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GTR Injector tuning(as seen in the turbo thread)


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#1 John1

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Posted 25 December 2009 - 12:50 PM

I put this in another thread, but I thought it may get lost. This may help out some people.

As far as tuning is concerned, there is a direct relationship between injector size, load and how the trans works. When a tuner puts larger injectors in the car, it changes two VERY IMPORTANT values, Theoretical Pulse Width and Base Fuel Schedule. The tuner must have an understanding on how to tune for larger injectors so the car can respond correctly. I am sure there a re A LOT of people out there with upgraded injectors that the trans is really bad in AUTO mode. This is due to an improperly scaled injector/load.

To scale injectors correctly, and subsequently, keep the trans running correctly, he must do the following.

1. Set the Target AFR table to the appropriate values...11.1..11.2...10.9 what ever you want the AFR to target.

2. The tuner must first adjust the FUEL MULTIPLIER(lower the number for a leaner response)...800cc approx -15 -20%

3. The tuner must then watch the AF Trims to see where the AFR Learning values are. We want a lean...115%. At idle and about 95-105% under cruise and under load the fuel curve is close to the BASE FUEL TABLE values. No need to go crazy with boost, just see that it does not drop below the desired target AFR.

4. If you upgraded to a larger MAF, I have seen about a 5%increase through the entire MAF curve is a good start. Keep in mind there is a MAX value at 4.91 Volts that you can not exceed 255...it is a physical limit of the ECU. Keep in mind the stock MAF curves vary for each bank. You may find keeping them a little closer to one another keeps the variation in each bank(AFR) closer...you will have to find out what the intakes/intercooler set up work best with.

5. Start the car and open the FUEL VE Table. In the beginning you will want to use the Trace feature to get a sense of where you are. You will use this table to smooth out the AFR Learning and the Fuel Curve. Cruise is in the 30 -60's, idle 16- 24s', and WOT is in the upper few columns172+. try not to do a Cell by Cell smoothing, rather keep the table rather smooth, 'V' and 'H' are your friends...LOL

6. Do a few VERY light load/boost pulls...no need to go to redline here. See what your AFR and Load-Theor Pulsewidth are doing. If your injectors are bigger than 750cc, your Theo PW will be off.

7. If the AF Learning and the THEO PW are too far off, look out trans and P0700! smile.gif This is where the last step comes in. manipulate the BASE FUEL SCHEDULE value to gain proper resolution in the tables. Reducing the value too far will put you in a worse situation(you would only raise it for smaller injectors than stock). Start with a 10% reduction for 750cc, 15% for 850cc or bigger. See what works best for the car.
Rinse and repeat. ;)

This is how to Properly scale injectors and load. Do not manipulate the Target AFR table to make large changes in the AFR curve. This will take time, but it will work. If you are having trouble, let me know and I will do what I can to help out.

I have been meaning to put this info up. I shared some of this with a few tuners, but I think there is enough people modding their injectors and the customers need to have their cars running properly. smile.gif

NOTE: If the GTR has upgraded Injectors, and they are installed right, the car may exhibit a misfire and clunking of the driveshaft. Some may think it is a Trans problem, it is NOT. Some injectors out there are not with in the acceptable OHM range and the ECU goes into a misfire state. The Driveshaft clunk is the tell tale sign. You can also emulate this condition by unplugging one injector to see what noise you are looking for.

I hope this helps a bit. We will keep the numbers coming. Thanks guys, and keep a look out for out new intake kits.

John

#2 thistle

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Posted 25 December 2009 - 02:41 PM

I've disassembled the airflow and fuel calculations in the ECU, so have a few refinements/suggestions to add to the mix.

Now the latest beta (1.8.1.0-12147 from Dec 15) has the injector latency offset and scalar the right way around, how about increasing the latency offset to reduce the trims at idle?

Target AFR is also corrected in the latest beta, what previously displayed in the fuel map as 0.75 lambda is really 0.80.

Since the fuel multiplier and the lookup from the MAF table are mulitplied you can use a higher fuel multiplier to mitigate the max of 255 in the MAF table.

