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Ram Air Causing Fouled Spark Plugs And Fast Idle

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Last summer I converted my L-88 style hood to ram air and immediately began fouling my spark plugs. But along with the spark plugs fouling it also was fast idling at every stop regardless of how far it had been driven. It turned out to be caused by the ram air as the incoming air was partially closing my choke butterfly which lifted the fast idle cam to it's first notch. As I live in an area where winter temperatures can drop into the low teens I wanted my choke to work but I also wanted it to QUIT working after my engine was warmed up. Hmm. I modified my #3310 Holley's choke housing so it is both spring and vacuum operated; the spring closing it and vacuum forcing it open once the engine was running. I started by installing two silicon A/C o-rings onto the choke pull-off piston and adding a 3/16" nipple to the bottom of the choke housing so vacuum could be applied to the bottom of the piston. Now the coil spring will close the choke butterfly but the moment the engine starts vacuum pulls the butterfly open and keeps it open.
 

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Hib Halverson

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I have the same hood with the same mod, ie: cut the back of the hood so the fresh air induction is functional. I have the same kind of carb, Holley 4150 with an automatic choke. Like yourself, I have the choke to make starting in cold weather easy. I pump the throttle once or twice then turn the key and it starts and runs at a fast idle until the choke comes off.

I've never had the air flow coming in from the back of the hood cause the choke plate to partially close.

That makes no sense that you'd have to go to the extent that you did to get the choke to work.

There's got to be some other problem.

How much clearance do you have between the bottom of your air cleaner top and the choke horn? Also, what are you running for an air filter?
 
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Ram Air

Hib, my hood is modified for a true RAM air as the air cleaner is totally sealed to the hood and the 2" X 14" air intake is in front of the radiator where the air pressure is the highest. At 60 mph it's showing 1" Hg of inlet pressure and 1-1/2" Hg at 80 mph. I'm running a 14" X 3" air filter with a highly modified drop base and Air Gap manifold with 1/4" removed from the carburetor mounting surface and ended up with only 1/16" hood clearance. At around 55-60 mph the incoming air pressure was slightly pivoting my choke butterfly which caused it to lift the fast idle cam up to it's first step; resulting in a 1100 rpm idle in DRIVE and sooty spark plugs. I could kick the fast idle off but it would be fast idling again at the next stop sign so I had to find a way to make my choke work and a way to make it NOT work. So my choke coil will close the butterfly for easy starting and then vacuum pulls it all the way open the moment the engine starts.

As my air cleaner base was cut down and dimpled so much the underside of the lid is only about 3/4" above the front/top of the choke butterfly so there is probably some turbulence there. The really slick thing is the RAM air gave me a 33% boost in fuel mileage; from 10-1/2 to 14 mpg and the obvious benefit of the cool air.

The 4" X 16" rectangular opening behind my air cleaner is just a vent to allow some engine heat to escape thru the rear of the hood so it's not the air inlet as it could appear to be. There is a wall between the 15-1/2" round air cleaner opening and that rectangular vent but you can't see it in these pictures.
 

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More On Ram Air

I never had any choke or fouled plug problems until I converted my hood to RAM air so I knew the RAM air was somehow causing the sudden problems. With the incoming air blowing right at the front of my air filter I think it was also blowing at the front of the choke butterfly; causing it to partially close and cause the fast idle cam to lift to the first notch. Once I modified my choke housing the problem vanished. The vacuum acting on the bottom of the choke pull off piston holds the butterfly open under a considerable force; more force than the incoming air provides. The best part of it was the huge increase in my fuel mileage that I wasn't expecting.
 

Vettehead Mikey

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At 60 mph it's showing 1" Hg of inlet pressure and 1-1/2" Hg at 80 mph. ..... so there is probably some turbulence there. The really slick thing is the RAM air gave me a 33% boost in fuel mileage; from 10-1/2 to 14 mpg and the obvious benefit of the cool air.



As per previous posts the carb air inlet temps of a C3 Corvette are within 1-2*F of ambient while the vehicle is in motion. There are no cool air gains to be had with ram air in this respect.

A 1" hg. change in air pressure is equivalent to about a 1,000 change in altitude or about a 1500 foot change for 1.5" hg. It would be ludicrous to suggest that such a minor change in altitude, only available while the vehicle is at highway speed or higher, would affect fuel consumption by even 3.3%, never mind 33%.

As there is something similar to a standard pleated paper air filter in place, it is equally ludicrous to suggest that the filtered air would be turbulent enough or have enough velocity to blow the choke plate partially closed. The engine is not consuming more air than without the ram air hood- why would the velocity or turbulence increase.

You keep calling yourself an 'engineer'. I presume you mean that your job was operating a railway locomotive and not any type of graduate mechanical or civil engineer. The fractured fairy tales under the guise of 'science' are getting tiresome. :eyerole
 

Antz81

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I could kick the fast idle off but it would be fast idling again at the next stop sign so I had to find a way to make my choke work and a way to make it NOT work. So my choke coil will close the butterfly for easy starting and then vacuum pulls it all the way open the moment the engine starts.

