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tsm1mt 01-02-2001 01:46 PM

Air cleaner vs. Mud hole
One of the courses I run around here (western Montana) likes to throw in a BIG mud hole near the finish line that likes to drown engines.

Including mine.

I've dumped the inner fenders (OK, never had 'em in the first place) and usually I see the water come up the front of the engine and surround the air filter (previous owner of my front clip had a big tall double-stacked filter setup, so there's a nice hole in the hood to watch all of this). The fire goes out.

My first thought was to use some flexible ducting to route the air intake from the carb throat (500cfm 2bbl Holley) to the former heater-duct and mount the air filter on the inside of the firewall.

I'm having some second thoughts about it though.. and might have a better idea.

The cheaper route is a 2" air filter extension/spacer ($9 from Jegs) for the current K&N.. the spendy route is an 8" tall K&N velocity stack.

The goal would be put the single K&N filter ABOVE the level of the hood.

I would then fill the gaping hole in the hood to allow just enough clearance for the tilt front clip to open and close around the filter housing.

A scoop would be fabricated with a rear opening. Since there's no windshield, there isn't a high likelihood of water coming IN from the rear - and the scoop would keep any over-the-hood water wave from getting to the filter on the front side.

Make the hole a decent fit to the air filter (and/or add replaceable panels to actually go UNDER the filter housing) and I can keep most of the water just engulfing the carb, but not wrapping around the filter and choking off the engine.

That sound like a good plan?

I've already tried various concoctions of Duct Tape and plastic bags to divert the water away from the air filter with no effect (well, some experiments have made it worse, not better).

I think the taller filter neck is the simplest solution.. if it'll work.

-Tom Mandera, Helena MT
M4x4A #576 - 1977 IH Scout II "Little Devil" - Comerized
Almost ready for Feb 10th in Cascade, MT

**DONOTDELETE** 01-02-2001 07:36 PM

Re: Air cleaner vs. Mud hole
Not seeing how the water spashes on your scout leaves me at a disadvantage, however I happen to like the idea of routing it through the firewall since that eliminates the possibility of spash back from the area between the firewall and hood or stray water thrown from the tires. Unless you've got the stack quite a bit higher than the hood I would be leary of that route. If you go the stack route I think I'd try and use a splash plate in front of the inlet to make sure water cannot be sucked in. For some reason I was thinking your scout ran full-size (width) axles which would create a lot of extra water action and that's what got me concerned. One other thing that might work (and what I use on mine now) is a covered top air cleaner (like the early-mid 60's mopars/oldsmobile/buicks used) and a smaller diam. baseplate, then the edge of the air cleaner lid has rubber riveted all around it to the point it's basically touching the intake. I've yet to have any problems with this setup, although it's not drawing the coldest air. I can't cut my hood or pull the heater core so I have to pull air from underhood (class rules). My unlimited truck pulls air from a duct through the firewall.
my junk

Jeeper99xj 01-02-2001 07:55 PM

Re: Air cleaner vs. Mud hole
Maybe try making a snorkle, I know that's what some of us that run water of unkonw depths with trail rigs. We just run a peice of pvc form the original air cleaner (now completly sealed) through the fender out and up the windshield and then usually top it with a k&n. You could also run it inside the cab.

'95 YJ Totaled!
Now All I have is an insurance Claim :( !

tsm1mt 01-03-2001 12:00 PM

Re: Air cleaner vs. Mud hole
I thought about a snorkel. The problem I see with a true snorkel setup is there's a bit of math involved in trying to make sure the snorkel is large enough to provide sufficient air to let the engine breath. This is an all-out race engine, and it sure does like as much air and fuel as it can get - and restricting it through a snorkel (or running a 6" diameter snorkel) is not entirely attractive.

I *could* just run the snorkel for the obstacle race, and run the regular open element air filter for the drags, but then that becomes a bother.

It may come down to it, of course.. that's where the "into the heater duct hole" idea comes from. I'm really only concerned about the "bow wave"/initial splash. I'm not doing deep water crossings - just a deep water hole that's maybe 3 truck lengths across. Problem is at 20mph it makes a big splash. ;-)


tsm1mt 01-03-2001 12:15 PM

Re: Air cleaner vs. Mud hole
I am running full width axles. No inner fenders, just the outer fenders and hood. The tires DO throw a lot of water!

As I mentioned, I've watched when I hit the mud holes and for the most part I'm only concerned with the engine bay water. It seems to all get deflected off the hood/outer fenders and comes INWARDS towards the carb. I've watched the wave sweep over the engine, surround the K&N, and snuff it out.

At the same time, very litte/none came OVER the hood and onto the filter - all of it came from the engine bay and came UP.

If I were running the double-stacked 10x3 (so.. 10x6) air filters the original owner ran (thus the hood hole), the second air filter would be almost fully outside of the hood.

