dubbleugly01

iTrader: (24)

So I'm running the Aquamist HFS-5 setup with 1000 cc injectors.

The question is, can you have too much nozzle for low injector duty cycles (big *** honkin injectors) so that you get inconsistent a/f's?

The issue I'm running into, anything less than 50% IDC, and my a/f's won't stay consistent. Once I get above 50% IDC though, everything smooths out and is predictable, and I see repeatable a/f's. But below 50% IDC, I vary by as much as a full a/f point (ie between 11.0 and 12. 0 a/f) pull to pull up to 50% IDC before things line out.

I'm running 4 x .4mm nozzles (direct port) plus a 1.0mm nozzle in the intake piping on the Shurflo pump that puts up 120 psi. Is there a limit on nozzle size that will either not create enough backpressure for good atomization, or cause uneven flow patterns or distribution issues and whacky a/f's at low IDC's?

JHowerton@Aquamist

iTrader: (1)

A few questions for you. Are you running a restrictor in the HSV? Did the system work differently in the past or has it worked this way since put together? Just trying to get a picture of the situation to better troubleshoot the issue.

At say 20psi head pressure, you are at 1200cc of injection. This is slightly over 25% to fuel which shouldn't be a big issue but with large injectors running a lower duty cycle, the system might like some sort of a restrictor to balance out the pressure across the HSV at low IDC. Just throwing an idea out, a bit of a shot in the dark without more info.

dubbleugly01

iTrader: (24)

The original setup was two nozzles (1.0mm and a .9mm) with 880 cc injectors, I was not running a restrictor with this setup, and the tune was very consistant with repeatable A/F's. Swapped to a direct port setup (4 x .4mm) plus a .5mm nozzle in the intake piping for a short period and that was easy to tune as well, and was consistant in A/F's.

Swapped to 1000 cc injectors (I was seeing 90% IDC on the 880's), and also upped the nozzle size in the intake piping to 1.0 mm to try and keep about the same meth to fuel ratio that would be necessarily impacted by the larger injectors. This is when the tune started to drift pull to pull below 5000 rpms.

I haven't run any restrictor pill for a couple years, when I switched to two relatively large nozzles, based on a post Richard made some time ago sayng it wasn't needed above a certain nozzle capacity. With a restrictor, you may not see the overflow protection indicative of a leak.

For tuning, I'm using an AEM ECU. The base map is tuned for pump gas only, no meth. When the meth is triggered (boost dependent at 8#'s), the AEM switches to the NOS fuel/timing maps, and that's where the fuel/timing corrections are being done.

Thanks for any help or personal experience anyone can offer.

JHowerton@Aquamist

iTrader: (1)

The restrictor is used to provide linearity across the lower part of the IDC range. It could be the fluid surging through the valve due to the larger jet sizes now and lower IDC . One more question, when it's drifting up and sown in AFR, is it drifting leaner from the target or getting richer based on past setups? You could try putting the .5mm back in to see if it's the systems interaction with the bigger injectors. If it goes away then it's to do with the flow rate now through the system.

dubbleugly01

iTrader: (24)

it seems to go both ways. Target is 11.4 a/f until I get this sorted, and it will range from 10.8 or so up to 12.2, give or take.

What size restrictor would you recommend? Seems any standard restrictor might choke flow at the upper end???? I can drill out one of the existing restrictor pills if I need a bigger orifice. The biggest I have is a .9mm.

JHowerton@Aquamist

iTrader: (1)

A ran some numbers but let me calculate one more item. Do you know how much your IDC has dropped with the bigger injectors at a give load? You said you were seeing 90% before, what is the max now?

dubbleugly01

iTrader: (24)

IDC is around 10-15% less than before at similer loads and rpms. Corresponds well with what one would think going from 880's to 1000's. It is running richer now, at least until I get it dialed in properly. Differrence being now it's about 11.4:1 vs 11.7:1 prior.

JHowerton@Aquamist

iTrader: (1)

I would pull the jets and make sure there are no clogs or issues with the system. It would be a good time to do a spray measurement test and make sure each jet is good.

I think you went a bit oversize with the 1.0mm jet. Your IDC changed 10-15% But you went up 25% or so in spray. I would change the 1.0 to a .7mm and make sure your check valve going to the 1.0mm(or what you change it to) is working correctly.

This jet change, along with doing a check of the whole system should yeild some results. Let us know how it changes.

dubbleugly01

iTrader: (24)

ugh, I was hoping this was going to be a theoritical exercise.

Thanks for the input Jeff.

JHowerton@Aquamist

iTrader: (1)

I could spout a bunch of theory, and some may actually be right, but without bench testing it here, all I can suggest is the above.