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Discussion Starter #1
Can anyone direct me to a post, writeup, discussion, article, chart, formula or any other method for selcting relatively proper sized injectors? Every modern day site or article I found bases it on flywheel horsepower, which is not a number I will have until it is dialed in and dynoed.
 

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Unless you plan on making 600+whp with a turbo or blower, just get deka 80s. No sense going any smaller.

Flywheel hp is a far more accurate number for rating injectors than whp.
 

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Base injector sizing off of expected HP range and BSFC (Brake specific fuel consumption). For pump gas, use .5 bsfc n/a and .6 bsfc for forced induction, and keep the duty cycle under 85% and you'll be in the ballpark. .5 and .6 are pretty pessimistic numbers, btw. NA engines routinely are around .45 and FI engines are typically around .5-.55.

This is how you do it:
Take total injector flow rate in lbs/hr - in the case of 80 lbs/hr, multiply 80 times 8 (you have 8 injectors) = 640. Multiply that by .80 (80% duty cycle) = 512. Divide 512 by .6 = 853. So, pessimistically speaking, 80 lb injectors on pump gas can support 853 hp at an 80% duty cycle. Most people who can't hit these numbers fail because of one of 2 reasons: fuel pump wiring is inadequate or fuel lines are restrictive.

You can also use the math to figure out approximate HP - especially if you have good data on your engine. For example; I've hit 84% duty cycle on my 80lb injectors on mineshaft air days. My BSFC is around .55 (I'm pushing the Whipple pretty hard, thus the not-so-great BSFC). Using the math, I get 977 hp. Take away the ~80 hp needed to turn the blower, and there you go - ~900 fwhp. Using wallace's hp from et calc, that's 684 rwhp at 9.83 & 140 mph at 3,550 lbs. I run a glide and have seen about 25% driveline loss (most of it from the converter) - take 900, multiply by .75 and you get 675 - pretty close - 675 vs 684 rwhp.

HTH.
 

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There's no harm in running bigger injectors than what you need. Better to have excess headroom left, than to have none at all.

I run deka 60's even though 42's would have been fine. Don't even think duty cycle goes above 60%. Still runs perfectly.
 

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Discussion Starter #6
So I guess that's a no.😂😂😂

Very well then, 80 lb injectors and a new engine management system to dial them back.

Can anyone please direct me to a reputable soource for genuine Deka's?
 

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Nobody has asked what is the combo you are looking to size injectors for. If you only need 24 lbs/hr injectors, 80 lbs will be horrible. Turning them down to 30% duty cycle seems like it will be problematic in itself.

Sorry if I missed something, but if a 300 rwhp combo is the plan, no need for 80's
 

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Nobody has asked what is the combo you are looking to size injectors for. If you only need 24 lbs/hr injectors, 80 lbs will be horrible. Turning them down to 30% duty cycle seems like it will be problematic in itself.

Sorry if I missed something, but if a 300 rwhp combo is the plan, no need for 80's

no point to.

the 80s perform just as good or better than what you suggest

and have room, so you dont have to buy twice
 

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Nobody has asked what is the combo you are looking to size injectors for. If you only need 24 lbs/hr injectors, 80 lbs will be horrible. Turning them down to 30% duty cycle seems like it will be problematic in itself.

Sorry if I missed something, but if a 300 rwhp combo is the plan, no need for 80's
Running deka 80s at the low end of their duty cycle isn’t a problem.
My 80s idle every bit as good, if not better than the 44s which they replaced.
 

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Discussion Starter #10
Current setup:
DSS 331 short block with low compression piston option (-13cc?)
AFR 165 heads with 61cc chambers
Motorsport 1.6 rockers
F303 cam (yeah yeah, whatever)
Trick Flow Track Heat intake w/spacer.
Accufab 75mm throttle body
Vortech s trim/ super fmu
C&L 80mm meter
Modified interceptor II (1st gen PMS)

I am currently using a set of 38# Lucas injectors I aquired used in 1998. They were used briefly prior to my acquiring them, and sat boxed up until I installed them in 2015. They probably have an additional 3000 miles on them, but I just don't trust them. I've had some fuel oddities recently, and having these flow tested is 1/3 the cost of replacing. Late 90's/ early 2000's standard would have called for 42# injectors. A lot has changed since then, so its time to make a few changes.

I was really dead set against yanking the old PMS, because I know this combo can run. I just dont have time in the near future to re clock the MAF 6 ways from Sunday and spend countless hours scouring my EVTM and Helm manual checking continuity and so on for a 29 year old harness/ computer. For a friend or customer yes, but not going to waste that time on my own junk. I have another car I'll hopefully start working on in a few years again after a 21 year hiatus, so I'm going to pick up a Holley HP and install it in this car for now.

