[WARIARGTO]

Used to run the ram air pan with the stock 65 GTO hood scoop opened up. With K&N filters this 464" setup was good to making 465 HP at the rear wheels. Seemed to be breathing OK as running 117MPH in a near 3800 pound car. As I'm putting the finishing touches on the activation circuit for the fogger, I'm wondering what I should do when I start hitting this thing with the juice as far as air intake. I can run the individual air cleaners and bases which I'm sure is adequate, breathing under the hood, or I can open up the hood scoop to a minimum required amount to support what the motor needs at the additional higher HP level with nos. Based on the information that I have, I'd like to know how big a scoop opening I would need to adequately let all those horses breathe easy. My estimate is around 700-750HP at the rear wheels on the juice.

1965 GTO
Nitrous Injected Tripower 464" Aluminum heads, Hydraulic cam
Vertically Gated M22 4-speed

[WARIARGTO]

Used to run the ram air pan with the stock 65 GTO hood scoop opened up. With K&N filters this 464" setup was good to making 465 HP at the rear wheels. Seemed to be breathing OK as running 117MPH in a near 3800 pound car. As I'm putting the finishing touches on the activation circuit for the fogger, I'm wondering what I should do when I start hitting this thing with the juice as far as air intake. I can run the individual air cleaners and bases which I'm sure is adequate, breathing under the hood, or I can open up the hood scoop to a minimum required amount to support what the motor needs at the additional higher HP level with nos. Based on the information that I have, I'd like to know how big a scoop opening I would need to adequately let all those horses breathe easy. My estimate is around 700-750HP at the rear wheels on the juice.

1965 GTO
Nitrous Injected Tripower 464" Aluminum heads, Hydraulic cam
Vertically Gated M22 4-speed

[Tom Vaught]

If the scoop was working well with the motor off the bottle it will work the same on the spray as the NOs has its own oxygen and fuel supplies and does not need additional air from the hood scoop.

Tom V.

[WARIARGTO]

Thanks tom, that is what I believed, and also why I chose to run a somewhat restrictive dual plane style intake with the fogger rather than a better flowing high rise single plane. But I guess if I rephrase what I'm looking for, I am wondering what formula(s) you use to arrive at an air intake opening size to feed a given motor displacement moving a certain amount of air at a maximum rpm. What would the requirement would be for a 464" motor that spins at 6000RPM? According to my calculations(464CI/1728=0.268519CF X 6000RPM=1611.114CFM). What formula would you use to determine what size opening would I need to feed 1611CFM? Also, I'm not even sure if I'm approaching this the right way, rather using a intake flow figure of 285cfm X 8= 2280cfm in the calculations instead of 1611cfm. Appreciate the help.

1965 GTO
Nitrous Injected Tripower 464" Aluminum heads, Hydraulic cam
Vertically Gated M22 4-speed

[Steve C.]

Somewhat related, this from a recent article about cold air systems in the 2/'03 Chevy High Performance magazine. It maybe of interest.

"If your building your own scoop, make sure the incoming-air opening is at least 10-15 percent larger than the carburetor venturi size. This typically equates to about a 20-to-25 aquare-inch opening in the scoop. For optimal performance, the roof of the scoop should be placed about 2 inches above the carburetor."

'Damn right it's a street car'

[WDCreech]

WARIARGTO,
Something seemed haywire with your calculations. After reading it several times, I figured it out. You multiplied the cubic feet by 6000rpm, but a four cycle engine only has an intake stroke on every other revolution. Just divide your total CFM by 2.

Bill

[Tom Vaught]

Quote:

"But I guess if I rephrase what I'm looking for, I am wondering what formula(s) you use to arrive at an air intake opening size to feed a given motor displacement moving a certain amount of air at a maximum rpm.

Per Grumpy Jenkins (what the he** did he know),
you need at least 30 square inches of area in the
hood scoop opening to make good power. All of the
area is needed at lower speeds, as the engine will
get some assistance from velocity under speed.

Question #2:

What would the requirement would be for a 464" motor that spins at 6000RPM? According to my calculations(464CI/1728=0.268519CF X 6000RPM=1611.114CFM). What formula would you use to determine what size opening would I need to feed 1611CFM? Also, I'm not even sure if I'm approaching this the right way, rather using a intake flow figure of 285cfm X 8= 2280cfm in the calculations instead of 1611cfm. Appreciate the help"

Formula is ((cid times rpm) / 3456) times V.E. =
air flow demand.

(464 times 6000 = 2784000) / 3456 = 805.55 cfm.

times V.E. (use .85 to .95 for most engines) so
684 cfm to 764 cfm.

There is always some airflow resistance so I use
.95 for good street stuff, 1.05 for bracket cars,
and 1.10 for fast drag cars 10.50 or faster.
1.10 would give you a number around 885 cfm.

Tom V.

[Tom Vaught]

There is a fine balancing act between having the scoop opening be too small and too large. It does
no good to have the air go into the scoop, turn around, and then exit the sides of the scoop at the front. This was the problem with the old 63
Max Wedge scoops and the Mustang SVO scoop. You
want the air to go into the scoop, slow down and convert from velocity to pressure, not have any severe turbulence over the carb(s), and not pick
up heat from the engine (need sealing plate to
hood). Having a relief slot in the hood or pan is bad as the velocity never changes to pressure.

Tom V.

