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BUSY BOLTERS Are you one?  The Shop Area
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Jul 21st, 2025 | | | | Joined: Oct 2012 Posts: 307 'Bolter | | 'Bolter Joined: Oct 2012 Posts: 307 | My 261 has an updraft carb and the air intake tube wraps around the engine to where the oil bath filter used to be. I put a K & N filter on it some years ago, but wondered if it's getting enough air. I've seen the small filters on single barrel carbs and original updraft carbs, but much larger filters on the stock downdraft types. The intake tube has only a 2 in diameter, so I've had a difficult time finding a larger element. Could Deve or someone else let me know the correct size to use please. Thanks
Last edited by Chaz 58; 04/02/2020 2:21 AM.
1958 Chevy Grumman Olson step van
| | | | | Joined: Mar 2010 Posts: 10,059 Renaissance Man | | Renaissance Man Joined: Mar 2010 Posts: 10,059 | I am no Deve, but the key to being able to get away with a small modern filter is the airflow rating of the element material in that filter.
Putting a paper air filer designed for a lawn mower in an original small filter seems like a dandy idea, but that filter doesn't allow enough air through it. It is designed for an engine with one or two cylinders in very dusty conditions (thus extra small holes in the paper, which restricts airflow).
What are the specs for your K&N filter?
You can test to see if a filter is too restrictive with a tachometer. At idle, check the RPM with the filter on, then with it off.
You can also do a performance test by driving like you stole it with the filter on, then with it off. You will need to rely on the seat of your pants to make the judgement of a difference.
Carl
1952 5-window - return to "as built" condition | 1950 3100 with a 235 and a T-5 transmission
| | | | | Joined: Oct 2012 Posts: 307 'Bolter | | 'Bolter Joined: Oct 2012 Posts: 307 | The filter seems a little restrictive compared to no filter. Enough so, I am looking for a larger air cleaner.
1958 Chevy Grumman Olson step van
| | | | | Joined: Jan 2002 Posts: 2,696 'Bolter | | 'Bolter Joined: Jan 2002 Posts: 2,696 | This is good info. Never thought about check the RPM's at idle with and then without the air cleaner on.
Craig My '50 Chevy 3100 5 window, '62-235cu, 3:55 rear My truck ....... Respect The Rust If I'm not working on my truck, '65 m00stang or VW camper, I'm fishing with the wife or smoking Salmon.
| | | | | Joined: Jan 2002 Posts: 2,696 'Bolter | | 'Bolter Joined: Jan 2002 Posts: 2,696 | So at idle, do the rpms increase with a filter on versus no filter?
Craig My '50 Chevy 3100 5 window, '62-235cu, 3:55 rear My truck ....... Respect The Rust If I'm not working on my truck, '65 m00stang or VW camper, I'm fishing with the wife or smoking Salmon.
| | | | | Joined: Mar 2004 Posts: 6,189 'Bolter | | 'Bolter Joined: Mar 2004 Posts: 6,189 | Low air flow = slower RPM...take the restrictive filter off and the RPM will go UP. Mike B  | | |
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