I want to get some new injectors because mine have been sitting for over 3 years. I am looking at the ford 24# injectors but wonder if that is enough.
I have a fresh LT1 with stock bore, ported heads and intake, 2.0/ 1.55 valves, LT4 hotcam, super comp headers / no cats, and electric water pump. I am hoping to get around 400 HP at the crank. If I use the formula Injector size (lb/hr) = (horsepower x 0.5)/ (no. of cylinders x 0.8) as a rule of thumb I come up with 31.25 so I would think I need 32# injectors. I have read allot of post and think for my set up the 32# are to big and am thinking of the 24# fords. Any input would be great on either the HP expectations or the injector size BTW I am also looking at a 52mm TB. I want to send my ECM off for tuning in the next day or two and need to decide on the injector size and TB.



[Modified by ejfagala, 8:38 PM 9/2/2003]

 

Ejfagala,

Everytime this subject comes up, at least on other boards I wind up in a battle over this.

Both Corky and I are running strong with our larger motors with great success.

The 24# injectors will be more than enough to supply your setup with fuel.

Here is the best posting of HP to injector size I have yet to see. All the others as you said, point to injectors that are HUGE.



If you notice the small text you see TPIS seems to be getting fed up with over claims of injector size also.

Remember that in your equation, the biggest guess is probably the most important to get the correct injector size. And that is the .5 in your equation, which is the BSFC. Or in laymans terms is the efficiency of your engine to burn that fuel and make the HP you want. The lower that number the smaller injector you can use and get away with.

:cheers:

 

:iagree: :cheers:

 

Thanks, that is what I was thinking exactly but could find no documentation to back up my line of reasoning(good info). I am going to get the ford 24#ers then and I think if I need a little more I can play with the FP a bit. What do you think about going to the bigger TB?

 

its not going to hurt you now and its there when you want to do more to the engine later :cheers:

 

:cheers:
Thanks for all the info guys,
I guess its the 52mm TB and 24# ford injectors (Ford parts on a chevy, whats this world coming to :lolg: )


[Modified by ejfagala, 10:02 PM 9/2/2003]

 

Of course you can take fuel pressure up to about 55psi which would give 10% higher flow (HP) from a set of injectors.

There is a chart on my site that lists HP supported by injectors which you can use to estimate what you will need to support 400chp.

After just checking my chart I'd say you can use 30lb/hr injectors at 50psi or 32lb/hr injectors at 45psi. I would suggest 30lb/hr as the optimum choice but since you have 32s, give them a try. A set of 24lb/hr injectors would only support about 385chp at 55psi, based on a BSFC of 0.50.

 

65zo1 if that is true then why is mine and jesse cars using 24lb injectors at 38-42 psi and making over 520 chp :cheers:

 

65Z01,

Guys you missed the entire point of my first post. Please look at my dyno graph in my sig. This is with 24# injectors, at 43psi. That makes them out to be about 27# injectors at the 43psi up from their rated pressure of 38psi.

I made 437RWhp and 536rw ft-lbs assuming 20% loss through the drivetrain, that is over 500chp and well over 600ft-lbs, and also keep in mind that these were uncorrected values! So the corrected would even be higher yet.

The pressure on these injectors CAN be turned up to a very high pressure with no adverse effect, so long as your pump is up to the task.

There is absolutely no need for him to get 30+# injectors. All that is going to do is create a nightmare to tune to, and drown his motor in fuel.

Read the chart above. Small injectors can make HUGE hp numbers at reasonable RPMs.

90% of the injectors charts I see are WAY WAY overkill. They look at only RPM and nothing else. When you look at idle especially, there is only so much trimming you can do to hold them back. So what you effectively do is buy a 36# injector, and try to trim is back to 20 some pounds. Well this is very ineffective and makes no sense whatso ever.