The latest beta also removes the previous incorrect injector scalars and adds a new beta injector scaling value which should allow a change of injectors with just an adjustment to this value and correction of the latency, without upsetting a load of other scalings. However, it does mean that if you then go for higher boost levels you'll saturate theoretical pulse width even more, but there is room in the base fuel schedule modifer to fix that independently.

Based on the physics models in the ECU, ideally:

Fuel multiplier, MAF calibration tables and VE table are for scaling MAF sensor tubes/different sensors
New beta injector scaling and corrected latencies are for scaling injectors
Base fuel schedule modifier is for keeping theoretical pulse width to a sensible range

But various compromises have been used to keep trims, TCM etc happy until new variables have been found. And because theoretical pulse width saturates so easily along with base fuel schedule modifier only being able to be increase by about 50% before it saturates, I'm not totally opposed to some adjustment to fuel multiplier as long as all the knock on effects are considered.

Investigation is ongoing re the torque signal to the TCM, the beta has a calculated load table that is analagous to a 350Z table that controlled the autobox lockup, but it doesn't seem to have that effect on the GTR. The aim would be nice to have an independent method of scaling this to sort clutch behaviour and avoid overtorque faults/refusing to shift, whilst being able to scale airflow meters and injectors according to the physics model in the ECU.

I'm nearly done on the ignition setup, but the relevant thing to add to this discussion is that the theoretical pulse width you end up with not only affects the combustion time lookup from the ignition table, but also influences through many other tables the ignition angle you end up with for a given combustion time. What can be said for now is that moving the combustion table by 1 either way moves the final ignition timing by the same amount all other things being equal except for gearchanges and very low throttle conditions.

#3 Martin Donnon

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Posted 25 December 2009 - 03:57 PM

Fantastic Thistle! :banghead:

#4 jm-imports

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Posted 25 December 2009 - 05:35 PM

NOTE: If the GTR has upgraded Injectors, and they are installed right, the car may exhibit a misfire and clunking of the driveshaft. Some may think it is a Trans problem, it is NOT. Some injectors out there are not with in the acceptable OHM range and the ECU goes into a misfire state. The Driveshaft clunk is the tell tale sign. You can also emulate this condition by unplugging one injector to see what noise you are looking for.

I hope this helps a bit. We will keep the numbers coming. Thanks guys, and keep a look out for out new intake kits.

John

which injectors i have the 950cc deutworks not fitted yet
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JUN R-1 = 4.0 STROKER - ETS HTA3586 = 1500BHP 8.3 qm 60ft 1,28.


#5 Mick

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Posted 25 December 2009 - 07:42 PM

which injectors i have the 950cc deutworks not fitted yet


Same here, got the 950's and yet to install.
Deutchworks know their stuff so i would not worry too much as other guys use their smaller GT-R injectors from them without any problem.

#6 John1

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Posted 25 December 2009 - 11:34 PM

In regard to the follow up, I do not have access to the beta test versions, so I can only tune with the tools as I have them provided to me. If you can get me the same software, I would be happy to validate/contribute to your addendum Thistle.

We only use DW Injectors on the GTR.

John

#7 speedracer

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Posted 26 December 2009 - 01:23 AM

How does the bigger injectors effect the over all drivability and fuel economy?

#8 thistle

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Posted 26 December 2009 - 04:09 AM

John you have an email. I don't want to post the link on here (or in fact far more detailed info that I could have done before and would love to discuss publically) as it will get into the wrong hands these days :(

#9 Mick

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Posted 26 December 2009 - 05:05 AM

John you have an email. I don't want to post the link on here (or in fact far more detailed info that I could have done before and would love to discuss publically) as it will get into the wrong hands these days :(


Russians?

#10 BoostCrzy

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Posted 26 December 2009 - 10:19 AM

great work guys....I hope to have some more scenarios to contribute testing on very soon.....thank you !!!....

-Jack
- Jack Cecil -

#11 John1

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Posted 26 December 2009 - 12:20 PM

John you have an email. I don't want to post the link on here (or in fact far more detailed info that I could have done before and would love to discuss publically) as it will get into the wrong hands these days :(


Thx. I will get on it asap.

#12 Harrison

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Posted 26 December 2009 - 01:17 PM

You guys are awesome! Thanks Akuma and Thistle.
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