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1974-76 Cadillac deville Carb Cold Air Inlet Duct Question?

Started by EAM 17806, March 31, 2018, 03:41:14 PM

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EAM 17806

Does anyone know why Cadillac would install the cold air inlet duct on 1974-1976 devilles with carburetors.  In 74 some contraption was installed in the middle of the duct, then in 75 it was modified a bit until in 76 it was removed completely.  What makes me curious is why was this duct directed right behind the driver's side headlights and not behind the air opening grille to allow cool air to flow through to the air cleaner and into the carb.  Obviously, by placing the air duct directly behind the headlights and not the grille would somewhat lessen the air flow to the air cleaner. Today I removed this duct from the air cleaner which allowed much more air into the  it which seems to have improved the acceleration, idle, etc.  The question is why would those brilliant engineers ever want to restrict somewhat this air flow.  Any thoughts, I'd like to read them from all you Cadillac engineers!   EAM
Ev Marabian

1976 Cadillac Coupe DeVille, 1989 Chevrolet Caprice Classic, 1990 Pontiac Bonneville and 1996 Buick Skylark

"Cadillac Kid" Greg Surfas 15364

EV,
The "contraption" is a sound attenuator, intended to reduce the inlet air sound level.  Of course as we get older, our hearing seems to not notice sounds like that.
Airflow through the inlet, and duct to the air cleaner are not restricted numerically enough to be a factor, and the routing does help the sound attenuation.
Cadillac Kid-Greg Surfas
Director Modified Chapter CLC
CLC #15364
66 Coupe deVille (now gone to the UK)
72 Eldo Cpe  (now cruising the sands in Quatar)
73 Coupe deVille
75 Coupe deElegance
76 Coupe deVille
79 Coupe de ville with "Paris" (pick up) option and 472 motor
514 inch motor now in '73-

EAM 17806

Quote from: "Cadillac Kid"  Greg Surfas 15364 on March 31, 2018, 05:46:33 PM
EV,
The "contraption" is a sound attenuator, intended to reduce the inlet air sound level.  Of course as we get older, our hearing seems to not notice sounds like that.
Airflow through the inlet, and duct to the air cleaner are not restricted numerically enough to be a factor, and the routing does help the sound attenuation.
Quote from: "Cadillac Kid"  Greg Surfas 15364 on March 31, 2018, 05:46:33 PM
EV,
The "contraption" is a sound attenuator, intended to reduce the inlet air sound level.  Of course as we get older, our hearing seems to not notice sounds like that.
Airflow through the inlet, and duct to the air cleaner are not restricted numerically enough to be a factor, and the routing does help the sound attenuation.
GREG:  Then why was it completely eliminated in 1976 (The sound attenuator) and still somewhat restricted the air flow since the inlet was placed right behind the headlights. So now the question is why does the 1976 devilles with a complete clear duct right to the air cleaner still have any relevance for improvement?  Much more air flow is flowing to the cleaner with the duct detached and I'm going to leave mine off.  EAM
Ev Marabian

1976 Cadillac Coupe DeVille, 1989 Chevrolet Caprice Classic, 1990 Pontiac Bonneville and 1996 Buick Skylark

"Cadillac Kid" Greg Surfas 15364

Cadillac Kid-Greg Surfas
Director Modified Chapter CLC
CLC #15364
66 Coupe deVille (now gone to the UK)
72 Eldo Cpe  (now cruising the sands in Quatar)
73 Coupe deVille
75 Coupe deElegance
76 Coupe deVille
79 Coupe de ville with "Paris" (pick up) option and 472 motor
514 inch motor now in '73-

EAM 17806

Quote from: "Cadillac Kid"  Greg Surfas 15364 on March 31, 2018, 07:43:33 PM
Ev<
And you measured this how?
Greg Surfas
Since the air inlet duct is placed right behind the headlights this obviously is restricting the air flow through the duct; with the duct removed from the air cleaner connection, air from whitin the engine area has complete access to the air cleaner without any slight restrictions at all.  Don't you agree there isn't any measurement needed for this obvious flow of air?  EAM
Ev Marabian

1976 Cadillac Coupe DeVille, 1989 Chevrolet Caprice Classic, 1990 Pontiac Bonneville and 1996 Buick Skylark

"Cadillac Kid" Greg Surfas 15364

Ev,
The air from the under hood area is much warmer, less dense and ANY POSSIBLE additional air would be offset by it's "poorer" conditions. Any and all "restrictions" on the inlet side as well as the exhaust side of the engine were figured into all the design of the motor's components.
Greg Surfas
Cadillac Kid-Greg Surfas
Director Modified Chapter CLC
CLC #15364
66 Coupe deVille (now gone to the UK)
72 Eldo Cpe  (now cruising the sands in Quatar)
73 Coupe deVille
75 Coupe deElegance
76 Coupe deVille
79 Coupe de ville with "Paris" (pick up) option and 472 motor
514 inch motor now in '73-

