Relay to retard timing for nitrous??

[SilverBullet6.0]

So, i work at a gm dealership and i hear all kinds of crap from customers who think they know it all. But occasionally, i get a guy that knows his stuff. But today i was intriguied by a statement by a customer, but i was busy and didnt question him on what he was saying. He had an 11 silverado 6.2 which had been tuned by a local tuner with hpt and was spraying a 150 wet shot. He seemed to know quite alot about the tuning process. But he made the statement that had "a relay wired up that was turned on by his nos arming switch which retarded 8* of timing, and when the nitrous was off, he basically had an optimum n/a tune." Is this even possible? I didnt think the gas burner computers had the ability to "switch tunes". Just your basic high and low octane tables dictated by the knock sensors/determined octane of the fuel.

[bartender_77]

So, i work at a gm dealership and i hear all kinds of crap from customers who think they know it all. But occasionally, i get a guy that knows his stuff. But today i was intriguied by a statement by a customer, but i was busy and didnt question him on what he was saying. He had an 11 silverado 6.2 which had been tuned by a local tuner with hpt and was spraying a 150 wet shot. He seemed to know quite alot about the tuning process. But he made the statement that had "a relay wired up that was turned on by his nos arming switch which retarded 8* of timing, and when the nitrous was off, he basically had an optimum n/a tune." Is this even possible? I didnt think the gas burner computers had the ability to "switch tunes". Just your basic high and low octane tables dictated by the knock sensors/determined octane of the fuel.

yes there is trick, look at the pic, that way it works is with a relay and resistor that you wire in a way that when the relay its on it bypasses the factory IAT sensor and it lies to the ecm and tells it that the IAT temperature is whatever the resistor dictates, for example, with the relay on and a 667 ohm resistor wired it will tell the ecm that the IAT are at 140 degress and then you can go on your tune to the IAT table and on the 140 column just set it to whatever you want it to pull -4,-6,-8 etc, hope it helps

[SilverBullet6.0]

Awesome! I figured it was a resistor trick, but didnt know if it was on the knock sensors or the iat. Thanks!

[SilverBullet6.0]

So what pins are "A" & "B" referencing, receiving from the ecm? Im assuming B is battery voltage from the ECM and A is the AIT high ref/voltage supply? Also, how do you determine what resistance value to use for the resistor? And what wattage does it need to be?

[bartender_77]

So what pins are "A" & "B" referencing, receiving from the ecm? Im assuming B is battery voltage from the ECM and A is the AIT high ref/voltage supply? Also, how do you determine what resistance value to use for the resistor? And what wattage does it need to be?

A and B its in reference to the 2 wires to go fro the IAT sensor to the ECM, that's why when the relay its on it sends the signal to the ECM from the resistor instead of the actual resistance coming from the IAT sensor so it will pull whatever timing you put on your IAT table, here are some resistor values

1188 ohms = 113 *F - 45 *C
973 ohms = 122 *F - 50 *C
667 ohms = 140 *F - 60 *C
467 ohms = 158 *F - 70 *C
332 ohms = 176 *F - 80 *C
241 ohms = 194 *F - 90 *C

[SilverBullet6.0]

So B is the low reference of the IAT?

[DSteck]

JD Stam? I did that. Haha.

That's exactly how his setup works.

[bartender_77]

So B is the low reference of the IAT?

A its Voltage from the ecm, B is Ground, IAT sensor works with resistance hence the trick that we can do, so the ecm its looking for how much resistance it sees by sending voltage to the IAT sensor thru the A wire and then it knows X amount of resistance equals x degress

[Ben Charles]

Yep this works very well

[SilverBullet6.0]

Thanks for clearing the a and b wires up!

[Blingole]

Im trying this with the ECT sensor since on some boosted apps your get some extreme intake air temps.

[carlrx7]

Im trying this with the ECT sensor since on some boosted apps your get some extreme intake air temps.

so go the other way with the resistor, make it see cold temps, nitrous is cold btw. hehe

[SilverBullet6.0]

so go the other way with the resistor, make it see cold temps, nitrous is cold btw. hehe

Wouldnt colder ect temps increase timing though?

[Ben Charles]

Wouldnt colder ect temps increase timing though?

IF you set it up to then yes, but for nitrous and the corresponding ECT have it pull timing

[snowvette]

Will this affect fueling?

[DSteck]

If you are SD tuned, it will impact fueling. MAF won't care.

There is a workaround though. Set your bias to be straight towards the IAT sensor and trick the ECT, then you're good.

[GPGTP]

There is a workaround though. Set your bias to be straight towards the IAT sensor and trick the ECT, then you're good.

what bias would you be refering to?

[SSUte01]

If you are SD tuned, it will impact fueling. MAF won't care.

There is a workaround though. Set your bias to be straight towards the IAT sensor and trick the ECT, then you're good.

I haven't tested bias effect as thoroughly on E38s mainly just low airflow stuff, but what about going other way; as in, bias towards the ECT for fueling and "trick" the IAT. That said, this has potential to fail miserably if you have a poor intake tract or a few other conditions.

I guess it depends on how much you are "tricking" either sensor. If your IAT is an accurate representation of intake charge and you're not going ridiculous with the ECT, re-thinking it, I tend to agree.

As stated, with MAF it doesn't really matter. SD, I guess it depends on your situation and setup and how much variation from reality you're introducing.

[backchannel]

For extra fuel with nos when iat resistor is used, set inj flow rate vs iat. I used .86 at 50C> [ used a resistor that read 60 C in the scanner]
This is for a dry setup

[DSteck]

Bias to full ECT will throw fueling off like crazy.