K&N top filter problems FYI

[ratdog]

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]

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]

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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[mdross1]

Well in my case and on a fairly stout 460 it was what this motor needed.All I could say after dealing with the big block and no where near enough room for a filter with the capacity to feed this motor at over 5000rpm's was Yee Haa! Now have a Davinci modified 1000cfm dbl pmp,the motor loves it.

[gsharapa]

I'm running the K&N 9 inch setup on a flat base with 2.75 filter on a single plane intake with base milled 1/2 inch on a big 496 FE. Car made 681 at the crank and runs great on the street. The front opening of the car is directed pretty good into the radiator with a lot of alumumin panels sealing off the rest of the engine compartment. Very pleased with the performance and would not agree with the statements of air can not go down the middle of the carb. Heck I ran lots of race cars with out air cleaners at all.....

[Dwight]

I have one of the K&N top filters hanging on my shop wall that I will sell cheap.

Didn't work on Coach's 408.

Dwight

[ratdog]

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

[Jac Mac]

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]

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?

[Jac Mac]

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]

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]

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...

[bobcowan]

Originally Posted by JBCOBRA

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.

Not always true. I can personally vouch for gaining more power by adjusting the scoop opening. I think it depends on the total set up; including the body in it's relationship to the engine bay. Not all Cobra replicas are equal.

Originally Posted by Jac Mac

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.

This is very true. You don't often run the engine to the max with the hood open and the nearly insignificant air flow of that giant fan.

Originally Posted by ERA Chas

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

I have personally seen - on the dyno - a mild 408W gain 12 hp simply by swapping the solid top for the K&N filter top on a 14"x3" round K&N filter. It happens, I'v seen it. Again, I think it depends on your set up.

[greg schroeder]

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]

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!

[greg schroeder]

If you can put more air into an engine then you can increase the fuel supply and produce more power.

If the Cobra is kept under 80 mph it probably doesn't matter either way, but a disadvantage to using a carbureted engine with a set fuel delivery value might be you don't have a computer to increase the fuel as load is increased with speed and while exponential amounts of air are being forced into the engine the faster you go.

It seems logical that the choice is either tune the engine for cruising around an have lean conditions at high speed or tune for high speed and have a rich condition at low speed. A forced air system without a computer seems would increase the effect.

Lower temperature air entering is always an advantage.

[Tommy]

I have run the K&N Filter top on my car for more than eight years. I've never done a side-by-side test with a regular top, so I can't offer an objective evaluation of that matter. However, after my last engine rebuild, I did tune the carb jets with the filter top and it runs fine with air from the scoop blasting down from above. I'll add that as an aerospace engineer, it's hard to me to guess what the airflow under the air filter might look like. It would take some serious testing or major supercomputer calculations for anyone to really know, and it would likely be different for each particular engine and set of conditions. ... All in all, I agree with Mr. Kirkham.

[ERA Chas]

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.

[elmariachi]

Ahhhh, the twins. What a sight to behold.

[JBCOBRA]

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.