[Tom Vaught]

Originally Posted by cgeise

Just a point to think about on this build, as an engine becomes more efficient in a N/A application I have heard that the net effect of adding NOS becomes less. I have no actual data on this, just something I have heard for a long time.

Some truth there.

Obviously if you have an engine with 9 to 1 compression ratio it is less efficient vs a 13 to 1 compression ratio engine.

With the 13 to 1 compression ratio engine it would seem that you are limited on how much additional NOS you can add to the engine without having issues.

With 9 to 1 compression ratio engine the ability to add more NOS is there before you reach the same issue point. (Same deal applies with boost as you know).

Having a better flowing cylinder head does not hurt you if the additional flow makes more HP and you need less NOS to reach the same final target number.

Tom V.

[LiL Jack]

Originally Posted by cmpgto

Hey Jack, if everything but paint is ready and you still have the car with you I think Paul Major has MIR rented tomorrow. He had a post on YB letting people know. Might get close to 70 tomorrow.

It still needs an alignment and set up. So I'm out anyway, too busy at work to take a day off.

[wreckmastr]

[Stan Weiss]

How many square inches is the opening of that scoop? It looks huge.

Stan

[Tom Vaught]

He will put a small air bleed slot on the scoop at the rear (before he is done), if it is not already there.
Hard to tell in the picture. Also the air will go into the center of the scoop, turn around, and go right back
out the front opening on either side of the air coming in with too large of a front opening creating lots of
turbulence over the carb barrels and vents making the carbs very unhappy going down the track.

Tom V.

[Jeff Kinsler]

Looks killer jack! !!

[Stan Weiss]

Originally Posted by Tom Vaught

He will put a small air bleed slot on the scoop at the rear (before he is done), if it is not already there.
Hard to tell in the picture. Also the air will go into the center of the scoop, turn around, and go right back
out the front opening on either side of the air coming in with too large of a front opening creating lots of
turbulence over the carb barrels and vents making the carbs very unhappy going down the track.

Tom V.

Tom,
I guess I needed to get out of the N/A mode where you want the scoop opening no bigger than needed and the scoop to be as air dynamic as possible. While also wanting the max Ram Air effect on the top end.

Stan

[Tom Vaught]

The Problem, Stan, is you need sufficient opening at idle to support the engine at LAUNCH RPM and past the first 150 feet of travel down the track. Then the air velocity of the vehicle takes over and now the air is rapidly being packed into the scoop and the carb is wanting a richer fuel calibration to make best power with the additional airflow.

A normal carb needs to be leaned out at the top end to be at the best power level on the top end. The emulsion circuit holes do that for you naturally aspirated.

If you have excess air constantly dumping out of the side of the scoop at different flow rates then the carbs are in constant confusion. The Pro Mod scoops can get away with the larger area 100 square inches of opening because the scoop housing has so much area behind the scoop opening before the carbs. See photo. I am afraid the retro look will not be the best design for Jack.

Tom V.

[wreckmastr]

Yeah because those look SOOO good on Pontiacs.. lol

[dda72]

Originally Posted by wreckmastr

Yeah because those look SOOO good on Pontiacs.. lol

Agree!!

[Tom Vaught]

Don't think you need the extra 4" vs the scoop I posted.

Tom V.

[David Holmberg]

Originally Posted by cgeise

Just a point to think about on this build, as an engine becomes more efficient in a N/A application I have heard that the net effect of adding NOS becomes less. I have no actual data on this, just something I have heard for a long time.

That is true with a NA motor. With a nitrous motor you cam it for the power you will be making on the bottle, so its less efficient NA. (I will add that big inch NA cams are much closer to nitrous cams today compared to 5 years ago)

[Tom Vaught]

Maybe some people figured out that moving a mass of air and fuel on a big engine required a given camshaft event timing and moving the same mass on a smaller engine with a given NA mass flow PLUS the mass flow of the NOS/fuel ends up being similar camshaft event timing.

Tom V.

[455firebird1969]

Originally Posted by Tom Vaught

Then the air velocity of the vehicle takes over and now the air is rapidly being packed into the scoop and the carb is wanting a richer fuel calibration to make best power with the additional airflow
Tom V.

Doesn't the carb meter the fuel in relation to the mass of air that goes through it? Wouldn't more air going through it just drag more fuel with it? Or does this richer requirement come from the higher pressure air inside the scoop affecting the vents and bleeds?

