85

im reaching the limits of my stock injectors (90%) and i'm not too sure what size to buy. at what % do you see the best hp?

boostB4beauty

well, i don't know exactly how much is the PERFECT duty cycle, but IMO you should try to run between 60 and 80% @ full boost. just my opinion.
i would not recommend anything over 90% for any period of time, as you probably know. Our motors that we turbo are too expensive to be lean-killing!!

96 GSR-T

80-85% to leave room, after that I would think the spray patterns start to be affected as well.

85

so why not run 50%? i guess there really is no reason...

i have 204cc injectors right now (yeah its a bike) and my next step up that i've seen is about 300cc. what do you think?

jetspeedz

i have a set of 550cc injectors for sale new in the box never used if anyone is interested 250 shipped to your door my loss

Albuquerquefx

Here's the simple reason: injectors also have a minimum duty cycle, not in percentage, but in milliseconds. If your motor at full power needs only a 50% duty cycle, then at idle (where it makes only ~5% of full power) is going to need about 2% duty cycle. If that 2% duty cycle is below 1msec, then your car either won't idle, or in order to make it idle at 1msec or better dwell times, it will be pig-rich.

So, injectors that hit ~80% duty cycle at full throttle mean you've got a solid chance of being able to idle correctly. If it needs more duty cycle, you're likely to start having problems with them sticking open. And if they're TOO big, then you're likely to start having problems with idle.

85

makes so much since! so does this in any way play into the dual injector setup? can you actually turn off an injector set one those?

Albuquerquefx

In cases where an injector is properly sized for the top-end of your motor's output, it is still entirely feasible that they just are not capable of idling or cruising correctly. As someone earlier in this thread alluded to, duty cycle can (greatly) affect the fuel injection spray pattern, which can also reduce fuel atomization. Fuel pressure also has a measurable impact on your fuel spray pattern.

Thus, to your point, dual fuel injectors per cylinder would allow you to have a smaller set of injectors that are efficiently sized for idle, cruise and light load, and then a second set that can augment the first set in times where you need the extra fuel. In every case that I've seen dual fuel injectors, the secondaries can be entirely disabled. The ECU's that support dual rails typically have a "crossover" point in the load map where both injector sets are enabled. You then typically have either two fuel maps (one for each set of injectors), or like my aging E6K, a single fuel map that - at a certain load bar - is injecting for both sets.

So my E6K map, if I had dual injection set up, would go from perhaps 3.3msec of injection time at the 11th load bar, to 1.2msec of injection time at the 12th load bar where both sets of injectors are firing (and thus, I would need WAY less injection time, but still keeping it over the 1msec lower threshold.)

Hopefully that makes sense.