Thanks for the info Scott (winders). I will increase the fuel pressure. Regarding a fuel damper, I am still running the fuel accumulator from the the CIS system - I think the accumulator is intended to smooth out pressure fluctuations?

Thanks for the info Dave (montauk). Yes, the MegaSquirt does have a screen to input the injector dead time. Not knowing any better, I have been using the default value of 1 ms. But I will look into this further and adjust as necessary....

http://forums.pelicanparts.com/uploa...1750511910.jpg

I looked at the last data log I recorded and yes, it looks like I will be running out of pulse width by the time I get to max rpm as the commanded pulse width at is 13.2 ms (1.0 ms dead time + 12.2 ms of fuel) at less than 6000 rpm.

http://forums.pelicanparts.com/uploa...1750511998.jpg

I will be making the fuel pressure adjustment, then make a testing run with auto tune. Then I will schedule another dyno session so Gary (Bains Tuning) can dial in the VE table.

From what I understand, the accumulator dampens pulses from the fuel pump but would not dampen pulses from fuel injectors. Are you using the stock CIS fuel pump? If you are not, I would probably ditch the accumulator and get a damper somewhere near the fuel rails.

Scott,

I'm still running the OE CIS fuel pump, accumulator, and fuel filter set up. My current fuel system (based on the installation diagrams with my kit) is a dead leg configuration. My current FPR has 2 in/out ports plus a return port at the bottom.

I know from reading some of your posts on the subject of fuel system design that you recommend a flow through system as the dead leg system can be prone to vapor lock, etc.

I think once I get the fuel pressure turned up to the 55-60 psi range and see the effect on VE table cell values and injector pulse widths, then I'll start planning the next step with my fuel system set up using a flow through design with the Radium FPRD-RA fuel pressure regulator with dampening.

Dan,

This is the guide/ sheet that I used to calculate injector dead times. Not sure if Megasquirt has the same sort of hardware test page.

https://docs.google.com/spreadsheets/d/1YOHLYERVBvFJWPd9v-q5CJqnmSxO_cNkOPxhmKbs7Vc/edit?gid=692277831#gid=692277831

VE Table Cell Values After Fuel Pressure Adjustment
 

This afternoon I adjusted the fuel pressure with the engine running from 38 psi to 55 psi. Almost immediately. I observed that the AFR at idle dropped from 14:1 to 12.7:1. On the VE table, I had to adjust the cell values in the idle region from 35 to 29 in order to bring the AFR back to my 14:1 target.

http://forums.pelicanparts.com/uploa...1750550820.jpg

Next, I took the car out for a testing run with TunerStudio running "Tune Analyze Live" (auto tune). I drove the car north out of Milpitas on I-680 running in 4 gear and accelerating up to near 5000 rpm whenever traffic would permit until I got to the top of the Sunol grade where I burned the auto tune changes to the ECU, saved the changes to the tune file, shut down my laptop and drove back down the hill and home.

Here is a close up of the VE table difference report: the left table is 55 psi fuel pressure and the right table is 38 psi fuel pressure (blue numbers on the right table are values that decreased, black values did not change as I was mostly running 3000-5000 rpm with 10-30 % TPS load).

The changes to the VE table cell values to achieve the same target AFR after the fuel pressure increase are significant, there are deltas of 10 or more.

http://forums.pelicanparts.com/uploa...1750551390.jpg

Next stop on this journey is to the dyno shop. I have already paid the reservation deposit and am waiting for an appointment date / time.

So in my last post I had turned up the fuel pressure from 38 psi to 55 psi, saw a reduction in AFR and adjusted for it by decreasing the cell values in the VE table.

Today, I went out and turned the fuel pressure up from 55 psi to 60 psi as Scott (winders) had recommended.

Happily, the AFR did NOT change so now I can have the benefit of an improved spray pattern and know that variations in the fuel pressure well above the 43.5 psi max injector flow pressure are not effecting the amount of fuel delivered per injector cycle.

I have a dyno tune session scheduled for next Tuesday and I will report more test results then.

Living and learning....

Dan,

Just a quick heads-up about your injectors—dead times are usually rated at 43.5 PSI, which is the pressure they're designed to operate at. In fact, the Maxxecu data lists 43.5PSI with their dead times. When you run them at 55 PSI, the injectors have to work harder to open, and that can increase latency. It might not seem like much, but it could affect your tune, especially at idle or during transient conditions.

Unless there's a specific reason you're targeting higher pressure, it might be worth asking your tuner about it. If the injectors are designed for 43.5 PSI, sticking with that baseline keeps things predictable—and makes published specs like dead time more accurate. Just something to consider while you're at the tuners.

Dave

Check the injector’s required pressure as too high of a pressure can also cause increased stress and wear on the injectors, seals, etc which can cause premature failure.

Also, if the pressure is too high (above 55-60) or too low (below 30-35) the spray pattern may be compromised.

As always, it’s injector specific as some are rated for high psi (up to 100psi) but most are not.


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Dave (montauk) & Julian (Showdown) thank you for your comments.

When I think back yesterday and I changed the fuel pressure from 55 psi to 60 psi, the AFR DID change. The AFR at idle went up from 14.0:1 to 14.5:1 which had to be from an increase in dead time (latency) / decrease in fuel flow time due to the higher fuel pressure as the ECU commands a PW time that is dead time + fuel flow time.

