Join Date: Jan 2009
Thanked 64 Times in 60 Posts
Right, but sometimes boost is the cheapest easiest way to get more air into the combustion chamber. Like John said, it would be better to get increased air into the combustion chamber other ways, I.E. A cam which will keep the valves open longer allowing more air to enter the combustion chamber, and or cylinder head porting.
Also like John said, compressed air equals more heat. Air flowing through the compressor housing on a turbo creates pressure in that housing and the pressure then creates heat. Thats why you start building more heat with the hx35. If you do something to reduce that pressure, I.E. change the size of the housing or change the compressor wheel itself, you will flow more air at lower pressure in the turbo. This equates to more flow but cooler air. This air backs up at the cylinder head and creates boost, the boost is still based off flow, The same amount of flow creates the same amount of boost. however, since it wasn't compressed and heated in the turbo itself, the result is cooler boost, therefore cooler air in the combustion chamber. Cooler air in the combustion chamber means more power and lower egt's because of a better more complete burn.
However, everything really needs to be paired right. If you just throw a turbo with a bigger comp wheel and housing on a truck with no fuel mods you will greatly suffer down low. It takes more exhaust to turn the larger wheel and get it spinning fast enough to flow air and produce pressure. When you aren't producing pressure, the engine is relying on Vacuum to draw air into the combustion chamber. If your Air Fuel controller is set up to flow lots of fuel at low boost, when your engine is starving for air before your turbo has spooled, it smoothers the flame, too much fuel, and not enough air to burn properly. This leads to smoke, low end heat, and can cause excessive ring wear as well. Also when you smoother the flame down low, it becomes harder for the truck to build RPM, lower and slower RPM building leads to more lag, and it just takes even longer for everything to get to be where you want/need it to be to work properly.
Thats why, with a larger turbo on the truck, I'm not a huge fan of running the AFC loose on a mechanically injected truck, or unplugging the map sensor on something like a 24v. Full fuel with no boost isn't the best thing in the world.
There are a lot of things that go into picking the right turbo(s) for your truck, and fueling and Tuning must be matched accordingly. Its easy to build a truck that puts out decent numbers, but its hard to make a truck that puts out big numbers and still functions well all around. Egt's, spool up, reliability, driving manners and of course the power you want.
Hope this helped a little. Sorry if it was disjointed, please feel free to correct any mistakes that you find or ask if you want a little clarification
2000 2500 reg. cab 4x4 auto 577hp
09 6.7L QC LB stick, 4x4.
TOTAL PERFORMANCE DIESEL 707-545-FUEL (3835)