[WARIARGTO]

Thank you very much for the info guys,Totally spaced the whole 4-stroke air movement cycling, thanks for picking that up bill. Taking that into consideration it looks like about 1/2 that 1611cfm number would be right in the ballpark taking into consideration VE. Don't know what I was thinking bringing in the intake flow numbers at max lift, must've hit my head on the corner of the hood in the right place and shut off the thinking part of the brain. I guess saturday night firewater and a good nights sleep helped the reset. Tom, I should've known that the air requirement formula I needed would be the same as sizing the carburation for a given displacement/rpm/VE. Thanks for posting it. So I guess "da grump" thought 30 sq inches was the number, but wouldn't that number be variable and change given different displacements/rpm/VE's? I wouldn't think a smaller say 350CI motor revving to 5000RPM at .90VE would have the same scoop opening needs as a race say 600CI motor going to 7500RPM? Since the smaller engine cannot use all the air, wouldn't that be the problem that you mentioned with the max wedge and SVO scoops?

1965 GTO
Nitrous Injected Tripower 464" Aluminum heads, Hydraulic cam
Vertically Gated M22 4-speed

[WARIARGTO]

Also, thanks steve for posting that from CHP. If I use that criteria, I come up with just over 8 square inches needed, assuming (2) 1 1/4" venturis per carb X 3 carbs. Does this sound right tom?

1965 GTO
Nitrous Injected Tripower 464" Aluminum heads, Hydraulic cam
Vertically Gated M22 4-speed

[Tom Vaught]

If the opening were 8 square inches the opening would have the same effect as the venturi in the carbs and would be an air flow restriction in the system (without doing any work- the venturis are designed to pull fuel out of the fuel bowls)

Forgive me Mechanical Engineers, I am using street terms and not what is really happening with the pressure differentials.

The question about the small engine vs the large engine: Grumpy's rule was the scoop opening normally sees 2.5 times the airflow at high speeds
as when the car is sitting on the line due to
the speed of the vehicle. When the engine is on
the line and reving at 7000 rpm it is moving a
lot of air through the scoop opening without any
assist from speed. He mentions putting a radius on the scoop opening to allow more ait through the scoop opening. A sharp edged hole normally will flow about 60% of a perfectly radiused hole.

This is why the "aero" scoops with the rounded edges work so well on cars like W. Johnson's and
Billy Glidden's cars.

If you make the scoop correctly you also get a slight "Boosting" effect from the velocity conversion to pressure.

Big Engines do need slightly larger openings then
smaller engines but a small opening will work like a restrictor carb and still flow the air but with a higher pressure drop across the opening
and some flow loss. Tom V.

[Steve C.]

Here is my situation.
I have a factory T/A scoop molded to the 'glass hood. With a Victor intake installed the carburetor is very close to the underside of the scoop, about 1-inch or so above the front vent tube. I presume the carb draws most of it's air from under the hood and very little from the small 2" x 10" (approx) opening that faces rearward.
Knowing the benifits of how colder air improves power I have considered using a pan under the carb and sealing it with rubber to the bottom of the hood, thus drawing cool air from the scoop opening.
However I have been concerned about the ability of the the relatvely small rear facing opening to furnish enough air. Plus the actual opening is really too far from the base of the windshield to be in a effective high pressure area. Also considered what could be a small volume avilable within the confines of the pan/scoop area sealed to the hood.
It's for this reason I have left it as is dispite drawing hot air from under the hood.
Any opinions Or advice ?
Thanks.

Based on the formula above I need 950 to 1000 cfm depending on the VE used.
(not sure of the exact correlation but the dyno sheet scfm numbers are 914-924 at peak power rpm with 108-110 VE% numbers at peak tq rpm)

'Damn right it's a street car'

[WARIARGTO]

So Tom, since you said that opening size would be a restriction at 8 in sq based on 10-15% over venturi size, should the opening size should be rather based on equal to/ 10-15% larger than cumalative throttle bore size?

1965 GTO
Nitrous Injected Tripower 464" Aluminum heads, Hydraulic cam
Vertically Gated M22 4-speed

[Tom Vaught]

That would be closer to the correct number.

On the holley vent tube being 1 inch away from the hood. Holley did a bunch of testing years ago,
and determined that you should normally have 1.5
inches above the vent. tube. What model carb?
Hp? If Hp and no choke tower you can trim the vent tubes sometimes about 1/2 inch like the 850
vent tubes which are really short. Tom V.

[shark landis]

P r square...no, wait...PI r ROUND!...CORNBREAD r square!!!

[shark landis]

Pi r square...no, wait...PI r ROUND!...CORNBREAD r square!!!

[Steve C.]

Tom- I normaly run a HP950 w/ 1" tubes installed.
It's not currently in place otherwise I'd measure, but the 1-inch or so distance was a ballpark based on memory. A carb spacer is typically in place so I have some adjustment.

[455-4+1]

Steve

Ditto on the factory shaker hood opening question

Mine is mounted on top of a Holley street dominator, 1" spacer, 850 annular mighty demon and then a radiused 2" spacer beneath a flat round aluminium plate which uses the stock shaker hood stainless ring to contain it (confussed ???)

The only air my car currently draws is through the rearward facing shaker hole. At first I thought this would be adequate but now am beginning to wonder

Any comments ??

Working on going faster!!!

[WARIARGTO]

Thanks go to tom for providing us with this kind of info. Thinking about it now, it makes perfect sense. Your air intake opening needs to be matched to your cumalative throttle bore area(not venturi size). Figure out this by measuring all the throttle bore diameters, then plug them each into a=(pi)(d/2)squared. Not sure how to type this, just a basic formula for area of a circle. Once you determine your total area for all the bores, compare it to the area of your scoop opening. If you have a 2" by 4" scoop opening,2"(L)X 4"(W)= 8 in sq(area). If it's a smaller number than what you determined for your carb, the scoop is too small. Enlarge accordingly. I believe tom agreed that 10-15% over carb throttle bore area would be close to the number needed for scoop air inlet size.

1965 GTO
Nitrous Injected Tripower 464" Aluminum heads, Hydraulic cam
Vertically Gated M22 4-speed

[PONTIAC DUDE]

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