I think I'll turn down the fuel pressure back to 43.5 psi (the gauge dial is course so probably 45 psi will be as close as possible) and see where the AFR comes in, adjust the VE table to achieve my desired 14.0:1 AFR and use the injector dead time Dave (montauk) found for the 0280155831 injectors and leave it alone.

I'll talk with Gary (the dyno tuner) about it on Tuesday before he runs the car on the dyno.

Sigh...

The Bosch 0280155831 is a Bosch EV6EL style injector that can run on systems pressures as high as 8 bar (116 psi). Running them at 60 psi (just over 4 bar) is not a problem in any way shape or form.

Again, the spray pattern is improved at 60 psi AND this reduces the duty cycle which was said to be at issue.

https://www.bosch-motorsport.com/media/downloads/injection_valve_ev_6_datasheet_51_en_2775912459.pd f

I'm done....

Thank you Scott (winders). I have been flip flopping. Yes, the 0280155831 injector is a Bosch EV6EL. I am staying at 60 psi. Now I'm done.

Scott,
The info sheet you posted lists flow rates at 3 bar. The dead time data I found is at 3 bar. If you run at a higher pressure, how do you set the dead times?
Dave

There are tables out there. I don't have specifics for the Bosch EV6 injectors.

I used Injector Dynamics ID1050x injectors with my MoTec M150 and Injector Dynamics supplied characteristics tables that automatically adjusted for changes in fuel pressure.

Here is some Bosch injector info:

https://www.bosch-motorsport.de/content/downloads/Raceparts/Resources/pdf/Basic%20Information_67843467_Injection_Valve_EV_14 .pdf


http://forums.pelicanparts.com/uploa...1750994397.jpg

For the 0280155831 injector: 31.4 gal/hr @ 3 bar (43.5 psi) becomes - FR2 = (4 bar / 3 bar)^1/2 x 31.4 = 36.2 gal/hr at 4 bar (58 psi), and
FR2 = (37 psi / 43.5 psi)^1/2 x 31.4 = 29.0 gal/hr at 37 psi

Note that with pressures higher than 3 bar, voltage to the injectors must be increased. So you’ll have to do something to drive more (more than 12v?) to the injectors if you raise the pressure above 3 bar…. That makes sense but also seems quite complicated and I don’t know if MegaSquirt has that capability- not sure if any ECU does… dunno.


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It makes sense. Higher pressure requires more work by the solenoid to open. Does running at 4 or 5 bar offer a measurable advantage for naturally aspirated engines?

Plus, you'll still need to create test bed to figure out the dead times if you can't find them published somewhere. One tuner told me that they prefer using the actual ECU to develop dead times not just a voltage range. That seems a bit over the top but I guess with high end stuff, you can't be too accurate.

I'm running with my ECU monitoring fuel pressure. My pressure regulator has the MAP connection to adjust fuel pressure based on manifold pressure but I decided not to connect it. If it turns out that I need it, I'll hook it up. So far, I haven't seen any issues. My logs show fuel pressure at 3 bar with extremely little variation regardless of operating conditions.

Excellent find.

On a speed density (a true volumetric efficiency fuel model) system you have to tell the ecu what the fuel pressure is either by inserting that pressure manually or having a fuel pressure transducer to feed the pressure in real time to the ecu, along with as complete as possible injector characterization, fuel choice chemistry, etc so that it ultimately knows the exact fuel mass being injected into the motor per injector pw.

The VE table in conjunction with environmental data and engine size is to tell the ecu how much air mass is in the combustion chamber.

And the Lambda table ultimately dictates what the end PW will be to meet the target air/fuel mixture.

I say all this in simplistic form as there are plenty of resources that explain in greater detail by people that are blessed with gifts in communication.

If you adjust the fuel pressure without telling the ecu that the operating fuel pressure has changed then it will have a direct effect on lambda (air/fuel mixture) that would require a VE table change to meet target since the ecu has no idea what the actual fuel mass is anymore. If you had a transducer on the fuel rail feeding the pressure in real time into the fuel calculation OR update the fuel pressure value to what guage pressure is then the adjustment in pressure will not have an effect on the air fuel mixture or the value in the VE table as the calibration will change the PW to meet the target lambda in the background.

With that being said, increase in fuel pressure from a semi typical 3 bar relative pressure will have greater atomization generally but that does depend on the injector design as well and when you get to the point of diminishing returns as an increase in pressure will also heat the fuel more, increase amperage at the pump and decrease flow at the pump which is fine if you have enough head room flow wise with your pump choice and you have wiring appropriate for the amperage the pump runs.

I highly recommend a fuel pulse damper on a dead headed rail and still recommend them for a flow through rail. You can tune around the injector pulse width "hammering" in most cases but the VE table will end up ugly as all hell and will not represent the true air mass in the motor at smaller pulse widths.

And another small point with regards to the injectors themselves. A good injector company will provide data that will encompass dead times and flow at various fuel pressures and voltages if that injector was designed for aftermarket use (i.e Injector Dynamics). If the injector was originally spec'd for an OEM manufacture then that injector data is proprietary and will not be shared so you have to either go by data provided by the internet which is highly suspect usually, provided by a vendor, or send them out to be characterized. Also this data changes depending on the hardware of your chosen ECU as not all injector drivers operate the same, this is a big selling point to Injector Dynamics as they provide ECU specific characterization data.

Thanks for posting this. I appreciate it.
Dave