Fuel Injector upgrade..yes or no?

Venom351R · Apr 13, 2008

First of all how much HP can a set of #24 injectors usually handle? Currently Im at 340 RWHP from the dyno sheet I got when I bought the car. Next month I'll be adding a Trick Flow R intake for the 351W and a custom grind cam shaft from ED Curtis. Im not positive of what these new additions will give me for power but it should push me to the 360ish RWHP mark so is this pushing past the limits of the #24 on a N/A motor? I have found a set of #30lb's that are pretty cheap so Im debating on snagging them now or if its not needed.

blksn955.o · Apr 13, 2008

Depends on the FP. If it is the stock FP then not a whole lot more than 19's.

Buddy of mine has a gen1 lightning with 185s and moved to 30's...I would atleast say 30's or larger. Just for piece of mind I would look at 36-42's.

final5-0 · Apr 13, 2008

I'd advise 30's at the VERY least

Talk to your tuner

If custom tuning, you most likely will run at OEM pressure so the inj's are gonna
act smaller than if you are running at elevated pressures.

Grady

Venom351R · Apr 13, 2008

so my #24's are probably maxed out as the car sits now? What are they usually rated for N/A power levels? I have a leaky injector (another thread in here) and Im debating on if I should replace all the O rings in the #24's or just go ahead and buy some bigger injectors. Then I have to get my meter recalibrated but I want to buy one of those new Digital mass air meters so I would avoid having to send it out for a new tune for it.

Black95GTS · Apr 14, 2008

If I had your combo, I'd be running 42# injectors at the stock fuel pressure.

Adam

Killercanary · Apr 14, 2008

I hope you make more than 360 with your new mods, and that being said I think if you have a way to get a set of 30's relatively cheap then do it. I'm running 24's and I'm at 355/365 to the wheels, and I'm swapping my heads and putting a fox TB on within the next month. I hope to be at ~375-380 to the wheels, and initially I'm keeping my 24's and I'll be upping the fuel pressure to around 50psi. I'm at 45psi now with the line off and I'm seeing a max of 85% duty cycle. At 85-90% duty cycle and 50psi i should be able to feed my beast at the 380rwhp mark. I am however adding a set of 60's to it as well, it just might be after I do all of this as I want back to back dyno test of the heads and I want to throw in too many variables.

Venom351R · Apr 14, 2008

Killercanary said:
I hope you make more than 360 with your new mods, and that being said I think if you have a way to get a set of 30's relatively cheap then do it. I'm running 24's and I'm at 355/365 to the wheels, and I'm swapping my heads and putting a fox TB on within the next month. I hope to be at ~375-380 to the wheels, and initially I'm keeping my 24's and I'll be upping the fuel pressure to around 50psi. I'm at 45psi now with the line off and I'm seeing a max of 85% duty cycle. At 85-90% duty cycle and 50psi i should be able to feed my beast at the 380rwhp mark. I am however adding a set of 60's to it as well, it just might be after I do all of this as I want back to back dyno test of the heads and I want to throw in too many variables.

I hope to pull more then 360 as well but Im not setting my expectations really high just in case it does not. I think I may just go with 42's b/c a vortech may find its way back on t his car at some point and if so I wont have to up grade again.

Vipersix · Apr 14, 2008

The fuel system seems to be the most misunderstood portion of a performance car and is usually way overkill, second only to the ignition system.

The power potential of an injector depends on numerous factors. The most important factors you need to worry about are fuel pressure and duty cycle. Most engine gurus will recommend no higher than an 80% duty cycle (the injector is only open 80% of the time under WOT). Fuel pressure will, in essence, bump your potential up by forcing more fuel in. This theory does have its limit, however; eventually the pressure will be so great as to not allow the injector to open.

So, to answer your question: Your average engine will see a max power potential of 385 hp or 307 hp @ 80%. Bumping up the fuel pressure to 50 psi as Killercanary suggested will net you another 40 hp.

Upgrading to 30's will get you nearly 100 hp (480@100%, 384@80%).

