I have been feeling the need to do a write up on this for sometime now. The more and more I learn about how tuners work for our trucks the more I feel like there is a serious amount of misinformation out there that REALLY needs to be corrected. What you guys pay your hard earned money for should return results beyond what some guy's distance friend thinks is awesome. This is not meant to explain the deep in's and outs, rather a rough idea of how things work and why some setups are good and others are not.
First let me explain how our trucks work on a basic level when you push the pedal down. IE: How does the VP44 know when and how to fuel? Info taken from vp44 CAN message - Dodge Diesel - Diesel Truck Resource Forums thanks to Jdonoghue and his work from ~ a decade ago. When I say there is nothing new in terms of magic inside the ecm or vp44 I mean it.
For a VP44 truck the ECM asks for a amount of power via a Canbus message which contains various things, but most importantly a Fueling command and a Timing command. The ECM has a number of tables that decide how much of each to add. I won't get into that because 1. I don't have that much insight into the workings inside the ECM, only the output from the ECM and 2. it's really not important to this converstation.
So the Fueling message is a 2^12 String of data, you don't need to understand computers, just know that the fueling message can range from 0 - 4095. It cannot be ANY bigger and I don't care what you have heard. Unless you were to rewrite how the ecm and vp44 talk to each other, hint you can't without Bosch letting you rewrite the VP44 coding...not gonna happen, you get a MAX fueling message of 4095. This is where that magic "65hp" limit comes from. The stock tune will max out around 3600 or roughly 235hp.
So for stock injectors, we won't worry about being to exact because it isn't important
0 = 0 hp engine off etc
2000 = 150 hp
3600 = a VERY rough 235 hp OEM Power
4095 = ~300hp worth of fuel
Timing is also a 2^12 string, again don't worry just know that it can only be 0 - 4095. You are gonna ask what does that mean in terms of * of advance BTC??? This is where things get a little fuze as the people do that know won't say, again really not important. However we know approx that the VP44 is mechanically limited in Timing Advance to ~30*
So VERY roughly again
0 = 0* ( maybe lolol doesn't really matter)
4095 = ~32* ****** HUGE GRAIN SALT. I don't know this for sure, but it doesn't matter to this convo.
Just know that we have to work within the Realm of the communication structure designed for the VP44 and ECM for canbus fueling. We have a MAX fuel amount of 4095 once you hit that you cannot add more fuel via canbus. That's where wiretap comes in.
Next lets look at what type of tuners we have for our Vp44 trucks and how they work on a basic level.
1. Ecm flashers: Smarty's Hypers tech Really anything you upload the ECM via OBD port.Ecm Flashers actually go into the OEM tables and alter fueling and timing. So where the stock ECM tune is asking for 2000 the new tune will ask for 2500, hence more power. Same goes to Timing, the tables are rewrote in the ecm to have a timing curve that is geared more towards performance and MPG rather than emissions standards.2. Canbus Tuners: Edge EZ Quadzilla ZXT, ts mvp, anything that plugs in under the hood to the data port.These tunes watch for what the ECM outputs then alters the fueling and timing message so the VP44 see's the command from the piggy back box. canbus only tuners really end up doing the same thing as ECM flashers. They both alter the canbus message within the limitations of what we talked about above. IE ~65 hp on stock injectors3. Wiretap only tuners: TST comp might be more not sure haha.The TST for example does not alter what the ecm asks for, it only watches for the fueling solenoid opening then holds it open for longer thus giving you more fuel and more power.4.Wiretap and canbus tuners: Edge Comp / juice, Quadzilla Adrenaline, redline.Boxes that do everything like the Edge comp / juice, redline / Quadzilla Adrenaline. do the same thing as the TST, but also alter the output from the ecm in the same exact way the canbus tuners do. Think of these tuners as an Canbus tuner plus a Wiretap box.
Lets remember that canbus fueling actually makes up the vast majority of fueling / power in our trucks. Wiretap adds a good amount of power, but not nearly as much as canbus fuel. On a stock truck canbus fuel alone will get you to 300 hp wiretap will only bring that up to ~420 hp according to ricer math on the hottest tuners. so ~75% of the power is actually coming from Canbus alone and wiretap adds another ~%25 on top. 300 hp is approx %75 of 420 hp.
So now that we have a basic understanding of tuners lets look at stacks and what they do.
Throughout this I am going to reference the Throttle pedal as if it was a volumn knob on a stereo. 0 = silent / engine off 10 being WOT or stereo as loud as it will go.
Let me start off by saying that there are good reasons to stack in some situtations. In my opinion you should never stack programmers that do the same thing.
