View Full Version : Injectors-When to upgrade?


NLang
09-03-2004, 10:53 PM
First off, this is an N/A motor sort of deal-no NOS, or boost involved. At what point would I have to upgrade my 28.8lb/hr fuel injectors? I've heard of hp ratings, but because hp can be built by simply reducing internal friction and rotating mass, how is hp a justifiable way to rate injectors? Isn't it more about displacement and an engine's max rpm? Thanks in advance for the input...

NLang
09-05-2004, 10:28 PM
You're breakin my balls guys, breakin my balls.... I thought this would be a pretty hot topic as I can't seem to find factual answers. Is there really a such a thing for such a topic? Is duty cycle a concern here?

ss rally red
09-06-2004, 08:16 PM
Wish I could answer you question, I am 408/390 N/A. I had a friend on here log some runs on hp tuners and was at 94% duty cycle at 6500 rpm. I recently finished a 5177 install and although I have a ractronics intake pump on the way I haven't decided which injectors to buy, but I did go ahead and spray once from mid second to 6K and into 3rd to 6K and it pulled hard!. I wont try it again until on a dyno w wideband with pump installed. I am interested to see if the stock injector duty cycle will be at 120 plus. I also would like to hear opinion on injector sizes.

NLang
09-08-2004, 12:53 PM
Going once...

Ryan02SS
09-08-2004, 01:07 PM
Also wondering the same thing? I'm planning on adding a lil 100 Kick in the Ass to my setup and am pretty sure the stock 02 28lbers are not up to the task.

NLang
09-09-2004, 01:15 AM
Going twice...

Nytmare
09-09-2004, 03:00 PM
I have some for sale

NLang
09-09-2004, 05:43 PM
I have some for sale
Ha, thanks, I think... :| I bought a set of 30lb/hr Accel's just in case. I just need a few answers before I go and spoil any chance of a refund by installing something I don't need. Thanks though...

SpeedyPAL
09-09-2004, 08:13 PM
There are a couple of constants that we need to be aware of before we determine what size injectors we need.

These are really simple but I'll touch on them anyway.

First:
The Duty Cycle that is mentioned in these calculations starts from the position of the crank where the injector first begins to fire until it needs to start to fire again. That is, two rotations of the crank or 720 degrees. So if the injector is continuously open it is operating at 100% duty cycle - that's not a good thing. It is common practice to size injectors for a maximum of 80% duty cycle.

Second:
All or I should say most injectors are rated by the manufacture at a fuel pressure of 43.5 PSI. So if your LS-1 FPR is running at 58 PSI then your injectors are capable of much more fuel.

You can calculate the change by applying the following formulas.

divide your fuel pressure by the rated pressure
in our example 58 divided by 43.5 = 1.333

find the square root of that number
in our case the sq root of 1.333 = 1.154

You next need to multiply the flow rate in pounds of fuel per hour at the manufactures rating at 43.5 PSI times the 1.154 derived above.
if we are looking at 28.8 lb/hr injectors then 28.8 X 1.154 = 33.235 lb/hr

Got that,

Next we need a very brief discussion of BSFC
Brake Specific Fuel Consumption is a measure of how efficiently your engine converts fuel to Horse Power. Most engines do this most effectively at wide open throttle when the intake and exhaust are doing their job in the most effective manner possible - in other words filling the cylinder completely - at6 all other times the BSFC is worse because the combustion chamber pressure is lower. i.e., compression is directly proportional to efficiency - or something like that. So what we do is to assume that the BSFC of a street engine is .50 pounds of fuel per horse power per hour. Really good race engines and airplane piston engines get this number down to .47 or lower, but for us we should use .50

With an understanding of the above we can then do the math.

The question is - how big an injector do you need to make 500HP at the flywheel.
We will assume that you have the necessary parts, heads, cam, intake and exhaust goodies and most important of all displacement to make the 500 HP. Fuel injectors can make HP by targeting the back of the intake with a heavy stream in place of an atomized spray but drivability will suffer and that's a whole different story.