Thus, a 5" "lift" on the air filter housing would definitely put it over the top of the hood. 8" would assure it (like the K&N velocity stacks). I would build a full "hood scoop" with a rear opening to cover up the air filter which would keep any splash from the front or sides that makes it over the hood from coming into the filter. The only patch for water to get in would be from the rear, and since there isn't a windshield to send the spray back at the scoop, and I don't plan on going *backwards* through the water.. I think it'd be alright.

The firewall "snorkel" is also very appealing - I KNOW it'll work, too. My only concern is getting a good fit to the air horn, and making sure whatever material I choose will be large enough to flow the air I need. It *is* a "small" displacement IH 304V8, but it has a bad thirst for air/fuel. I had a 350cfm 2bbl on it at first and I had a rev-limiter at 4000rpm. It couldn't suck enough air in. With the 500cfm I'm pulling 5000rpm at the end of the drags, and I still think it needs more. Might just be I need to jet up again, maybe I need to retard the timing a tad.. could be the air filter or a number of things. The motor is only 7 months old and barely broken in.. and gets thirstier every pass. I'm looking for a bit over 6000rpm out of it. 350hp/400lbs-ft from my little dump truck IH 304. ;)

If I would stop shredding the suspension, I might actually get back to some dialing in on the engine (at the last race I S-ed the springs in the drags, then tried to end-o the truck in the obstacle race.. just finished fixing *that* mess.. )

How large of ducting do you use to feed your 440? Any signs of it choking it off at high RPM?

If I had a factory enclosed filter housing lying around to use I might be more inclined to try something different (heck, that would solve a lot of the problem right there).. but I don't. They're all in use.. and if I'm going to *BUY* a new filter housing, might as well look n' see if there's a better solution first.

I'm still leaning towards the velocity stack. If I can get the filter up out of the water *AND* improve engine efficiency at the same time.. how can that be all-bad? ;-)



The_Sandman_454 01-03-2001 01:17 PM

Re: Air cleaner vs. Mud hole
<font face="Comic Sans MS">Ok here's what I'd do. I would use 2 3.5" or 4" snorkels (one at each side) with one K&N 360 cone air filter on top of each. Keep in mind when you double the size of the tube, you quadruple the inside area of it. Use as few bends as possible to help keep air flowing properly. Might look a little unusual, but if you set it up right, you'll be able to remove the snorkels when you're done mud running so it doesn't look quite so funny. Just a thought. [img]/wwwthreads_images/icons/crazy.gif[/img]

Tim "Sandman"

ORC Land Use columnist:
My November article on ORC

TEX 01-03-2001 03:01 PM

Re: Air cleaner vs. Mud hole
<font color=purple>Here's what I do. Not perfect, but it works for me. I have a oil drainpan upside down over my air filter. Still allows cool air & under hood air. Doesn't restrict airflow, & shields most if not all the slop. It's by no means waterproof, but a big step up from an open filter sticking through the hood [img]/wwwthreads_images/icons/smile.gif[/img]</font color=purple>


**DONOTDELETE** 01-03-2001 05:32 PM

Re: Air cleaner vs. Mud hole
The first cap/duct I tried on my 440 was one off of a '88 cadillac (4.9 Deville), it fit perfect on the carb, was low and bent just right to mate up to the firewall....a thing of beauty really :)......the down side was that at 3500 it was out of air.

I then ran a home made setup that was made from a 6" air inlet from a diesel truck, not near as pretty, and at the moment no provision for an air cleaner but it functions well. If memory serves the engine bay of your scout is pretty tight and that may not be an option.

The way you describe the splash you might be just fine with what you are planning, I've seen a lot of guys running the same setup with no problems so it can't be all bad. I hit quite a few tracks with deep water, and with a windshield the water comes from all directions so I'm a little anal about it.

tsm1mt 01-04-2001 12:37 PM

Re: Air cleaner vs. Mud hole
> If memory serves the engine bay of your scout is pretty
>tight and that may not be an option.

My engine bay isn't so tight. No inner fenders, no heater, no battery, etc. Only thing "cluttering" the engine bay are the shock hoops.

>The way you describe the splash you might be just fine with
> what you are planning, I've seen a lot of guys running the
> same setup with no problems so it can't be all bad. I hit

That's what I was hoping to hear. :-) "BTDT and it works well enough."

>quite a few tracks with deep water, and with a windshield
>the water comes from all directions so I'm a little anal
> about it.

For the M4x4A rules, the windshield isn't needed and it's just extra weight and one more thing to break. If I were to run NMRO there are a number of other things I'd have to upgrade as well - we only require 1/8" *aluminum* U-joint shields.. I'm told NMRO wants 1/4" steel, etc. (I'm running 1/8" steel currently)

I did find a video clip that demonstrates a little of what happens when I hit the water. In this clip we'd tried hanging plastic sheeting for "inner fenders" as well as covering up the big hole in the hood. I really think it made it MUCH worse and just channelled everything right into the air filter.

(FWIW, I was trying to slow up and get the front tires into the water and THEN hit the throttle - but got on it too soon)

Just under 2Mb

There's a larger/high-def version at:

Thanks everyone,


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