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Author Topic: Injector Calculator  (Read 2760 times)
Ft. Campbell Busa
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« on: October 27, 2010, 04:10:48 PM »

 :thumbup:

http://www.modulardepot.com/?show=fuelcalc
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Fast Nasty
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Super_Dave
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« Reply #1 on: October 31, 2010, 05:36:45 PM »

I don't put much faith in those calculators, I've got a 360 RWHP 306, and am getting injector duty cycles into the low 90's at 39PSI. A buddy of mine has a more drag oriented car, 4.56's 306, A5 trans, 2700 pounds, with 30# injectors, it gets injector duty cycle into the high 90's at 39 PSI. I think rate of acceleration has some to do with how big of an injector you'd need, as compared to just how much power they'll support at 100% duty cycle
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Wrenchhead627
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« Reply #2 on: November 01, 2010, 01:50:03 PM »

What!!!!! if you are running 100% duty cycle that means your injectors never close they are always open it is recommended that at most 85% anything more than that you should step it up or turn up your fuel pressure. If you run them higher than 85% for too long you risk burning up your injector.
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TooNuts
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« Reply #3 on: November 01, 2010, 03:28:46 PM »

I agree with Wrenchhead on this anytime you over 85 percent you should upgrade. Might be some HP in there!
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Ft. Campbell Busa
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« Reply #4 on: November 01, 2010, 07:13:31 PM »

The old rule I always hear on duty cycle also was 85%.
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Fast Nasty
2007 GSXR 1000 Lock up, N2O, Sidewinder, stretched, and slammed 5 sec street bike!
Turbo Nasty
83 Buick T-Type.....87 GN Intercooled, Meth Injected, 70mm Turbo, BG down pipe, Magnaflow, 60lb Inj!
Black Nasty
2006 GSXR 1300(SOLD)
graymutt88
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« Reply #5 on: November 02, 2010, 06:31:30 AM »

for the most part i agree,but when my old 306 was running my 24's were 95% at 5500 and after that it was going crazy!

when i installed 30's i was still running 88% and when i pushed it to 7k i was getting no more than 90%

now when driving and cruzing i never saw over 50%

so i say if you are holding the rpm's/engine load at over 85% for long period's of time like time trial's or circuit racing then yes upgrade to a more suitable injector but if you are street and strip running you will not see 90% duty cycle time no more than .025 of a second unless you are doug then a full second...my dss motor had perfect pistons cylinder walls ect when tore apart and that was with 9yrs of 24's and 1 week of 30's...lol!

also acceleration timing n/a or bossted plays a even larger role in choosing the right injector to cover a certain % of duty cycle..psi is forced air..duh...but when you can't control the fuel at higher rpm's then the increased boost can/will destoy stuff compared to n/a applications..
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bender460
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« Reply #6 on: February 01, 2011, 06:15:11 PM »

   Any advantage to targeting a lower duty cycle? Like 40-50%......And I do not mean idle and fuel mileage here.    All out acceleration. For me that means 5k-8k WOT. I can also tune injector timing.
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92lx
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4bangstang
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« Reply #7 on: April 06, 2011, 07:35:22 PM »

According to that calc My car makes almost 300 hp which is about right but with my new 55# injectors and same variables I can make 468!!??
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4bangstang
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« Reply #8 on: May 17, 2011, 06:41:34 PM »

Hig imp injectors are safe around 80-85% low impedance can be fine at 90%-95%
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QuickShift5.0
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« Reply #9 on: May 06, 2012, 08:05:26 AM »

   Any advantage to targeting a lower duty cycle? Like 40-50%......And I do not mean idle and fuel mileage here.    All out acceleration. For me that means 5k-8k WOT. I can also tune injector timing.

Good question! But , its going to be a battle playing with that. The injectors would have to be substantially larger in order to deliver the amount of fuel you need @8k for a 40% DC. Which is probably not an issue, but your idle time will suffer unless the injectors have a really low minimum pulse width.

There may be some ET or power there. I'm not sure, but if there was, only thing I could think it would be from would be the fuel pattern out of the injectors. Better atomization @40% rather than 90%?
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bender460
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« Reply #10 on: May 07, 2012, 10:24:15 AM »

   My thoughts are along these lines... Lets say 85% duty cycle.... 720* / 85% is 612*.... So lets say your cam is 240* at .050..... So +/- 50% of the fuel is being delivered onto a closed valve... Good or bad???

   It almost seems logical to me as far as atomization is concerned to spray as much fuel as possible at the highest intake air velocity's and that would be when the valve is open.


 :huh:     :grin:
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92lx
Stock block Flat top  347
TFS highprts, CI TLSR, Probe shafts 1.6
super vic, 39lb inj, Wilson 4500 TB
Megasquirt MS3x
EFI tuning by myself
Ultimate 5400rpm 8" converter
Full Team Z front end, rear
10.94 @ 123
sbf
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« Reply #11 on: May 07, 2012, 05:44:52 PM »

  So +/- 50% of the fuel is being delivered onto a closed valve... Good or bad???

   It almost seems logical to me as far as atomization is concerned to spray as much fuel as possible at the highest intake air velocity's and that would be when the valve is open.

That is the logical time to spray, but its not done.  Most of the OEM type efi setups have their open injector (start) point late in the compression stroke (especially the earlier stuff), so the fuel shot can be sitting around for some time before the intake valve actually opens.     
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bender460
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« Reply #12 on: May 09, 2012, 05:37:39 PM »

    The fuel sitting around is the part I do not like. With an A9L ecu one can tune the injector timing. Thinking a larger injector could and should lessen the fuel sitting around if tuned accordingly.

     But as far as a max effort drag setup is it beneficial?? My cam is 253* at .050... In the tune you set the close degrees so when to close the injector ???? 200* or 150* of cam timing?? With a larger injector you would have enough time or a smaller range of crank degrees the injector needs to spray the fuel. One could move it around a bit.

  One could also be completely wasting his time!!  :grin: 

 pop
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92lx
Stock block Flat top  347
TFS highprts, CI TLSR, Probe shafts 1.6
super vic, 39lb inj, Wilson 4500 TB
Megasquirt MS3x
EFI tuning by myself
Ultimate 5400rpm 8" converter
Full Team Z front end, rear
10.94 @ 123
sbf
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« Reply #13 on: May 10, 2012, 03:35:17 AM »

The fuel "sitting around" probably is not as bad as it seems.... you are getting the benefits of evaporation and its cooling effects whilst it is. 
I don't think you'll notice too much difference playing with shut off points on a max effort deal, more to do with idle quality and emissions at low speed running.
Only shooting the fuel when the valve is open would mean running very large injectors to get the job done in the small time "window"  and the result would likely be negative.... the bigger the injector, the bigger the droplet size will be.
Don't forget that the old mechanical injection setups that racers used.... and still do.... is not a "timed" injection deal, its a constant flow setup and its "injecting" fuel continually ??!!
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