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Sizing Injectors for high reving motors

 
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whittlebeast



Joined: 04 Sep 2008
Posts: 36

PostPosted: Tue Sep 29, 2015 4:35 pm    Post subject: Sizing Injectors for high reving motors Reply with quote

Here is a calculator I put together for calcing the max allowable Duty Cycle of the injectors. The typical calculator that you find on the net does not account for high reving motors.

http://www.nbs-stl.com/MLVDemo/Injector%20Max%20DC.xls As an example 8000 RPM gives 80% 9000 RPM gives 77.5%

This sheet works by allowing the injector enough time to reset after the fueling event. This is the DC that you feed into a calculator that you use in the RC Engineering calculator.

http://www.rceng.com/technical.aspx

Estimate your crank HP.

Number of injectors is obvious.

Brake specific fuel consumption of .6

Use the max Duty Cycle from the spread sheet above for the Max RPM you plan to run

43.5 PSI Fuel Pressure as this is really the difference between your absolute pressure in the intake compared to the absolute pressure in the fuel rail.

Keep in mind, your tune must be set up for whatever injectors you choose. This is not just a size thing but injector size is the largest part of this setup in the ECU.

If you don't have Excel at home, here is a screen shot of the Sheet

Maximum acceptable duty cycle to allow reliable fueling

Injector Reset Time (ms)
________3__________

________RPM____Max Allowable Duty Cycle
________6000_______85.0%
________6200_______84.5%
________6400_______84.0%
________6600_______83.5%
________6800_______83.0%
________7000_______82.5%
________7200_______82.0%
________7400_______81.5%
________7600_______81.0%
________7800_______80.5%
________8000_______80.0%
________8200_______79.5%
________8400_______79.0%
________8600_______78.5%
________8800_______78.0%
________9000_______77.5%
________9200_______77.0%
________9400_______76.5%
________9600_______76.0%
________9800_______75.5%
_______10000_______75.0%

Andy
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whittlebeast



Joined: 04 Sep 2008
Posts: 36

PostPosted: Fri Oct 02, 2015 3:46 am    Post subject: Reply with quote

Here is what it looks like in MegaLogViewer HD. This motor is right on the edge of running out of injector at WOT.

http://www.nbs-stl.com/MLVDemo/975%20Duty%20Cycle%20Reserve.png

Andy
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riceracing



Joined: 27 Apr 2013
Posts: 288

PostPosted: Wed Dec 30, 2015 3:22 pm    Post subject: Reply with quote

Laughing
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joe90



Joined: 19 Mar 2013
Posts: 382
Location: under the car

PostPosted: Sun Jan 03, 2016 4:42 pm    Post subject: Reply with quote

If an injector requires 3msec to close, it's not a very good injector.
In reality you can run much greater IDCs
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whittlebeast



Joined: 04 Sep 2008
Posts: 36

PostPosted: Sun Jan 03, 2016 4:56 pm    Post subject: Reply with quote

Remember that the injector has to fully discharge (field fully collapsed) to get it's normal dead time.

We can debate what the "real" time is but it is not 0. The standard time appears to be 3 ms.

Andy
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joe90



Joined: 19 Mar 2013
Posts: 382
Location: under the car

PostPosted: Sun Jan 03, 2016 9:02 pm    Post subject: Reply with quote

whittlebeast wrote:
Remember that the injector has to fully discharge (field fully collapsed) to get it's normal dead time.



No, it doesn't.
The current falls to a point where there's no longer enough to keep it open.
It's often about half the current required to make it open in the first place.


Injector dead time is actually the difference between the opening delay and the closing delay.
1 msec should be plenty.
It also depends on the circuit that's used to drive them so a motec will be different from other ECUs.


When people upgrade injectors , they always end up with wrong dead times......that's why.
Because they use dead times off the net which were measured on a motec when they're not using a motec.