This graph above is one of the few I tend to agree with. Kudos to TPIS on this one. And remember they build performance motors, so that should tell you something also. :cheers:

 

i have a dyno....everytime an L98 car comes in they have an adjustable regulator set way too high..dont put any more fuel into the engine than it can efficiently burn off! leave some room for the oxygen..please. steve
:)

 

65zo1 i was looking at a moroso power speed calculator and if you take your best et of 13:07 and my best et of 11:07 its coming up 180 hp difference
then if you take your best mph 104 and my best mph is 124 mph it comes up with 200 hp difference
thats about 80% more power than you are making with 24lb injectors at 38-42 psi can you explain this one :cheers:

 

Considering I will probably have Jesse tune my ECM I am going with the 24# injectors and 52mm TB. I hope my old 84 has 12's in her and wan't the best set up I can afford with these two items being the last for a while with the exeption of the ECM.

 

what happens if instead of going CI you go 8psi of boost at the manifold?

 

I can't believe that more people are not interested in this chart. :confused: Seems to me that eveyone is always pushing larger injectors based on this or that. This seems to be straight from a pretty reputable Tuned Port specialist.

Just seems to me this would be a bit of an eye opener, and right along the lines of what a few of us keep saying about injectors.

Lets here what you think.

For the guy with the turbo or the SC, typically the BSFC is lower for a Turbo/SC car. There are many thing you have to look at. Many guys need to run FMU on these types of setups. :cheers:

 

ski_down_it, that truely amazes me to see that kind of HP supported by effectively 27lb/hr (I agree here) injectors.

The equation I'm using is:
BSHP = (Injector Size) * (Numb. Cylinders) * (Duty Cycle) / BSFC
or
BSHP = (Injector Size) * 8 * 0.8 / 0.50 = (Injector Size) * 12.80
where a BSFC of 0.50 is suggested for a NA TPI engine.

So, you can see that 27lb/hr injectors, at 44psi should only support 345chp.

If this equation is sound the only way you can be turning 500chp is with a BSFC of about 0.35 for your engine.

I'm not disputing your data nor that of TPIS, just trying to correlate it with the above equation, which I had taken to be correct.

I had thought the equation to be correct because running my stock 22lb/hr (rated at 44psi) injectors runningn at 48 psi support 295chp, which is right on the money for a BSFC of 0.50. This is verified by dyno pulls and by trap speed & vehicle weight calculations.

So, assuming a BSFC of 0.50, if he ran 30lb/hr (rated at 44spi) injectors at 46psi, they should support 400chp.

This is an interesting thread...are you guys running modified TPI or other intakes? I'm just wondering why the BSFC is so low for your cases.

 

The pressure on these injectors CAN be turned up to a very high pressure with no adverse effect, so long as your pump is up to the task.

from what i have read this is not a true statement as i understand it higher fuel pressure usually means better fuel atomizationbut also makes injector work harder when opening and increased fuel pressure also slows injector responce time and all this can also greatly shorten the life of the injectors. also there is such a thing as duty cycle and anything over the maximum 80% duty cycle for long term causes injectors to heat up equalling shorter life also.
proper formula i belive is:

(BHP X BSFC)
---------------------------------- =INJECTOR SIZE
NO. OF INJECTORS X 0.8

where (bhp)=brake horsepower should be accurate and (bsfc)=brake specific fuel consumtion which is often estamated at 0.45 to 0.50 for normally aspirated engines..
and the scaler 0.8 adjusts the calculated injector size to produce the fuel necessary for peak power at 80% duty cycle....
based on this i would say figuring your estimated 400hp at the estimated bsfc it comes out to 29.375 # injectors and at a max 80% duty cycle and at your stock fuel pressure looks like 30# injectors are what i would go with but someone please correct me and explain this to me if wrong as i am here to learn and not to step on toes .....just my opinion
:cheers:

 

ladystoy69 what really is shorter injector life instead of 100,000 miles maybe 70,000-80,000 miles if thats the case does it really come into play :cheers:

 

65Zo1 and Ladystoy,

I understand your dismay with the equations and that is my exact point of posting this topic. To stir up some thoughts and get us all thinking about this injector sizing decisions we are all faced with when we start to mod our motors.

I truely believe that MANY MANY of the problems associated with tuning and performance are directly related to the injectors people choose.

We first have to put into perspective a few critical things. First and formost is BSFC.....what is it, and what catagory does your motor fall into? Its basically the efficiency, determining what catagory your in is well nothing better than a guess.

