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Originally Posted by boosted331
What are you talking about, seriously. Turbocharger RPM is almost directly related to boost pressure. Increase shaft speed, increase boost, it's a pretty simple phenomenon. You increase the exhaust flow, it spins the turbine wheel faster, makes more boost, if the gate is big enough it bypasses more exhaust, if it isn't big enough you get boost creep, pretty simple. I don't know what the hell you're talking about, but it doesn't really make sense.
Secondly, I don't know about you but every single diesel I've seen that doesn't use a variable geometry turbo does use a wastegate, to prevent overspinning the turbo, just like you mentioned in the first part of your post 
I wonder how many people have tried to make posts on here to sound smart-assy, only to discover they're totally wrong? Bully Dog makes diesel performance parts. They have a nitrous kit for diesels. Nitrous express has a kit specifically for diesels ( http://www.nitrousexpress.com/News/NXd.htm). NOS makes a nitrous kit specifically for diesels ( http://www.jegs.com/cgi-bin/ncommerc...81&prmenbr=361)
What's that again about nitrous not working on diesels? |
Turbocharger speed, if we talk about the compressor relates to pressure ratio and airflow, have you ever seen a compressor map with the shaft speeds litsted? If you take a look at one you will notice that shaft speed tend to increase at high flow rates without using high boost pressures, so when not using oversized turbochargers there is a risk of overspeeding the turbocharger. The thing is that when you overspeed a turbocharger it's hardly ever noticed since most people don't have the sensors for measuring the turbo speed.
Today many diesels are equipped with variable geometry turbines. Wastegates have been used on some basicly at later years to increase low speed torque (by allowing a smaller turbine/turbocharger), diesels are stable and do not require a wastegate, which is why they were the most common application for turbochargers (the wastegate was introduced on the automobile market on the late seventies for use in gasoline engines).
The wastgates that are found on some turbochargers for diesels are usually smaller than wastegates for gasoline engines and are not designed to handle high flow rates.
All wastgates work by when reaching a certain pressure, often called "cracking pressure", the wastegate lifts off from its seat. The maximum boost pressure will then depend on, except on the cracking pressure, the amount the wastegate will open when the pressure increase. The cracking pressure depends on the spring load when the wastegate is closed and the amount the wastegate is opening on the spring rate, that if we exclude the wastegate deisgn and position. So maximum boost is basicly a balance between exhaust flow and wastegate lift.
A wastegate can also open because of a high exhaust pressure, this can sometimes occur when using small wastegate actuators. High performance units often use much larger actuators in comparison with valve area and harder springs and therefore rarely opens becuase of exhaust pressure alone.
The most simple way to increase power on a diesel engine is to increase the fuel flow, diesels work with an excess of air and there is oxygen enough to burn more fuel. Remember that diesels doesn't use a throttle plate and consume all the air that they can, only regulating torque by the fuel flow. The only reason that more fuel isn't added original is because of exhaust emissions and fuel economy (leaner = more efficient).
Adding nitrous will do nothing, it will only increase the excess of oxygen unless the fuel flow is increased, and you don't increase fuel flow on a diesel like with a gasoline engine where you simply can increase fuel pressure or add an extra injector in the intake. Adding the extra fuel is the complicated part when tuning a diesel engine, increasing the oxygen can simply be done by increase the boost pressure as the engine will not suffer from engine knock like a gasoline engine.
Adding nitrous is basicly to waste money when one can increase boost instead, nitrous doesn't offer the simplicity that it offers on gasoline engines.