Big RPM drop with stelling /helling

[KobraKarl]

Well I guess i'm not done tuning these carbs yet after all...............I received my Stelling/Helling cleaners yesterday and of course bolted them right on for a spin down to a perfomance auto show. As soon as it fired up the rpm';s went to 1600, and I thought it was the choke and the fast idle cam ............after it was warm it was still doing 15/1600 ???????????? I reset the idle screw and went.................

does this mean i have an air leak?
does this mean i have my idle too rich?
should i have expected this?
does this mean I should always tune with these cleaners in place?
does this mean i might be a moron?


Any help appreciated thanks Karl

[Tom T.]

Karl,

Get the K&N filters, they flow much better. Enzo at Finishline has them. You probably should tune with them on, but that's just my opinion. After all, that's how the car will be run.

TT

[speed220mph]

What it may mean is the Stelling/Helling air-filter assemblies may have been less of a restriction than the filters you replaced, thus leaning out the A/F mixture and increasing idle rpm. If this is the case, you should notice an obvious increase in power and fuel mileage.

Another possibility is the change in airflow through the filter assemblies may have improved fuel atomization and vaporization through the carburetors and in the intake runners, resulting in improved combustion. Either way, pressure drop or airflow change, you found an improvement. This being the case, think about using K&N filters.

By the way, alway tune carburetors with the complete induction system in place, which includes the air cleaners. And, no, you're not a moron. Induction systems have confounded the best fuel-systems people at one time or another. Regardless, there's always a simple reason why things happen that don't seem so simple at the time.

Good luck.

[NROTOXIN]

Karl,

rpm drop or increase?

curtis

[KobraKarl]

Speed,

I had tuned them without filters old or new.

Tom T,

The K&N are a 1/2" taller than stock S&H, i can shred toilet paper between the acorn nut and the bottem of my hood now!


Curtis,

600 rpm increase!

[A Snake]

Just FYI, when I had my 427 S/O dynoed, (single 4bbl) it was done without an aircleaner. Just out of curiosity, we put on the Stellings & Helling unit and gave it another pull. No other changes were made. The engine lost 61 BHP.

I'd suggest the following:

1. Go with the K&N for general driving and maybe track use.

2. Unless you plan to put on 20,000 miles a year, do as I did and run no aircleaner. Just put it on for shows when the hood will be open. And no, you won't ruin the engine unless some knothead drops a bold down the carb. As much oil as these engines use and as often as the oil is changed, you'll have a hard time causing injury.

Just some thoughts from one who has already been there.

Al

[KobraKarl]

I just realized I posted "RPM DROP" @#$%#$%^# It should have read "RPM INCREASE" Cripes.......................

Try Again? thanks, Karl the moron

[Bob Parmenter]

Gosh Karl, it's hard to argue with any of your self characterizations.

Al's experience with losing 61hp pretty much tells the tale. Major restriction going on, you're running richer now, which probably contributes to the higher rpm.

Between the shallow sides, and inefficient filter media, there's a lot of opportunity for limiting air volume. I'd go with the suggestion to bag the mustachioed smiley faces, except for all those sun shiney show days we have, for a good K&N setup. Look into the xtreme line with the filter in the top piece as well to maximize air flow. There should be a drop base unit that will give you some space relief. Personally I think you should run a filter(s), gotta keep those rocks, birds, and little children out of the engine.

[Bob Putnam]

Dyno work should always be done with as much equipment as possible to duplicate the engine in the car. Large horsepower losses such as experienced by Al may as much a result of changing the mixture as much as any restriction of the air flow.
Karl's change may have from a slightly richer mixer at idle due to higher vacuum, or better use of "standoff" fuel that sometimes hovers above the carb intake.

[Ron61]

A Snake,

You are correct about running with no air filter except I live in a very dusty area and would have a motor full of sludge in about 100 miles. But I have ran mine for short drives when working on it with the filter off and noticed a seat of the pants increase. I did go to the K&N Filter and that made a huge difference over the filter I was using. I do change my oil very often and after any hard, long run. Some people around here think I am crazy to use so much oil but I feel oil is cheaper than motors. And I do my tuning with the filter on and everything just like I drive it.

