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Thread: Timing retard for nitrous. What do you do?

  1. #1

    Timing retard for nitrous. What do you do?

    So I have did a lot of reading on this topic, and I've tried all the methods I've heard of. Once and for all I'd like to hear some real results from other tuners who have had success with their methods as well as the negative side (if any) for each method.

    The first method I would say is the IAT timing trick. Its a simple concept and seems to work....but I hear that it will effect fueling on SD tunes. My question is this: If you wire the relay to trigger only while the solenoids are powered what difference would this make? Wouldn't the change that it may make to the NA tune just get soaked up with tuning via the fuel jet or fuel pressure if using a standalone? Are people saying that the change from a day when the iat was truely something like 40 degrees compared to 100 degrees create a drastic difference in the final afr? How much would the afr really change?

    Second is the TCS timing tables. Send ground to the appropriate pin of the pcm and you have a tuneable timing retard table....or do you? I just tried this on a 2000 SS Camaro and the timing retard doesn't remain on for the entire duration of the run. The retard goes away even though we confirmed that the ground was still present for the entire run. Its my understanding that certain vehicles/os may have a time maximum for this, but the 2000 camaro does not to my knowledge.

    Third, is the 2 bar os method. Wire a relay to slam 5 volts to the map sensor when activated. This I have read will allow you to tune the fuel via the ve table in the bottom row. Also, I have read it will register more airflow so that the timing will dip farther down into the table allowing for timing to be pulled out right on the main table. I tried this for the first time today. For a dry system, I'm sure it would work as advertised, but I'm tuning wet. I did get it to work properly and logged 210 kpa while the relay was active. While making test pulls with the nitrous bottle closed and the standalone un-plugged I quickly realized I needed to cut the values in the VE for the 210 row in half. Once I did this the afr was really close to where it was making a normal NA pull up in the 95 and 100 kpa rows.

    With the afr correct, the g/cyl was pretty much the same in the 210 kpa row as it was in the 95 row. Therefore, simply changing to the 2 bar didn't seem to give me the ability to alter timing for the nitrous at all. I went ahead and pulled a safe amount of timing in the main table and proceeded to spray the car. Again, no real change to the g/cyl of airflow. There was a pretty nasty lean spike at the hit, so I raised the figures in the 210 kpa row and appropriate rpm range and all the sudden the g/cyl jumped up a fair amount.

    Now I'm sure for a dry kit having these numbers jacked up a good bit more than 50% of what the values are in the 95/100 kpa rows would allow you to tune for timing retard....but in my case, the car was overly rich after that initial lean spike, and I don't really want to lower the fuel supply via the fuel jets or pressure as they are supplying race fuel while I have 93 pump gas in the primary tank.

    Sooo, is there something I'm missing or am I left to fine tune the fuel with this method and then doing the iat resistor mod anyway to get a control over the timing? The car has a 300 shot on it, so its not like we can just pull the timing in the main table for all conditions and live with the hp loss.
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  2. #2
    The lean bump in the dyno graph doesn't really show up like that on the log using an autometer wideband in the car. It did have a lean spike on the am wideband on the inital hit at 3500 rpms, and then both widebands pretty much match from 5200 rpms on out. The lean area where the throttle is first hit on both runs graphed is just due to the wideband being installed at the end of the tailpipe...it doesn't show up like that on the log.

    I'm about ready to just throw the wideband out the window when doing nitrous tuning....
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  3. #3
    I posted a graph not long ago from another car with a much smaller shot that had a very similar afr graph when spraying. Many opinions were discussed, but nothing we did could really smooth out the afr until I tuned it dry. With this car, it can't be the iat trick playing with fueling...and this car is pure SD tuned with a flat out perfect afr when the spray isn't flowing.

