K&N top filter problems FYI

ratdog · #1 (**permalink**) 04-04-2011, 11:18 AM

I had a 14" round filter and a chrome top on my car and ordered a K&N top filter from summit thinking it would help flow and car run like a dog at speed. My carb didn't like the air pushed from hood scoop to carb at all, I paid 77.00 and now can't use it, Im glad I didn't throw out my chrome top !!!...just for FYI

undy · #2 (**permalink**) 04-04-2011, 12:03 PM

Not to rain on anyone's parade but years ago, just after they came out, I had heard bad things about K&N's filter lids from several reputable sources. The increased carb intake air turbulence caused by the lid "typically" negated and sometimes adversely affected engine output. I have always stayed away from them.

CobraEd · #3 (**permalink**) 04-04-2011, 12:22 PM

I have heard bad things about them too. Apparently carbs are designed to have flow from the side OR the top. Not both. Causes turbulance and a lack of laminar flow.

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ratdog · #4 (**permalink**) 04-04-2011, 12:38 PM

and they look so cool,they may work great without a hood scoop???

Jac Mac · #5 (**permalink**) 04-04-2011, 01:28 PM

I wonder if it really was the top filter or other factors:
1. Could the filter top be too close to the carb vent tubes.
2. Is air really entering the engine bay/carb via the scoop . Do a (wool tuft) test while driving & check what its doin out there.
3. Lots of hot air gathers at highest point under the hood, if there is not a lot of air going in the scoop, guess what your engine is now trying to breath.
4. With that in mind air cleaner should really be sealed to the scoop.

slider701 · #6 (**permalink**) 04-04-2011, 01:41 PM

What if the extra air coming in is just leaning the carb out (ram air effect) ?

Did the OP try going up on the jets to richen it up some?

ERA Chas · #7 (**permalink**) 04-04-2011, 01:45 PM

Laminar flow and turbulence my ass. Jac has it right. I did this a decade ago. Immediate response improvement, no stall on hard braking, pulls to 6800 with zero restriction. Feels like 20 more HP dynamically-but you won't see it on a dyno.

Jac Mac · #8 (**permalink**) 04-04-2011, 02:51 PM

Thats because most dynos are not mounted on the back of a raised flat bed doing 80 mph down the freeway

Waste of time trying to diagnose stuff like this on a dyno with the hood open & no 'real world' airflow into the carbs.

ERA Chas · #9 (**permalink**) 04-04-2011, 03:10 PM

Quote:

Originally Posted by Jac Mac

Waste of time trying to diagnose stuff like this on a dyno with the hood open & no 'real world' airflow into the carbs.

Agreed-that's why I said 'feels like 20' more. Very noticeable improvement in pull at the top end.

ratdog · #10 (**permalink**) 04-04-2011, 04:19 PM

I put chrome top back on my 14" filter and took off the K&N top filter and car run better, I could run up to 55 on highway and it surged and didn't run right, I put old top back on and it runs great, you all decide, I know what I plan on doing, it is not doing back on...

CobraEd · #11 (**permalink**) 04-04-2011, 05:37 PM

It is a well documented problem seen over and over again.

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elmariachi · #12 (**permalink**) 04-04-2011, 07:12 PM

Ahhhh, the twins. What a sight to behold.

Tom Kirkham · #13 (**permalink**) 04-04-2011, 08:09 PM

Quote:

Originally Posted by ratdog

I put chrome top back on my 14" filter and took off the K&N top filter and car run better, I could run up to 55 on highway and it surged and didn't run right, I put old top back on and it runs great, you all decide, I know what I plan on doing, it is not doing back on...

Sounds like your old air filter is acting like a choke. The new air cleaner was allowing more air, thus the lean condition. Tune your carb to the new air filter and you will make more power.

greg schroeder · #14 (**permalink**) 04-04-2011, 08:47 PM

Quote:

Originally Posted by slider701

What if the extra air coming in is just leaning the carb out (ram air effect) ?

Did the OP try going up on the jets to richen it up some?

Exactly! and with how terrible the coefficient of drag is on a Cobra the last thing needed is jamming more air in.

Ant · #15 (**permalink**) 04-05-2011, 12:29 AM

I have seen a heap of very very fast track cars with the K&N extreme top on them, and they normally have outside air ducted in, not underbonnet heated air!
I would think that KN have made a better flowing air filter where there isnt room for a great 4 -6" high filter, although the extreme filter needs a good space above it for the air to turn in..

Jac, Chaz and Tom you have all hit it right on, firstly tune you carb to suit the filter, then you might be able to make a simple alloy tray with the Moroso foam sealer around it to get free cold air from your scoop, as hopefully separating the under hood pressure should make a difference, and then I would do a some mixture checks. I cant see a major difference in jetting providing your carb is correct for your engine and normally you dont need to go too far from std jetting. I had the Jac Mac scenario of air filter top to close to the bowl air tubes and ended up about 10 sizes rich, until we cut tubes on an angle to stop the air flowing across the carb affecting the way the fuel flows through the main jets, and I went back to std jetting etc!

JBCOBRA · #16 (**permalink**) 04-05-2011, 05:22 AM

You realize that unless you have your carb(s) sealed like ERAchas, the hoodscoop doesn't let air in at speed. Actually the opposite is true. The Big hole in the front of the car lets in so much air that some of that air is forced out the hood scoop.

ratdog · #17 (**permalink**) 04-05-2011, 06:21 AM

It was pushing so much air from the hood scoop that the top of the K&N filter that had the red oil, most of the oil was gone around the center of the filter.
anyway car running great again and it will not be the last time I try something and flushed money down the drain.

rodneym · #18 (**permalink**) 04-05-2011, 10:00 AM

Purdy, Chas.

The only thing you need are some magnesium wheels.

My bad. I forgot that the sanding sound I hear is you cleaning your mags.

ERA Chas · #19 (**permalink**) 04-05-2011, 11:42 AM

Quote:

Originally Posted by rodneym

Purdy, Chas.

The only thing you need are some magnesium wheels.

My bad. I forgot that the sanding sound I hear is you cleaning your mags.

SPEAKING OF WHICH...what's this week's latest silence--er-WORD?? Reply in your Hali thread-don't wanna get yelled at...

Jac Mac · #20 (**permalink**) 04-05-2011, 01:08 PM

Quote:

Originally Posted by ratdog

It was pushing so much air from the hood scoop that the top of the K&N filter that had the red oil, most of the oil was gone around the center of the filter.
anyway car running great again and it will not be the last time I try something and flushed money down the drain.

I would suggest that the reason for the 'red oil' being absent from the center of the filter top was due to the 'stand off' fuel being too close to the filter top & literally washing the 'red oil' out of the filter top, which brings me back to the instance that Ant also brought up, getting too close to the bowl vent tubes...... feel free to try & prove us wrong, make up a simple tray with foam like Chas setup that seals against the hood/scoop,& ensure that there is at least 1/2" to 3/4" from bowl vent tubes to filter top ( a simple ring of 3/4" square draft seal rubber between main filter & base will accomplish that ). I think you will be pleasantly surprised at the result, I know I was, only other question I have with your car was that 55 mph you mentioned, is that a misprint?, most of the ones I work with have a '1' in front of the '55'....