Nitrous Wet shot and BE fueling

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Nitrous Wet shot and BE fueling

Unread postby 96pushrod » Tue Mar 12, 2019 8:49 pm

So I'm installing a nitrous plate for my trickflow R intake on my 95 mustang. It currently has a 347 with a built bottom end, it should be able to handle the 125 shot I plan on hitting it with.

Currently the car has 44lb injectors, a 255lph fuel pump, and the stock SN95 fuel rails. I'm fairly certain the fuel system should be able to handle the extra fuel and air requirements of the NOS syetem.

Currently my commanded AFR is 12.58 under high loads, and I'm right in the ballpark at 12.5-12.6.

My question is: when I add the wet shot system, would it be wise to richen up the commanded fueling to around 11.5 or will the nitrous system add the required fuel?

I'll start with a small shot at first and see what wideband readings are. I'm just seeing what the general consensus is.

Any input is appreciated.
96pushrod
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Joined: Tue Mar 12, 2019 8:37 pm
Name: Nick
Vehicle Information: 1995 Mustang T4M0
347 10.8 static CR
11R 205 heads, box r intake, 75mm TB, custom cam, 44lb injectors, pro-m 80 MAF, A5 transmission, 4.10 gears
TFX Plate nitrous system

Re: Nitrous Wet shot and BE fueling

Unread postby decipha » Tue Mar 12, 2019 11:44 pm

hey nick welcome to the forum

To properly tune nitrous the most accurate way requires a really broad understanding of how the ecu functions. If you hadn't already go ahead and read all the write ups on the homepage.

when you spray nitrous your maf sensor voltage reduces significantly and as a result your load drops which gives you a lot more spark and a lot less fuel

thus you cannot run the same n/a tune that you do when you spray nitrous unless you have custom code in the ecu that knows about the nitrous like the nitrous code I wrote for gufx a few years back. I have not written any nitrous code for cbaza at least I hadn't officially released any yet, it is in the works though but won't be complete for a while still.

The safest method when limited to the stock programming is to just fail the maf and use the inferred load table which is also known as the load with failed maf table FN1036A.

If you hadn't already, go dial in fn035 your peak load scaling function. Make sure the PRLDSW scalar is set to 0 so the ecu uses fn035 for perload instead of fn1036a as it does stock (prldsw==2). If your tune doesn't have PRLDSW==0 then you will have to rescale perload in your fuel tables. Scale the perload axis so that you command your 12.6 from 0.90 to 1.00 perload and 11.5 at 1.05 perload on up. After you've done that and have dialed in fn035 and have verified your wot perload is as close to 1.00 as you can get it consistently (but certainly not under 0.95 ). Plug in your actual wot LOAD values in the top row of fn1036a. You'll have to do a wot pull in a high gear to get the bottom portion dialed in at low rpm. Make sure your top row axis of fn1036a is an actual TPREL value you can reach. If it has a stock value of 800 or so you will never be able to reach that. I would recommend setting it to something fairly low like 550 but make sure when you change it your function is chronological so you don't corrupt it. I assume you know this already that all functions x axis have to be chronological and the top most and bottom most values on the x axis can never be changed.

Anywho, now that your top row is your actual n/a load values, take the top row and copy it to the 2nd to top row for spark reference later on. Now take the top row again and multiply it by how much power you plan on picking up. So if your going to spray a 50 shot to start off with and your currently making 340hp. Take 390/340 == 1.15

Go multiply the top row by 1.15

as you can see its not exact science and you will have to adjust it based on what your actually making power wise and what you actually gain based on what your spraying. It would be safer to start off with slightly more and adjust it down leaning it out rather than not enough and being too lean and having to add fuel.

If you aren't aware, FN1036A top row is always in use. The active cells returned value is always divided by the top row for PCT_LOAD. So therefore, FN1036A must be in chronological order thus the top row value can NEVER be lower than any of the lower rows values or it will corrupt the ecu's calculations and probably cause a hard ecu reset every time.

