Nitrous timing modifier idea...

[eclipse5302]

Ok, so when you spray you are supposed to pull out a bit of timing. Instead of making a "nitrous only" tune with that timing permanently removed, what about using the "IAT Spark Advance Correction" table? Here is my idea...

I will mention for starters that this car is never driven in temps less than 50 degrees. This is a 1991 Cutlass Supreme with a 2002 L67 3800 SC V6.

So figure out what value resistor is needed to tell the PCM that the incoming air temp is below a certain value, say 0 degrees or less. Then, use the normally closed contacts of a relay to utilize the factory IAT sensor, but then energize the coil to switch to this specific value resistor when on spray. On the IAT Spark Advance Correction table, at 0 degrees and below, remove the necessary timing for nitrous, like -4 degrees.

Is this a silly idea, or would it actually work? Are there any issues with doing something like this; like would this affect any other areas of the tune?

[Perforator]

I think that's the way zzp's happy knob works. It simulates a temperature from the iat sensor and then you modify your iat spark table to add or remove timing based on what temperature you dial up with the happy knob.

[eclipse5302]

Then this should work. I think I will wire it up today and do some scans. I should be able to see what happens (both to timing and fueling) when I hit the button...and if it does work this will be a great way to pull timing for nitrous while running all factory components.

[eclipse5302]

FYI - this worked like a champ. I hit the nitrous, the PCM thinks the IAT is -22, and per the IAT correction table it pulls out whatever timing I tell it to. Really works well!

[TDCRacing]

So basicly when the button is pressed your somehow making the PCM think that the IAT is reading -22 and what ever amount of timing you set it to pull it does.Correct? Explain how you made the ''switch'' so that when you push the button it reacts with the IAT

[eclipse5302]

That's exactly how it works.

Use a standard 12v relay. You cut the IAT signal wire (tan), and connect each end to contacts 30 and 87a on the relay. Make sure the IAT wire going to the PCM is on contact 30. This way when the relay is not energized, the standard IAT signal is intact. Contact 87 gets connected to one end of a resistor, and the other end of the resistor goes to ground. When the relay is energized (like when spraying), the IAT signal is interrupted and switched to the resistor value, which makes the PCM think it's reading -22. I forget what value I used, but I played with a few until I got an improbable IAT degree reading, because I didn't want timing coming out when I didn't want it to (for example you wouldn't want 50 degrees because you could hit that on a cold day, but it will never be -22 for me).

Then, in the IAT correction table, I put all three rows (all the rows surrounding my target temp, inclusive) to -4 degrees for all columns. I'm sure this can be fine tuned a bit, like maybe less retard in the lower columns.

And then I went for a drive. I clicked the relay (without nitrous) and I saw the timing drop -4 every time. Whether 100% TPS or idle, it worked like a champ.

I then did some searching, and to my dismay this idea isn't new. I guess everything has been invented.

[TDCRacing]

Really becaused i havent heard of it before...not for nitrouse anyway...So basicly with use of the relay,when you push the nitrous button your basicly telling the pcm that the IAT is bad when the button is pressed and the whatever amount of timing that yolu set at that temp will be pulled....correct?


Who else has thought of this?

[eclipse5302]

I don't know - I just saw someone mention using the "relay trick" after I got it working and I was looking to see if it was an original idea or not. He could have been talking about something else too though.

Although I could have skipped the resistor and just failed out the IAT, I decided to lock it to a number that fell into the values of the IAT table. Maybe it doesn't make a difference...

[TDCRacing]

Well thats what i ment. how do you hake it fall to a certain number in the IAT table? Seems like you could only make it Fall to the number it fails to...if that makes sense. Or is that what the resistor is for. The guy that was talking about the happy knob from zzp is to adjust timing on the fly. It not an actual nitrous timing retard. You turn the knob and it sets it to that much or that less timing and to change it back you simply turn the knob

[eclipse5302]

I just use a resistor to make it fall to a specific temp, and then I modify the timing for that temp. I could just fail it completely (no resistor) and make all negative temps on the IAT table pull the desired timing, but I felt it would be safer to lock it to a temp that was actually on the table and modify that temp. I hope that makes sense...

[TDCRacing]

Yes perfectly. When the iat fails it goes to 99*F i belive. I was going to ask if you thought it might be safer if you could do it this way.I know it's not likley for the resistor to fail but im sure it's possible. I may talk to you a little later if i decide to go the nitrous route and ask a cupple more questions.

[eclipse5302]

Sure, let me know if you need anything.

[J.Brown]

Yeah his idea works well, i thought up the same thing a few years ago i never actually made the device but i had a guy on LS1tech i asked about it and he too was using the samething. I was making it for our Trans Am but the few degrees of timing i need pulled doesn't matter enough to me so i just run the nitrous tune all the time.

[edgZ06]

I've been using this setup for a few years, and it works well.

The only drawback is that it takes a few millieconds to switch over so it works better without a purge kit.

The purge kit will make the nitrous hit to hard and with the slight timing delay can cause knock on dip in.

I use a resistor value that shows the IATs atabout 180 degrees. Showing -20 you just have to check your fuel tables to make sure you aren't adding extra fuel, unless of course you need it.

[GPGTP]

do you guys remember what resistor you used?

[eclipse5302]

Don't remember exactly - I just grabbed a few higher values and tried them while watching the scanner to get the IAT value I wanted.

[GPGTP]

do you have a pic of how you wired it up?

[IndeedSS]

Basically it's a cost effective version of this http://www.3800performance.com/Merch...roduct_Count=1

In 05 I took a ride in a Impala with alchy injection. The owner used this along with his Aeroforce gauge to turn up the timing until it knocked when using the alchy.

If you use a cheap variable resistor to find the right resistance for the IAT reading you are trying to achieve, it will save you a lot of experimenting and time.

[murphinator]

sounds like the opposite of zzp's race pellet which plugs into the iat harness and tells the iat that it is -30c coupled with their pcm 1.0's which all have +4* timing at that temp

[passingpower]

A 56 kilo ohm resistor wil fake the PCM into thinking the intake is at -22 F (thats green-blue-orange-gold for anyone thats looking through scrap for one). The only difference between this nitro switch and the race pellet is that ZZP cals are set to add 4 deg timing as opposed to pulling 4 deg. Happy knobs just select from several set values to simulate several temperatures. You can get the full temp/resistance table by downloading the online manual for Casper's timing commander. Something I really liked about those instructions is they explained why we'd want to pull lots of timing on the -40 deg 100kohm setting. In case of an open circuit failure (or as the relay is switching from sensor to resistor) timing is pulled instead of added.
eclipse, you covered that by setting -40 deg, -22 deg, and -4 deg to pull 4 deg of timing.