It is commonly accepted that you shouldn't stack 2 boxes that do timing. The thought with Stacking Timing boxes is it over advances timing causing issues. Generally unsafe I suppose. Not sure if I believe that fully, but regardless your truck will run like garbage, and you feel that in the butt dyno. We all agree it's not a good idea.
Oh the Butt dyno....we'll get to that in a second.
But people seem to ignore the same thought process for canbus fueling. You ask ANY tuner and they would tell you that too much fuel is a bad thing for performance. We all know that "flooding" the turbo results in poor performance. So why is that the same mindset does not apply to the fueling side of tuning in the same way as the timing? Reason that no one seems to care is that there is inheriently no high risk of damage and the Butt Dyno says it works. Kinda like the facebook, if someone says it's ok on facebook then we are all good. So the masses tend to ignore overfueling as being bad.
So the Butt Dyno,
We REALLY need to understand that the Butt Dyno is NOT an indicator of power. The only thing the butt dyno is good for is telling you when an abrupt change in torque happens. Not how much of a change, only when. You can take 2 trucks, one of them with a VERY smooth torque curve that ramps up sooner / more power and another with a torque curve that ramps up VERY quick once 1700 rpm is reached. According to the butt dyno the latter truck is faster...but we know that is not true. So Butt Dyno is basically a change in power light bulb. "Yep power changed"
So back on topic.
So if we think about our 0 - 4095 fueling message as being directly related to 0-10 on our volume knob on the stereo ( obviously in the real world it isn't linear, but in this example it is). So loudness on canbus is 0-10.
So here we have a data log from a normal DD drive on OEM fueling on the "canin" column, you can see that in stock form once you are moving you normally see a canbus message of above 1000. So you range for fueling if you want to get going is no longer 0 - 3600, rather ~1000-3600 which makes sense it takes power to move the truck down the road. So in Stock form our volume knob has a range of 2.5-8. 2.5 = 1000 and 8 being 3600 or stock tuning max
Whats important to note is that our volume knob is stuck going no lower than 2.5 when you step on the pedal to catch the mustang in front of you. So our knobs 0 position is now 2.5 as the truck needs to move down the road.
So what happens when we add one tuner say smarty on top of OEM? Say the tuner addes %20 fuel down low, great we all love power.... Our low limit is already 2.5, but we added ~%20 up top also. cool now our knob goes up to 10. Awesome news!
So what happens if we stack 2 boxes that do Canbus Fueling? So down low the Smarty tuning in the ECM is asking for %20 over stock when you hit the skinny pedal. then the canbus piggy back box is intercepting that fueling command of (OEM + %20) and adding it's own fuel on top. So we end up with (OEM + %20) + %20 as the lowest amount of fuel we get when we want to pass someone. The stack doesn't give us more top end due to the limited size of the fueling message IE: 10 on our stereo. So our range of fueling is now %50 min and still %100 max, so our stereo only works between 5 and 10. So our volume knob's 0 is now 5. Not exactly what I would call a good setup.
so here's a visual idea of what I mean. You can see how the stacked setup just maxes out fueling sooner, Kepe in mind our trucks fueling is in no way linear, but you can see how stacking just causes overfueling.
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Most stock guys won't really see this as an issue, but what you need to see is that your throttle movement is limited to %50 of what it used to be. Same max power, it's just all moved between 0 and %50 throttle position durning DD driving. Anything over %50 is reaching that max fueling message size of 4095. so if you go to %60 you truck is just as fast as it was at %50 throttle and so forth.
It is easy to see that you are just maxing out fueling sooner and sooner with less and less throttle travel IE less and less control over your truck.
Stacking tuners is like only being able to control your volume on your stereo between 5 and 10. You'd be pissed if your radio never went below 5, why do you want your truck to drive the same way?
I would suggest rather than just trying to max out your fueling sooner for more power you should just size your injectors correctly. You can buy injectors all day long for the same cost of a stack. Bigger injectors have the opposite effect if you can control fueling. It will give you more resolution in your pedal movement for the same allowable canbus message.
IE: 7 x .009 injectors
0 = 0 off
2000 = 200 hp
4095 = 400hp on ricer math. ( we know thats not true)
but you can see you can use injectors and canbus together to give you move power without limiting how much throttle movement you actually have before you hit %100 fueling.
More control is a good thing. It's a brave new world, tune your truck correctly and use the throttle if you want power.
So when should you stack? It's easy....Only stack things that do different things. You only need 1 box that does each thing, canbus fueling ( from the ecm or piggy back) + timing + wiretap( if you want it). The only thing you gain by stacking boxes that do the same things is a lighter wallet. You get no more power at the cost of less control over your truck.