[john marcella]

I'm no expert on hood scoops but I think that front carburetors going to be really pissed off with that scoop Jack. I think carb way too close to the opening of the scoop. All the information that I've gotten from extremely good sources tells me that your scoop does not have enough internal area and the opening is far too big. You only want the opening large enough so the pressure within the scoop does not go negative when leaving the starting line or just barely negative.
I think with that larger opening and that close to the front carburetor that the air is going to buffet and play havoc on the air bleeds and bowl vents of that front carburetor. Again I'm no expert on the subject.

[BDHABT]

Originally Posted by wreckmastr

Yeah because those look SOOO good on Pontiacs.. lol

That is the ugliest car ever;dont care how fast it is.

[BADDTA]

Originally Posted by BDHABT

That is the ugliest car ever;dont care how fast it is.

X2. Dolphins are supposed to be in the ocean not on top of car hoods! If that guy narrows the rear just a little more...he could have a duallie. Lol

Brian

[Tom Vaught]

Originally Posted by 455firebird1969

Doesn't the carb meter the fuel in relation to the mass of air that goes through it? Wouldn't more air going through it just drag more fuel with it? Or does this richer requirement come from the higher pressure air inside the scoop affecting the vents and bleeds?

Carburetors do not maintain a constant fuel-air ratio with changes in atmospheric density, but meters the fuel in proportion to the square root of the air density, whereby richness of mixture is increased unless compensating devices of some mechanical nature are applied in an attempt to maintain constancy of the mixture.

The carburetor works on Bernoulli's principle: the faster air moves, the lower its static pressure, and the higher its dynamic pressure. The throttle (accelerator) linkage does not directly control the flow of liquid fuel. Instead, it actuates carburetor mechanisms which meter the flow of air being pulled into the engine. The speed of this flow, and therefore its pressure, determines the amount of fuel drawn into the airstream.

Varying air velocity in the Carburetor Venturi alters the fuel flow to the venturi nozzle or "Booster".

So no, a carburetor cannot compensate for a change of mass flow thru it.

Boosted Engine carburetors basically have a "Power Circuit" that when activated sends
lots of extra fuel thru the carburetor when the engines sees a positive pressure in the manifold. The carburetor becomes an on-off switch adding lots of extra fuel when the engine sees boost.

Tom V.

A scoop might get you 1 psi of Boost pressure but you would have to use power valves to switch on that extra fuel when it saw that positive pressure and NA Dominator Race carbs do not use Power Valves.

[wreckmastr]

Originally Posted by BDHABT

That is the ugliest car ever;dont care how fast it is.

LMAO. .... What makes it even worse is that thing is a turd. Mid to high 8's

[455firebird1969]

Originally Posted by Tom Vaught

Carburetors do not maintain a constant fuel-air ratio with changes in atmospheric density, but meters the fuel in proportion to the square root of the air density, whereby richness of mixture is increased unless compensating devices of some mechanical nature are applied in an attempt to maintain constancy of the mixture.

The carburetor works on Bernoulli's principle: the faster air moves, the lower its static pressure, and the higher its dynamic pressure. The throttle (accelerator) linkage does not directly control the flow of liquid fuel. Instead, it actuates carburetor mechanisms which meter the flow of air being pulled into the engine. The speed of this flow, and therefore its pressure, determines the amount of fuel drawn into the airstream.

Varying air velocity in the Carburetor Venturi alters the fuel flow to the venturi nozzle or "Booster".

So no, a carburetor cannot compensate for a change of mass flow thru it.

Boosted Engine carburetors basically have a "Power Circuit" that when activated sends
lots of extra fuel thru the carburetor when the engines sees a positive pressure in the manifold. The carburetor becomes an on-off switch adding lots of extra fuel when the engine sees boost.

Tom V.

A scoop might get you 1 psi of Boost pressure but you would have to use power valves to switch on that extra fuel when it saw that positive pressure and NA Dominator Race carbs do not use Power Valves.

What you are saying, is the way I understand it. How does the slightly denser air (due to the use of a air scoop) change the amount of fuel metered? For every unit of air that passes through the carb, fuel is added (metered) at a fixed rate, is it not?

I run a RamAirbox.com system that uses ram air through the headlight openings. I have heard others claim this type of system will lean out or require more jet on the big end, but I disagree. My understanding of the way a carb works is it will meter the fuel based on the amount of air that passes through it. If you put more air throught it, it adds more fuel, maintaining the mixture rate. Is this not the way it works?