Foretravel Owners' Forum For owners and Fans of Foretravel Motorcoaches September 14, 2025 ...

Main engine air intake pre-filter

April 14, 2014, 11:09:54 pm

Was planning to re-route the air intake to the engine filter so that it didn't suck the road dust from the rear wheels into the filter.  After looking this all over, I decided to add a pre-filter that can be easily accessed and cleaned or changed as needed at a much lower cost than buying filter elements on a regular basis.  I removed the old mushroom looking cover and added my new filter housing in its place.  The filter media is very inexpensive and can be blown out or replaced as seen fit.  It is sized to not choke down the air required to run the engine.  See attached photo for finished product.  ----  Fritz

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Re: Main engine air intake pre-filter

Reply #1 – April 15, 2014, 09:02:34 am

Looks good.

Continue to monitor air filter minder reading to make sure it does not offer too much additional restriction.

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Re: Main engine air intake pre-filter

Reply #2 – April 15, 2014, 10:18:36 pm

Made a small run today and have not seen any rise in D/P across the filters, so --  looking good so far.  When the D/P comes up, I'll clean it and see if the only rise is in the pre-filter.  It is hard to engineer this kind of thing, so the empirical data is very important.  Thanks and have a great day  ----  Fritz

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Re: Main engine air intake pre-filter

Reply #3 – April 16, 2014, 04:31:55 am

I am going to change the air filter intake on our U300 to the later style like Kent has on his. The later models run a plastic 6 inch or so tube across the bottom part of the radiator and then making a 90 degree turn, it goes up to a intake much higher on the side of the body. Ours just funnels all the dirt from the back wheels into the air cleaner. What were they thinking?

Pierce

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Re: Main engine air intake pre-filter

Reply #4 – April 16, 2014, 11:24:22 am

Pierce  ----  I looked at routing ours up to a higher point, but settled on this arrangement.  Do you have the rear radiator on your rig?  I wonder about the increased length of the intake pipe and how much the associated drag will impact your air supply.  A larger pipe may be worth considering.  Have fun and have a great day  ----  Fritz

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Re: Main engine air intake pre-filter

Reply #5 – April 16, 2014, 03:44:06 pm

Fritz,

Yes, rear radiator. Part of the problem is the large open area between the 4x8" air intake and the radiator air intake. Bad enough taking air from the radiator but the gap allows all the road dirt to go directly into the filter.

The factory changed it sometime in 1993 but we have the older style. A 6" inside diameter is the largest pipe that will fit between the radiator and the louvers. That gives just over 28 square inches ( .7854 x diameter squared ) and should be OK but I will check for loss after installation.

I noticed a large difference in power changing from a very dirty cleaner to a new one. Our Detroit 2 cycles need a large amount of air because of firing every stroke compared to every other in a 4 stroke engine.

Pierce

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Re: Main engine air intake pre-filter

Reply #6 – April 16, 2014, 09:48:11 pm

My 3208T has a six inch intake opening also.  I dont know much about 2 strokers, but the D/P monitor should keep you well informed.  I'll keep watching mine also to see how it goes over time  ----  Hope it all works well and that you have a great time doing it.  ----  Fritz

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Re: Main engine air intake pre-filter

Reply #7 – April 16, 2014, 10:29:05 pm

My 2000 c 8.3 air intake also was a bad design by FOT but my deflector sorted that out. Same filter now for 2 yrs and 20k miles + and still just a nice shade of grey. Filter minder has not changed at all.
JohnH

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