Fuel injectors for Siamese code
Turbo Mini Forums

This is just my attempt at getting some data correlated with respect to Fuel injectors that are of use when tuning with the MS2 sequential Siamese code.

Some of the information, mainly the Siemens injector data is “best guess”, based on the interpretation of the only data sheet I can find.
The other information is either from the “Manufacturers” website or from information supplied via email from the manufacturer.

At this point I only have information for 3 injectors, but getting the information is proving somewhat difficult.



To start, this is just basic information: Injection Window.

This is the maximum injection window available when using the Siamese code.
25% duty represents the absolute maximum injector pulse that can be used before the potential for pulse overlap could occur.
20% represents a safe maximum injection window, allowing extra time for injector pulse additions such as acceleration enrichment or warm up enrichment, etc.



So for example, I have a RPM limit of ~6000RPM (that was just my choice when having the engine built and specifying the cam I wanted to use).
This gives me a maximum Injection window of 5ms at 25% duty or preferable 4ms at 20% duty





So far I have information gathered for 3 injectors:

RC Fuel injection PL4-1000 - (Used by Rod S)
Siemens Deka 875cc/min (FI114992) - (These are the injectors I currently use)
Injector Dynamics 1050x

All the data is based on testing at 43.5PSI fuel pressure and 13.8v.

Flow v Pulse width:







The information provided by the manufacturers was pretty basic, only including the linear flow range, so the lower portion of the graph is not going to be a true representation of the flow characteristics.

For the Siemens Deka data: I have had to use a very small graph from the data sheet to calculate what I think is the correct cc/min flow from their mg/pulse data. I have also added a “best fit” linear flow trace in the graph.









Injector spray pattern:








Injector dead time/ offset/ Latency:













Below table represents estimated offset values for the Siemens fI114992 from above graph, measured in PDF viewer.





Finally, some very basic calculations of maximum support BHP.
This is based on basic injector sizing calculators which can be found all over the internet.

(Injector size (in lbs/hr) x % duty cycle / BSFC) * number of injectors


I have used a BSFC of 0.55 for my calculations

Edit - This is based on using 4 injectors with injector staging active. Obviously, if only using 2 injectors, just halve the BHP.





Included are graph traces for both 25% and 20% duty cycle.

Of note, the Siemens Deka 20% duty line does actually fit in line with real world. During my Last dyno session, we hit 193 BHP at 5444RPM, the logs indicate a duty cycle of 18.1%.


Hopefully I have kept this simple and not made any big cock ups in the information.



Edit 23/9/2020 - Deadtime/ Offset data added after posted discussions on 22/9/2020

Edited by Graham T on 23rd Sep, 2020.

’77 Clubman build thread
http://www.turbominis.co.uk/forums/index.php?p=vt&tid=618189

Siamese 5 port EFI testing
http://www.turbominis.co.uk/forums/index.php?p=vt&tid=611675

Hi Graham,

Thank you for your interesting plots. Some time ago I created an injector sizing calculation in excel based on the Ideal Gas Law Equation, assuming 1 injector per port. I'm attaching it here, perhaps it can be of use to someone.


Edit: I can't seem to upload a .zip file. Any help ?

Edited by Barrieri on 20th Sep, 2020.

Schrödinger's cat - so which one am I ???

Thanks for sharing.

Just one comment: you use the term "opening time". Checking manulas for MS2 and MS3, the terms used in the setup menus are now "dead time" for MS2 or "offset" for MS3. The values required are given in the Siemens Deka datasheets and are lower than you have used.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

’77 Clubman build thread
http://www.turbominis.co.uk/forums/index.php?p=vt&tid=618189

Siamese 5 port EFI testing
http://www.turbominis.co.uk/forums/index.php?p=vt&tid=611675

dont you take one from the other graham ?

so dead time 0.6 s

Medusa + injection = too much torque for the dyno ..https://youtu.be/qg5o0_tJxYM

I think the issue is how you interpret all these quoted phrases, "open time", "close time", "dead time" and a few others.

If "open time" 1.3mS plus "close time" 0.7mS was equal to "dead time" it would be 2.0mS and seriously slow, even for a modern high-z injector.

The reality is that the injectors still flow partially during their open and close windows so open/close times aren't going to show what the total fuel is at low pulse widths.

Plus none of them, low or high z are actually linear at low pulse widths.

So you have to take the manufacturers data with a pinch of salt at low pulse widths.

And just use real world experience from all of them.

Schrödinger's cat - so which one am I ???

The fueling equation used by MS is based on a linear relationship between pulse width and fuel delivered. Pulse width being the time the injector is activated electrically. The linear relationship does not pass through 0, it is offset by a pulse width value that realtes to a theoretical zero flow.

It is not based on opening or closing time but by testing the injectors on a rig. Although it is probably best estimated by subtracting closing from opening times.

Siemans give the "offset" value on the datasheet and that is the best one to use.

MS3 allows input of the low pulse width characteristic given on the datasheet.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

Thanks Robert, Rod and Paul.

First post now edited to add the manufacturers tables graphs for dead time/ offset/ Latency.

’77 Clubman build thread
http://www.turbominis.co.uk/forums/index.php?p=vt&tid=618189

Siamese 5 port EFI testing
http://www.turbominis.co.uk/forums/index.php?p=vt&tid=611675