I'm starting to think there is a direct relationship between boost at cruise and the air filter, that is the flowing capacity of the filter setup. I'm no turbo guru so I thought I'd ask here. A little background behind the reason...

On the excursion, I put in most of the mods last spring, shortly after we got it. I've never been very happy with the low boost at cruising speeds, usually about 1 psi. It can still get up to 25psi no problem. I've leak tested the system, no leaks, and everything is very clean. This is with the ais filter system.

I was comparing that to the f350, which at cruising speeds is boosting right around 5psi, running a 6637.

I'm getting ready to take the f350 on a road trip, so I've been soundproofing in an effort to make it easier to converse on the road. The latest change was switching to an ais filter setup, as I've been happy with the lower noise in the ex. Now suddenly on cruise I'm boosting 1-2 psi.... and can still hit 25psi no problem. When I installed the ais I ran my boost leak detector and found one small leak, which I fixed.

So, is there a direct relationship between the air filter setup, and boost numbers?

 

Yes and no.


Yes in that it can show up as a difference on the boost gauge from time to time. No in that at low-load situations it really doesn't matter.

Consider the variables that go into different setups: flow vs filtration, cold air vs engine compartment, etc.


For example: a 6637 is drawing in hot engine compartment air, while an AIS is going to feed off cooler air and shielded from the engine bay. Just temperature differences alone will show various readings on the boost gauge. Hotter temps will read higher boost, even though technically there's less dense air.

On the flip side, the AIS media is less porous, so technically speaking it does require a bit more to pull in airflow than a 6637. Under low-load situations where the turbo really isn't working, you'll see a slight drop in boost. However, it's really negligible since the AIS media is designed to work just fine with the 7.3L, without sacrificing power, fuel economy, etc.

In the end it's nothing to be concerned with. When the motor needs air and the turbo spools, the AIS will flow more than enough for a stock charger. If you had a much bigger turbo setup and far larger CFM requirements, then the AIS would be a restriction. In your case, it's not.


It's very general but hopefully that helps explain a few things.

 

I would be happy with less boost at cruising speed that means better mileage.

 

I had the AIS for years, and it read the same at cruise as my S&B at cruise as your 6637 does at cruise - about 4 PSI at 65 MPH on the flat, 5 PSI at 75 MPH. More boost is better fuel economy if the fuel delivery is the same, but more boost because of more throttle is no fuel saver.

The AIS isn't lowering your cruise boost. How are you getting that 1 PSI reading - gauge or OBDII? Did anything else change when you installed the AIS?

 

I was thinking that more boost was better, I know it sure reduces spool time if you have to pass. I've got a mechanical gauge, it is still functioning the same as before. ie if I touch the gas petal it moves up, and will go to 25 if I push it. The only other thing I did when I installed the ais was the boost leak test.

 

How much pressure did you apply during the leak test? Did you isolate the CCV? What leak did you fix? Where is the mechanical gauge attached? Did you check to make sure the boost gauge hose is secure and not cracked?

 

Since diesels do not continuously run at a set stoichiometric air/fuel ratio, the amount of boost alone is not an indicator of economy. The actual amount of fuel demanded will determine the fuel economy, and the amount of boost will be determined by the fuel demand, RPM's, temperatures, load, etc.

That said, often times you can draw a fairly accurate guesstimate of fuel economy based on known boost levels on a diesel.

However, in the case of this thread it's not really going to make a difference. It's just a few PSI difference at a very low-load situation, due to changes in filtration rate and temperatures. In the end, the OP would be extremely hard pressed to find an actual change in fuel economy due to the intake swap. If he does, it means something went wrong somewhere.

 

You don't need much boost if it means better mileage.

 

One other thing to note.....

Many boost gauges are not exactly the most accurate at low pressures. The combo boost/vacuum gauges will give you better readings below 5 psi. But for the average boost gauge, that first 5 psi reading can be affected by the smallest of factors.

 

20psi
isolated the ccv
tightened the clamp on the passenger lower plenum
sprayed soapy water where the boost line connects, which is through the aih plug, didn't check the whole hose though.

Seeing that pocket said that smallest of factors can affect the reading, I did pull the gauge pod out a few inches the other day in order to run the power line for the new dash cam through the headliner, maybe the line or fitting to the gauge was disturbed at that time.