Simply,
multiply the desired HP X the assumed BSFC
our example 500 X .50 = 250 pounds of fuel per hour

then multiply the number of injectors X the assumed duty cycle.
our example 8 injectors X .80 duty cycle = 6.40

then divide the pounds of fuel per hour by the injectors X duty cycle
our example 250 / 6.4 = 39.063

Keep in mind that you will need a set of 40 lb/hr injectors only if you are running your fuel rail at 43.5 PSI. if your running it at 58PSI then you can use 34.5 pound per hour injectors or be reasonable, use the next larger size like 36lb/hr injectors.

Good luck

If you have any questions take a look at WWW.rceng.com/technical
Russ does injectors better that any one I know.

SpeedyPAL

NLang
09-10-2004, 01:43 AM
I certainly appreciate the time put into the above explanation. I had the formula in a few books, I just don't understand the rating system's 'grounds'.

The question above "why are injectors are rated for hp and not displacement"---denyed again...Based on the info. above, and using 15% as loss in HP from the flywheel to the wheels, this is what I come up with. The number followed by a '%' is the duty cycle of the injectors. I listed both the 24's and 28.8's that supposedly came stock on our F-bodies, as well as the 30's and 36's that are ready available A/M's.

FLYHP/RWHP @58psi-26.4OEM / 28.8OEM / 30SVO=34.62 / 36=41.54

360 / 306____/_____85%____/____---_____/____---____/____---

380 / 323____/_____90%____/____83%____/____---____/____---

413 / 351____/_____98%____/____90%____/____---_____/___---

435 / 370____/____103%____/____94%____/____79%____/___---

453 / 385____/____107%____/____98%____/____82%____/___---

470 / 400____/____111%____/___102%____/____85%____/___71%

500 / 425____/____118%____/___109%____/____90%____/___75%

535 / 455____/____127%____/___116%____/____97%____/___81%

565 / 480____/____ ----____/___----_____/____102%____/___85%

588 / 500____/____ ----____/___----_____/____106%____/___89%

Now, all you guys out here throwing down 400-440+RWHP with factory 26.4lb/hr injectors, what do you think about this little theory? Look at the chart...How is it possible for an injector to overstep 100% duty cycle? Doesn't 100% mean maximum? Why would the calculation involve power at all? Shouldn't it be about displacement and max rpm? To me it just seems a tad, well, stupid. Anyway, I guess you guys have a little graph to refer to without needing calculations...

CountryMuzicZ28
09-10-2004, 12:28 PM
There are a couple of constants that we need to be aware of before we determine what size injectors we need.

These are really simple but I'll touch on them anyway.

First:
The Duty Cycle that is mentioned in these calculations starts from the position of the crank where the injector first begins to fire until it needs to start to fire again. That is, two rotations of the crank or 720 degrees. So if the injector is continuously open it is operating at 100% duty cycle - that's not a good thing. It is common practice to size injectors for a maximum of 80% duty cycle.

Second:
All or I should say most injectors are rated by the manufacture at a fuel pressure of 43.5 PSI. So if your LS-1 FPR is running at 58 PSI then your injectors are capable of much more fuel.

You can calculate the change by applying the following formulas.

divide your fuel pressure by the rated pressure
in our example 58 divided by 43.5 = 1.333

find the square root of that number
in our case the sq root of 1.333 = 1.154

You next need to multiply the flow rate in pounds of fuel per hour at the manufactures rating at 43.5 PSI times the 1.154 derived above.
if we are looking at 28.8 lb/hr injectors then 28.8 X 1.154 = 33.235 lb/hr

Got that,

Next we need a very brief discussion of BSFC
Brake Specific Fuel Consumption is a measure of how efficiently your engine converts fuel to Horse Power. Most engines do this most effectively at wide open throttle when the intake and exhaust are doing their job in the most effective manner possible - in other words filling the cylinder completely - at6 all other times the BSFC is worse because the combustion chamber pressure is lower. i.e., compression is directly proportional to efficiency - or something like that. So what we do is to assume that the BSFC of a street engine is .50 pounds of fuel per horse power per hour. Really good race engines and airplane piston engines get this number down to .47 or lower, but for us we should use .50

With an understanding of the above we can then do the math.

The question is - how big an injector do you need to make 500HP at the flywheel.
We will assume that you have the necessary parts, heads, cam, intake and exhaust goodies and most important of all displacement to make the 500 HP. Fuel injectors can make HP by targeting the back of the intake with a heavy stream in place of an atomized spray but drivability will suffer and that's a whole different story.

