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Discussion Starter #1
Guys
History long short
I purchased 740cc injectors but I didnt know about venom issues, so they came and we think they are larger than 850cc, I later got the Zemulator from Ash (to finally solve injector size issue and a final tuning), we will be tuning the car at the Dyno soon.
I read in some other topics that if injectors are larger than 850cc I might need a bigger fuel pump, is this true?
how can I find out it I will need it, I am ussing the car now but I am not boosting more than 7psi until I get it to the Dyno, car is doing ok at 7psi, but I am trying to find out if I will need a larger fuel pump before I take it to the dyno.

Thanks for your comments guys.
 

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Injecor size has nothing exactly to do with the fuel pump. The fuel pump can only supply so much fuel which im not sure how much that is. Now persay it cant flow enough fuel to keep up with 850cc injectors at a 90% duty cycle then yes youd need a higher volume pump. But you wont be taking your injectors to that high of a duty cycle. Find out the flow rate on the fuel pump and im sure i can scrounge around and fine the mathmatical formula to tell you how much HP it can flow. Injector size doesnt matter HP does.
 

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Don't sweat the flow capacity of the TT fuel pump unless you're planning on over 650hp. Like Cville300zx said, the pump only needs to supply enough fuel to provide the flow and pressure requirements of the injectors at the duty cycle being used at that time. At idle the injectors will only be open for a millisecond or two. At WOT it will depend on many factors, but it is very unlikely that you'll be pushing anything more then 75% with injectors of that size. The TT fuel pump has been able to keep up with 600HP+ engines, so don't worry too much about that until you get there.

The bigger problem with huge injectors is at idle. The problem being too much fuel for the minimum duration that the injectors can be controlled. The ECU can only control the injectors down too a minimum pulse width. Below that and the injector opening times become unreliable. Chances are you'll never get a clean smooth idle with 850cc injectors.
 

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Discussion Starter #5
Thanks a lot guys!!!
based on that I will take the car to Dyno, it was affraid that is I take it there and at the middle of the test I found that the fuel pump is an issue, I was going to have to take the car out and pay twice for the tuning.


Since I have Z Emulator from Ash I think I can control the fuel at idle.

And mickiemagik, I dont want to take apart the engine to get the injectors flowtested, my engine is just totally customized and it looks just very nice so I dont want to go one step back.

But just fyi, venom injectors sucks!!!

I will let you know how it goes.

 

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Weather you use Ash's Zemulator or not has nothing to do with the problems you'll see at idle. The issue is not how to change the fuel mappings. The problem is with the minimum pulse width capability of the Z32 ECU. You see, the ECU's hardware, the mapping bit resolution, along with the injectors coil and valve characteristics, decides what the absolute minimum pulse width can be. Each step of the ECU fuel mapping has a finite range of timing adjustment. When you get into extremely large injectors the amount of time needed to produce the desired amount of fuel gets so small that the ECU's hardware and base resolution can't provide you with a number that's acceptable for an ideal idle. In many cases it will be either too lean or too rich. Each pulse of the injector consists of basically two parts. One part is what is call the "Void Blastoff time". This is the time it takes for the injector to respond to the initial pulse of the injector driver. The second time is the amount of time needed to meter fuel. When the pulse width gets too small the, void blastoff time becomes the predominant part of the injector pulse calculation. The time required to open the injectors is not entirely stable and thus the dispensed amount of fuel will very slightly from pulse to pulse. With smaller injectors this slight variation does not have a dramatic impact on the amount of dispensed fuel since the predominant part of the equation is still the metering amount. The problem with the larger injectors is that one mapping value will give you a slightly lean condition, but if you increase the value by one the A/F goes slightly richer then needed. The instability in the void blastoff time will cause the metered amount of fuel to very slightly from cycle to cycle. It doesn't necessarily mean that the idle will be horrible, it simply means that it may not be as stable as you would like.
 

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Discussion Starter #7
JT240Z
Thanks for the explanation
I saw in Zemulator that you can change two additional numbers when configuring the injector size.

Injector Void (ms): 90 is the standar
Injector Blast (ms): 75 is the standar.

Do you think if I change this parameter I might have some lucky and get a good idle stability?

Again thanks a lot.
 

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Yes, those parameters will most likely have to be changed as well as the injector K-Value and individual fuel mappings. Even with those changes you will still have some issues related to total injector pulse requirements. Like I said in my earlier post. The problem is not what to adjust, but that of the resolution of each adjustment. The ECU controls timings in predefined increments based on the resolution of each setting. Think of each adjustment as a multi position switch. You can change the switch from one position to the next, but you can't change the switch to be in between positions. This is what is meant by step resolution and is usually defined by the conversion resolution and related hardware involved. In some cases you have very fine adjustment capability and in other cases you have relatively course adjustments. Ash's, or any other ECU re mapping program for that matter, can not change some of these fundamental adjustment step sizes. Because the idle condition is the point that typically requires the smallest pulse duration, it is at that point that most of these resolution issues come into play. You may also find similar problems when you get into light throttle cruise conditions as well. These problems typically show up when doing drive ability tuning and are manifested as surging or pulsing when at cruise conditions.

Good luck on the re tune and let us know how it ends up. To me, if the Venom injectors tend to run on the rich side, then the 550 Venoms may be a pretty good alternative for those seeking a slightly larger injector then the Nismo 555's. This would give you the benefits of additional fuel without the idle issues I've described above that can be associated when using larger (730 or 850+cc) injectors . The only problems I can see are getting matched sets of injectors from Venom and having the system custom tuned.

I would like to hear Ash's take on what would be considered the largest injector on a VG30 that can be used without any impact on idle quality, emissions or drive ability. He has far more experience on the VG engine then I and would provide a good refference for this kind of discussion.



Post Edited (Jan 16, 4:51pm)
 

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I beleive your right. The 555's are about as large as you want without any impact on idle, emissions or drive ability. I was just wondering if Ash was here and if he had some experience with overly large injectors that he would like to share. What to change and what to expect.
 
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