Ron

[wicked fast]

Put the filter base and lid on the carb as it would fit with the filter
installed.
First thing that I noticed is how close the choke horn is to
the top of the air cleaner.
This almost chokes off the engine with the air cleaner lid.
I plan on using a Proform main body that
has had the choke milled off.
Should cure the potential problem.
Cheers,
Bill Cook

[speed220mph]

Well Karl, things make a lot more sense now. The filter, which is restricting airflow, is fattening up the A/F mixture.

By the way, your carbs are of the "reverse-idle" type? Idle screws work on the air bleeds rather than idle fuel feed. The reverse system is enrichens when the screws are run in and leaned when backed out.

There are cases where a good air-cleaner assembly helps airflow, but the original Cobra intake system is not one of them. It's too bad that Shelby didn't go with a larger scoop that would accommodate a more efficient filtering system. So, we must now pay the price to keep our Cobras "original".

When you need serious power, remove the air-cleaners all together, but running with unfiltered air will cause excessive top-end wear--rings, bores and pistons.

[KobraKarl]

Speed,
the carbs are stock 1964 duals with the 4160 bodies , I think they are conventional idle screws (counter clockwise = rich?)

Bob Parmenter,
The bottom of the s&h filter base is right on top of the carb now (about an 1/8" clearance ) maybe the next step is to examine the motor mounts...........does someone make a thinner one?

Bob Putnam
Standoff fuel? I hadnt heard of that one?

[Mr.Fixit]

First off, you don't need a choke with dual quads. Second, I would start by looking for a mechanical interference between the aircleaner assemblies and the carb. Have motor running and remove/install filters and their bases/lids. I haven't seen a 600 rpm idle change due to fuel mixture alone, it is an airflow issue. Maybe the lids are forcing the choke shut and getting you into fast idle cam territory.

[SCOBRAC]

Your air filters are not the problem. I think your car is just haunted.. in all seriousness you reassembled something incorrectly, thinking back to your carb flooding and questions regarding rebuilding and tuning Holley Carbs.. (was that in Dec.)

I suspect you got something stuck in an air bleed or other other orfice that has significantly changed your mixture.. As for the 61 bhp loss noted earlier, same concept.. final tuning especially when you are looking at dyno time / cost should be done with all periferal accessories in place when possible then and only then can you make a judgement on mixture / jeting bleed sizes..

[Turk]

About a year or so ago, there was a thread comparing almost ALL air filters.

If my memory serves me right, the differences between K& N to Napa, to K-Mart and up to NO filter had almost no effect on the HP.
This was a study done by a respectful organization not two guys in a garage.

Can someone resurrect that thread for a second visit?

TURK

[southernfriedcj]

Driving a car without an airfilter would seem to be a good way to invite an engine fire. If you have backfire through the carb(s), you better be fast with the fire extinguisher! I've never put a burning Cobra out, but I put several hundred car fires out in my time on the Atlanta Fire Dept.

[Ron61]

I remember the thread Turk referred to and it basically said that as long as you don't use a really restrictive air filter like some of the small ones that are for show you won't gain any big amount. So far as driving without a filter, not only is it a possible fire hazard as mentioned by southernfriedcj but you get every bug and anything else that comes through the hood scoop into the engine. Not at all a good idea here where it is so dusty.

Ron

[KobraKarl]

Haunted ??!! Naaaaw .................well she is a little spooky..........

I have checked aad re-checked every thing, and there is no mechanical interferance with the new housing.

I am going to take a little of every ones advise and use the very porous brown filter media.that also came with the set. This is also a little taller so I am going to use a bol tconnector under the lid and secure it with a hex button bolt (should gain me 3/8")

Now i wonder if I will have a big RPM drop??????

As always thanks for your replys Karl

[SCOBRAC]

HMMMMMMMmmmm.. (psychic sound)

You got something different than before.. Not 1600 but not normal.. This will happen as barometric pressure changes and as whatever the obrsruction is changes.. This will happen again and again until the obstruction either clears itself or gets lodged into one position..

Take the carb off and blow it out with chemtool.. Try that before you tear them down.. It might work.. Buy some thin wire (or welding torch cleaner) and clean the air bleeds, be careful not to use anything hardened or abrasive that will change their flow characteristics or scratch the orfices..