Compression Ignition Addict
Join Date: Aug 2011
Location: Full-Time Camper in Ca.
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I will be the first to admit, when tuning first came out for the 6.7 I was totally shocked to see the amount of fuel these injectors can deliver.
In fact I had to apologize to Bentley.
Since then here is what I have concluded.
This is all just my opinion but I did use good numbers where possible.
I consider 3200 pulse width a maximum number.
At 4500 rpm and 32 degrees of timing this is injecting fuel about 50/50 before and after top dead center.
In some engines that longer on time has a tendency to heat cycle and crack the pistons at the lip.
The 6.7 pistons are an open bowl design (no lip). In my opinion this piston bowl design works well in a higher pulse width application.
A stock cp4 delivers 180 lph of fuel at 30000 psi.
A stock injector delivers 22 lph of fuel at 1200 pulse and 30000 psi.
At 2200 pulse the injector will deliver 45 lph of fuel.
This is the area the injection amount that in theory will start to drain rail with 2 cp4 pumps.
The duramax lbz cp3 pump will deliver 230 lph at 26000 psi.
A cp3 /cp4 dual setup will deliver some additional fuel.
The fuel should still top out at about 2800- 3000 pulse width.
Consider that lower pressure in the injector will slow the operation of the injector down. That means more of the on time will be used to operate the injector versus deliver fuel.
That being said with the cp3 adding volume to the rail the cp4 should still be able to hold the pressure at 30000.
It would seem it would take dual 55% over cp4 pumps to deliver sufficient fuel to the injectors at a 3200 micro second on time.
The information in this post is by no means absolute facts.
These are just some rough figures I put together so that we could get a discussion moving forward.
Please if anyone has more precise figures add them in.
I started looking at this a while ago when a customers sent in a set of 6.7 injectors to take 45% over. We did them and then flowed them on the test bench. We had to turn the pulse on the test bench down because at standard test specs they maxed out the machine.
It might just be your opinion, but as always, n appreciated one.
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