"Injections per engine cycle". Can someone clarify

nickturner22066 · Post by **nickturner22066** » Tue Mar 28, 2006 6:27 pm

I understand what "injections per engine cycle" means, but I was wondering how to optimize this setting with the type of engine you have. I have an inline 4 cylinder, DOHC engine. I rough tuned the engine with 2 injections per engine cycle, and alternating injector staging. My idle was fairly hard to tune, and I couldn't get the Pulse Width lower than about 4.2 . Tonight, I switched the injections per engine cycle to 4, and my idle smoothed out significantly. My injector pulse width dropped to 2.1 as well (divided in half).

So this is my question: How do you determine the number of injections per engine cycle that works best for your application? Thanks,

bleoh · Post by **bleoh** » Wed Mar 29, 2006 9:26 am

I did it the same way you did, try different settings and see what works best.

nickturner22066 · Post by **nickturner22066** » Thu Mar 30, 2006 4:38 am

But how do you know what works best? Are you just supposed to use the # of injections that you can tune your idle with best? Or will you notice a power difference under wide open throttle? I guess that I am a little hesitant to start changing settings like this, and then run my engine as hard as I can. I don't want to underfuel it too much at WOT.

keithmac · Post by **keithmac** » Thu Mar 30, 2006 2:02 pm

It depends on the injector size and how they fuel at full rpm/ full load. I used 4 alt and had to go down to 2 alt because the DutyCycle was too high when the engine was flat out, most people take 80% as the maximum healthy dutycycle. The injectors will close twice as many times in 4alt, the time it takes them to close and reopen will affect the total fuel injected if you`re at their limits.

KGB · Post by **KGB** » Thu Mar 30, 2006 4:23 pm

There is a fixed overhead per squirt (injector open/close time), and in my view, changing the number of injections alleviates the fuel pressure loss a tiny bit. In my car for example, if I have one injection/cycle, all 4 injectors would have to fire at the same time but since my factory fuel rail is fed serially, I could potentially benefit from using alternate injection with 2 injections/cycle. Anything higher though doesn't help me