINE OFF. Corky had his down in the mid 30# range with the vac line off to get the correct AFR.

So noone here is cranking any exuburant amount of pressure on the injectors. I added 100+ pounds to the car since last racing it. New full 3" Duel exhaust running through mufflers, a roll bar, harnesses, over a 1/2 tank of gas....my race weight before the exhaust and bar was 3340 with my in the car. Now its easily 3450#. I was able even in the extreme rich state get two new bests. A 1.49 60' time, and a new best 1/8 mile MPH =>97.51MPH.

That is what Corky and I are trying to tell everyone. Corky smashed several of his best times Saturday including an 11.02@120MPH. My best was 11.2@121. If I could have leaned the car out with the pressure, I too would have probably been able to run in the low teens or 11.0x. The DA wasn't even that great.

The reason we brought up FP is that you can if needed increase the pressure. But hell Corky was running less than the Ford SVOs are rated at, so he was running even less than 24# and got several new bests. Our cars are run hard, nearly every other weekend. Corky probably have well over 200 runs on that motor, and I have in the neighborhood of probably 60 or more. Neither of our engines are showing any signs of problems, in fact every time we go they get quicker. My plugs all looked perfect. No signs of detonation nothing.

When a car goes way lean, like my first few runs of the season when the tank did not have enough has in it and the fuel moved away from the pickup, the car falls FLAT on its face, especially at WOT. Neither of our cars do that.

In regards to your formulas, I am very familiar with them all. And they are the root of all the problems with people over injecting their cars. 90% of the people out there do not have the ability or the knowhow to get the desired AFR with a BIG injector, hence they suffer performance as a result.

The problem with the Formulas is the assumptions that must be made at the beginning of the calcs. First is BSFC. When you backtrack through Corky and my setups, you realize that our BSFC is somewhere around .33 Now using the formulas and tabels outlining BSFC you would at a min used .45

Let do the math with my current pressure of 43psi

sqrt(43/38)x24=25.5# inj

(25.5 x 8 x.85)/.45 = 385hp This is making the wrong assumption for BSFC

(25.5 x 8 x.85)/.33 = 510hp This is using what my car is making right now. Everything indicated that this HP is correct. MPH/ETs/race weight etc. That may be a little low actually, since my DYNOs are uncorrected.

Working backwards through the equations to get the desired HP we curently are getting using the wrong assumption for BSFC, you would have bought 33.75# injectors. That is a About 25% overkill. Not to mention we are just starting to tickle these injectors at 43psi. So we have more than enough room to move, go to different intakes etc.

My whole point of posting this topic was the motor of nowdays with the components especially can't be gaged by BSFC figures of the past.

Hell Corky said with his trip to Carlisle he metered his fuel usage, not by the onboard display, but with the old fashion, add full tank, record milage, travel X distance, refill record gallons etc. He got 19 mph, including milage of around town Carlise. How many cars in the 70-80s got 19mpg on a 500 HP motor that ran 11.02 at the strip? Efficiency is what it boils down to. More with less is being done. :cheers:

 

Here is some more food for thought. Here is a log with the pressure at 43psi, vac line off. Keep in mind we shift this at 52-5400 RPM. The areas in read are over 85% DC. Also we are running PIG rich here, 02mv at 920 AFR at 11.7-9 most likely, so more PW needs to be pulled at WOT. This would reduce the PWs even further.



if you needed more RPM, all you would need to do is go back and raise the pressure. Done deal. :cheers: