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post #1 of 13 (permalink) Old 02-06-2006, 09:43 AM Thread Starter
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Injector Sizing Question

I’m placing this question in the Misc. since this really doesn’t apply to a MN12 and it more of a “theory” type question.

So here goes:
At what point (size wise) can an injector not be turned off quick enough to provide good idle?

I know there are many cars out there running huge injectors and making massive amount of power… but I’ve never seen these in a streetable vehicle, only racing vehicles. Everything I’ve researched about injector sizing is that when you go to the larger injectors to support a lot of power, you get to a point where the injector can’t be managed properly at idle/low rpm and the engine runs rich and won't idle for crap. I also know that a lot of the exotics are running dual injectors to alleviate this problem (and be more efficient) (I think the Ford GT is running dual injectors).

I’m starting to do the machine work on the intake manifold for my truck and I have to decide whether to run one or two injectors per runner (I’m getting ready to weld in the injector bosses). The application is a roots (GMC 6-53) blown 472 cu. in. running about 6 to 8 psi. at about 5000 rpm max.

Does anyone have any experience with large hp/tq/injectors? Thoughts, suggestions, etc.

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post #2 of 13 (permalink) Old 02-06-2006, 02:00 PM
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Do you have a way to control dual injectors?
I think you'll have more leeway than the 4.6. The increased size of the engine will forgive some of the idling problems. What HP do you plan to make? Find what size injector would be required and that will help the decision.


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post #3 of 13 (permalink) Old 02-06-2006, 02:23 PM
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Are you really set in using that blower? Is it the small or large displacement blower? That is a strange blower for a BB engine. 60lb injectors would do with that level of boost with no problem.

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post #4 of 13 (permalink) Old 02-06-2006, 02:25 PM Thread Starter
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There are ways out there to control a second set of injectors. Some complex, and some fairly simple. (And my best friend builds control systems for industrial gas turbine engines for a living. )

Here is basically (and one I just happened to find when searching for "dual injector control) what I'm looking at except on a V8 application:
http://www.2gnt.com/www/corbin/8inj.html

As for the the hp, I know that a built 460 can easily make 500 hp/500 ft. lbs. N/A. if running good heads (FRPP crate motor for example).

So adding about 40% to 50% to that with a roots blower will result in 600 to 750 hp. (Obviously that is a WAG as a LOT of things come into play!!)

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post #5 of 13 (permalink) Old 02-06-2006, 02:30 PM Thread Starter
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Quote:
Originally Posted by tbirdbrain
Are you really set in using that blower? Is it the small or large displacement blower? That is a strange blower for a BB engine. 60lb injectors would do with that level of boost with no problem.
Yep. It displaces about 200 cfm per revolution and looks almost identical to a Weiand/B&M 174 blower. It is a two lobe (not 3 lobe like the 73 series) and uses engine oil pressure to support the shaft instead of bearings. I'm pretty confident that if I keep it below 10K rpm (blower speed) it should live fine.

I like it due to the low profile and it should handle the low rpm that this big block will be seeing. The only drawback is the total lack of aftermarket parts for this style supercharger.

And I already own it.

Info on misc. blowers... I didn't know there were different size 6-53's... guess I need to break out the measuring stick.
http://www.fordflathead.com/basic_measurements.html

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post #6 of 13 (permalink) Old 02-06-2006, 02:54 PM
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I am familiar with the different variations of their blowers which is what prompted me to ask the question.
The small bore version is only about 11” long and the big bore version is around 15”. They are,
by design, not exactly the normal first choice for an auto engine project because they
tend to be a little ‘tolerance loose’ which when paired with a diesel engine doesn’t bother
anyone but might bother some when used with a gas engine.

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post #7 of 13 (permalink) Old 02-06-2006, 03:09 PM Thread Starter
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Thanks for the replies! The more input, the better.

I called my machine shop and the 6-53 I have is 13", so that should be about 209 cu. in. per revolution. According to the chart (I have no idea if it is accurate or not), there are different sized 6 - 53's (10.9" and 13.1" where-as the 8-53 is 15")

I agree that they are loose, but that can easily be overcome by installing teflon tip on the rotor tips (aka. B&M/Weiand) and setting the end plate tolerances correctly. The looseness isn't nearly as critical on an injected engine as with a carbureted engine (with the carb on top of the blower) since the fuel doesn't need to be kept in a suspension. Granted the overall efficiency will be down, but for my application, I "think" it should be ok.

