Spinmonster

I have a C6 with an LS2 H/C/4.10's. The car makes 471 through 4.10's N/A and I have a 75 to 100 dry shot depending on the time of year for traction. Please dont jump to an answer to my question based on shot size because once I feel confident the system is reliable, it may go up quite a bit.

I used a version of the IAT resistor mod that adds a SERIES resitor to the IAT and the relay unpowered shunts the resistor out so that when I arm the system, the relay removes the shunt and the series resistance climbs to make the IAT read about 14 degrees. I have the nozzles point away from the MAF so I dont have the chance of MAF damage or a nozzle moving and change the fueling. This way the MAF reads the N2O evenly and the PCM gives my commanded 12.8:1 fuel rather than the typical concentrated shot at the MAF to get an over rich fueling. Upon system activation the series resistor makes the PCM read the lower part of the IAT table where I have 3degrees pulled. As the real temps climb outside and the car really needs to pull timing because its 95+ degrees outside the IAT is still contributing to the overall resistance of the circiut and accesses a row higher and it pulls the additional timing.

My tune is with HPtuners that I did myself and I also used the IAT vs injector flow rate table and commanded that when the IAT accesses the lower temps/columns, it adds 8% fuel to give me 11.8:1 when the system is armed.

What I want to do is change the relay trigger from the arm switch to the firing button and the IAT relay engages only during the spray. What I am concerned about is that when I release the button, the IAT instantly puts fuel and timing back to full N/A but there is still N2O in the intake chamber for a fraction of a second. Does this represent a danger since the car can still be climbing in RPM under full load, and at the last moment the N2O fires from the solenoid at exactly the same time the timing and fuel go back to full N/A levels? My scans show it chages really fast comming up and down on the button.

I know timing tuners have a delay that can be used. Is this the reason for that delay? If it is a danager I can rewire so that the window switch turns off the solenoid but my thumb switch controls the IAT relay. It makes the wiring kind of ugly in there.

Any input? Anyone scan and have an observation on this?

I like this system better than HSW switch in that a failure in the system has it revert to a safe tune. If the bottle runs out (or low) the system is still ok for N/A operation and I dont have to worry if an electronic circiut is functioning. If a timing tricker fails you wont know and if the HSW doesnt work, its a bad situation. My relay for the IAT is also in the solenoid circiut so that if the IAT relay fails and the timing isnt pulled then the solenoid cant fire either.

I like the redundant safety.

I want to thank the guys that did the research on this stuff and contribute. In all honesty I came up with the idea fro my circiut on my own and didnt realize anyone thought of it until I did a search and found this was done in a different form with a fixed resistor. I like mine better because the IAT still functions and higher real temps contribute to a higher level on the IAT table so additional timing comes out on really hot days. I have to credit you guys with being the first though. Got some serious brains out there.

Alt

iTrader: (6)

Why not just pull the timing directly from the spark table? Robert56 has a writeup of this floating around somewhere. Can that be done with the Gen IV PCM? I don't have my HPTuners on this comp so I cannot go in depth at the moment but you would go about logging gm/cyl NA and for the values above that, which you would see on the bottle you retard the timing for. I know I am missing a couple of steps forward and back but that is the main theory behind it. So you can have a great NA tune along with a dry tune w/o having to change anything.

Spinmonster

As I have stated it isnt just timing my IAT series resistor does. It also adjusts fueling. Why would I want to pull timing while not on the bottle? Contrary to popular opinion 3 degrees on my tune was 8rwhp and 12rwtq.

While my finger isnt on the firing button I am running not only better timing, but optimum fuel. Also pointing the nozzles directly at the MAF is much more likely to cause an MAF failure in which case you get a severe lean condition. I wasnt looking fro the easy way out. My system is much safer in that there isnt an electrical ciciut to fail. If my IAT relay doesnt click over to pull the timing of lower the A/F ratio, neither does the nitrous solenoid. If the MAF does fail, the fuel is still calculated in speed density and the commanded air fuel ratio drops because I altered the IAT/ injector flow rate table.

My question still is would I have a lean spkie when I release the firing button if I chose to use the circiut that way and not have it wired to the arming button in which case it is running rich and pulling timing while I am N/A and hunting?