In other words your choke no longer operates correctly. Once the engine starts it's open instead of slowly opening as the engine warms up.
 

Vettehead Mikey

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In other words your choke no longer operates correctly. Once the engine starts it's open instead of slowly opening as the engine warms up.

Plus the amount of turbulence created going stop sign to stop sign, supposedly the cause of the choke plate issue, is non existent.
 
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As per previous posts the carb air inlet temps of a C3 Corvette are within 1-2*F of ambient while the vehicle is in motion. There are no cool air gains to be had with ram air in this respect.

A 1" hg. change in air pressure is equivalent to about a 1,000 change in altitude or about a 1500 foot change for 1.5" hg. It would be ludicrous to suggest that such a minor change in altitude, only available while the vehicle is at highway speed or higher, would affect fuel consumption by even 3.3%, never mind 33%.

As there is something similar to a standard pleated paper air filter in place, it is equally ludicrous to suggest that the filtered air would be turbulent enough or have enough velocity to blow the choke plate partially closed. The engine is not consuming more air than without the ram air hood- why would the velocity or turbulence increase.

You keep calling yourself an 'engineer'. I presume you mean that your job was operating a railway locomotive and not any type of graduate mechanical or civil engineer. The fractured fairy tales under the guise of 'science' are getting tiresome. :eyerole


I am real sorry about an error I made so I'll correct it right now. I'm seeing an increase of 1" Wc (water column) at 60 mph and a 1-1/2" Wc at 80 mph. So I stand corrected. So you're telling us the HOT blast of air coming out of the rear of the radiator is just ambient temperature? If no heat is being shed at the radiator what is the point in using a radiator if it doesn't do anything?

So again I ask you to explain why my choke butterfly was partially closing and lifting the fast idle cam when it reached cruising speeds only after I converted my hood to ram air.
 

Vettehead Mikey

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I am real sorry about an error I made so I'll correct it right now. I'm seeing an increase of 1" Wc (water column) at 60 mph and a 1-1/2" Wc at 80 mph. So I stand corrected. So you're telling us the HOT blast of air coming out of the rear of the radiator is just ambient temperature? If no heat is being shed at the radiator what is the point in using a radiator if it doesn't do anything?

So again I ask you to explain why my choke butterfly was partially closing and lifting the fast idle cam when it reached cruising speeds only after I converted my hood to ram air.

You tell us why the choke plate doesn't reopen when the car slows down. There tons of factory and homemade ram air set ups from the era. Not one person has reported the condition you mention.

You've previous admitted not really knowing what the inlet temperatures are, pre- and post mod, and are therefore just guessing. I've measured mine precisely with and without ram air on a C3 and know exactly what the difference is: 1-2*F anywhere between legal highway limits up to 100 mph. You ass-u-me far too much with your psuedo-science.

1" of water column is equal to 0.036 psi. That's equivalent to a change in altitude of about 80 feet, on a hot day. Please explain how such a minute change could affect fuel consumption so drastically, and precisely how you measured it in order to come to your conclusion.

Did Trump operate an engineering school too? :chuckle
 
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You tell us why the choke plate doesn't reopen when the car slows down. There tons of factory and homemade ram air set ups from the era. Not one person has reported the condition you mention.

You've previous admitted not really knowing what the inlet temperatures are, pre- and post mod, and are therefore just guessing. I've measured mine precisely with and without ram air on a C3 and know exactly what the difference is: 1-2*F anywhere between legal highway limits up to 100 mph. You ass-u-me far too much with your psuedo-science.

1" of water column is equal to 0.036 psi. That's equivalent to a change in altitude of about 80 feet, on a hot day. Please explain how such a minute change could affect fuel consumption so drastically, and precisely how you measured it in order to come to your conclusion.

Did Trump operate an engineering school too? :chuckle


I asked you to tell us why my engine was fast idling EVERY TIME after running at cruising speed and you dodged the question.

As I reduced my speed the choke butterfly most certainly did reopen but the fast idle cam was still engaged. So according to your uh "testing" you determined the ambient air does NOT get hotter as it passes thru the radiator core? Do you think "cold air" packages are just a gimmick? Do you think radiators are unneeded gimmicks as are fan clutches?

Under hood temperatures get brutally hot when a vehicle is traveling down the highway on a summer day and as the speed increases the under hood temperature also increases. On a 100 degree summer day it's quite normal for the under hood temperature to reach 400 degrees and that is a LOT hotter than the 100 degree ambient temperature.
 

kpic

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Did Trump operate an engineering school too? :chuckle

That Sir, is a keeper.

Toobroke....
They're being nice. Point is, you have something totally hosed and your version of a ram air device has nothing to do with it.

I'm not going to ask how you set up a manometer to measure air flow on a moving vehicle. As I don't need basted in more of your bull manure.

