Open or closed crankcase breather

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Jul 31, 2003 | 11:26 AM

Redone

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From: St. Louis, MO

Open or closed crankcase breather

I've got a '79 F150 w/ 351M and I'm looking at replacing the crankcase breather unit with something that will allow more outside air into the carburetor. I know the cooler the air the better, to a certain point.

Ideas? Facts?

-Chris

Jul 31, 2003 | 12:06 PM

johnsalterego

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From: Dallas/Fort Worth

Open or closed crankcase breather

Usually the PCV valve draws the 'bad air' out of the motor - the only time the breather side will really allow any significant crankcase gasses into the air cleaner is a.) when your foot is on the floor and there isn't enough vacuum to run the PCV valve, or b.) the motor is worn out and has lots of blow by the PCV can't keep up with. I don't know that the slight difference the breather makes in intake temperature is worth the buildup of the combustion acids inside the block (not to mention the motor will stay cleaner on the outside if it's sucked into the motor instead of pucked out onto a valve cover). Just my opinion; I'm sure some of the 'every last pony' folks here will dissagree!

I don't know what state you live in; if your truck has to pass a visual emissions inspection that is one of the things they will look for. However if you keep the original setup laying around it's easy enough to swap back on just to get the sticker...

Jul 31, 2003 | 12:54 PM

bubbaf250

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Open or closed crankcase breather

Relative to the air inhaled by the carb, crankcase breather output is insignificant (unless you have really horrible blowby). You can run an open crankcase breather if you really want to, but as John said, it is not emissions legal.

Another option to improve the engine's breathing potential some (though it probably wouldn't make a difference with a stock-ish 351M) is switching the air filter housing to the larger 460/HO unit. Overall diameter (17") is somewhat larger than stock, but it fits on the stock 2V carb and it retains all the OEM temp sensors and cold-air snorkel. The filter element for the 17" housing has about 30% more area than the element in the stock 351M/400 housing.

Jul 31, 2003 | 12:54 PM

Redone

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From: St. Louis, MO

Open or closed crankcase breather

Okay, what about closed or open air filter for the carburetor? When I say open I mean something like you would see at a show where the filter is visible.

-Chris

Nevermind...I posted this before I got Bubbas' reply notice.

Last edited by Redone; Jul 31, 2003 at 12:56 PM.

Jul 31, 2003 | 02:09 PM

bubbaf250

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Open or closed crankcase breather

Open air filters suck hot air from under the hood into the carb.

They're a great deal if you want to lose about 5-10 hp or so.

Jul 31, 2003 | 02:15 PM

Redone

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From: St. Louis, MO

Open or closed crankcase breather

Quote:

They're a great deal if you want to lose about 5-10 hp or so.

Okay, I guess I'll stay away from that idea. Thanks.

-Chris

Jul 31, 2003 | 02:19 PM

Redone

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From: St. Louis, MO

Open or closed crankcase breather

Forgot to include this in my original post.

I'm looking for ways to increase my fuel economy without sacrificing a few HP. By-the-way, with a stock setup what should I be expecting?

-Chris