Originally Posted by Randy WS6

Here is how I did mine , I use EFI-Live COS-5 , and use their custom operating system for my second stage 200 dry shot for adding fuel and pulling timing, but it will only do one stage, So I needed a second timing pulled for my first stage 300 wet shot direct port . I pull timing @ 14*F ,because the EFI-Live (B5911 Spark IAT) Table only goes down to 14*F. and so I used a resistor that pulled at 16*F . My car is a pro street ,so I'm not planning to drive it in that temp any way. In the attachment I made is how I done mine. I added the wiring schematics for the IAT & ECT for the LS1 F-Body's if any body needs them .

Originally Posted by poor_red_neck

Sorry to post on an old thread.

Unfortunately I don't have access to HP Tuners and can't justify the cost yet.

Will be installing a Nitrous Express 150 wet plate kit with MSD window switch 3K-6K. L76 G8.

I've read of using the IAT trick but to increase temperature to pull 5-6 degrees. This of course has the side effect of leaning out AFR. However since this is only going to be in cicuit when N20 is active, couldn't the fuel jet account for this?

I plan to have a wideband, and will tune by reading the plugs, and monitoring AFR. If budget allows, might consider something like the Innovate PSN-1 to de-activate it if AFR goes too lean.

Am I of "sound mind" thinking that a properly sized fuel Jet (confirmed with plug reading and AFR readings) will compensate for the PCM's leaning out of the fuel mixture when using the IAT trick to spoof increased air temp to pull timing?

This is purely for a street car, might goto the track once a year. Daily driver. Not looking to pickup every .10/sec I can, just alot of fun every now and then with the bottle. FI would be too tempting every day, every stop light.

Originally Posted by Pontisteve

Without the tuning software, and the tune in your car loaded up, you wouldn't be able to see exactly what tables you're hitting by raising the IAT, or what those tables are doing. How would you know how hot you need to trick the IAT into reading, in order to pull x amount of timing? And how much timing is it pulling already at the real temp?

Although you might be able to get around this by viewing a free software download and looking at a tune from the repository, you really need to know what is happening in your specific tune.

Plus, making the IAT hot might make other IAT-related tables kick in, such as perhaps a fuel enrichment table or some other compensation. Who knows what. You would have to look thru the whole tune to see if anything else gets affected.

The mass airflow model will be self-compensating, so spoofing the PCM on the IAT value wouldn't affect it. The speed density model is affected by IAT though, and a higher IAT would lean out the AFR some. You could make up for this by enriching the fuel using the nitrous kit beyond what the kit itself requires.

Given the risky nature of this, and the benefits of custom tuning your car NA, I would consider investing in HP Tuners first, then adding on nitrous once the motor is tuned to the max.

Originally Posted by Pontisteve

The IAT mod works well, but I prefer to see it used in the cold temp range that you'll never be in instead of the hot temp range. It would then add fuel instead of taking away fuel. You could also shut the VE table off and run mostly on the MAF table, which doesn't care about IAT.

One thing to consider here is resistor consistency. Most resistors have a 5% accuracy, but they can be had in 1 or 2% as well. Having tuning software allows you to tailor the resistor to exactly where you want to be in the tune. Otherwise, if you blindly follow internet instructions, you might end up pulling the wrong amount of timing. The HP Tuners suite is worth it for the scantool function alone.

If the price tag seems too steep, consider just paying a professional tuner to do the IAT mod for you. While he's in there, he might as well wake up the engine for you, because it's set to run way too safe from the factory for what we're up to.

Originally Posted by bensrat

2012 Camaro RS LFX motor...same engine u helped tmenees2 in the caddy do last year. I will get some new pics posted for u. Really appreciate the help! Guess I should ask, if my IAT reading is -17 does that have to match my IAT in the chart or I can use any IAT from the chart as long as its not more negative in temp then -17?

These are the same table names (except the numbers are for my car)as the original post on page 1. I will repost mine again after work tonight.

Originally Posted by Carlos Rivera

Hey Bensrat,

I'm doing this mod to my 2013 LFX, what resistors did you use and what temp? I'm in Puerto Rico so no cold weather here, I have everything in place for a 100 shot, I'm using a NOS kit and a NOS window switch, all I need is to retard spark when arming the NOS and off to the dyno.

Thanks!!

Originally Posted by rocket5979

Below is an electrical diagram of how everything will be wired.



