K&N top filter problems FYI

[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.

[ratdog]

Vent tubes on carb had to be cut so the filter top would fit, I don't have them to close to filter top.

[mreid]

Sounds like it would be worth sealing the air cleaner to the scoop and seeing if that makes a big difference. Why did you go with the filter top to begin with? Were you experiencing too little induction air at higher engine speeds?

[JBCOBRA]

There are advantages and disadvantages to sealing the hood/carb(s)
Sealed will net higher performance. The downside is after driving and turning off the car, when you go to re-fire after sitting for say 10 minutes to an hour, the vapor lock factor took over as the heat could not escape the engine compartment without opening the hood.

[ERA Chas]

Originally Posted by JBCOBRA

The downside is after driving and turning off the car, when you go to re-fire after sitting for say 10 minutes to an hour, the vapor lock factor took over as the heat could not escape the engine compartment without opening the hood.

-hence the electric pump feeding the mechanical...

[JBCOBRA]

Hi chas
I should get one of those and seal my carb back up.
Rain would be interesting though

[ERA Chas]

Although not an everyday occurrence, I never had a rain problem. Rain causes lots more problems than stalling-like zero visibility, traction and discomfort...And I just generally avoid rain or sit it out and be safe.
Electric pumps are valuable to avoid battery-killing extended cranking when cold starting after a long period too.

[JBCOBRA]

Every year the wife and drive to Watkins Glen and back for the Vintage Grand Prix in September. It is about 300 miles each way through the mountains. I have encountered almost every kind of weather. It is truely an adventure in motoring LOL Although my experiences in bad weather doesn't even scratch the surface compared to Jim Kellogg! LOL
On one of these trips I realized that hood scoops don't do sqwat except let air out unless they sealed.
We were running through a downpour, and thought maybe I should stuff something in the hoodscoop to keep water out of the carb. I opened to hood and Voila' the engine and air cleaner are totally dry.

You can see us in the beginning of this video. No idea who took it

http://www.youtube.com/watch?v=EpdO8Dy7_iQ

[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.


.

[ERA Chas]

Ed-the guy runs 10 sec 1/4 miles. He knows what a carb does.

[CobraEd]

Originally Posted by ERA Chas

Ed-the guy runs 10 sec 1/4 miles. He knows what a carb does.

Then why did he say it can be set for cruising economy OR power???? He said it, not me.

What he said is incorrect. There ARE two mixture circuits an a carb and you can set the idle/low speed circuit for good cruising economy and jet the mains for strong WOT power. He said you could have one or the other as per his quote.


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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.

[Jac Mac]

Originally Posted by ratdog

Vent tubes on carb had to be cut so the filter top would fit, I don't have them to close to filter top.

So now we are getting to the real picture. If you had to trim the the vent tubes to fit the filter top originally, then the filter top being approx 1/2" thicker than your original air cleaner lid must be very close to the top of the choke horn also, if thats the case then the filter top 'will' be inducing a restriction & change of flow & pressure as the carb 'see's' it. Remember if you create a restriction at that point the signal to the venturis is increased, drawing in more fuel.( A bit like pulling the choke on partially ).

Now is the carb to hood distance that small that you have to run this current main airfilter height, or could you simply fit a longer air cleaner stud & element or possibly trim a bit more out from the hood under the scoop to allow the taller element etc.

In relation to some of the other posts, have you ever had a hard look at a Daytona Coupe carb air inlet??

[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...

[YerDugliness]

I've kept a good eye on this thread b/c I recently replaced the cheap Mr. Gasket air cleaner assembly on my replica with a 9" K&N X-Stream assembly. My only problem so far has been getting adequate hood clearance...for that I had to "abandon" the very nicely radiused base that came with the K&N and use the one from the Mr. Gasket. I ground it down to the point that it stands only about 1/4" above the carb air cleaner mount and I have about 1/4" of clearance now. I chose the X-Stream assembly b/c it seemed to promise greater filter area if not greater filter operation. I have mentioned that with only 1/4" of clearance above the X-Stream's filter top, I'm not sure how much contribution the assembly provides from the top.

Next mechanical improvement to the Cobra includes a repalcement of the current Edelbrock Performer/Edelbrock Thunder combo for an Edelbrock Performer RPM Air-Gap intake and a Quick-Fuel carb....which will absolutely, I'm sure, bring about a scramble for adequate hood clearance again. I already know the Air-Gap sits taller than the Performer, so unless the Q-F is "shorter" than the Edelbrock, I'll be considering alternatives to improve hood clearance again.

I'd like to gain enough hood clearance to retain the current 3" K&N filter AND be able to use the nicely radiused carb base that came with the K&N. I'm told that using Mustang covertible engine/transmission mounts will lower the engine by 3/4", and if that isn't enough I can always have the carb pad on the Air-Gap milled off a bit, perhaps as much as 1/2" or so.

I can't say whether the X-Stream assembly works better than the old Mr. Gasket assembly or not, but I can't imagine that it would work worse, and once I get adequate hood clearance I might just add a taller side element to gain more filtration area.

Cheers from Dugly

[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

[bobcowan]

Originally Posted by mreid

Sounds like it would be worth sealing the air cleaner to the scoop and seeing if that makes a big difference.

I'v considered this. But when I look at it, I can't see trying to feed that big engine at 6,500 rpm's through that one little hole.