I have exactly no idea what that combo makes hp wise. 300...400....? Not concerned in the least if it makes a few lbs of boost and runs well without grenading. I knew a ton of people that used to run similar combos, but nobody ever had the spare coin to have their car dynoed. I figured there was a formula based on displacement/ heads/cam ect to select injector size.
 

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Current setup:
DSS 331 short block with low compression piston option (-13cc?)
AFR 165 heads with 61cc chambers
Motorsport 1.6 rockers
F303 cam (yeah yeah, whatever)
Trick Flow Track Heat intake w/spacer.
Accufab 75mm throttle body
Vortech s trim/ super fmu
C&L 80mm meter
Modified interceptor II (1st gen PMS)

I am currently using a set of 38# Lucas injectors I aquired used in 1998. They were used briefly prior to my acquiring them, and sat boxed up until I installed them in 2015. They probably have an additional 3000 miles on them, but I just don't trust them. I've had some fuel oddities recently, and having these flow tested is 1/3 the cost of replacing. Late 90's/ early 2000's standard would have called for 42# injectors. A lot has changed since then, so its time to make a few changes.

I was really dead set against yanking the old PMS, because I know this combo can run. I just dont have time in the near future to re clock the MAF 6 ways from Sunday and spend countless hours scouring my EVTM and Helm manual checking continuity and so on for a 29 year old harness/ computer. For a friend or customer yes, but not going to waste that time on my own junk. I have another car I'll hopefully start working on in a few years again after a 21 year hiatus, so I'm going to pick up a Holley HP and install it in this car for now.

I have exactly no idea what that combo makes hp wise. 300...400....? Not concerned in the least if it makes a few lbs of boost and runs well without grenading. I knew a ton of people that used to run similar combos, but nobody ever had the spare coin to have their car dynoed. I figured there was a formula based on displacement/ heads/cam ect to select injector size.
How much power it is making all depends on how hard you are spinning the blower and the timing you are using. If you have the timing in decent shape and are making 15 psi, you should be making 500-520 or so to the wheels. With pump gas you should be running around 20-24 degrees of timing at full tilt. What you have is a pretty basic 1990s combo for these cars.
 

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Discussion Starter #12
How much power it is making all depends on how hard you are spinning the blower and the timing you are using. If you have the timing in decent shape and are making 15 psi, you should be making 500-520 or so to the wheels. With pump gas you should be running around 20-24 degrees of timing at full tilt. What you have is a pretty basic 1990s combo for these cars.
Yes, very basic and underwhelming. A good deal of it was actually purchased in the 90's for a different project.

Dss and all the blower bracketry went in late 2012. Blower went on in 2015 once it had about 3k miles on it. It has about 6k miles on it now and its never really come together properly. Largely due to a faulty Dynamod module I recently repalced when relocating the TFI and several age related issues.

This vehicle will be on pump gas and thus far has only seen 5-6 psi. Timing is very conservative as it wasnt really dialed in yet. Once I get proper injectors and the HP EFI all dialed, I will swap pulleys and make some proper boost.
 

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Yes, very basic and underwhelming. A good deal of it was actually purchased in the 90's for a different project.

Dss and all the blower bracketry went in late 2012. Blower went on in 2015 once it had about 3k miles on it. It has about 6k miles on it now and its never really come together properly. Largely due to a faulty Dynamod module I recently repalced when relocating the TFI and several age related issues.

This vehicle will be on pump gas and thus far has only seen 5-6 psi. Timing is very conservative as it wasnt really dialed in yet. Once I get proper injectors and the HP EFI all dialed, I will swap pulleys and make some proper boost.
You can run a lot more boost than what you are running as long as you have the fuel pump for it. 10 psi should be no problem. Id love to have that car to cruise in.
 

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Discussion Starter #14
You can run a lot more boost than what you are running as long as you have the fuel pump for it. 10 psi should be no problem. Id love to have that car to cruise in.
Something like 10psi is The end goal fot this car. I'm building a low compression 393 for my 71 coupe that will have a super low mileage r-trim hopefully putting out near 18lbs.

I have the car and I'd love to cruise in it too.😂😭😂

The pump I am going to upgrade soon. Its a BBK drop in feeding the T-rex. I used the stock fuel supply line as the return and ran 1/2" stainless for the supply. There weren't many options at the time, so I modified a stock pickup. Removed the stock lines and put the stock feed hardline in the rerun port with a -6 brazed on and bent a piece of 1/2" stainless as the pickup with a -8 fitting brazed.

I'll most likely use a stealth pump or walbro. Not sure if there is an intank option that will allow me to ditch the T-rex, its so damn loud.
 

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Discussion Starter #15
So does anyone have a recommendation for where to purchase genuine Deka injectors???
 

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A911E97P1225

^^^enter that into the coupon code box to get $50 off a set of 8 deka 80s
 
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