I have always used a BSFC of .65 for a forced induction engine. Using you example of a BFSC of .55, I get a little higher injector size than you do:

300hp/4(cylinders)=75x.55(BSFC)=41.25/.8(duty cycle)=51.56x10.2(conversion from lb/hr to cc/min)=525.9cc/min.

Using a BSFC of .65, the injector requirement jumps to 621cc/min at 300 hp. Being that no one in this thread is at 300 hp creates a need for even bigger injectors. At 350 hp and a BSFC of .65 the injector size needed is 725.1. At .55 BSFC the injector size needed is 613.5.

Now just because a stock turbo'd Evo will run the stock injectors out to 99% idc doesn't mean it's a good idea. I see mine losing control at 95% idc. At 100% idc a 550cc/min injector will allow 392 hp using a BSFC of .55, or 331 hp using a BSFC of .65. This is why I am upgrading injectors, the math doesn't lie.

Sorry for high-jacking your thread 4tun8, I'm just trying to lend some facts to the conversation.

 

I just recently made 303whp on a low-reading mustang dyno.

I have 720cc injectors and stock turbo, my duty cycles are:

79% at 7,000rpm
74% at 6,000rpm
68% at 5,000rpm

I'd post the excel sheet but its huge.

Keep in mind I am taking -23 fuel out at 7k + with an ECU + EMS

 

If your hitting 97% idc, taking fuel out will decrease the idc, not adding it. Remember the duty cycle increases with fuel need, so obviously taking fuel out will decrease the amount of fuel the injector is supplying, thus reducing the duty cycle.

It doesn't suprise me you hare hitting 97% on stock injectors with your mods, a bone stock evo is about 90% idc or so. -/+ (since they run pig **** rich up top stock, about 10.1 / 9 AFR)

That is why my duty cycle is so much lower with 720cc. I am -23 fuel 7k+ on a ECU + EMS.

 

I guess this comes down to what your definition of maxed out is. My definition of maxed out is 90% plus duty cycle. Yes you can go over that, but in my mind it's not a good idea.

You can make 350+ so by the math provided you can infact max out your injectors on the stock turbo.

 

If i take fuel out my car will blow up...... I run a solid 11.4 AFR up until 6k rpm then it starts going leaner up to red line. I know how duty cycle changes with need....

 

Well that pretty much means you need more injector no? Unless your tune is trash.

 

listen, it is NO surprise that your injectors are maxed out.....what are we all trying to do when it comes to tuning???? run the maximum amount of boost and timing while keeping the car safe....so timing plus boost= FUEL COMSUMPTION! i run 22 psi with about 21 degrees of timing on top, i'm adding 12% fuel on top of eveything else with stock injectors. We only run 550cc injectors....that will go to sh|t really quick with the amount of boost and timing we run. The idea of safe injector duty cycle is 80%-90% nothing above...i run 98%, its not reliable but i can't afford new injectors.

 

But you can afford a new motor when your injectors overheat and shut down?

Let's see... $400 or $3,000?

 

you think so?