K&N top filter problems FYI

[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...

[CobraEd]

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


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[Tom Kirkham]

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.

[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.

[ERA Chas]

Originally Posted by bobcowan

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.

I agree Bob but the real benefits I found come from the car's forward movement and the colder ambient intake temp-added HP you don't see on the dyno.

[JBCOBRA]

Originally Posted by ERA Chas

I agree Bob but the real benefits I found come from the car's forward movement and the colder ambient intake temp-added HP you don't see on the dyno.

I am sure it works great, because your carbs are sealed to the hood.

Unsealed carbs...ever notice that when driving in the rain the air filter does not get wet from the rain?
Try taping some yarn to the front edge of the scoop and you will see for yourself.

[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.

[CobraEd]

Originally Posted by greg schroeder

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.

This is why carbs have an idle/low speed circuit for low to mid range part throttle cruising and main jets for wider fully open throttle opening and high power.

You can set the low speed circuit lean for good cruising economy and set the main jets rich for max power. That is what a carb does.


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[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]

Originally Posted by Tommy

I have run the K&N Filter top on my car for more than eight years.

So obviously Tommy, the cars runs better with it -right??
I think all the science boils down to-it works better or not.
Mine works better-no fears about vents, clearance, turbulence or linguine...

[Jimbocobra]

Here are a couple dyno sheets. The filter top got 9 more hp in this example. It was a back-to-back test. I also got my highest dyno numbers using it. There is a science to this so I don't claim to know the answer, I suspect that after reading all of your posts you are all right; it depends on the car, jetting, air flow, turbulance and that dyno testing may not always be conclusive, but in THIS CASE, the filter top made more HP. It seems an unreasonable conclusion that the filter top would never produce more HP for any car set up or engine and carb combo or that it will always have turbulance or air flow issues. But, it seems just as unreasonable to dismiss all of these first hand accounts about airflow problems, but now you have at least one dyno test to support the "pro filter-top camp". Dyno Sheet - HP and Torque Question