Performance pages HP reading

[stevert]

Question.
In the past I have seen the 640 mark on my performance pages. The last 2-3 drives it has not gone over 600 ( stops at 600). The car feels fine and I might not be hitting redline. It is 85 degrees and pretty humid. The car is a bone stock 2013. Anyone have thoughts? Heat soak or is something up? There are NO codes ( knock on wood).

[Steve M]

Gen 4s and 5s pull a pretty significant amount of timing when the inlet temps go over 77°F.

If it is 85°F ambient, you can bet your IATs are +15-20° over that mark.

Under those conditions, I wouldn't expect to receive full power, at least not with the stock calibration.

You can keep that from happening by changing the calibration, but you'd be doing so at your own risk.

[CNU_Physics]

So looking at HPTuners this is interesting...you have two tables for pulling timing, IAT and MAT. It says the IAT source is MAT though, so I guess its pulling from that table?

This is what your tables are looking like as reference so you know how much timing is being pulled.
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[SRT_BluByU]

I didnt know the gen v had a MAT sensor.. i thought just an IAT?

[Steve M]

I didnt know the gen v had a MAT sensor.. i thought just an IAT?

It does not...the only sensor on the intake manifold is the absolute pressure sensor that plugs in the passenger side toward the back of the manifold by the cowl.

The PCM does reference MAT in that particular instance though, so it is a calculated value, although I'm not sure if it is just a straight offset of the IAT (which reside in the MAF sensors) or something more complicated (a function of both the measured IAT and MAP).

With HPTuners, you can select the source (either IAT or MAT). Also keep in mind that the PCM linearly interpolates between values. As an example, for the IAT table, 25°C (77°F) shows that it would pull 0° of timing. The next cell is 30°C (86°F), where it would pull 3° of timing. That means that it will pull 1° at 80°F, and 2° at 83°F.

On top of that, the PCM also adds fuel at a rate proportional to the amount of timing pulled, so it is a double whammy in the power department. As a reference, just going from 12.6:1 AFR (0.857 lambda) to 12.8:1 AFR (0.87 lambda) on my car made a difference of around 10-15 HP based on my change in trap speeds at the drag strip with no other changes.

[SRT_BluByU]

a bit confusing for sure - is the stock Gen V ECM pulling timing based on the IAT table or MAT table (if not MAT exists)?

[Pappy]

It would be interesting to see a graph comparing timing retard to hp produced. I have talked about this before, but out here in the hot desert, I monitor IAT and it is easy to feel the hp loss when the IATs start going up. Worse than that, after the IAT sensors heat soak (usually worse after shutting the car down for a few minutes), the IAT never fully recovers. I often see 40+ degrees above ambient. Start at 105 degrees outside and that is significant. I won't even get on track with the IATs up - no fun - feels like a loss of about 200 hp. Cable pointed out that it also pulls timing with higher water temps.

[Steve M]

a bit confusing for sure - is the stock Gen V ECM pulling timing based on the IAT table or MAT table (if not MAT exists)?

It isn't exactly clear...someone like Winkles would know. It could just be an HPTuners thing (although I doubt it), but even without an MAT sensor, it could still be calculated based on some assumptions.


It would be interesting to see a graph comparing timing retard to hp produced. I have talked about this before, but out here in the hot desert, I monitor IAT and it is easy to feel the hp loss when the IATs start going up. Worse than that, after the IAT sensors heat soak (usually worse after shutting the car down for a few minutes), the IAT never fully recovers. I often see 40+ degrees above ambient. Start at 105 degrees outside and that is significant. I won't even get on track with the IATs up - no fun - feels like a loss of about 200 hp. Cable pointed out that it also pulls timing with higher water temps.

Yep...once everything is heat soaked, that's pretty much it. After you've reached that point, you have to be willing to leave it parked with the hood open for at least about 30 minutes to get it back under control, possibly longer.

The first time I ever experienced it in my Gen 4 was trying to merge on to a highway after sitting for an extended period at a traffic light on a warm day. It felt like I was dragging a boat anchor.

[usmcfieldmp]

I'm guessing you'd know if it did and would have said something, but does the MAP have the MAT incorporated? Just throwing out a guess; my Cobalt is setup that way and I know a number of GM MAP's have that dual functionality. In the OE configuration, my MAF would read IAT's pre-supercharger and the MAP would read IAT's post-intercooler.

[Steve M]

I'm guessing you'd know if it did and would have said something, but does the MAP have the MAT incorporated? Just throwing out a guess; my Cobalt is setup that way and I know a number of GM MAP's have that dual functionality. In the OE configuration, my MAF would read IAT's pre-supercharger and the MAP would read IAT's post-intercooler.

I had not considered that. I don't think the Gen 4/5 Viper MAP sensor has dual-functionality though.

The Gen 4/5 MAP sensor has 3 wires with the following pin-outs:

https://i.ibb.co/Jv8Pw5Q/Viper-MAP-Sensor-Pin-Outs.png

If it had a temp sensor, I'd expect it to have more wires. As an example, the Gen 4/5 MAF sensor (with incorporated IAT sensors) has 4 wires with the following pin-outs:

https://i.ibb.co/pb8d3zF/Viper-MAF-Sensor-Pin-Outs.png

I could be missing something though.

[usmcfieldmp]

I'm sure you're right. My MAP is a 4-wire Bosch sensor; pin 2 being for the NTC thermistor.

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