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Breathless 427
I need some advice - I currently have an 8.25" air cleaner assembly on my 427 and I know it's just not getting the air it needs. It runs rich and I really don't care about "that authentic look". I can put it on the engine when showing the car (which is almost never). If I believe the K&N formula for surface area, I'm 2/3 short at 6000 RPM. The correct size seems to be 14" diameter by 3" height. The carb is a 650 CFM Street Demon. What is everyone else using for air cleaners? K&N? Rush? All suggestions are very welcome - including part numbers if you have them. The hood clearance is always a problem and the K&N adds 4.67" to the carb flange as a drop base won't fit with the electric choke. I'll see if I have that much clearance after work today.
Thanks Tim |
Go to the following link for determining if your air cleaner is a restriction. I was really glad to find out that mine was NOT.
http://www.secondstrike.com/Technica...leanerCalc.asp |
I dynoded my engine with a oval cobra style air cleaner with the K & N air filter & a 4" tall round assembly. It seamed there was no difference. As far as height, It was fine untill I steped up from the Edelbrock RPM to the Edelbrock Jr. intake (like a air gap). I had to shave the carb. surface .250 for hood clearence.
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My 427 has two fours with the S&H cleaner housings and K&N filters. I don't know the diameter but they are pretty small in order to clear each other. The depth is about 1.75 inches so all in all these babies are small. I dynoed the car with and without the air cleaners and saw no difference. I think the need for big air cleaners is sometimes overstated.
Jack Z. |
How about your carb? 650 seems small for 427ci.
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I agree with new, I think something like 750-850 would work much better.
Tim |
Try a 750 or up to 830, properly jetted and set up, with the right power valves, and see how much better it runs without an air cleaner first. Then get a bigger air cleaner.
I too thought my 9" K&N was big enough. Ran it for 2 years that way. Just switched out to a larger one again and it runs slightly better across the board from idle to higher rpms. I had a stellings before that and it was choking my motor off. I don't know if I believe those flow tests any longer. |
Tim, check my pics, I also thought the K&N were a bit restrictive so I made these tops. Anything that passes through 180 micron SS wire mesh will be easily digested.
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When Keith Craft built my 496 FE with 2x4 carbs, I asked for a dyno comparison of filters vs no filters. I have the S&H air cleaner housings with K&N filters. The result was a 9 HP loss using the filters. Another data point to ponder.
Robert |
I now have a fine collection of air cleaners and I can tell you that size has something to do with it.
The air scoop has an inside size of about 10.5 inches. Some cars have more. I tried a lowered 14", that hit the corners of the scoop area and the inside of the hood if I rocked the engine. I tried the long "Cobra" look. That air cleaner would "windmill" as you drove down the street. I have a 6" that is too tall, if you put a base on the clears the float adjusters. So, I use the Edelbrock triflow or a 3.5" high 10" round filter. I think you can see it if you go to the pics area and view the engine. Hope this helps. |
Measured the clearence last night and a 3" (total 4.67") filter won't fit under the hood. The engine runs well with adequate power but I'm sure it's starving for air with the S&H filter and does run rich. I initially thought the 650 was undersized but slogging through the Demon site, it appears to be fine for the engine as a street machine. I'd like to hear what the engine guys around here think - Keith and George if they stumble across this thread.
I'll go look at the Edlebrock site. The stainless screen is cool and looks like the Extreme top from K&N. That may be the solution. Tim |
If you are going to retain a low profile (Approx 2" tall) filter assembly, regardless of the make or design, eliminate the choke housing unless absolutely necessary. With a short filter the choke housing inhibits the airflow tremendously AND will affect the jetting due to pressure drop on the float bowl vents inside the filter housing. Your fuel curve will look like the road to Pikes Peak.
:D Rick |
Well, I've ordered an 11" K&N X-stream filter - total height ~ 3.5". The only issue at this point may be clearance with the float adjustment screws fore and aft. I'm thinking about either using a .5" spacer ring if they interfere or drilling two holes, slightly larger than the adjustment screws, in the filter base. I don't think the holes should have much if any impact on air flow dynamics but would welcome any comments.
Thanks Tim[u] |
Doug, Here is how you solve the problems with the float adjusting screws.
http://www.cobranet.com/coppermine/a...l_IMG_0206.JPG |
Thanks Racer - Just need to find the right grommets - looks pretty straight forward.....
Tim |
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