1961ba427

iTrader: (26)

I just did heads (not AI or LE but 274/221 cfm @ 197cc) and a CC503 on my stock 95k mile long block. Still have the stock injectors and fuel pressure regulator. My tuner said my injectors are already @ 107% duty cycle at 6,000 rpm and that I need to swap to at least 30#. After reading this IDK what to do. When I say just did, I mean I literally have less than 100 miles since the work. No track or dyno time. I've only been able to get on it a couple times due to wet roads and traffic.

1961ba427

iTrader: (26)

Also wouldn't the SVO 24# injectors that Gizmo mentions working well for him be alot more than our stock 24#'s due to the different pressure they are rated at?

lt1slowz28

the ford injector numbers are usually around 36 psi, so the difference isn't much, I dont think...



what I'm interested in is what kind of dwell times the injectors see... that, I think along with pressures makes a nice little delta vee of a sweet spot of atomization and efficiency.

TravisMcGill2000

iTrader: (2)

Hey gizmo come to my house this weekend. I wana pick ur brain for awhile. Lol thanks for the help

GIZMO

iTrader: (8)

Talk to my friends, I don´t have many brain cells left.

I hope to be home from Mexico tomorrow...

GIZMO

iTrader: (8)

The same goes for the 42 lb injectors in my LS7.

GIZMO

iTrader: (8)

bowtienut

iTrader: (1)

That "107% duty cycle" doesn't mean squat from what I've seen. Some shts n giggles calculation the logging software performs. The real test is if it goes lean on a wideband. Your tuner should have told you that you "need to swap to at MOST 30#."
Assuming you're gonna dyno tune it, yes 30# would be a sure bet to have in there prior to dyno day. But, chances are you'd also be OK installing an adjustable FPR just in case it shows lean with the 24's at stock pressure.

nitrous2fast

iTrader: (2)

Duty cycle limits are not just by what HP you are making but also at what rpm. Duty cycle is the percentage of injector open time versus calculated time available for injector fueling window. Also the BFSC play a factor in what determines the size of injector. A vehicle with a BFSC of .6 will need a lot more injector than a vehicle with a .5 BFSC (assuming the vehicles make the same HP).

flyinZ

iTrader: (15)

So, how do you figure what injector your engine needs? Is there a formula for that or something?

nitrous2fast

iTrader: (2)

Yes there is.... I actually don't remember off the top of my head but you need your vehicle's BSFC and the rpms you will be running, engine disp, and something else.... Ill get it when i get home...lol

1961ba427

iTrader: (26)

I had heard that svo 30# are actually about 36# at our stock pressure. The keyword there is "heard". I'm not trying to spread misinformation as I don't claim to be an expert or even knowledgeable on the subject. IF that is correct then the svo 24# that Gizmo runs would be near 30# at our pressure which would explain them working so well at his performance levels is the way I read it. My tuner did not recommend me to run 30# Ford injectors, he recommended injectors capable of 30# at my stock pressure. In that case would the svo 24#'s be a good set to look at for my application?

gregrob

iTrader: (8)

The difference is significant and should be accounted for in the tune.

bowtienut

iTrader: (1)

Flow rate for my 30# SVO's is set at 31.5 pph in my tune. stock pressure.
That's what Bryan at pcmforless had in the program before we dyno tuned it, and it was close enough.

1961ba427

iTrader: (26)

So do those sound about right for my combination then?

CNC ported heads, cc503 with 1.7:1 rockers, ported intake, 58mm TB, stock shortblock, GM .028" head gaskets, TPIS Longtubes, EWP, !AIR, !Cats, !EGR, Underdriven crank/overdriven alt pulley, T56, 1969 Impala 12 Bolt with 4.11's. Some suspension mods. No weight removed.

bowtienut

iTrader: (1)

"those".....are you talking about 24# SVO's?
Honestly, if you're buying injectors, I'd go with SVO 30#. If you already had some SVO 24's, I'd say try them.

1961ba427

iTrader: (26)

Sorry for the confusion. By "those" I meant svo 30# that you mentioned running. I currently have my original 1997 stock 24# injectors. Thanks for all the help.

moehorsepower

iTrader: (3)

Its tough in a way to determine exactly what injector you want in order to get a set duty cycle if that's what you are looking for. All combos are the same but different meaning, how many miles are on your current injectors how may WOT runs have you made. When we had the shop some Heads & cam LS cars would be int he 100+ % duty cycle while others with the same setups be within the so called 85%. If your car isn't a 50/50 street & strip car then duty cycle really doesn't mean a lot as long as you can reach your target A/F. This past weekend I tune an LT, heads, cam ect with stock injectors and at the upper RPM's he was hitting 117% duty cycle, That wasn't the issue, it was that I couldn't obtain the desired A/F in the 5000 + RPM range.

nitrous2fast

iTrader: (2)

Ok here is a good example of what a 30# Ford injector will hold. If you are willing to push duty cycle to 95% and run the fuel pressure to a measily 50#, those injectors will, by way of calculation, support 517 HP. Of course on a pretty efficient engine. A boosted motor would be different.