Simply,
multiply the desired HP X the assumed BSFC
our example 500 X .50 = 250 pounds of fuel per hour

then multiply the number of injectors X the assumed duty cycle.
our example 8 injectors X .80 duty cycle = 6.40

then divide the pounds of fuel per hour by the injectors X duty cycle
our example 250 / 6.4 = 39.063

Keep in mind that you will need a set of 40 lb/hr injectors only if you are running your fuel rail at 43.5 PSI. if your running it at 58PSI then you can use 34.5 pound per hour injectors or be reasonable, use the next larger size like 36lb/hr injectors.

Good luck

If you have any questions take a look at WWW.rceng.com/technical
Russ does injectors better that any one I know.

SpeedyPALThanks for the formulas!

John_D.
09-12-2004, 10:27 AM
How is it possible for an injector to overstep 100% duty cycle? Doesn't 100% mean maximum?

Why would the calculation involve power at all? Shouldn't it be about displacement and max rpm?


A calculation may come up with a number greater than 100%, but you're right, the pcm can't physically hold an injector open longer than 100% of the cycle...

If it was only about displacement and rpm, then all our engines would be putting out identical horsepower, regardless of mods. (assuming they were all tuned correctly). But we do have different hp levels (and different fuel requirements). The higher hp engines are configured to take (and effectively utilize) more fuel than the lower hp engines. Whether it's a cam, a better flowing head, better flowing exhaust, etc.

The hp number has a very strong correlation to the amount of fuel used (needed) in that particular engine combo. (ignoring the subtle changes in ignition timing, oil viscosity, stuff like that.)


p.s. the 28.8's are rated at 58 psi already, and i think in your table you considered them as rated at 43.5 and scaled them up to 58 psi.

Malibu Vette
09-12-2004, 10:53 AM
Soo,
Are the SVO 30 pound injectors 34.5 pound on our cars?

dlandsvZ28
09-12-2004, 12:20 PM
Most injectors are rated at 3 Bar flow rate.

If SVO 30.0's are rated at 3Bar (43.51 psi) then at 4Bar (58.02 psi) they convert to 34.6 lbs.-hr (according to "Chevy LS1/LS6 Performance/Cristopher Endres".

However, I have seen where it is stated that SVO 30.0 are same as 36.0/4Bar ????????????

John_D.
09-12-2004, 12:23 PM
I haven't done the math going in that direction, but it sounds about right.

I have done the math going the other way, and our 28.8's are like a "normally" rated 24. So an svo 30 flows about 6 more lbs than a 28.8 ls1 injector... Because of the different fuel pressure used in the ratings it's a bigger difference that it would seem on the surface. 20-25% more fuel capacity.

NLang
09-12-2004, 04:00 PM
There are some private sellers claiming that the 30lb/hr SVO's flow 36lbs. @ 58psi, but that is incorrect. They flow 34.6 @ 58psi. I guess I was given false information (as atleast 25% of the time here) that the supposed 28.8's that some came from the factory with were rated at 3 bar which would've made them 33.24 @ 58psi. But, not correct either...I don't understand how it's possible for all these people here to be running around 450RWHP with factory injectors. They'd be are running over 120% duty cycle...Can no one make sense of the possibility of this?...

Unforgiven1
09-13-2004, 10:57 PM
Damn even though this is going somewhat over my head, this is an awesome fuggin thread. Sticky this crap if it gets any better! I wish I could contribute...but I'm not smart enough. LoL. So I'll just comment.

jdustu
09-13-2004, 11:07 PM
Damn even though this is going somewhat over my head, this is an awesome fuggin thread. Sticky this crap if it gets any better! I wish I could contribute...but I'm not smart enough. LoL. So I'll just comment.:stupid:......i'm guessing if you come up with a percentage higher than 100, it just means the injectors are too small(meaning they would need to do more than they are capable of[100%] to work correctly)......did i just contribute? if not, jut let me think that i did....

ataylors
09-14-2004, 12:23 AM
There are some private sellers claiming that the 30lb/hr SVO's flow 36lbs. @ 58psi, but that is incorrect. They flow 34.6 @ 58psi. I guess I was given false information (as atleast 25% of the time here) that the supposed 28.8's that some came from the factory with were rated at 3 bar which would've made them 33.24 @ 58psi. But, not correct either...I don't understand how it's possible for all these people here to be running around 450RWHP with factory injectors. They'd be are running over 120% duty cycle...Can no one make sense of the possibility of this?...


