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Staged Injection How-To

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 Post subject: Staged Injection How-To
PostPosted: Mon May 27, 2013 7:30 pm 
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Location: Tempe, AZ
I spent the weekend tuning a staged injection car, and realized it required some thinking. I found one really good post from Nate on there that gave the keys, so I thought I'd repost my findings to help those in the future.

So, Ben is running some 440cc injectors and a bank of 1600cc injectors on top of that. Running E85, approx. 3bar fuel pressure. Opening time on the 440ccs was about 1.8ms, opening time on the 1600ccs was about 1.2ms based on trying to get it to idle on just those. We did some pulls with the 440s, and they were tapped out at 5700rpm running 15psi and about 20ms pulsewidth.

I decided to set the clamp for the small injectors to 10ms. I may raise this up a bit, but it works for now. I basically didn't want it to possibly transition from the big to small injectors at high rpm on wastegate pressure to simplify tuning. Setting that was easy, just go to Injection Parameters tab and set the PW Clamp on the channels running your small injectors to 10.

On the three channels running the big injectors (they are kind of batched), I set the main gain to .275 to start with (440/1600). This normalizes the flow/pulsewidth throughout the map--IE, 1ms of fuel on the 440s injects the same amount of fuel as .275ms on the big injectors (assuming both injectors are flowing in their normal range).

The Idle Adjust field is the major player in staged injection. This required some fine tuning due to the opening time of the large injectors. The Idle Adjust is an absolute pulsewidth, meaning the channel is offset by that amount absolutely based on the calculated pulsewidth from the fuel map and main scaler. The pulsewidth that channel runs at is affected by the Main Gain though, which is under the influence of the physical characteristics of the injector. In an ideal world, if your small injectors were clamped at 10ms, you would set the Idle Adjust to -10, as it would start to run the channel the big injectors are on once calculated pulsewidth exceeds 10ms. However, the injectors need 1.2ms to open and start flowing fuel. To make sure they get that physical, actual opening time, you have to factor the Main Gain in to the equation. 1.2ms*(1600/440)=3.6ms of 'calculated' opening time for the big injectors. I added that to the Idle Adjust, meaning I entered a value of -5.4, and I was immediately really really close. I think I finally settled on -5.8 or so and a gain of .285, but there is a perfectly seamless transition when the big injectors come in with that...as the small ones hit the 10ms clamp, the big ones hit about 1.25ms just as they start to flow predictably and the air:fuel stays perfectly steady with no major humps/bumps in the Basic Map. Cool!

There were a couple of other issues I found. I set the three channels up as their own events in the Phase Table. One channel fired at 0deg, one at 240deg, and one at 480deg. This caused a misfire on cylinder 1 even with the big injectors disabled. Figuring the software didn't like having two phases on the same angle, I set them to 5, 245, and 485. This fixed the misfire, but caused very weird tach behavior--it was like the tach was drunk. It read accurately, but was very wobbly. None of these new phases had the 'Drv. Tach' box checked. I finally moved the secondary injector channels to be paired up with existing injection/ignition events, and everything started working normally. It was kind of odd.

All in all, with all of the fancy modern 1600cc and 2000cc injectors out now, the staged injection is probably unnecessary. At the 300kpa we were running, he's hitting about 50% duty cycle on the big injectors. But I learned a lot about the 034 fuelling model and it does work very well at its intended purpose--providing shitloads of fuel at full throttle while giving great idle/low load characteristics.

Sam

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 Post subject: Re: Staged Injection How-To
PostPosted: Tue May 28, 2013 8:14 am 
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Joined: Mon Jun 13, 2005 1:17 pm
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Location: Farmington Hills, MI
Very cool post.

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 Post subject: Re: Staged Injection How-To
PostPosted: Thu May 30, 2013 12:03 pm 
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Joined: Tue Mar 12, 2013 6:38 am
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Location: Ashland NH
hmm, some good feedback in here.

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