I've used a manometer to measure "air flow" for the tubes in HF RF amps.

"Unfortunately small blowers aren't very good at generating pressure. Propeller-fan blowers are useless for this purpose because they are designed only to move air against a very low resistance. You need the centrifugal type of blower shown in Fig 2. Fig 4 is a rough estimate of the pressure generated by such blowers, according to the diameter of the vaned 'hamster wheel' inside which moves the air. Note: this information is only valid for motor speeds of 2600-2800RPM. Do not use a blower with a lower motor speed than this - it definitely won't give you the pressure you need. Also, do not remove the casing of the blower, as suggested in one long-running ARRL design for 144MHz. There's a reason for that special 'snail' shape, and the blower won't develop much pressure without it. According to Fig 4, either one or two 4CX250s in the configuration of Fig 2 will need a blower with about a 4.5-5in wheel diameter, such as the Airflow Developments 45CTL or the Air Control Installations VBL5/3. The more common '4in' blowers are marginal, and if your amplifier continues to survive using one of those, it's a tribute to the valves and not the blower! There's a lot more detail in Chapter 6 of The VHF/UHF DX Book (see RSGB Bookshelf, pages 94, 95)."
Blowers for power amplifiers

Yes, I'm a Ham operator.


You keep calling yourself an 'engineer'. I presume you mean that your job was operating a railway locomotive and not any type of graduate mechanical or civil engineer. The fractured fairy tales under the guise of 'science' are getting tiresome. :eyerole

You forgot maintenance engineer. ;)

"Fractured fairy tales" is 2 classic keepers in one evening. A few steps above my basted in bull manure.

Toobroke.....
The problem is you don't make enough sense for anyone here to help you.
 

kpic

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I work with maintenance engineers. They think toobrokes theories are quite good...


Well good for a laugh anyway. :chuckle

Where I used to work a maintenance engineer who is into 60s Ford Mustangs and he thinks; well I can't post what he thinks when it comes to toobroke..

All my hobbies have torque or recoil. Or I find enjoyment yapping about a bud;s 1969 Cutlass S as I do another bud's 64 Wildcat Vert.
As, unlike 2broke, they know what they are talking about. :w:w
 

dougelam

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I never had any choke or fouled plug problems until I converted my hood to RAM air so I knew the RAM air was somehow causing the sudden problems. With the incoming air blowing right at the front of my air filter I think it was also blowing at the front of the choke butterfly; causing it to partially close and cause the fast idle cam to lift to the first notch. Once I modified my choke housing the problem vanished. The vacuum acting on the bottom of the choke pull off piston holds the butterfly open under a considerable force; more force than the incoming air provides. The best part of it was the huge increase in my fuel mileage that I wasn't expecting.
First off how in the hell does one get better fuel economy AND gas fouled spark plugs at the same time?
Second how does one get more CFM from one's DIY ram air hood?
Especially after they claim it is fixed,
43e732dc69890764a54e07c3638456d2.jpg


Now I'm not an engineer by trade but as I remember it Ram air hoods weren't very effective on street cars not unlike useless headers with mufflers attached. I believe they do nothing but look good ;)

I DO KNOW choke blades are designed to stay open from air velocity so someone must have a bad choke coil or whatever he uses to open it.

Now for the fuel milage increase it sounds like someone un-restricted their air intake system by accident ☺

Sent from my SM-T530NU using Tapatalk
 
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After I got my Ram Air constructed I was quite surprised to find my engine fast idling at every stop after having it up to a cruising speed. As long as I putted around at a slow speed the choke and fast idle stayed off but the moment I took it up to 55-60 mph I found it fast idling again. On a Holley it takes very little movement of the choke butterfly to lift the fast idle cam to it's first notch so I could only assume the incoming air was buffeting the butterfly and also causing an exceptionally rich air/fuel mixture. After I modified my choke and used vacuum to pull it completely off my problem vanished. Yes, I would like my choke to remain on a little bit longer but my goal was to get it to work long enough to get my engine started in real cold weather.

As far as the 33% mileage gain goes I keep tract of my fuel mileage at every fill-up. Prior to the Ram Air every tank netted 10-1/2 mpg and after I got it installed every tank netted 14 mpg. I think that is pretty good considering it only got 8 mpg when I bought it 6 years ago. It was a bone-stock 365 hp 454" with TH400 and 3.08 gears. Now it has a 10 to 1 compression, Magnum cam, Air Gap with a #3310 Holley, A beefed TH700R4, and 3.70 gears. So I increased it's power by maybe 75-80 hp and am getting 75% better fuel mileage. Sounds like I'm doing something right, wouldn't you say?
 

kpic

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I'm running the 286-H Competition Cams hydraulic flat tappet with a 236/236 duration and .556"/.556" lift (part #11-318-4). With the 3.08 gears my engine rpm was too low for adequate runner velocity so when I switched to the 3.70's the runner velocity and fuel mileage increased. And I'm running a #3310 with an electric choke.
 

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