  4. #4
    Senior Tuner Ben Charles's Avatar
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    Tick I happen to like the IAT relay mod, but instead of putting it at a higher IAT activation (leans in out in SD) put it on the lower IAT (-40 or whatever the low point is for the OS). This way when tuning in SD and fueling is right on during N/A pulls the fueling will just be richer when you hit the switch to lower the IAT. To compensate here you can just play with the IAT multiplier(some OS don't have this) by taking fuel out or with the WET KIT fuel pill.

    IF you do a dry shot Id use the PE IAT multiplier to add fuel (wouldn't bother with the MAF) and you can even use the AFR spark Advance table to adjust timing here based off your Commanded AFR. For example a 150 Dry shot you may command 1.35 AFR to add extra fuel for nitrous and either use the IAT table for your relay or the AFR spark advance table to pull timing.

    The TCS method works, but since that is a early OS the timing is hidden, maybe Chris can add it in there, I'm sure its there in the program.

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  5. #5
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    Quote Originally Posted by Tick View Post
    The lean bump in the dyno graph doesn't really show up like that on the log using an autometer wideband in the car. It did have a lean spike on the am wideband on the inital hit at 3500 rpms, and then both widebands pretty much match from 5200 rpms on out. The lean area where the throttle is first hit on both runs graphed is just due to the wideband being installed at the end of the tailpipe...it doesn't show up like that on the log.

    I'm about ready to just throw the wideband out the window when doing nitrous tuning....
    I am just going out on a limb here just because i only reference a wideband and tune nitrous setup's by reading a plug but, i do alot of OLSD Tunes as well as my own car being a 400" Mast intake & headed nitrous motor on a similar sized kit but a fogger.. I would start and take a look at your VE.. Not a bash by any means, The 100 kpa row in the VE at 3,600 rpm is 94 then 4,000 rpm is 93.. Then when the kit comes on it jumps to 155 kpa @ 4,000 rpm and your fueling is only 91 and it goes lean.. Go ahead and match up the the number's (from 100kpa to 155kpa) and smooth the VE out it should clean all that up.. Hard transition's in fueling will do exactly what the log is showing.
    I haven't made a million post's so im not a super tooner

  6. #6
    Quote Originally Posted by n20kid View Post
    I am just going out on a limb here just because i only reference a wideband and tune nitrous setup's by reading a plug but, i do alot of OLSD Tunes as well as my own car being a 400" Mast intake & headed nitrous motor on a similar sized kit but a fogger.. I would start and take a look at your VE.. Not a bash by any means, The 100 kpa row in the VE at 3,600 rpm is 94 then 4,000 rpm is 93.. Then when the kit comes on it jumps to 155 kpa @ 4,000 rpm and your fueling is only 91 and it goes lean.. Go ahead and match up the the number's (from 100kpa to 155kpa) and smooth the VE out it should clean all that up.. Hard transition's in fueling will do exactly what the log is showing.
    Thanks for the advice. Something you brought up leads me to another question however. When the nitrous comes on it doesn't jump to 155 kpa on the main table or chart display....it jumps to 209.6kpa. For some reason however it is logging the kpa in the histogram as 155. I think because it was set up to log map kpa and the main chart had map 2 bar and map being logged. Perhaps it was taking the average of the two somehow?

    Either way, I'm sure its using the 210 row of the ve....and I started out with it being half of what was in the 100 row to even be close. Since then, I added a lot to the values where it hits the nitrous (for the lean spike on the log) and that is what caused the g/cyl to jump up and look all screwed up in the log. If I run it without the nitrous and standalone flowing it will transition to the 210kpa row pretty seamlessly and maintain a nice afr through the pull (before I jacked the numbers up to compensate for the lean spike).

    When I first tried to test the system with values in the 210 row the same as the 100 row the car literally misfired at 3500 rpms (where the 5 volts is applied to the map) and the g/cyl showed 1.9x lol! Cutting the 210 row in half allowed the car to make a seamless pull. Doubling the map kpa from what it really was required me to cut the values in the ve in that map row in half....