This last part of the above paragraph is where people first go wrong. 65zo1, you yourself said you typically use a .5, as many do for starting out. Now in my case, had I done that I would have needed 42# injectors!!! But when calculated out you see my BSFC is .35 for the power I am putting out and the injectors I DO have.

This is my point exactly. Right from the get-go you are guessing for probably one of the most important part of your setup. But many say, better to be bigger than too small. That is not necessarily true, since you have the flexability to increase your fuel pressure and make the smaller injectors perform at a larger size.

This in my opinion is 100x better to do, if you find your a little short, than realizing your dumping tons of fuel into your motor and need to try to back it off. First probably your going to lower the pressure (which most injectors need a specified min pressure to atomize the fuel efficiently. Dropping the pressure back to a redicualous pressure to stop fuel supply, is much much harder than you may think. This coupled with the poor atomization, reduces the motors efficiency to raise your BSFC. Not something you really want to do. We build better motors with better components to make the efficiency go up or the BSFC to go down, not the other way around. Especially not to just accomodate a formula that chose the wrong injectors for us. This leads me to my next point.

When were these formulas, or more specifically the BSFC values that are used come up with. We all know the more efficient a motor is the lower the BSFC will go. Were these designated values done back in the late 70s or early to mid 80s? I really do not know. I have seen them where they list motors like n/a street BSFC=.5 etc etc.

Now let me ask.....Keeping in mind the less efficient and engine is...the bigger the injectors needs to be. I like to think of it as you need a certain amount of fuel, but since the motor is not efficient, you need to make up for the "lost" fuel and hence need the bigger injectors. Conversly, the more efficient, the better it utilizes the injector, therefore you can get away with a smaller injector.

With that in mind, let me ask if you think the "street" motor of a cross fire vette of 84 is as efficient as the LS1 of today? Do you think the .5 bsfc is still valid, or do you think the tables need revamped? Remember who pushes the market with most of the information...the injector companies. Do you really think they want you to know you can probably make upwards of 450chp with your stock injectors? How much do you think that would cut into their market? A BUNCH.

I actually would not be afraid to use my stock injectors to run this setup. I would obvously need to raise the pressure a little. To which I have YET to see any proof that running the injectors at higher pressures decreases the life. Or that even running above 80% duty cycle does either. In my mind and experience, the higher the pressure the more the fuel is atomized and easier for the airstream to carry and more importanly mix with the air in the cylinder evenly. Low pressures make more of a dribble, or drop type that probably rolls into the cylinder along the manifold walls.

All in all, I think the fact that we ARE able to run smaller injectors with our setups is proof in itself that it can be done and done effectively. TPIS is a performance supplier, not only of parts but cars also. They have customer like lingenfelter etc that demand the most of their services. I think it says something when the lingenfelters/TPIS and alikes are telling us to not run big injectors, Please call us before purchasing. Read the small writing along the chart above I supplied.

:rant: :lurk:


[Modified by ski_dwn_it, 8:23 AM 9/5/2003]

 

From a real world application I can tell you that the 24's will work for your setup and they won't be holding you back from a horsepower standpoint. However, they will be running at an extrememly high duty cycle which makes some people nervous.

IMHO I believe a 30 is optimal for this setup. It's not so much more that it screws your fuel tables all up, so it's easier to tune out. It's also just big enough to get the duty cycle down to something a little closer to optimal.

I've got factory 24's back in my car right now and I'm enjoying actually having all the MPG readouts correct.

 

From this discussion I see that as I increase HP I should bump fuel pressure and then tune the motor for max HP. It may well be that with a properly designed set of mods the BSFC for my L98 will drop due to increased efficiency; so requiring less fuel flow per CHP generated.

Then, if I feel fuel pressure is too high for the injectors, I can properly size them to my needs.

I agree that is is better to run smaller injectors with higher fuel pressure than the reverse. Though running pressure too high or pushing the duty cycle over 85% could cause lockup problems.

Indeed it would be very interesting to see the BSFC numbers for injectors in say an early L98 vs those in an LS1 or LS6 motor. Some good info in here. :cheers: