I am logging some injector duty cycles up to 109 lately @ 6800 rpms.
What will happen if i don't upgrade these? What is it hurting? This is n/a.

I have a racetronix kit and a 150 wet kit that i want to start using more often.

 

The potential issues are mostly leaning out the motor and decreasing injector life. If you normally only race with a wet kit, you could just up the fueling on spray, and not redline the motor NA. This would be the cheap way around doing the fuel system right.

 

Hey man, you wont lean the motor out that way. Injector duty cycle is based on crank rotation, not camshaft rotation. So basically having 100% duty cycle your injectors are open half the time, it takes 200% DC until they are open all of the time, this explains why you can be above 100% DC and continue to richen the motor up... It is not very effecient this way though, because you are spraying fuel on the back of the intake valve when it is closed so that obviously does not work so well.

I would however consider upgrading them as an insurance policy, injectors don't like being open a lot. If you are hitting 100%+ often, I would upgrade them.

 

That info is completely incorrect.

 

how so? DC is calculated based on crank rotation, the cam rotates 1/2 the speed of the crank. Most DC calculators use the Otto cycle (once during the 4 strokes) 100% dc means open all the time for 1 of the 4 strokes (which is an entire revolution of the crank, 1/2 a revolution for the cam), 200% is technically not full time open, because I guess 400% would be open for the entire 4 strokes, because 100% equates to just the intake stroke itself. So 100% DC is just for one stoke, 100%+ open after the intake valve begins to close for the compression stroke (this is ineffective, obviously). As I stated above, the last 100% is not as "good" or as legit as the first 100 but can still continue to richen the motor up some, and 109% DC is still ok, but the injectors will not last. That is why I said for him to upgrade his injectors. The problem comes into play more when you get WAY above 100% you start to hit the valve when it is completely closed, therefore you are not adding fuel to the candles and it will lean out, not to mention it is a waste of fuel.

how else can you explain being able to go richer, even after 100% DC?

is this not correct? Its how I see things...

 

Every DC calc I have seen does it correctly. Every two turns of the crank completes an entire 4 cycle process. 6000rpm is a good place for an example, as the math is simplified because of 60 seconds to a minute. At 6000rpm, the motor completes 3000 complete cycles per minute. This equals 50 cycles per second, leaving 20ms available in which to inject fuel. The DC caclulators in the stickies here, as well as in any tuning programs I have seen will show 100% duty cycle when the PW exceeds 20ms at 6000rpm. The ability to seemingly go richer after 100% DC is more likely due to slight variations in the actual vs reported injector open time or some other innacuracy.

 

according to Greg Banish, in most OEM applications you spray fuel on top of a closed valve to avoid fuel getting 'pulled out' through the cylinder and out of the exhaust.

other than that, i totally agree with gametech

 

 

now you are getting into cams, and overlap that is a whole new ball game when it comes to effective fueling.

I was mainly trying to focus on there is only 1 stroke where the intake valve is open ready to accept fuel. However, you need to keep in mind that you can continue to spray fuel whenever you want, in the end only the valve is going to determine when it goes into the motor. You are right about there being 2 rotations to complete 4 cycles, 1 of which is the intake cycle. This means that any fuel sprayed ontop of the intake valve during the other 3 cycles is still going into the motor when the valve opens, regardless of what anyone says. There is an effective window of opportunity though, and effectiveness and effeciency start to dwindle when you move passed it. Point is, you can continue to richen the mixture up well beyond 100% DC and it will not be because of inaccuracies of measurement.

Does this not make sense to anyone else? I swear its true. but go ahead and don't believe me.

edit: explain to me at what DC are the injectors are open 100% of the time then?

 

The injectors ARE open 100% of the time at 100% DC. However, that includes the time it takes to open the injector and the time it takes to close the injector. So depending on whether or not the computer takes opening and closing offsets into account, you might be a millisecond or so short of actual 100%DC when the computer shows you have hit 100%. For example, in the 6000rpm scenario, a 1ms innacuracy out of a possible 20ms could mean a 5% difference in fueling.

 

I swear they aren't man, and by the way its 50revs per second at 3000 rpm, not 6000. 40ms per 2 rev. Keep in mind there are 2 total revs per cycle, so at 100% dc the injectors are open 2 of the 4 strokes or 1 rev. If the injectors were open all the time it would be 200% or 2 revs aka open for all 4 strokes. Make sense yet?

I know i said 400% before but I was just tired. 200% would be all the time open.

 

Let me try to explain the math better. At 6000rpm, there are 100 revs per second. This means only 10ms per rev. However, it takes two revs to complete a cycle, so you have 20ms during which to inject fuel.

 

I get what you are saying now and its not the same as how I understand things but it still bothers me, something does not add up. I've seen cars go into the 120+ range and still not ever lean out lower than commanded.... so somethings wrong somewhere is all I'm saying. Maybe these computers cant calculate the IPW correctly at all?

 

Now you understand what I meant about inaccuracies of measurement. If you go to an even higher rpm, a 1ms miscalculation can be even more than a 5% difference.

 

yeah no joke about that, but 20+ % inaccurate? Something is funky about that. I can recall guys going above that when spraying with no ill effects to the AFR at all. This is at like 6500 or so. oh well, I went above 100% all the time with my old setup and no issues as far as leaning out the mixture even a small amount. So DC calculations with these cars should be taken with a grain of salt that is for sure.

edit: for ***** and if I can get my hands on one, I might hook a portable oscope up to an injector and go log and see what I see as far as activation of th einjector and compare to my data logging, this could be interesting...

 

Understanding math and theory is only a good first step to seeing what really works. The oscilloscope idea is great. It can really be scary how far reality can deviate from theory.

 

believe me, I know. There have been many situations where things have looked GREAT on paper but didn't work at all and vice versa. I understood the math, I was just thinking differently. To me 100% is 100% of 1 revolution, not 2. Anyway, I will see if I can get a hold of one of the laptop log software oscopes. I think a friend of mine might have one.

 

That evaluation of what I wrote IS correct.
edit--Frost knows what I mean.

 

Yeah tapped is tapped, and 100% DC is maxed out, not 200%.

 

+1. Exactly right.