Keep in mind that you CAN get too large of an injector. As the injector gets larger the minimum fuel flow gets larger as well which can wreak havoc on your idle characteristics. For instance, if you were to jump up to 42's as someone recommended, your power potential would be in the neighborhood of 672 hp. Expecting 360 hp out of your motor will render these 42# injectors into the 55% duty cycle range. Basically you are only using your injectors half the time. 55% isn't a bad range, though it is far from optimal.

One option you may consider, since the 30#'s are apparently a good deal, is to simply up your fuel pressure once/if you get a blower. 30#'s will satisfy your current needs with no difficulties whatsoever and a small increase in fuel pressure, say 3 - 5 psi, will net you all you need for a blower as well. Top it with an FMU and you're money!

But, if you prefer to leave your system at stock pressure (which is not a bad idea) then I would recommend getting 42#'s if you know you'll upgrade to a blower.

FYI: Injector Sizing Formula
Power = (Number of Inj. * Inj. Flow * Duty Cycle) / BFSC (usually around .5)
384 = (8 * 30 * .8) / .5

Venom351R · Apr 14, 2008

Vipersix said:
The fuel system seems to be the most misunderstood portion of a performance car and is usually way overkill, second only to the ignition system.

The power potential of an injector depends on numerous factors. The most important factors you need to worry about are fuel pressure and duty cycle. Most engine gurus will recommend no higher than an 80% duty cycle (the injector is only open 80% of the time under WOT). Fuel pressure will, in essence, bump your potential up by forcing more fuel in. This theory does have its limit, however; eventually the pressure will be so great as to not allow the injector to open.

So, to answer your question: Your average engine will see a max power potential of 385 hp or 307 hp @ 80%. Bumping up the fuel pressure to 50 psi as Killercanary suggested will net you another 40 hp.

Upgrading to 30's will get you nearly 100 hp (480@100%, 384@80%).

Keep in mind that you CAN get too large of an injector. As the injector gets larger the minimum fuel flow gets larger as well which can wreak havoc on your idle characteristics. For instance, if you were to jump up to 42's as someone recommended, your power potential would be in the neighborhood of 672 hp. Expecting 360 hp out of your motor will render these 42# injectors into the 55% duty cycle range. Basically you are only using your injectors half the time. 55% isn't a bad range, though it is far from optimal.

One option you may consider, since the 30#'s are apparently a good deal, is to simply up your fuel pressure once/if you get a blower. 30#'s will satisfy your current needs with no difficulties whatsoever and a small increase in fuel pressure, say 3 - 5 psi, will net you all you need for a blower as well. Top it with an FMU and you're money!

But, if you prefer to leave your system at stock pressure (which is not a bad idea) then I would recommend getting 42#'s if you know you'll upgrade to a blower.

FYI: Injector Sizing Formula
Power = (Number of Inj. * Inj. Flow * Duty Cycle) / BFSC (usually around .5)
384 = (8 * 30 * .8) / .5

Thanks for the break down. Fuel system and ignition are two things I need to learn more about. Im not positive on the blower option at this point just something I am throwing around but for now the car is deff staying N/A so with that said would it be better to just go up to #30's now and if need be go with #42's later on if I do go the boost route? I have quite a few goals I want to reach with the car while it is N/A so even if I do get a supercharger it would not be for awhile, further enough down the road so if I did have to move up injector sizes once again it wouldn't be a big deal. Right now I just plan on staying N/A for the time being and I just dont want to get to the dyno after the mods are on and find out I dont have enough injector to go WOT for a dyno or track runs thats why I want to get it done now and not have to go back to the dyno once they are upgraded.

Vipersix · Apr 14, 2008

The biggest factor will be expected power output. What do you estimate your max output will be at the crank?

Venom351R · Apr 14, 2008

Vipersix said:
The biggest factor will be expected power output. What do you estimate your max output will be at the crank?

