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Discussion Starter #1
I guess I have never really made good power but did some street tuning today and my injector duty cycle was 99% at 6k. I thought that 365's are good up to 220whp or so. Running 13psi on the new twinscrew design. I have a pulley that will run to about 17-20 psi and I am not sure if the 440's will suffice. What size injectors do you turbo guys use at 200+ power levels?

Ron
 

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440s are only good to about 230, and that's at a very high duty cycle.

I'd say 550s are good.

That's what I am running.. RC engineering PL9-550
 

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230 at the wheels right?

uspspro said:
440s are only good to about 230, and that's at a very high duty cycle.

I'd say 550s are good.

That's what I am running.. RC engineering PL9-550
You mean 230 at the wheels right? so about 275 HP at the crank. I've just switched to 440s and I'm actually suprised at how little difference I'm seeing in the duty cycles compared to the 365s. At 13psi I'm seeing close to 80% duty cycle, my AFR is on the rich side tho, I think I should be able to knock that down a good 5% when I make it to the dyno. The 365s were hitting 85% at 12 psi. I suspect I'm making in the low 200s right now. I'm hoping they are more than enough for my turbo, ie. if the wastegate ever brakes it shouldn't go much higher than 17psi which is hopefully below 100% duty cycle.

Neil
 

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also what fuel pump..

Back when I was at 205rwhp the 440s were at almost 100% duty cycle... BUT that was with the stock fuel pump. That is about as far as the stock fuel pump can take you.

I have a Walbro 255 and RC 550's now. Now the fuel system shouldnt have a problem with 300rwhp

Marco
 

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Discussion Starter #6
I have not checked the pressure, but I am assuming all is fine. The twinscrew is sucking so much air with the 3 inch tb and inlet that I guess I simply need more injector but I did not think I would need more injector at 13psi. So I guess I am forced to slap in the 550's, especially if the 440's are going to give me similar results. I am using a turbo supra fuel pump.

Thanks
Ron
 

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Discussion Starter #8
Sorry I was not very clear. I am running a Link standalone ecu. Interesting thing is that before the upgraded plumbing and more boost I was at 85% (stock tb). Now with the 3 inch and less boost I am at 99% at 6k. Guess that means I am putting in ample air huh!

Ron
 

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That's what I was about to mention, the ECU or standalone doesn't really care what the injector size is, once it is programed it will shoot the duty cycle up every time it senses full throttle, you need to somehow fool it into thinking it is inhaling less air and then it will lower the duty cycle. Does that make sense?? I guess what I'm saying is that the more air goes in the higher the duty cycle.
 

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Discussion Starter #10
I think it would be ok to fool a black box, but I would rather stay true with a standalone and just get the bigger injectors.
Any thoughts?
Ron
 

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yeah.. most EMS software has a way you can just plug in your new injector size, and it will derive a new map based on your old map.

So that way you are pretty close before fine tuning on the dyno.

Marco
 

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Marco, that's exactly what I'm referring to, that just by changing injector size doesn't necessarily alters the duty cycle.
 

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Well. Upping your injector size will lead to your map having shorter "injector open" times. This will lower your duty cycle.

So by switching to larger injectors.. and then making a new fuel map (which, in most caases, can be done as I said above). The duty cycles will end up being lower.

So... you are right. Just changing the injectors = same duty cycle and running pig rich

Changing injectors and running a new fuel map for them = same A/F curve and lower duty cycles.

Marco
 

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uspspro said:
440s are only good to about 230, and that's at a very high duty cycle.

I'd say 550s are good.

That's what I am running.. RC engineering PL9-550
It might be due to fuel pressure differences, but in the 3sgte camp many people are reliably making 260-270 whp on stock 440 injectors and stock fuel pressure.

If the pump can keep up, you can just increase fuel pressure to around 49psi base (which is what ATS racing does for the 3sgte regulators) and I think 300whp is possible without danger on 440 injectors.

Check out ATS racing website or search the 3sgte forum for more details.
 

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at what duty cycle... I really dont want to go over 80%... Ill do 85% if I have to but that's it.
 