"Cadillac Kid" Greg Surfas 15364

At idle or at very slow speed, of course the engine are flow quantities are low, but at high speed when air flow requirements increase, the "barn door" aerodynamics of these cars actually helps, and the location of the air inlet is in a high pressure area, thus actually helping th4 air flow as oppose to the area behind the radiator which is at  a lower pressure.
Greg Surfas
Cadillac Kid-Greg Surfas
Director Modified Chapter CLC
CLC #15364
66 Coupe deVille (now gone to the UK)
72 Eldo Cpe  (now cruising the sands in Quatar)
73 Coupe deVille
75 Coupe deElegance
76 Coupe deVille
79 Coupe de ville with "Paris" (pick up) option and 472 motor
514 inch motor now in '73-

EAM 17806

Quote from: "Cadillac Kid"  Greg Surfas 15364 on April 01, 2018, 04:01:06 AM
At idle or at very slow speed, of course the engine are flow quantities are low, but at high speed when air flow requirements increase, the "barn door" aerodynamics of these cars actually helps, and the location of the air inlet is in a high pressure area, thus actually helping th4 air flow as oppose to the area behind the radiator which is at  a lower pressure.
Greg Surfas
GREG!  I can't understand where you state the present location of the air inlet is in a high pressure area when it's blocked by the headlights and its framework. Much better cool air flow would be behind the grille area not the radiator section which of course would be at a lower pressure. I'm assuming you believe there is more cool air coming in from the air inlet behind the headlights than opposed to a smaller amount coming from the fan air pressure into the air cleaner funnel.  Well Greg, this discussion sure is interesting to me but at this point I still can't contemplate why the placement of the air inlet was put behind the headlights instead of the grille where much more cool air would have been directed to the air cleaner/carb. Greg, your thoughts are highly respected.  EAM
Ev Marabian

1976 Cadillac Coupe DeVille, 1989 Chevrolet Caprice Classic, 1990 Pontiac Bonneville and 1996 Buick Skylark

savemy67

Hello Ev,

It does seem counter-intuitive to place the air inlet behind the headlight assembly.  However, if one thinks in terms of air flow, the air is not being pushed into the air inlet.  It is being sucked into the air inlet by the vacuum created by the pistons' intake stroke.  Even at the max RPM of the engine (around 4500), the cross sectional area of the intake duct and its placement are sufficient to allow enough air to be sucked into the engine.

If the max RPM of the engine was 9000 or higher, that would be a different situation, and a higher rate of intake air would be needed, perhaps necessitating a different air inlet location.  Remember too, that intake has to be considered in conjunction with exhaust, so the Cadillac engineers couldn't consider one without the other.  Many modify their engines on the intake side but neglect to modify the exhaust - usually because it is more expensive to modify the exhaust.

You can drive your car straight into a hurricane force headwind, and the ram-air effect will have negligible results.  A turbo or supercharger is the ticket.  At 450 MPH, the P-51 relied on ram airflow only for cooling.  The air is too thin at 15,000 feet.

Respectfully submitted
Christopher Winter
Christopher Winter
1967 Sedan DeVille hardtop

"Cadillac Kid" Greg Surfas 15364

Ev

Just one (more) last thing.  In the era we are discussing Cadillac Motor Divisions's Engineering Department did not use computers for computer simulations, they did not use CFD to see if their ideas worked.  What they did was develop a design, make the devices and then using a multiplicity of instrumentation, try out that design/device in real world conditions. 
If the design did not live up to expectations it was modified until it did.
Again, at speed, say 60 MPH when the engine turning at say 2100 RPM  intake air flow requirements are 302 cubic feet per minute (CFM)
Figuring all devices in the inlet air stream from the intake through the air filter inlet, the pressure drop at 302 CFM is just about 0.777 inches of water column.
At 60 MPH the velocity pressure (of the air in front of the car) is 1.738 inches of water column.
Any pressure drop in the inlet tract to the air cleaner is overcome by taking the high pressure air from a relatively calm, high pressure point.
Air behind the grill is turbulent and velocity directed to the radiator.
If you want you can do the calcs yourself to verify my math.
Greg Surfas
Cadillac Kid-Greg Surfas
Director Modified Chapter CLC
CLC #15364
66 Coupe deVille (now gone to the UK)
72 Eldo Cpe  (now cruising the sands in Quatar)
73 Coupe deVille
75 Coupe deElegance
76 Coupe deVille
79 Coupe de ville with "Paris" (pick up) option and 472 motor
514 inch motor now in '73-

EAM 17806

Quote from: savemy67 on April 01, 2018, 10:10:12 AM
Hello Ev,

It does seem counter-intuitive to place the air inlet behind the headlight assembly.  However, if one thinks in terms of air flow, the air is not being pushed into the air inlet.  It is being sucked into the air inlet by the vacuum created by the pistons' intake stroke.  Even at the max RPM of the engine (around 4500), the cross sectional area of the intake duct and its placement are sufficient to allow enough air to be sucked into the engine.