If you really want to go through the whole exercise properly, you'll measure the current it takes to open the injector.
You'll then measure the current it has to drop to before it closes.
The current is dependent on voltage, resistance and inductance as well as circuitry, when closing the injector the "clamp voltage" is very important.
You can make an injector slow to release just by putting a diode across it..........which of course is what you don't want.
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whittlebeast



Joined: 04 Sep 2008
Posts: 36

PostPosted: Mon Jan 04, 2016 6:44 pm    Post subject: Reply with quote

Think thru what happens at say 16000 RPM and 85% Duty Cycle.
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fire



Joined: 26 Oct 2009
Posts: 103

PostPosted: Tue Jan 05, 2016 4:22 am    Post subject: Reply with quote

whittlebeast wrote:
Remember that the injector has to fully discharge (field fully collapsed) to get it's normal dead time.

We can debate what the "real" time is but it is not 0. The standard time appears to be 3 ms.

Andy


Research flyback circuits. On good flyback closing time of injector is less than 0.5ms
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Pantera EFI



Joined: 12 Feb 2005
Posts: 1718
Location: So. California

PostPosted: Sat Feb 13, 2016 7:43 am    Post subject: Injector Control : Flyback Current Reply with quote

Most modern drivers have a "built in" diode to protect the device.
Many ECU's designed in the 1980-1990's used a CS-452/3 Cherry Driver with NO "clamp diode".
My ECU882 uses a IRL Mosfet (130mj clamp@56 volts) AND another external flyback diode@39 volts to "speed" field reduction.

One should check with the EMS manufacturer to find the fuel injector clamp diode, if any, voltage and mj current capacity.

Thus ANY ECU/FIC could benefit with a "matched" flyback Zener installed in the wiring harness.
That clamp voltage is injector specific to frequency/energy/supply voltage.

My most modern ECU "drives" the injector "both" ways, positive to ground.

The above methods will reduce "dead time"

Lance
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Lost in Data



Joined: 28 Apr 2016
Posts: 5

PostPosted: Thu May 12, 2016 5:11 am    Post subject: Mountains and molehills... Reply with quote

What may be considered stratospheric engine speeds for one application is mundane in others - stroke length, piston speeds, and all that. Look no further than your average performance street motorcycle.

I don't think anyone here would consider the average ECU in a motorcycle either advanced in design, or cutting edge in the components used. And the injectors tend to be similar to, or the same as, those found in economy cars. And these Nikasil plated aluminum bores are all about light weight, not particularly great cylinder sealing, great specific torque output, or amazingly low brake specifics.

I would suggest looking at what is commonly done with a ten year old Suzuki GSXR 1000 at 13000 rpm or a Hayabusa turning only 12000 rpm to develop peak power with an ECU that is not much more advanced than a pocket calculator - using common Keihin injectors.

A late model Yamaha R6 turning over 18,000 rpm on the local road track does not require anything special for injector or ECU/drivers, nor is it limited in duty cycle to the point the OP would suggest.

And to throw a wrench into the conversation, these engines are not wild idling, narrow operating range race engines.

Just something to consider.
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whittlebeast



Joined: 04 Sep 2008
Posts: 36

PostPosted: Thu May 12, 2016 5:19 am    Post subject: Reply with quote

My FZ1 Yamaha runs at about 65% DC at WOT. What are the latest 600 running?
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Lost in Data



Joined: 28 Apr 2016
Posts: 5

PostPosted: Thu May 12, 2016 6:05 am    Post subject: Reply with quote

A stock 2015 R1 makes peak power at 12,300 rpm. Less than 4100 FPS average piston speeds.

A 2015 AMA superstock (Yamaha/YEC race kit only parts) R1 runs 79 to 80% DC at 15,000 rpm. That is still less than 5000 fps average piston speed. This changes with how much you bias flow to upper or lower injectors.

The R6 in similar trim tends to prefer that the upper injector runs at near maximum DC - 85-86% from peak torque to peak power rpm. The problem is that this has to be adjusted with air density to prevent issues with maxing out the DC limit in the software. There is a big difference between racing in Feb at 35-40 degrees F and July/August at 110-122 degrees F track temps.
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