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Here is some info I'd like to pass on. Duty cycle is directly dependent upon two things, injector pulse width and RPM

Generally speaking on our ECM's, by just installing larger injectors and not changing your fuel mapping, the duty cycle won't change, installing a larger fuel pump, or raising the fuel pressure, the duty cycle won't change.

These things are all interdependent and must be accounted for when tuning, closed loop systems will try to take care of some of it, but only to a point. Remapping the fuel is the best option.


As for RPM, here is a good one.. at 4000 RPM the engine is running 2000 "cycles per min" (4 cycle engine only one power stroke in each 2 revs) That is 33.33 cycles in a second or only 0.030 seconds for one engine "cycle"
There is only 0.030 seconds to inject ALL of the fuel needed into that cylinder, otherwise, we are already into the next engine cycle.

As RPM rises, the time available to inject the needed fuel is reduced, at 6000 rpm is only 0.020 seconds

However, the intake valve is close for part of the 0.020 seconds, Lets look at a 256 intake cam.
720 degrees in a cycle (remember 4 stroke engine) 720/256 = 2.81 so.. only during about 1/3 of the rotation is the injector actually pointing at an open valve...
So.. we actually only have 0.020/3= 0.0067 of time when the injector is REALLY injecting fuel into the open valve, the rest of the time, it's shooting at the back side.


There is a point of diminishing returns, again, as RPM rises the less time is available, at 7200 there is only 0.0166 seconds available for each cycle.


If you above 80% duty cycle, the injectors start to reach a "float" point, similar to valve springs, before the injector even has time to close, it's already being asked to open again. This is bad, Go to larger injectors and have your map retuned.



Obviously there are limits, if the injectors are TOO large, they can't make a short enough pulse to keep from flooding the engine at idle, this is where staged injection comes into play, but that is another story.


Also, think about the 720 degrees/256 degree issue... What good is all the hype (in other discussions) about sequential injection when all it really means is that there is even LESS time to inject fuel?
Answer: Theres not, sequential system typically are only sequential below 1500 RPM's to keep a smooth idle and reduce emissions, above 1500 they gang fire, if they didn't they could never get the needed fuel in, there wouldn't be enough time.
 

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uspspro said:
at what duty cycle... I really dont want to go over 80%... Ill do 85% if I have to but that's it.
That was considered "safe", meaning, I think about 85%.

this is also assuming that the power is made at about 11.5:1 AFR. If it is being made at a richer AFR then the 440's will never make it.

Even with what I am saying, I think 550 are a better choice, considering the tuning ability of the stand alone ECU and the ability of the 550's to go to 320-330whp for future growth.
 

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Discussion Starter #18
I understand what ever injector I use I will need a retune, but I guess I always thought the 365's where good to 210-220whp. I think 550's might be the ticket since I would like to run more boost.

Ron
 

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yeah.. extra potential never hurts when you have an EMS ;)

get some new 550's from RC. I paid under $300 shipped for all four from horsepowerfreaks.com

Marco
 

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califcarm said:
this is also assuming that the power is made at about 11.5:1 AFR.
Here is another internet myth being passed on.

FACT: AFR has very little effect on power output.

Simple to see.. While on a dyno (I mean a real dyno, not a Dynojet POS) run the engine up to 5000 RPM's and adjust the load on the dyno to hold it there. Then keep opening the throttle until your making 10 psi of boost.

Now, watch the torque output the dyno is showing and vary the fuel for the engine. You will see only a VERY little change in the power output from 11.5:1 all the way to 17:1 You might start to hear some knocking, but the power dosen't change much.

Now adjust the area for an AFR your comfortable with, and go over to the spark tables, and start adjusting the ignition timing, WHILE still watching the power output on the dyno (and sitting at the same 5000 rpm and 10 psi of boost, and being held there by the load on the dyno)
You will see a HUGE swing in the power output as the timing is changed.


Ignition timing has a DIRECT effect on power output.
Adjusting the AFR will alter the timing needed slightly, but adjusting the AFR alone only make a small change in power output.

But don't take my word for it, try yourself the next time your on a dyno. (Again a REAL dyno, not a Dynojet)



John
 
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