Air Cleaner Quandary

**spd4me** · February 24th, 2004, 10:03 PM

This is for any air cleaner or carborator experts. I've got this bad 396W Stroker with the Trick Flow heads and a Holly 750. I have a K & N 14" dia by 21/2" high air cleaner with a solid chrome top. I runs strong all way up to 6,000. I figured the more air the better so I bought a $85. K & N Xtreme Air Cleaner Top. When the motor reaches 4,000 it really starts to sputter and cough. Its really embarrassing when your running down the interstate next to a turbo Porsche. Could it be I need a bigger jet?

**jhaynie** · February 24th, 2004, 10:32 PM

I'm not a mechanic by any stretch, but I can't believe changing filters would have that drastic of an affect on the fuel/air delivery. Maybe it is some other problem. If you put the old filter back in does it fix the problem?

John

**eliminator** · February 24th, 2004, 10:47 PM

I tend to agree with John, I would say their are other issues present. Re-jetting would not help that problem. I would pull my carburetor and pull the float bowls and check to see it the powervalve was loose or a jet had backed out. There are several things it could be really, even the sparkplugs. You will just have to isolate the problem, ignition, or fuel/air problem.

Rick

**pgermond** · February 24th, 2004, 10:57 PM

Did somebody swap out your MSD chip [8D]

Phil

427 Roadster, #4279436
Southern Automotive FE
3:31 and Toploader

Roseville (N.Cal)

**Copper01** · February 24th, 2004, 11:12 PM

You might also want to check your fuel filter. By the time you hit 4,000 rpm, you're eating gas at a pretty good clip and if your filter is dirty, you may start experiencing fuel starvation that wouldn't be evident at lower rpm's.

Ben
Unique 427
SA 427SO w/ Toploader
Guardsman Blue w/ White Stripes

**Jim Harding** · February 25th, 2004, 02:51 AM

Well before you go and rip and tear into the carb, do like John said.... put the old top on the filter and try it agian.... although I don't think that a new top should make that much difference, at least eliminate it first.

Jim Harding
La Plata, Maryland

1982 #3004

**ericeckhoff** · February 25th, 2004, 01:23 PM

I had same problem when I changed air cleaner top. The air coming in the hood scoop hit the air cleaner from the front and top and messed up the air flow (top of air cleaner smelled like gas). Taping off the hood scoop cured the problem but didn't look very good so I built a deflector for the front of the air cleaner base to drop 2 in below base and 1 in above cleaner. It keeps hot air from radiator away from carb and gets great flow from hood scoop.Works for me--good luck.See photo link.
Eric
http://www.clubcobra.com/photopost/d...801update2.jpg

**spd4me** · February 26th, 2004, 02:46 AM

John I can drive down the hwy and it sputter. Stop and put the solid top on and it runs great. I think Eric may be onto something.
Eric Your saying the air flow characteristics are messing up the sucking in of air thru filter? Did you rivit that shield to the bottom of air cleaner? Have you ever seen a NASCAR air cleaner? They only allow air to enter from the rear. Maybe that's to pull the cooler air in from the back of hood and not from front where it's hotter. Anyway I'll go find a piece of shinney metal.

**WBofTN** · February 26th, 2004, 02:56 AM

spd:
Your right NASCAR does pull air from the base of the windshield - its cool
and less turbulant.
WB

'93 Unique 427/351W/4sp

**ericeckhoff** · February 26th, 2004, 03:20 AM

Yes, I rivited it to 2 L brackets with 1/4 inch space between filter and shield so it still breathes all around and still clears distributor. Drove car in today and seems to work good. Let me know if you want more pictures.
Eric
ericeckhoff@comcast.net

**excelguru** · February 26th, 2004, 11:23 AM

Here's what's happening: at highway speeds, the air rushing across the top of your X-Treme air filter cover is actually siphoning the air/fuel mixture UP AND OUT of the carb! Others have reported similar results (search CC). You can even argue (and win the argument) that at some speeds, air is actually EXITING the hood scoop. Sounds crazy, huh?

Keith

Unique Motorcars
Southern Automotive
Bruce Bunn (the painter)

My Photo Album

**jhaynie** · February 26th, 2004, 09:41 PM

It would be interesting to be able to measure HP at speed (with the wind, won't work on a dyno) and see if there is actually a net gain, or loss from installing the xtreme filter. If air is getting sucked out, like Keith said, it could be hurting performance, although it may be so slight, you would not even notice it.

JOhn

**eliminator** · February 26th, 2004, 11:01 PM

So much for these filters on Cobra's, sometimes better is not always good.

Rick

**Brent** · February 26th, 2004, 11:18 PM

There is such a thing as too much air. A stoichiometric mixture is the perfect mixture combination of fuel and air for maximum combustion, (around 14 parts air to 1 part fuel).An engine calculation based on rpm and CCs will determine how many pounds of fuel per hour the engine will require. This is the base jetting for Fuel injection TBI or IR,Carb sizing,or IR carbs. The only difference is you are dividing the lbs of fuel by 8 for IR applications.
We had to draw air from outside with a fan when we would dyno the SC engine. As soon as we would hit the throttle it would create a negetave pressure in the room and HP would drop. Sad to say we were stupid and chased the problem for a couple of days. Increasing the fan speed did help until we hit a point and then it made no difference.

Brent

**jhaynie** · February 26th, 2004, 11:31 PM

Yeah, I think it would be difficult to simulate 70mph down the road throught he hoodscoop in a shop environment. I'm sure someone has figured out some way to do it, but I don't know what it is.

**JerryBP** · February 26th, 2004, 11:54 PM

Some of the Pantera guys found out that the X-Treme wont work at more than 50 mph on a Pantera as the air flow is from the engine compartment up and out over the rear deck, pulls air out of the carb.

Work in Progress, Unique 427-9429 400+hp 351C Tremec 3550-2 5spd Coal Black
by Bruce, Greg & Jerry Porter Caldwell, Ohio

**spd4me** · February 27th, 2004, 01:02 AM

I'm really amazed at how much knowledge all you guys have. Like they say in my business LESS IS MORE. By the way Eric, how did you know to do the shield trick? I'll probably make up one and try it. Hate to waste $85.00 on filter. I wonder if that's why the FIA race cars had that funny round hole shield in the scoop.

**JerryBP** · February 27th, 2004, 01:15 AM

In fact I remember reading somewhere that controling air flow around the carbs at high speed was the reason for the Turkey Pan.

Work in Progress, Unique 427-9429 400+hp 351C Tremec 3550-2 5spd Coal Black
by Bruce, Greg & Jerry Porter Caldwell, Ohio

**clayfoushee** · February 27th, 2004, 01:41 AM

Very interesting thread......don't have anything intelligent to add other than my experience with my single carb, turkey pan, equipped side-oiler has never stumbled up to the 6K rev limiter. Sounds like there was a real good reason for the turkey pan.

Clay

'98 Unique #9299, 427FE side oiler, top-loader (close), 3.31 rear

Annapolis, MD

**ericeckhoff** · February 27th, 2004, 01:56 AM

I had seen deflectors on several older performance cars including the turkey pan on the Cobra and the early front engine Ferrari 250 and Testerrosa . I like the better (cfm) breathing of a larger filter at lower speeds since I drive at 7-11000 feet above the sea so I didn't want the 8 1/2 inch filter with the turkey pan even though they look cool. Just my trials with my toy. Enjoy !

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