In order for the failed maf table to be used in cbaza there's a few scalars that need to be changed, they are:
0xDCF2 - TPBKFLOW - Backflow TPREL Min - set it to 550 or so
0xDCF6 - NBKFLOW_H - Backflow RPM Max - set it above your max rpm, say 8000 rpm to be safe
0xDCFA - NBKFLOW_L - Backflow RPM Min - set it to the rpm you want to spray at, say 3000 rpm

For a 50,100 or even 125 shot a 12.0 afr is safe. You can start off by shooting for 11.5 until you dial it in though and back it off seeing how it responds. To back it off you simply change the 11.5 you command in your fuel table to 12.0 and you will get it (after you have it dialed in.)

Also, I would recommend you forget about AFR and start using LAMBDA. The sooner you do the more proficient tuner you will become since lambda is the fuel error. It just makes life significantly easier. Just remember
11.7 == 0.80 lambda
12.0 == 0.82 lambda
12.5 == 0.85 lambda
12.8 == 0.875 lambda
14.64 == 1.000 lambda

Doing the above so far will only take care of fuel. Its much safer to use the direct port injectors to supply fuel (dry shot) rather than spraying a wet shot which doesn't give each cylinder the same amount of fuel causing some to run leaner than others. Thus you won't need to hook up your fuel supply to the fuel solenoid. If you have a plug you can plug the fuel nozzle in your plate.

Now for spark, you tune it just as you would otherwise and treat it the same as if you were boosted. Assuming you have your spark table dialed in go toss another 2 columns above your wot n/a loads and command 2 degrees less spark at 15% more LOAD than n/a and 5 degrees less spark at 35% more LOAD than n/a wot LOAD.

Remember that second to top row of FN1036A ? You can use that for referencing your n/a wot LOAD to make it easier to reference and keep track of.

REMEMBER: Perload is for fuel table scaling ONLY. Spark table scaling uses only LOAD not perload.

post back if you do not understand all of this and I can explain it better as its imperative you understand how it all works in order to tune it correctly.
Remember, Perload is for fuel. Load is for spark.
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Re: Nitrous Wet shot and BE fueling

Unread postby 96pushrod » Wed Mar 13, 2019 10:12 am

Thank you Michael, your write ups have been a huge help in this endeavor.

I guess my initial thinking was that I would simply create another dedicated nitrous tune by simply retarding my timing tables for each 50 hp step up.

Am I incorrect in thinking the plate system will add enough fuel via the nozzles to compensate for the extra o2 that will be burned as well? This is one of the reasons I was thinking the wet shot would be ideal for what I’m looking to do.

If this won’t work though, I’m all ears.

I appreciate it.
96pushrod
User
 
Posts: 2
Joined: Tue Mar 12, 2019 8:37 pm
Name: Nick
Vehicle Information: 1995 Mustang T4M0
347 10.8 static CR
11R 205 heads, box r intake, 75mm TB, custom cam, 44lb injectors, pro-m 80 MAF, A5 transmission, 4.10 gears
TFX Plate nitrous system

Re: Nitrous Wet shot and BE fueling

Unread postby decipha » Wed Mar 13, 2019 5:30 pm

you can jet the plate to give you your fuel in a wet shot but its not ideal. since you have 44lb injectors you have adequate fuel for more accurate port injection. Its safer and more accurate no reason not to use it.

but yea you can use the wet shot if you'd like.
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decipha
Tooner
 
Posts: 16199
Joined: Mon Jul 15, 2013 5:29 pm
Location: New Orleans, LA
Name: Michael Ponthieux
Vehicle Information: Supercoupin' x10
90 (4x 5spds) - Dante, Ruby, Daja, Ava
91 4r70w - Skarlett
92 (2x) 5spd & auto - Bianqa, Andrea
93 auto - Danika
94 5spd Rionda
95 auto Aisha
Vehicle 2 Information: Others:
00 Lincoln LS - Luanda
98 Camaro SS - Bounquisha
02 Harley F-150 - Sasasha
03 Marauder - DyShyKy
00 Explorer 5L - Bernyce
07 GMC 2500HD 6L - Veranafer


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