Remember that fuel pressure plays a part in this also.

dlandsvZ28
09-14-2004, 01:14 AM
According to "Chevy LS1/LS6 Performance/Cristopher Endres" maximum horsepower at 4 bar (100/80 % duty cycle) for LS1/LS6 injectors are:

1997-1998 LS1 4 bar rwhp 572/458
1999-2000 LS1/LS6 4 bar rwhp 536/429
2001-2003 LS1/LS6 4 bar rwhp 572/458

I think part of the answer to your question is that those with motors making 500 rwhp are running wet kits which assists fuel delivery which keeps the motor from running lean. So even though the injector is running at almost 100 % duty cycle part of the time during a 10-12 second run, the extra fuel from the wet kit is assisting fuel delivery to keep from going lean since the stock injector can't supply enough fuel (maybe).

In addition we have to assume the fuel pump has been upgraded to supply the extra fuel requirements from the nearly 100 % duty cycle of the injector and fuel solenoid from the wet kit during a WOT 10-12 second run.

But....the PCM doesn't recognize the wet kit assist, so based on manifold absolute pressure (and other parameters) of an engine actually approaching 450-500 hp, the pcm finds the correct cell and calculates base pulse width and tries to compensate to supply fuel by maximizing the duty cycle to nearly 100 if not 100% but only during brief periods of time (since the run only lasts 10-12 seconds)

I doubt the stock injectors will last very long in a 500 rwhp motor if the motor is held at WOT for an extended period of time. The injectors would probably overheat quickly and fail.

So I think the question is how seconds/fractions of a second are the injectors at 100 % duty cycle during a WOT 10-11 second run for those motors with stock injectors with 450-500 rwhp?

If the answer is only 1 or 2 seconds during a WOT run, then this probably explains why we can push the envelope just a little bit but not very often, or suffer dire consequences (go lean and blow up).

NLang
09-14-2004, 01:49 AM
I'm talking 450+RWHP w/ factory 26.4 and 28.8 fuel injectors on 100% N/A cars-no NOS and additional fuel. No offense, and considering where I stand w/ fuel experience (some-not my master in school...), I think it's safe to say that Mr. Endres has miscalculated to say the least. There's no way that's correct, sorry...
Accel, which I'm sure we all have heard of, said their 32's would work, but recommended their 36lb/hr injectors, which are rated @ 3 bar (43.51psi), for anyone reaching the 480-500RW mark. Those put out 41.54lb/hr @ 4bar (58.02psi). That's a lot of fuel. I know a lot of people running those injectors. They have a good rep. I thought they were all over doing it with the 36's. It turns out that is what I'll need myself within the next couple weeks...
Another thing...there are a lot of dealers offering different styles of injectors. All of them have different hp ratings per the style of injector or manufacturer. So, I guess that sort of kicks that that formula up there ^ out the window...It's recommended that everyone call the manufacturer of their choice now before choosing a size for their app. I was told this by four different companies.
I think many people's questions have been answered throughout this thread. It's too bad there really isn't a true answer OR equasion. The equasion could've gotten you in the ballpark some yrs back, but there are now just too many diff. styles to choose from-all having diff. HP ratings. Good luck everyone!

Racetronix
09-14-2004, 02:58 AM
Why worry about the bare minimum requirements?
Just get a set of Delphi 42's and tune them for the build of your motor.
Delphi 42's are more than enough for most LS1 motors and are just as manageable as the factory injector. They are quite affordable too!

Turbo Buick owners don't play the injector game every time they bolt another HP item on their motors. Many just buy 50's even for a fairly stock motor and just recalibrate the ECM as they build more power!