But back to the original question: Can a 60 lb. injector be turned on and off quick enough to provide proper atomization at 1000 rpm on a 472 engine?

I guess I need to find specs that tie injector pulse width vs. fuel injected vs. injector reaction time vs. fuel requirement at idle. That’s all I need.

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84 F250 Dually w/6.9L Diesel (7.3L IDI pending)
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post #8 of 13 (permalink) Old 02-06-2006, 03:30 PM
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the answr to the injector question is yes. 60lb has no more problem with short duty cycle than any other. (with one execption, that being high rail pressure >60psi)

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post #9 of 13 (permalink) Old 02-06-2006, 03:33 PM
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Quote:
Originally Posted by 94 Daily Driven 4.6L
Thanks for the replies! The more input, the better.

I called my machine shop and the 6-53 I have is 13", so that should be about 209 cu. in. per revolution. According to the chart (I have no idea if it is accurate or not), there are different sized 6 - 53's (10.9" and 13.1" where-as the 8-53 is 15")

I agree that they are loose, but that can easily be overcome by installing teflon tip on the rotor tips (aka. B&M/Weiand) and setting the end plate tolerances correctly. The looseness isn't nearly as critical on an injected engine as with a carbureted engine (with the carb on top of the blower) since the fuel doesn't need to be kept in a suspension. Granted the overall efficiency will be down, but for my application, I "think" it should be ok.

But back to the original question: Can a 60 lb. injector be turned on and off quick enough to provide proper atomization at 1000 rpm on a 472 engine?

I guess I need to find specs that tie injector pulse width vs. fuel injected vs. injector reaction time vs. fuel requirement at idle. That’s all I need.

Something to keep in mind, your pulsewidth with those 60lb injectors will be larger than most people running a 60lb injector becaude you're running such high displacement. Most people don't go higher than 350-400cid without going carb'd.

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post #10 of 13 (permalink) Old 02-07-2006, 12:59 AM
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it depends on what/how youre compensating for the larger injectors.

if you have a tuning program that compensates for the increased global percentages and injector dead time over stock sized injectors, you can run larger injectors in the same manner as the stock ones. this is a better setup over a portfueler type where youll have a secondary set of injectors that come on when needed(WOT).

with DSMlink, i do two things to plug in almost any injector i could ever need to run. take stock injector size(450cc) and devide that by new injector size(say, 950cc), and move the decimal to the right two spaces. thats my global compensation(47-48%). dial that into the fuel slider. then i go online and find the dead time(Usec), which for FIC 950cc's are 315ms. plug that into the Usec box, press "copy to ecu" and bang. done. my car is now generally tuned(though i still have 500rpm fuel sliders for precise fuel control from 0-10k rpm's) to those huge injectors, and does not have the laggy effects of running larger injectors without dead time compensation. people with this program are running up to 1600cc injectors while still getting daily driveability and mileage of stock fuel setup, until, of course, they go WOT and use those 1600's to their ability, which i dont know if you know it, but 1600cc's arent needed until youre well into the 70lbs/min+ range and well into single digits.

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post #11 of 13 (permalink) Old 02-07-2006, 06:13 AM Thread Starter
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I would DEFINITELY prefer to run a single injector and just be able to tune it for whatever the engine needs no matter what the operating parameters. The DSMlink looks nice, but I couldn’t find anywhere where it would interface with any Ford EEC’s, which is what I’m planning on using since the 5.0L MAF systems seems to be what most people are running when they do EFI retrofits. And there is a TFI’d module distributor available for the 460! Additionally, the amount of “hands on” knowledge is definitely out there for tuning a 5.0L’s EEC.

I hadn’t thought about the larger displacement needing more fuel at idle (duh!!) as AverageJoe mentioned. I guess I need to get down and dirty and start doing some calculations of actual fuel requirements at idle, cruise, and WOT.

Thanks again for the input.

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post #12 of 13 (permalink) Old 02-07-2006, 12:46 PM
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Depending on just how much effort you want to put into learning to tune your own car, you can run the 5.0L EEC-IV (preferably an A9L) and use SCT, TwEECer, or even the old EEC-Tuner to do everything DSM tuner does...

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post #13 of 13 (permalink) Old 02-07-2006, 12:52 PM Thread Starter
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That is exactly what I had planned on doing. There is a dyno about an hour from my house with a guy that is very knowledgeable on the 5.0L EEC's. I've already talked briefly with him on this subject and he doesn’t see anything that would be a “show stopper”.

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