Oh what the hey, might as well jump in on the fun!! First off, with exhaust size, Let me just say back when I got my truck, I ran a 15.2 1/4 with stock straight pipe exhaust, kwik filter, and an Edge evolution. Despite all the theories and physics behind it, the stock exhaust is (straight piped) not that restrictive. 3.5dp to 4" = more than most will need. 4"dp= looks cool.

With that said, I did the 4" MBRP, and the fit and finish on it are superb, including the 4"dp mating to the turbo. Just secently had it apart and it did not leak at all on the turbo side.

And the theory of it all. Bottom line is Heat=Energy. Energy=Heat. Period. end of discussion. They are one in the same. The more heat that is dissipated from the exhaust gasses, the less energy the exhaust contains. And at the same time, the hotter the molecules are, the faster they travel. Hot gasses travel faster than cool gasses. The velocity(speed) of these superheated gassees is far greater than that of cooler gasses. The turbo capitalizes on that high velocity of the hot gasses via a spinning turbine. As the gasses cool, they slow down and become lazy, not unlike some of us... . Well the volume of air hasn't changed, and just like a freeway, the slower the cars go, the more lanes of traffic you need to move the same volume of cars. The cooler(slower) the exhaust gasses, the more room you need to move the same volume. The real debate is just HOW much room is needed to move the given gasses. Interestingly enough, the harder you push your engine, the hotter it gets, and the more gasses you can move in a given space. There, I did my part to clarify absolutely nothing, but throw some more theory in the mix.

 

LOL , that was my feeling, i got it of my chest, here you go,

but you put it better than i did

 

Once again you guys are arguing with me and all I said the it is not heat alone nor is it gas velocity. But you should consider that the all factors. If you really understand thermodynamics and physics related to heat transfer you will understand what I am saying. Heat in air is nothing more that excited gas molecules the are LESS dense. Heat is only energy and movement of molecules. Gas velocity make the turbine spin, BOTTOM OF THE LINE. Heat makes the turbo effective because the expanded gasses (from heat) move faster on the exhaust side than the drag of the intake side, creating a compounding effect. The sole reason we can use a turbo is because exhaust gasses are hotter and create more velocity over the turbine. The turbine WILL NOT spin without gas flow over the turbine. But you fellows seem to think heat makes it spin. If heat makes this thing spin then you should get a noble prize for creating a machine that turns ambient heat into mechanical energy via a turbine. Ask youself how does a turbine engine work. Simply put it takes air and heats it and funnels the exhaust to create mechanical energy via gas spinning the turbine. How does a hydroelectric power plant work. Simply put water runs through a turbine and spins it due to the pressure of water creating a flow through the turbine. Buy or make two toy pin wheels. Now put one in the oven and look to see if it spins. Blow on the other to see if it spins. The sole reason a turbo works it due to the combination of heat and gas velocity which is created and continually pumped into a confined environment cause the gas to try and equalized with atmospheric pressure (via through your turbo and out you exhaust). Bottom of the line and once again. YOU HAVE TO HAVE BOTH OR THE TURBO DOES NOT WORK. By the way cooler air is more dense and if it had the same pressure and rate of flow of the exhaust gas it would spin the turbo faster and more evenly. I will not post again to tell you that you have it right but must understand that you need both. Have a nice day.

 

F250, thanks for your responsiveness. I didn't mean to step on any bodies toes, just trying to share knowledge..

Good example of the heat deal, ever see those candles with the spiral that is hung over it, it starts spinning the spiral from the heat energy..Hold a turbo in a housing upright and apply heat from the bottom and it will spin.

There is some interection between the heat energy and the velocities of the gasses, heat expansion is the key.