And yes... some of the injector info out there is a bit out of wack!

gametech
09-17-2004, 09:23 PM
I fully agree. Anyone into speed knows that they have never made their last mod. Why not just buy good size injectors to start with? You will find a few guys in the truck section using 43# asm injectors. The factory computer seems to have no problem controlling these, and it is nice to have the overhead for those smaller blower pulleys and bigger intercoolers that fedex always seems to be delivering.

ataylors
09-17-2004, 09:26 PM
You have to think of an injector like a scale, you dont want to get a 5000 lb scale to weight something that is 2 oz..

gametech
09-17-2004, 09:45 PM
It is true that you can get injectors that are too big, but the factory computer seems to have no problem controlling some fairly large injectors. As long as idle quality and light load performance doesn't suffer, why not just get plenty of injector to start with?

Racetronix
09-17-2004, 09:53 PM
You have to think of an injector like a scale, you dont want to get a 5000 lb scale to weight something that is 2 oz..
That is a very poor analogy.
Besides, that is all relative to the resolution of the scale and how much FAT you might put on down the road.:jest:

In the case of an injector as long as the PW can be made stable and narrow enough to maintain the desired A/F at idle then there are usually few if any issues. The real problem is with tuners who have difficulty understanding and tuning larger injectors for good drivability and AE fueling. LS1 computers are very capable allowing them to support a wide range of injectors while still maintaining factory type mileage and drivability with increased HP.

As stated before an ECM from a Turbo Buick used in 1986 can be tuned to support injectors upwards of 86lb/hr on a small 231CI V6. Why do many V8 tuners fear large injectors so much and pray on a customer's fears with old school rhetoric??? :confused: A good tuner can work magic. A poor tuner will wield excuses.

NLang
09-18-2004, 01:47 AM
Well, first off, Those HUGE Delphi's you're speaking of are $80+ EACH. That's beyond ridiculous for someone who could NEVER use them. My worries were lack of fuel atomization at lower rpm with injectors that are too large, overcycling causing detonation with small injectors, and paying loads more for big injectors w/o needing them (I'm WAY over budget). I went with a set of 1k mile flow matched/balanced CPR Racing 'disk' type injectors. They'll spit out plenty for the 500RW combo(630hp max), and didn't cost me much (for their size and life-time guarantee anyway).
I've certainly appreciated all the input. Please keep it up as I'm not the only gear-head out there lacking in the fuel department. How about instead of 'sure, you can use them', conjure up some details explaining how, why, and any dissadvantages to going overboard or underboard. That's what this place is for, right?
Again, thanks guys.

dynocar
09-19-2004, 10:01 PM
Don't be too big or too small. We all know that there are good formulas to help guide us for proper injector sizing for various applications. A fuel injector has to have enough time to fully open and close its valve (pintle, ball or disc) for accurate cyl to cyl fuel distribution. If the injector flow is too large, at idle and cruise, its valve's pulse width (time that valve is open) may not have enough time to fully open before it has to close again to limit fuel flow. With these valves uncontrollably floating with each injectors individual valve movement characteristics, each cylinder will receive a different amount of fuel, some too lean causing misfires and stumbling. For many styles of injectors we do not want to see less then approx. a 1.5 ms pulse width. At the other end of the scale, if an injector is too small, during high HP and RPM applications, the valve will stay open too long and not have enough time to fully close. This condition can cause cyl to cyl fuel distribution problems possibly damaging an engine because one or more cylinders are running too lean because again, each injector will flow dramatically differently. To prevent this we try to stay under 80%, some say 90% duty cycle. Injectors are not designed to run fully open all the time due to the possiblity of failure due to overheating and the lack of any flow control capabilities. Different injector types have better dynamic ranges then others, the disc usually the best and the ball type usually the worst because of their differing valve weights. Also, different engines require more or less fuel per HP, a term called BSFC (brake specific fuel consumption). Well designed engines have lower BSFCs then mismatched ones, thus require less injector per HP. Boost applications usually have higher BSFC, so more injector per HP. Varying charging voltages will also affect this issue. Recently we dialed in a trailored drag car without an alternator. He later decided to add one (EFI, 2 fans, electric water pump, huge electric fuel pump, lots of guages and lights) and car went much slower. No, it was not the extra HP to run alternator. His car went real rich because he went from approx 10 Volts to 13.5 Volts to the injectors causing them to fully open quicker. We recalibrated A/F and he went faster then before.

EJ