Modifying air intake on 04 Marquis

[Doug Wray]

I have a 40 foot 04 Marquis with C-12 engine... I recently replace the stock exhaust with a turbo muffler... Much  better power...
My questions is has anyone modified the air intake on the outside of the air filter?
It appears very small and having read that Monaco added additional intakes to some of it's coaches makes me think that the air intake is too small for the C-12 engine... Even after installing a new Donaldson air filter the filter gauge show a lot of restriction...
I am considering having the air intake enlarged... Any ideas??? Thanks...

[Lee Welbanks]

Doug,

More air is always a good thing, on my 06 PT I am going to go up to the same filter used for the C15 it will be easy change as the only difference is the C15 filter has a larger dia. The inlet and outlets are both 7".
I have not seen how yours is piped or any of the sizes in and out of the filter.

[Larry Haynes]

I am interested in this discussion.  when I bought my 06 Patriot with the C13 525 hp, the filter guage was at 19" of water.  So figuring maintenance was behind I changed to the C15 air filter.  no difference. Went on a 3 k trip and the filter gauge went to 22.  (No off road)

Having several over the road trucks I have never seen this until many miles into the normal maintenance cycle.

So I when it warms up I am going to run a prescribed path that will exercise the engine.
1) air filter as found
2) air filter with the snorkel disconnected drawing air from the engine compartment
3) if weather allows, no air filter at all, short distance up the 3 % grade we have nearby

It makes no sense to me. But want to understand it.
I plan on replacing the muffler with the aero turbine 5050xl as this cat is anemic compared to my OR C12.  also adding a new Raycor filter at 125 gph with a prime pump.

So I hope we can share data
Larry H
2006 Patriot Thunder
Cat c13 525 hp

[Lee Welbanks]

Larry,

I would suggest taking it to a shop that has a dyno to do your testing. What kind of boost pressure are you seeing with 100% load at about 1300 rpm's. Mine pulls a steady 47 psi boost and this thing pulls hard.

[Fred Brooks]

     Hi Doug, I agree with Lee. You can spend a lot of money pursuing this engineering. The problem I have seen over the years is the "false positive" you get from the air filter indicator. Because these coaches have so much power, they are fun to drive with your foot in it. If the Dyno says your getting what your promised and there is no black smoke, Enjoy!     Fred Brooks

[Dick Simonis]

My 2000 PT had two small aero mufflers when I bought but didn't think much about the exhaust except it really rapped going down steep grades in a canyon with the Jake on high.  I also noticed that after a long hard pull with my foot on the floor the intake minder would be up to about the 1/3 point even with a new filter.

Now with my Marquis and the original muffler the minder does't budge and even with more HP seems sluggish compared to the PT.  Granted I have more weight but I think the difference in the filter minder reading is interesting enough to make me want to change to an aero.

[Tom and Pam Brown]

I posted this when I had it completed.  For those of you interested I bought the scoop at Summit.

The result was better fuel mileage, averages about 1/2 to 3/4 mpg better depending on speed and wind conditions.

[Dick Simonis]

Looking at the pic Tom posted reminds me that my Marquis also has that screen on the air intake which my PT did not.  Believe it or not that screen could be a restriction to air flow since it's not 100% open area.  In addition, it will probably increase the turbulence of the air flow which may or may not be important and I'm not even sure it has a useful purpose.

[David T. Richelderfer]

Okay... I want a scoop and I want to keep the screen... the scoop to "press" more air into the intake and the screen to keep out the yellow jackets and other critters when the coach sits parked at home for weeks at a time.  5 to 5.5 mpg is insidious mileage.

[Tom and Pam Brown]

The screen in mine I added to keep birds from building a nest.  As for as turbulence goes that was the reason I added the scoop.  The turbulence down the side of the coach was keeping air out of the flat intake(my opinion). 
It seemed to be a correct opinion as the fuel mileage increased. My first trip with the scoop was the same route and time of year for comparison.  I drove normally in the way down and decreased my speed on the return.  I even fueled at the same stations and stopped at the same rest areas to walk the dog. 

Probably seems a bit much but doing fuel mileage tests for Caterpillar in the past gave me the process to,utilize to be as accurate as possible.

[Lee Welbanks]

I posted this when I had it completed.  For those of you interested I bought the scoop at Summit.

The result was better fuel mileage, averages about 1/2 to 3/4 mpg better depending on speed and wind conditions.

Tom, How big is that air intake and where is it located on the side of the coach? I often wondered what a person could see if you were to use gorilla tape and tape ribbon on the side of a coach and take it down the road and have somebody along side to video what the wind was doing, kind of like a redneck wind tunnel. The air intake on my PT is up high on the left rear corner and its pretty good sized, the tube into the air cleaner is 7". My air cleaner vac gauge hardly ever moves, I replaced the air cleaner last yr just because and my mileage went up a tick.

[Tom and Pam Brown]

The opening seems to be about 6X12 if I recall.  I did tape ribbon around the intake before I modified the scoop to make sure it would increase flow.  I drove along side my DW a few miles and watched.
The flow was intermittent as wind and traffic moved about.  I would have preferred a deeper scoop but could not find one already manufactured.

Hope this helps.

[Lee Welbanks]

I could be all wet but that opening with the screen and metal cover doesn't look like it would flow much air, got too much in the path.

[Dick Simonis]

If I had my coach here I would measure the slots and figure the open area.  Need to see if it's more or less than the circular area of the intake hose.  Plus, I still think that screen blocks off 40 to 60% of the open area.

On the other hand, I suspect the filter minder takes all of the inlet air restrictions into account not just the air filter itself.

[Lee Welbanks]

Oh my PT the intake is 7" tube which is 38 sqin the air filter and intake tube are all the same size. Cat says this setup flow plenty of air for my C13, would be interesting to install a differential pressure gauge across the air cleaner just to see what one would get. I don't think my air cleaner has hardly any restriction with how large a area it has.