6NZ low power question

The only thing I've seen happen while trying to adjust the boost on a stock turbo is...........nothing. As boost increases so does the Exhaust Gas Back Pressure in the exhaust manifold. The net Hp gain is zero. The throttle response usually picks up and everybody thinks Hp has increased........throttle response isn't Hp. Under full load on a dyno the actual hp increase due to boost being higher is....... none. One way to increase Hp is to add fuel and air.

If you want to add Hp with a turbo upgrade only, you have to increase the turbine wheel diameter to decrease Exhaust Gas Back Pressure in the exhaust manifold this makes the turbo more efficient, but can also limit the working RPM range of the engine. The Stage 1 turbo is a good example of trying to have your cake and eat it at the same time. It does have a larger turbine wheel in it, but to get it to spool quickly it has the same A/R Ratio turbine exhaust housing on it as the wastegated housing for a 550 CAT. Now it also has a larger compressor wheel. With the fact we've slowed it down by increasing the diameter of the turbine wheel we have to move the same CFM of air to support the combustion of the fuel properly. To do this the compressor wheel needs to be larger. The reason this design is more efficient is because you never drive the truck at full boost and Hp all the time. While cruising at low to mid boost conditions in the low to mid RPM range of the engine its larger turbine wheel allows the exhaust gases to exit the engine with less restriction than the wastegated turbo.........so you do gain a Hp and fuel mileage advantage in this RPM and working range of the engine. But under high RPM and boost conditions the advantage starts disappearing and falls very closely in line with the standard turbo. Now the next question is how often do you run the engine at high RPM at MAX boost? Not very often, if ever, so you do utilize the Hp and fuel mileage gain of upgrading the turbo to what everybody refers to as a Stage 1. This has been proven on a Engine Dynamometer by BorgWarner testing these different parts and turbo combinations on a stock CAT engine. The efficiency gain of the Stage 1 turbo had a net Hp increase of less than 10 Hp at max RPM this is less than a 2% increase in power...........as I said you need to add fuel and air to increase Hp. This turbo is more efficient than a stock turbo and it is very fast responding to fuel inputs compared to a stock turbo. With this being said the actual gain is in the acceleration rate of the engine(how fast the engine RPM rises per second). As boost increases quickly with this design turbo...........the ECM responds by adding fuel quicker. So in the low to mid range the ECM goes to the highest portion of the fuel tables, this gives you a wider power band, because the stock turbo won't raise the boost as quickly or as high in that RPM range of the engine. So the peak power at 2100 RPM only increases 5-8 hp, but the low to mid range RPM power increases more with this design.........another way to fool the ECM into adding fuel in a certain RPM range for better performance

 

Do those turbos work better for a stock replacement even on say a 475hp?

 

It will work, but you won't have any realized improvements in Hp or fuel mileage doing this.

BW has a vast selection of parts that allow you to build something similar to the Stage 1 that will work very well if the customer doesn't want to increase the power rating to the 550 or higher ratings. I've sold one of these in the past to a customer that was looking for a turbo with faster response and higher boost in the low to mid range of the engine for fuel mileage gains

 

I was just wondering since its brand new and much cheaper then a Cat rebuild.

 

Yes Peterbilt had a problem with these gauge snubbers coming apart. Peterbilt wrote a technical service bulletin about this back in 04 or 05........I forgot about it They had a new part number to replace them with, but I went with a traditional gauge snubber you could adjust to save the gauge from the pressure spikes in the fuel system. You'll need to do something or you'll lose the gauge shortly.