Providing the previous Dyno numbers on the car are correct (it was done down in FL I live in Maine) I probably at or just over 400 at the crank now with a 15% Drive train loss. Im running 107MPH in the 1/4 mile so I belive the numbers are pretty accurate for what Ive seen it do at the track. I figure with these new mods it should put me in the ball park of 360-380 RWHP which breaks down to 415-440 at the crank given a 15% drive train loss. I dont see the car pulling more then 380 at the wheels but you never know, Im not sure how much the custom cam, Trick flow R and DBX digital mass air meter will actually pick up for me. I suppose I should air on the side of caution and if these numbers are pushing the limit of what 30# will do then I should go with 42#. Id just hate to get to the dyno with #30's on and have them past the 80% duty cycle

BlackVert · Apr 14, 2008

yes, imo, 42#ers are in order

Vipersix · Apr 14, 2008

Well, it really just depends on what brand you choose and how much you are willing to spend. Generally, the larger injectors are more money. Here's a general outlook of popular injector sizes with their output @ 80%:

34# - 435hp
36# - 461hp
40# - 512hp
42# - 538hp

I would recommend the 36#, this will allow expansion up to mid 600 hp.

Venom351R · Apr 14, 2008

I did find a set of #36's that were not priced that bad.

Vipersix · Apr 14, 2008

The 36# injectors will be running at approximately 76% if you are producing your high estimate of power and will allow expansion to about 520hp@90% which is easily acceptable. If you still exceed the 520 horses at a later date you can simply increase your fuel pressure to 50 psi and see over 550hp.

What's amazing about injectors is that if you built your engine really well, it doesn't take as much fuel to get the same output. Theoretically you could see upwards of 575hp@80% at stock pressure.

final5-0 · Apr 14, 2008

Those charts you find all over the web can be so misleading

Just a few things to consider

Those charts are always referenced in fwhp NOT rwhp which we all relate to

You of course got the drive line loss and if using an auto more still to think about

As for the low pulse width conditions ...............

Yes it is true ... the larger the inj size ... the more of an issue it is gonna be

But ... Then again ... Things are as they really are

Once you're at that level of performance

How many peeps try and run such a combo with the outdated Cheat Method
the meter manufactures devised way back in the day

I mean ... most folk at that level are gonna custom tune which can make large
inj's idle and cruise like a little stocker Stang anyway.

Running inj's at elevated levels works

but it is a bit of a band-aid
or
a kind of ... work around approach .........

at solving the problem of inj's that are too small IMHO

Anyway ... just my two cents worth as they say

Grady

Venom351R · Apr 14, 2008

The car will be getting a dyno tune as well so there will be some further tweeking. I found some #36's very low miles (few hundred) for $200. I think I'll snag those ones while I can. Thank for all the input and info. I would go with 42's but I think it would be a tad bit over kill as of now, perhaps once there is boost on it but that wont be this year and maybe not even next year either.

Black95GTS · Apr 15, 2008

36 pound injectors will work for sure! Snag those 36s while you can, they are becoming harder and harder to find and a good set for 200 bucks is a steal.

I advocate running larger injectors because I believe in running injectors at the manufacturer's spec. I write specfications at work all the time. I know what leaves my desk will not be exactly what gets built, btu I put the numbers and calcs on the specification for a reason.

So if Ford says run it at 39.5 PSI, then I will do that. The only reason I can see for ever bumping the fuel pressure to "make it work" would be if I was in between builds and wanted/needed to drive the car while funds built for the correct size and tune. Don't skimp on the fuel system!

Adam

ShortThrow50 · Apr 15, 2008

24's would be fine with that setup. people always go overkill. but if if your gettin 30's for cheap go ahead and grab em. if you dont grab them, let me know where i can get them cause i have a s -trim on and i think its time for me to upgrade from my 24 pounders

Venom351R · Apr 15, 2008

ShortThrow50 said:
24's would be fine with that setup. people always go overkill. but if if your gettin 30's for cheap go ahead and grab em. if you dont grab them, let me know where i can get them cause i have a s -trim on and i think its time for me to upgrade from my 24 pounders

Your probably going to have to go higher then 30#'s. I had 30's on my 95 GT w/ a Paxton Novi 2000 (stock heads cam) 339 RWHP and the 30's were working hard.

Fuel Injector upgrade..yes or no?

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