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Max Karman Frequency to send to computer?

2K views 17 replies 7 participants last post by  2Nol 
#1 ·
Just wondering if anyone knows around what Karman frequency will cause fuel cut? at full load. I have seen 2256 sent to the computer so far at 6988 RPM. I would rather know i have a few hundred Hz to go as a safe gaurd. fuel cut at 15PSI singing at 7K rpm's would be bad.

I KNOW the numbers are set in stone and are related to other engine aspects. what have you seen on your logs. what numbers have you seen send you into fuel cut.

is there a magic threshold.. a "getting close" number to avoid.

What is the highest you have logged?
Full load. full temp. Ambient air and no knock?
 
#2 ·
look in the emange ultimate thread, there is a post about where to put the maf ceiling per rpm.

I've hit fuel cut at high boost and rpm plenty of times and never hurt anything. The engine doesn't go lean when this happens, combustion stops completely. The factory would've have designed it this way if it would hurt the motor. It is designed to save the engine from leaning out.
 
#4 ·
i guess im use to my old turbo dodges form the 80's fuel cut under boost = cracked piston lands.

anyone wanna chime in with Hz levels they have seen? just would like to know if im close. or at least be able to tune my FP up and down to give my self 200Hz or so leaveway.
 
#6 ·
Sorry for digging out an old thread. I just logged my MAF signal with e-manage blue and it gave me a readout of ~2200Hz@5500rpm@12psi. I couldn't go higher as I've run out of a road :p.
I've been recently experiencing random fuel-cuts and I'm suspecting some leaks in the intake. Is it possible that a leak is responsible for such high karman values? I assume, that the leak is somewhere between turbos and the throttle (turbos are pumping the best they can - this is why the MAF reads so high - but it goes out into the atmosphere).

Am I thinking right?
 
#8 ·
You`re on the brink at 2200hz!. Plus it alters with RPM, the lower the RPM the lower the threshold (I`ve hit it at 3000 rpm while tuning my output map..).

I have my Karman Hz output table set to 2000hz peak at 7000rpm.
 
#9 ·
Stock Fuel Cut table: (99 ROM)
<table>
<td>
RPM:
500
1000
1500
2000
2500
3000
3500
4000
4500
5000
5500
6000
</td>
<td>
LOAD:
162.5
162.5
167.5
172.5
192.5
210
205
202.5
197.5
197.5
197.5
197.5
</td>
</table>

Greg will have to chime in with what the load relates to HZ readings, I don't want to tell you guys incorrect info.
 
#10 ·
Yeah, that's what i suspected. I will have my intake disassembled and reassembled on friday night.
And yes, it runs rich as hell. AFR never comes over 12 while idling (which is shitty also btw) It is so rich I need to open my windows while in traffic. Fuel fumes are nice, but only on a gas station. They give me headache while I'm driving.

Thanks Forrest for the table.
 
#11 ·
I have been breaking 2300Hz on my SAFC now. 450's and maxed out 9b's.
no fuel cut since i installed 450's but i was hitting fuel cut on 9b's with stock injectors and about 15PSI.
 
#14 ·
That's because psi is nothing even closely resembling airflow. The ECU bases everything (even fuel cut) off airflow. Yes more boost usually means more airflow but never does X psi always mean the same airflow. Air volume is always changing depending on your driving and atmospheric conditions.
 
#13 · (Edited)
Well... Fuel cut is based on engine load not raw HZ readings from the MAF. Load quite simply is just Air_Count * MAF_Size / 65536. This is uncompensated Load (meaning Air Temp and Baro haven't been applied yet).

When you're running a piggy back you're changing the HZ the ECU sees. So your input values into the piggy back can be any number, but its the output HZ the ECU sees which the ECU uses to base its engine load compensation.

Btw, you'll see peak load numbers down in the 3k-4krpm range typically depending on your turbo setup.
 
#15 · (Edited)
Yeah I know that. But I think that those japaneese engineers back in early 90' tuned the ECU so it can run in every conditions car can encounter. I mean that stock boost, on stock boost solenoid should work flawlessly. For me, it doesn't. And it happens always when it hits about 2200 - 2300Hz on the AFM.

I've made a home-made pressure tester out of some PVC piping, old bicycle valve stem and a condom. And it seems like the problem is somewhere on the passenger side. I dont't know yet. Maybe its the intercooler, maybe the piping. I'll figure it out on friday :)
 
#16 ·
Yeah I know that. But I think that those japaneese engineers back in early 90' tuned the ECU so it can run in every conditions car can encounter. I mean that stock boost, on stock boost solenoid should work flawlessly. For me, it doesn't. And it happens always when it hits about 2200 - 2300Hz on the AFM.
I really don't think you do. See, the stock boost solenoid doesn't know or care about boost. It regulates the turbos based on airflow. My 100% stock car will boost 14psi when its 90 degrees outside and it'll boost 10psi when its cold. I can boost as high as 16 psi before hitting fuel cut in the summer time.

Is your car stock?
 
#17 ·
I'm honestly wondering if the problem you're running into is even fuel cut at all, or just spark blow out.

Not sure what you're using for a logger but if you can, log engine load and see if your numbers get anywhere close to the table Forest Gump posted.
 
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