Speed density tuning questions
01-30-2018, 06:49 AM
#61
10 Second Club
Thread Starter
iTrader: (2)
I agree with you guys on a daily it's probably best to stick with a maf. My car is just a week end toy that will over time move more and more towards emphasis on strip performance. It already has a spool in it and while fine on the street I wouldn't recommend that for a daily either.
I've found that the biggest issue is getting an accurate iat in SD. My issues pretty much disappeared after moving the sensor from before the blower to right before the throttle body. I have a huge intercooler and my iat driving is barely over ambient. The only time I see a lean idle now is after shutting the car off and firing it up again in a short time. Even then it drops right down as soon as I get moving. I've seen guys tune idle leaner on purpose than I'm seeing now even after a quick restart. I also live in a small town so my stop and go driving doesn't involve sitting in one place very long either.
I've found that the biggest issue is getting an accurate iat in SD. My issues pretty much disappeared after moving the sensor from before the blower to right before the throttle body. I have a huge intercooler and my iat driving is barely over ambient. The only time I see a lean idle now is after shutting the car off and firing it up again in a short time. Even then it drops right down as soon as I get moving. I've seen guys tune idle leaner on purpose than I'm seeing now even after a quick restart. I also live in a small town so my stop and go driving doesn't involve sitting in one place very long either.
01-30-2018, 11:05 AM
#62
TECH Fanatic
Cool, I'm glad to know that the GM engineers didn't just forget that temperature affects density. 
It makes sense to use an ECT compensation at low airflow since the block & heads will heat the intake charge a little bit when the air is moving very slowly. I never thought of that before. Subarus generally run closed-loop at low airflow, so the ECU just deals with it automagically.
Ironically, there are a bunch of Subarus out there with GM IAT sensors in the intake manifolds. (Including mine.) The factory system has the MAF/IAT unit right behind the air filter presumably just because the MAF sensor works better there and it needs to know IAT to work properly... but of course with SD fueling you really want the temperature in the manifold, and GM sensors play nice with Subaru's IAT input.
Where is the IAT sensor on the factory Gen III setups? Does it vary by car?
It makes sense to use an ECT compensation at low airflow since the block & heads will heat the intake charge a little bit when the air is moving very slowly. I never thought of that before. Subarus generally run closed-loop at low airflow, so the ECU just deals with it automagically.
Ironically, there are a bunch of Subarus out there with GM IAT sensors in the intake manifolds. (Including mine.) The factory system has the MAF/IAT unit right behind the air filter presumably just because the MAF sensor works better there and it needs to know IAT to work properly... but of course with SD fueling you really want the temperature in the manifold, and GM sensors play nice with Subaru's IAT input.
Where is the IAT sensor on the factory Gen III setups? Does it vary by car?
Anyway, yeah the ECT affecting the heat in slow moving air is actually the definition of heatsoak. As in air gets soaked with heat from the block and radiator when it's not moving very quickly. This is why biasing the ECT at low a/f makes perfect sense. It is a pretty genius design really.
On the 4th gen Camaros (gen III pcm's) the IAT is right in the air box, above the radiator. It's really not a great place for it, since the radiator obviously gets crazy hot right there. Mine exceeds 160* at idle if you let it sit long enough. I can't speak for all vehicles, though. On newer designs, the IAT is sometimes built right into the MAF. If it has 5 wires, than the IAT is part of the MAF sensor. There are adapter harnesses out there to convert back to the separated sensor set up. I have one on mine. I got that from TSP.
01-30-2018, 11:23 AM
#63
TECH Fanatic
For adjusting the bias, it will be a while before I can actually test this out for real, but I made a histo in idle logs that I have that plot the actual afr on a IAT temp and lb/hr (matching the table). You can easily see where the afr starts to stray off, and at what a/f. I'm thinking that making 1 or 2% adjustments and watching this histo is a start. Keep in mind VE must also be redone every time you adjust it. It might take a while, so be prepared for that. VE affects the bias, and the bias affects the VE. It's a vicious circle really, but worth it IMO.
02-05-2018, 06:12 AM
#66
TECH Fanatic
In general, MAFs work by use of a heated element inside. As you turn the key on, the element is heated to a specific temperature. As air passes over it, it then requires more and more voltage to keep it at that temperature. More air = more voltage. GM uses hertz to measure this. Ford uses voltage. Same concept for either of them.
02-05-2018, 01:21 PM
#67
Got it. I did some research on them. Seems like they're somewhat picky in regards to their location, but not difficult to mount. I need to check my harness to see if there's a plug for a maf. Thanks everyone!
02-05-2018, 01:48 PM
#68
TECH Senior Member
The main thing with mounting MAF's is to have a straight airflow. GM specifies putting it so there is about 6" straight tube before and after the MAF. There might be a little flexibility in that, but you get the idea.
02-05-2018, 03:16 PM
#69
TECH Fanatic
I forgot to add that if you tune a Mustang, it requires a human sacrifice to unlock the PCM. Just head on down to the nearest carshow and do a burnout. The car will take care of the rest.
Dodges require a living sacrifice to the dark lord. I use kittens. Just head down to the local supermarket in the spring and pick up a box of kittens, and that should be enough to get the tune done. No actual tuning is required though, Satan takes care of that himself. The Demon comes stock with an alter in the trunk.
GM just wants your money and a bunch of your time.
Dodges require a living sacrifice to the dark lord. I use kittens. Just head down to the local supermarket in the spring and pick up a box of kittens, and that should be enough to get the tune done. No actual tuning is required though, Satan takes care of that himself. The Demon comes stock with an alter in the trunk.
GM just wants your money and a bunch of your time.
02-05-2018, 03:49 PM
#70
TECH Senior Member
I forgot to add that if you tune a Mustang, it requires a human sacrifice to unlock the PCM. Just head on down to the nearest carshow and do a burnout. The car will take care of the rest.
Dodges require a living sacrifice to the dark lord. I use kittens. Just head down to the local supermarket in the spring and pick up a box of kittens, and that should be enough to get the tune done. No actual tuning is required though, Satan takes care of that himself. The Demon comes stock with an alter in the trunk.
GM just wants your money and a bunch of your time.
Dodges require a living sacrifice to the dark lord. I use kittens. Just head down to the local supermarket in the spring and pick up a box of kittens, and that should be enough to get the tune done. No actual tuning is required though, Satan takes care of that himself. The Demon comes stock with an alter in the trunk.
GM just wants your money and a bunch of your time.
Carry on....
02-05-2018, 04:20 PM
#72
TECH Fanatic
So long as it's a cute little baby goat, then absolutely. The dark lord accepts many cute fluffy animals as penance. Just verify in the tune that the work is done after, you should see a lot of sixes. In fact, every table is just sixes.
02-05-2018, 05:22 PM
#75
TECH Fanatic
). I'm cool with the car becoming possessed by dark spirits, so long as they leave me alone. It's also a good idea to have some holy water on hand to banish the demons from your laptop if needed.