The basic gist of how to wire this is so that when the relays are not powered the signal travels from the ECU, through the IATS, and back to the ECU like it would in stock form. Then when the relays are powered by 12 volts they will switch connection with the pins so that the IATS is temporarily taken out of the circuit and instead the resistors are connected for the ECU to “see” and think it is encountering -40*F IAT’s. Normally I am very adamant about not tricking the ECU with false signals, but in this case it is for the purpose of being on the safe side versus some other hack-job trick to gain power at the cost of safety so it will be ok. The IATS does not have a positive and negative pole so you don’t have to worry much about which wire coming from the ECU that you hook up to which Pin 30 on Relay #1 or #2. For those of you who are also skilled in DC wiring I understand that there is more than one way to wire the relay(s) in this box to allot the IATS signal to be bypassed, but this is the way I prefer to do it. So that is what my diagram is geared towards. NOTE: DO NOT USE CRIMPED BUTT CONNECTORS to connect the wires! You will have a total of 6 wires exiting the box that will route to various places on the car. The first two will be the 12v power and ground wires that activate the relays themselves, in the diagram above that would be the single red and single black wire that split off and each route to pins 85 and 86 on the relays. Then the next two wires that exit will be the wires that will connect to your wires coming from the IATS. In the diagram above those would be the wires coming from pin 87a on each of the relays. The last 2 wires that will exit the box will be the ones that attach to your vehicle electrical harness. According to the diagram above these will be the wires coming from pin 30 on each of the relays.


Activating the Box: Now there are a few options of how you can send 12 volts of power to these relays. You can just keep it simple and run an extra power wire to the box from your nitrous master arm switch or you can run 12 volts from the solenoid activation wire in your nitrous controller. The first choice will mean that the ECU will “see” a -40*F IAT at all times that the master arm switch is flipped, while the second choice will mean that the ECU will only “see” a -40*F IAT when the solenoids are being powered (aka spraying). Before some of you start asking, well why trick the ECU into thinking it is seeing -40*F temps when the nitrous is sure to cool down the IAT’s to that cold of a temp in reality? Well the difference is that there will ALWAYS be a delay time between what the actual intake temps have dropped to on the nitrous versus what the IATS is reading. The IATS just aren’t quick enough to react to temperature changes to keep the engine from knocking for the first few seconds of nitrous activation which is what gives this mod purpose. The ECU only checks IAT’s 2 times a second so in theory if you hook the box up to a solenoid trigger wire then there can be a chance of a slight delay between when the noids are powered versus when the computer “sees” the -40*F temp and pulls timing. Just something to think about.

Locating the Box: While you could seal the box with silicone and keep it under the hood I would suggest that it be located inside the cabin somewhere, perhaps under the dash somewhere. You don’t really need access to the box to activate it so it can be tucked up somewhere hidden. Just make sure that if you mount the box away from the IATS that you make good connections with solder and heat shrink tubing on all sensor wire connections so that you don’t inadvertently add more resistance that isn’t accounted for in the IATS Calibration Table.

Extra options/Multiple Timing Retard Settings: One other item worth mentioning is for those of you who may want to retard different amounts of timing with the flip of a rotary switch for whatever reason. You can use this box for that too but you will need to do a few extra things. First off you will need to go to the next coldest cell in the IATS Spark Adder and Multiplier Tables and input whatever spark retard value in them. Then reference the IATS Calibration Table to see what amount of IATS resistance in ohms that ECU expects to see with that temperature so you know how much total resistance your resistor(s) need to add up to or slightly exceed when wired in series. After this you will add in the rotary switch between Pin 87 on Relay #1 and Pin 87 on Relay #2. The wire coming from Pin 87 on Relay #1 will go to the common pole on the rotary switch. Then the first resistor set for the coldest IAT Spark Retard setting will go on Pole #1 of the rotary switch and connect to Pin 87 on Relay #2. The second resistor set for the second coldest IAT Spark Retard setting will connect to rotary switch Pole #2 and connect to Pin 87 on Relay #2 also, and so on and so forth for further Spark Retard settings. Just remember that you are limited on the amount of IATS Spark Adder temperature cells that you can use before getting into cells that you may actually use while daily driving your car in normal weather.






This is the resistance, measured in the thousands of ohms, that the ECU will see when the box is powered thus making it think it is encountering -40*F intake temps.


I hope this mod helps those of you who want an inexpensive and effective way to retard your spark timing while spraying nitrous. There are some other options for how you can set your timing retard without having access to HP Tuners or other tuning platform so if you want to do something like this but don’t have the ability to modify your tune itself, just ask and alternative options can be provided. They aren’t quite as good as directly modifying the IAT Spark Tables, but it is a viable second option. Overall it is a pretty simple setup, especially if you are familiar with DC wiring and have access to HP Tuners, EFILive, or other GM custom tuning platform.