Spinmonster

Although the calculation of the timing table load to see what you run N/A and then adjusting the tables for timing pulled is a great 1/4 mile track idea when you run through each gear to redline and the timing table is hit that way stright through each gear, but in the real world, a roll-on race can and does hit cells you commanded lower timing values. For Ex: when I did 0-130 runs from a stand still to see hwat cells were affected, it hit one path of cells through the table, but then scans show that when you do a sudden roll on in 2nd gear, it hit some of those cells since the start of the pull through that gear started at a much lower rpm had entered 2nd gear on a 1-2 shift and it was 5k rpms. Flooring the car when I am at 3krpms in 2nd gear doesnt hit the same cells. Further, firing N2O in the upper gears when you didnt wind the gear below it such as 3rd gear at 3500rpm (instead of 5k rpms on the 2-3 shift) uses many cells in common with N/A operation.

That theory sounds great when you read it but doesnt compare to doing it on an independant set of IAT conditions. Unlike other fixed resistor IAT mods, mine still adjusts for ambient temperature. If it is 98 degrees out the car needs to pul 2-3 degrees just from the real heat plus the timing needed for the shot. My IAT is removed from the system with a fixed resistor in its place. It still adds to the resistence of the circiut and moves the IAT table cells higher on the botom of the IAT table where I command the 3 fro the shot plus and additional 2 degrees pulled fro the hot day's temps.
Why wouldnt you look into a system that altered the timing and fuel only on the firing button?

Alt

iTrader: (6)

Well you've gone past what information or theory I could provide and enlightened me to some other ideas. I hope that someone else will chime in and be able to assist you with this dilemma. Granted, do you currently have a lean condition now when you let off of the nitrous, you could be chasing a theoretical phantom.

Spinmonster

I was trying to avoid haveing to go to the start line and reduce the shot down to see what happens on a low nitrous level. I can pull timing permanantly in the base tune and see if it goes lean as I let off with a very small shot.

I was hoping there would be someone with some real world experience.

Thanks for contributing anyway.

Spinmonster

Attached is a screen shot of the IAT base timing and IAT vs Injector flow rate tables. Since my IAT is still in the circiut the hotter weather is compensated for with a different timing value in higher levels in the low end of the timing table. The -4 column is primarily hit correstponding to the 86 degree column off the shot. As the ambient temps climb, the IAT table still goes to a higher temp but still in the low end of the table. It never hits those temps where I live but if it were critical you could revise the table for winter temps.

STATIE

I was setting up a very similar system to yours, and I also thought I was an Einstien for being the first to think up the theory behind it untill I found people with similar setups on here.

I too wanted full NA power available when off the gas but wasn't worried about the small period between arming & firing.

I was going to use the IAT spark advance table in HPT as well but was going to completely shunt the IAT sensor out of the circuit and put it into the very high (temps) side of the tables (which you should never see) when the system was armed and pull the timing from there.
My tuner is now tuning it as per "ALT" above as that is an even better system but beyond a hack like me to do.
Your system where the actual IAT temps are still contributing is probably better than my original one as additional timing will still be pulled on a really hot day - but how much this would matter considering thee cooling effects of gas I couldn't tell you.

I can't help you on the real world experience on whether it leans out on an instantaneous shut off but if you were worried about it or it is in fact an issue you could wire in a delay off relay/timer to keep the resistor in the IAT circuit for a second or 2 after the gas switches off if you wanted to.
It just complicates the system somewhat - which was part of the reason for going the IAT/tune way V timing trickers in the first place.
The other problem I see with yours is if the actual IAT temps shift you into the columns in your table where no timing is pulled you are in trouble if on the gas.

Spinmonster

It cant. Even if the IAT broke, the minumum resistance in the circiut would be 10k and thus it would still be in the cells I have timing commong out.

One last thing, on a 75 shot and 11.8:1 I have no Knock retard and thus dont need the timing pulled at all. Its a safety measure people put into the system. If I fire the 75 shot with 12.8:1 I get 1 degree KR. Most people are way too conservative with the timing issues but conservative is good.