Wanting to shed some light on a subject that just seems to have a tremendous amount of misconception out there and to be honest it just drives me nuts to read when I see it.
PEAK BOOST
I commonly see posts with folks comparing their 'Peak Boost' numbers like its a penile measuring contest, thinking that the higher the boost the higher the power (on the same turbo'd and fueled truck) and hopefully this will hopefully show that this is absolutely not the case... at all..
Todays live tuning specimen was a 2017 with nothing more than a pump, KC turbo, and a tune. The goal was to collect data and once again prove that simply a higher peak boost DOES NOT equate to higher horsepower!! You need to understand, boost in itself is just a measurement of pressure, and pressure by definition in any application possible, is restriction to flow..
BLUE LINE TUNE
RED LINE TUNE
RED LINE TUNE
Lets dumb it down to just talking about right at 2700rpm, approximately the peak power for both files with this turbo and fuel set up. Same exact tunes, same timing, same rail, same pulse, same everything, just simply VGT adjustments on the Blue Line Tune to make HIGHER peak boost. As you can see, with maintaining 39-41 PSI of boost through the meat of the pull, the truck was down a consistent amount of power vs the Red Line Tune only making 33-35 PSI of boost. Why is this?? How could this be?? The internet says more boost more power right??
Well, again, what is boost.. pressure.. restriction to flow.. remember? Look at the back pressure difference of the 2 logs at 2700rpm. To make more peak boost of the Blue Line Tune, it is done with forcing the turbo to work harder, we do that by moving vane positioning, so to make that beloved high 40 psi, we are at 65 psi of exhaust back pressure. Now that is not necessarily bad at all, but the Red Line Tune was able to make more power with only 33-35 PSI with only 48 PSI of back pressure..
Still following? Make sense? I can make this truck or even a stock turbo'd truck make 45+ PSI of boost just with the tuning, and all that will happen is it will make even less power, create more lost efficiency, create even more heat, and be much much harder on the engine and turbo. Essentially, in order to make that higher boost, we are effectively restricting the exhaust trying to leave the engine and now our air FLOW is being affected.
Well, again, what is boost.. pressure.. restriction to flow.. remember? Look at the back pressure difference of the 2 logs at 2700rpm. To make more peak boost of the Blue Line Tune, it is done with forcing the turbo to work harder, we do that by moving vane positioning, so to make that beloved high 40 psi, we are at 65 psi of exhaust back pressure. Now that is not necessarily bad at all, but the Red Line Tune was able to make more power with only 33-35 PSI with only 48 PSI of back pressure..
Still following? Make sense? I can make this truck or even a stock turbo'd truck make 45+ PSI of boost just with the tuning, and all that will happen is it will make even less power, create more lost efficiency, create even more heat, and be much much harder on the engine and turbo. Essentially, in order to make that higher boost, we are effectively restricting the exhaust trying to leave the engine and now our air FLOW is being affected.
And that is what matters, flow. It is about the air flow efficiency from entering the turbo through the compressor all the way to exiting the turbo and turbine. If we can move the air in and out efficiently, while driving the turbo accordingly, it will net the most efficient way that particular turbo will run and ultimately the most efficient way to make power. Hope you are still following.
Now, this is not to say this means the turbo should just be wide open all the time, or that pressures cant be too low.. All of the driving range the ratio's need to be managed, sometimes purposely high sometimes purposely low where needed, it is what allows a VGT to spool quickly and have the great drivability attributes that VGT turbos are known for. If the VGT is too open, truck runs like a dog, lazy to get going, etc I have seen logs from some others that will even have back pressure lower than boost during the normal driving range, or even at WOT, a great way to make a VGT drive like a Non VGT lol.. But if too aggressive it can run into surge situations, high EGT, smoke control issues, loss of power, etc. There is a fine line, a sweet spot of efficiency, for every RPM, load, and gross airflow situation to calibrating any of these VGT turbos, whether it be a stock or aftermarket turbo.
So.. once again, and many of you who speak to me regularly already know how much I talk about this subject, hopefully many end users can get a better understanding and stop trying to compare and flex nonsense when comparing like for like trucks with the same hardware..
HIGHER PEAK BOOST DOES NOT MEAN MORE POWER. Boost in a VGT application is simply a by-product of a symphony of physics working together. Where the peak boost ends up, is where it ends up if calibrated correctly for that application.
HIGHER PEAK BOOST DOES NOT MEAN MORE POWER. Boost in a VGT application is simply a by-product of a symphony of physics working together. Where the peak boost ends up, is where it ends up if calibrated correctly for that application.