I'm a little puzzled as to why some believe the VVT requires backpressure to operate. I've only been around the PSD for about a month and have owned other diesels for years.
Our family has been racing for many, many years with superchargers & turbos so I feel I'm pretty good with boosted engines. (388hp out of 2.0 liter acura and 1700+ from a BB chevy. 600+hp from sb's is easy)

So back to my question-
A turbo isn't effected by backpressure from an operational view except for performance losses due to too much in the exhaust. The best exhaust for a turbo engine is none in all cases I'm aware of. Yes fed laws require an exhaust so we make due with bigger pipes and low restriction mufflers. The goal is to allow the turbo to spin-up asap & produce boost. So why be concerned over BP?
The VVT from what I understand can produce small amounts of backpressure via vane position during certain times to enhaunce EGR flow. (mine is disconnected and closed so it's no longer a variable)
Ford choose the Garrett VVT option primarily to reduce noise, improve throttle response, and help the EGR function. Garrett makes a fine turbo btw.
So.......
Many folks here appear concerned over BP (backpressure) and exhaust pipe size? Why? If the EGR is disabled, and the following are installed- air kit, bigger exhaust, and an enigine fuel module are utilized then you have effectively done what you can to maybe increase air flow thru the engine by 2 1/2 times.

I guess maybe I missed something about the Ford / International PSD???


Wekiwa

 

So if I disconect my EGR then the turbo is no longer a variable vain? Therfore the it acts like a older turbo off of a 7.3? And no longer dependant on back pressure?

 

The VVT is always variable w/ wo the EGR. By disabling the EGR you force all the exhaust flow to the turbine wheel. This also stops the gunk from plugging the intake manifold.

Wekiwa

 

Hi, I followed the step by step instructions on the Egr disconnect procedure...My check engine light and fault codes appeared on my Diablo preditor diagnostics page...I cleared the code and the check engine light went out for only 2 minutes and then came back on...How is this done or is there another problen with my truck

 

how do you disconnect the EGR

 

I will agree, I disconnected EGR and check engine light came on

 

My understanding is that the trucks with the California Emissions systems ** will turn the check engine light on, but others will not when the EGR is disconnected.

** This also includes trucks for CA, ME, MA, NY, VT as they use the same emissions system.

Chris

 

That is true. Trucks built going to california have the check engine light come on. Mine was from Idaho so when my EGR "fell off" it did not trip the CEL.

 

Look at the goodies covered in the "TECH" folder. Its ya know, a few lines down from top of page..

 

It is not a matter of backpressure for it to operate but more along the line of being able to monitor it. Pressure sensors have a sensitivity to them, if you trying to sense pressure changes lower than the sensitivity(larger exhaust, etc.), the computer won't recieve an acurate reading from the sensor. With a known orfice(size of the piping to the cat) and with a pressure reading, engineers can calculate how much volume is passing thru the turbo. Knowing the volume, the engineers can "map out" the volume /boost output curve(given output of a pump/fan at a know speed/pressure drop) of the turbo. They can better program the ECM to control the engine/turbo better (make it meet emissions).

When it come down to make as much horsepower as possible, yes less backpressure is better, but then your not worried about emission or economy either.

 

Good post.

 

WeKiwa-thanks for bringing this up. It's been bothering me a while too...

Maybe it would be nifty if one of the programmers took the exhaust back pressure reading into account with one of their performance tunes and someone offered a sensor that would work with your free-er flowing exhaust...rather than ignoring the sensor and making changes that keep it from working properly how about trying to work WITH the sensors we have and still feed the ECU all of the data it needs to run as well as possible?

-pretty much the same idea as the recalibrated MAF's all the NA folks get...this is just on the other side.

 

Thank you all for the info! So based on the above responses if I installed a 4" down pipe with 5" exhaust with no cat I would have problems? The check engine light would always be on due to low back pressure? I would like to put a 5" system on my truck if possible.

 

Ok, heres the skinny on EVVT's and back pressure, as I have said before and your tierd of hearing, Im an off-road engineer (diesel engines and stuff), but this does give me some really good contacts contacts, got ahold of a guy at cat that deals soley with this type of turbo. he confirmed what crash said regarding emmisions bs, im fighting it right now with particulate filters, stupid gov regulations, but back on point, the optimum is to have a vacume on the outlet of this or any turbo, since thats not really possible (with the exception of running a hundred and having airflow draw the exuast out) you want atmospheric pressure at the exaust outlet from the turbo, so boys, go to town on pipe diameter, besides it will help keep EGT down.

Bone

 

So bigger is better?