If the max RPM of the engine was 9000 or higher, that would be a different situation, and a higher rate of intake air would be needed, perhaps necessitating a different air inlet location.  Remember too, that intake has to be considered in conjunction with exhaust, so the Cadillac engineers couldn't consider one without the other.  Many modify their engines on the intake side but neglect to modify the exhaust - usually because it is more expensive to modify the exhaust.

You can drive your car straight into a hurricane force headwind, and the ram-air effect will have negligible results.  A turbo or supercharger is the ticket.  At 450 MPH, the P-51 relied on ram airflow only for cooling.  The air is too thin at 15,000 feet.

Respectfully submitted
Christopher Winter
CHRIS!  Are you implying that it is the cool air that is necessary to enter the air inlet as opposed to too much warm air entering the air cleaner funnel?  Then it would appear the engineers were minimizing the direct cool air flow to contemplate the relevance of the exhaust too, would that have been their objective?  EAM
Ev Marabian

1976 Cadillac Coupe DeVille, 1989 Chevrolet Caprice Classic, 1990 Pontiac Bonneville and 1996 Buick Skylark

"Cadillac Kid" Greg Surfas 15364

How are the calcs coming Ev?  It is ust a simple conservation of energy balance along with the conversion of static to velocity back to static pressure equations.
Basic air flow along with some sound attenuation equation.

Chris,
The P-51 was liquid cooled.  The coolant and oil heat exchangers were below the fuselage and accessed by a thermally controlled shutter.  Kelley Johnson used the principle of energy conversion in the design of the "duct" that conveyed high speed, high velocity pressure ram air through the heat exchangers where some pressure was "used up" passing through.  This would have normally resulted in drag to the air frame, but by converting the residual pressure (after the heat exchangers)into velocity pressure the air exited the air duct at whaty ammounted to "boost" conditions.  By simple air flow design he added additional speed to the aircraft with out additional horsepower or fuel consumption.
Greg Surfas
Cadillac Kid-Greg Surfas
Director Modified Chapter CLC
CLC #15364
66 Coupe deVille (now gone to the UK)
72 Eldo Cpe  (now cruising the sands in Quatar)
73 Coupe deVille
75 Coupe deElegance
76 Coupe deVille
79 Coupe de ville with "Paris" (pick up) option and 472 motor
514 inch motor now in '73-

EAM 17806

We all would presume this cool air inlet duct system has a good concept behind it, then why didn't the other GM DIVISIONS pick it up in their cars, such as, Chevrolet, etc?  My 1989 Chev Caprice Classic 5.0 ltr (305 cu) didn't pick up this concept nor the years before that too, Why? Just a thought for some knowledge!   EAM
Ev Marabian

1976 Cadillac Coupe DeVille, 1989 Chevrolet Caprice Classic, 1990 Pontiac Bonneville and 1996 Buick Skylark

"Cadillac Kid" Greg Surfas 15364

They all did later on, but the device cost money.
Greg Surfas
Cadillac Kid-Greg Surfas
Director Modified Chapter CLC
CLC #15364
66 Coupe deVille (now gone to the UK)
72 Eldo Cpe  (now cruising the sands in Quatar)
73 Coupe deVille
75 Coupe deElegance
76 Coupe deVille
79 Coupe de ville with "Paris" (pick up) option and 472 motor
514 inch motor now in '73-

EAM 17806

Quote from: "Cadillac Kid"  Greg Surfas 15364 on April 02, 2018, 05:29:07 PM
They all did later on, but the device cost money.
Greg Surfas
GREG: How costly could this device be.  I can't imagine that would be the reason for not installing on the other GM cars until much later. Cadillac did it in 1974 and Chevrolet still didn't have it up to 1990, that's 16 years.  About what years did they start putting this into GM cars.  There really isn't anything to the material to refrain them for installing it until much later; one cheap plastic duct and a plastic small housing at the inlet. It would be quite interesting if someone could shed some light as to why it took GM so long to implement this in other GM cars.  Thanks for all your sensible info on this subject Greg.  EAM
Ev Marabian

1976 Cadillac Coupe DeVille, 1989 Chevrolet Caprice Classic, 1990 Pontiac Bonneville and 1996 Buick Skylark

The Tassie Devil(le)

It would be all about cost, and the necessity for performance at "normal" operating conditions, as in travelling at the speed limits.   Racing is different.

