Max boost for injectors?

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silfourty
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Max boost for injectors?

Post by silfourty »

I am about to be getting the old coupe back on the road and was considering upping the boost using the wastegate springs I have. Now my problem lies with just how much boost I can put to my engine without exceeding my 550CC DW injectors. I have been running 13PSI with the Large Green spring in my Tial 38mm waste gate. I have a small blue and small red which would get me around 19psi using the large green and small red. I am quite certain the 550s would not be able to keep up with the nearly 22psi of the green/blue combo.

Any input would be helpful. Of course, I SHOULD just go back with 13 psi I had before, but where's the fun in that?

edit:
setup-
KA24DEt with forged innerds, T3 63ar, fmic 550cc dw injectors, nistune.
silfourty
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Re: Max boost for injectors?

Post by silfourty »

And of course suggested threads show up AFTER I post this one. They were helpful, so I guess nevermind, but if you wanna put in your 2 cents, I'd love to hear it.
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beercandrifter
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Re: Max boost for injectors?

Post by beercandrifter »

just so you know

There is not a direct correlation between the amount of boost and injector sizes. Each turbo produces a different amount of power for each PSI of pressure.

How you can tell if you have enough room left

1) get the compressor map for your turbo
2) get the efficiency conversion (how much power at max efficiency per psi)
2) calculate your max pressure, see if it is still within in your compressor map
4) calculate the drop in power at that range in the compressor map due to loss in efficiency
5) add the power at your maximum pressure plus the base power of the engine
6) use a fuel injector sizing calculator to determine if the hp supported by injectors is greater than the total power calculated in step 5
7) If the power output of the engine is higher than the ~80% max duty cycle of the injectors at stock fuel pressure, reduce the pressure or increase fuel injector size/retune
91 240sx Hatch: HomeBrwd
25psi hx35/8.8:1/264^2 cams/95lb injectors/Megasquirt 2/ka24de build **RIP**
T56/4.8 LSx/LS9 Cam/60lb injectors/comp 918 springs/Megasquirt 3/all custom wiring
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street_240sx
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Re: Max boost for injectors?

Post by street_240sx »

Thank you beercan!!!! I hate how everyone thinks boost pressure is directly related to well.... everything. Boost pressure is just a reference to how much restriction in the manifold there is. 12psi on a t25 is not even the same as 12psi on a gt30.


As for the OP find a good calculator online. Enter your goals, like said above try to keep duty cycle around 80%, yes you can go higher but its not suggested due to higher rates of wear on injectors causing failure
03 evo8 gsr: stroker 2.3 ;)

04 evo8 gsr: totalled

96 integra gsr: sold

89 s13 coupe: stock dohc, gt3076, megasquirt

started 3/15/08, running 1/18/09, finally turbo 2/9/14 lmfao
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beercandrifter
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Re: Max boost for injectors?

Post by beercandrifter »

street_240sx wrote:try to keep duty cycle around 80%, yes you can go higher but its not suggested due to higher rates of wear on injectors causing failure
np

you also want to keep that 20% duty cycle buffer in there in case of boost spikes or other operating conditions that may consume more fuel than you plan for, otherwise your engine will be starved for fuel and then bad things happen.
91 240sx Hatch: HomeBrwd
25psi hx35/8.8:1/264^2 cams/95lb injectors/Megasquirt 2/ka24de build **RIP**
T56/4.8 LSx/LS9 Cam/60lb injectors/comp 918 springs/Megasquirt 3/all custom wiring
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