What Cadillac Engineers designed was good for the requirements of the smooth operation of a luxury passenger vehicle.   Don't forget that they designed the heated air from the outside of the Exhaust Manifold to hasten up engine warm-up.   All about comfort, and meeting the Pollution Control regulations.

Bruce. >:D
'72 Eldorado Convertible (LHD)
'70 Ranchero Squire (RHD)
'74 Chris Craft Gull Wing (SH)
'02 VX Series II Holden Commodore SS Sedan
(Past President Modified Chapter)

Past Cars of significance - to me
1935 Ford 3 Window Coupe
1936 Ford 5 Window Coupe
1937 Chevrolet Sports Coupe
1955 Chevrolet Convertible
1959 Ford Fairlane Ranch Wagon
1960 Cadillac CDV
1972 Cadillac Eldorado Coupe

EAM 17806

Quote from: The Tassie Devil(le) on April 02, 2018, 09:45:11 PM
It would be all about cost, and the necessity for performance at "normal" operating conditions, as in travelling at the speed limits.   Racing is different.

What Cadillac Engineers designed was good for the requirements of the smooth operation of a luxury passenger vehicle.   Don't forget that they designed the heated air from the outside of the Exhaust Manifold to hasten up engine warm-up.   All about comfort, and meeting the Pollution Control regulations.

Bruce. >:D
BRUCE: The cost of the plastic duct material and the plastic hub at the inlet cannot be a relevant reason for not installing these devices; there wasn't much cost at all for these items to refrain GM for installation at the factory;  there must be a purpose why they didn"t and it wouldn't be the cost.  EAM
Ev Marabian

1976 Cadillac Coupe DeVille, 1989 Chevrolet Caprice Classic, 1990 Pontiac Bonneville and 1996 Buick Skylark

"Cadillac Kid" Greg Surfas 15364

Ev,
If the inlet fitting, the hose and the installation cost a total of $10.00 then the number Chevrolet "bean counters" wopuld look at would be something like $10,000,000.  "Now that would be a nice chunk of change to give the stockholders" says he in the mirror.
Ev,
Why on earth are you asking questions that only the dead can answer.  That's what they did.
Greg Surfas
Cadillac Kid-Greg Surfas
Director Modified Chapter CLC
CLC #15364
66 Coupe deVille (now gone to the UK)
72 Eldo Cpe  (now cruising the sands in Quatar)
73 Coupe deVille
75 Coupe deElegance
76 Coupe deVille
79 Coupe de ville with "Paris" (pick up) option and 472 motor
514 inch motor now in '73-

Chas

Factory GM's initial use of flexible ducting to the air cleaner assembly was around 1966 on the Oldsmobile 442 (dual snorkel ducting). The air inlets were mounted in an open slot in the bumper. The diameter of the 442 flexible duct would put the hose on my 1976 Coupe to shame! I believe that the first use of air cleaner ducting was on the factory Ford Thunderbolt race cars of the early '60's. My 2004 four wheel drive Dodge truck has ducting to the air cleaner, with the inlet located in the right fenderwell!
1967 Coupe DeVille
1970 Coupe DeVille
1976 Coupe DeVille
1983 Coupe DeVille
1977 Harley Cafe Racer
1991 Harley Fat Boy
1957 Harley Hardtail
1949 Lusse Bumper Car
If you're 25 years old and not a liberal, you have no heart. If you're 45 years old and not a conservative, you have no money!

mikanystrom

I have a 1976 Trans Am 455 and I am pretty sure (the car is parked inaccessibly and I haven't seen it for a while) it has a similar snorkel design with a snorkel that ends behind the driver's side headlamp.  It's longer than the one on a '74 Cadillac (and doesn't have the intake resonator that the Cadillac has).

The hood shaker was blocked off from the factory for noise (or maybe for the intake air heat?) but the blocker was very poorly attached, so it really breathes through the shaker.

Ah I found a similar one.  Way back in 73...

http://st.hotrod.com/uploads/sites/21/2014/10/1973-Pontiac-Super-Duty-Trans-Am-Underhood.jpg
1970 De Ville Convertible
1993 Fleetwood Brougham
1970 Series 75 Formal Sedan
1968 Eldorado "Purple Sister"
------------------------------------------------
1976 Pontiac Firebird Trans Am 455 4-spd
1999 Camaro SS Convertible 6-spd
1999 Honda CBR 1100XX :-)