Anyone tested Cats for performance?
Drifting
Joined: Oct 2006
Posts: 1,934
Likes: 3
From: Citrus Heights California
According to Lingenfelter scavenging effects air flow. He claims that an exhaust opening that is too large will decrease air flow velocity and the scavenging effect on the exhaust system. Decreased air flow velocity will decrease HP and torgue. Bigger is not always better. The faster the air flows through the intake, engine and exhaust the greater the efficiency. A 3' exhaust on a low hp engine would equal less HP and torque.
Drifting
Joined: Oct 2006
Posts: 1,934
Likes: 3
From: Citrus Heights California
The higher the velocity of the exhaust gas flow the greater the scavenging effects. Scavenging actually sucks air through the motor. If gases are forced through a smaller opening the speed is increased. Take the same exhaust gases and dump them into a larger tube and the gases slow down. It's called the venturi effect. All you have to do is place your thumb over the end of a garden hose and you will see what I mean.
Team Owner
Joined: May 2002
Posts: 24,337
Likes: 25
From: San Diego , CA Double Yellow DirtBags 1985..Z51..6-speed
I'm agreeing with you. High velocity causes the low pressure at the port. This can occur because it's not a steady state system, and this is where the flow testing does us no good.
Venturi effect is something entirely different. And the garden hose, well... that has nothing to do with anything.
Venturi effect is something entirely different. And the garden hose, well... that has nothing to do with anything.
Drifting
Joined: Oct 2006
Posts: 1,934
Likes: 3
From: Citrus Heights California
I'm agreeing with you. High velocity causes the low pressure at the port. This can occur because it's not a steady state system, and this is where the flow testing does us no good.
Venturi effect is something entirely different. And the garden hose, well... that has nothing to do with anything.
Venturi effect is something entirely different. And the garden hose, well... that has nothing to do with anything.
The Venturi effect is a special case of Bernoulli's principle, in the case of fluid or air flow through a tube or pipe with a constriction in it. The fluid must speed up in the restriction, reducing its pressure and producing a partial vacuum via the Bernoulli effect. It is named after Giovanni Battista Venturi, (1746–1822), an Italian physicist.
A fluid passing through smoothly varying constrictions is subject to changes in velocity and pressure in order to satisfy the conservation of mass-flux (flow rate). The reduction in pressure in the constriction can be understood by conservation of energy: the fluid (or gas) gains kinetic energy as it enters the constriction, and that energy is supplied by a pressure gradient force from behind. The pressure gradient reduces the pressure in the constriction, in reaction to the acceleration. Likewise, as the fluid leaves the constriction, it is slowed by a pressure gradient force that raises the pressure back to the ambient level.
The limiting case of the Venturi effect is choked flow, in which a constriction in a pipe or channel limits the total flow rate through the channel, because the pressure cannot drop below zero in the constriction. Choked flow is used to control the delivery rate of water and other fluids through spigots and other valves.
I'll try another analogy:
A Good example of the Venturi effect is a jet engine. Jet fuel is squeezed, ignited, forced through a venturi and blasted out the exhaust. The exhaust creates so much thrust it pushes the plane through the air. Now imagine that thrust sucking air through your engine.
Team Owner
Joined: May 2002
Posts: 24,337
Likes: 25
From: San Diego , CA Double Yellow DirtBags 1985..Z51..6-speed
Venturi effect is used in spray cans, carburetors, etc.
It has nothing to do with exhaust scavenging.
Exhaust scavenging is caused by exhaust pulses carrying momentum creating a slight suction. It doesn't happen in steady state flow. Scavenging and VE can be increased by tuning primary length to catch negative wave reflections from a previous exhaust stroke during the next exhaust valve event.
Venturi effect can occur in steady state flow, exhaust scavenging does not.
It has nothing to do with exhaust scavenging.
Exhaust scavenging is caused by exhaust pulses carrying momentum creating a slight suction. It doesn't happen in steady state flow. Scavenging and VE can be increased by tuning primary length to catch negative wave reflections from a previous exhaust stroke during the next exhaust valve event.
Venturi effect can occur in steady state flow, exhaust scavenging does not.
Drifting
Joined: Oct 2006
Posts: 1,934
Likes: 3
From: Citrus Heights California
Venturi effect is used in spray cans, carburetors, etc.
It has nothing to do with exhaust scavenging.
Exhaust scavenging is caused by exhaust pulses carrying momentum creating a slight suction. It doesn't happen in steady state flow. Scavenging and VE can be increased by tuning primary length to catch negative wave reflections from a previous exhaust stroke during the next exhaust valve event.
Venturi effect can occur in steady state flow, exhaust scavenging does not.
It has nothing to do with exhaust scavenging.
Exhaust scavenging is caused by exhaust pulses carrying momentum creating a slight suction. It doesn't happen in steady state flow. Scavenging and VE can be increased by tuning primary length to catch negative wave reflections from a previous exhaust stroke during the next exhaust valve event.
Venturi effect can occur in steady state flow, exhaust scavenging does not.
Peace OUT!
Team Owner
Joined: May 2002
Posts: 24,337
Likes: 25
From: San Diego , CA Double Yellow DirtBags 1985..Z51..6-speed
Stay in school!
I'll throw you a bone though, in that some header collectors can use a venturi effect to increase scavenging on the other cylinders. Anyhow, go stick some venturis in your primaries and let me know how your dyno testing goes.
I'll throw you a bone though, in that some header collectors can use a venturi effect to increase scavenging on the other cylinders. Anyhow, go stick some venturis in your primaries and let me know how your dyno testing goes.
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Drifting
Joined: Oct 2006
Posts: 1,934
Likes: 3
From: Citrus Heights California
All I am saying is that bigger is not always better. I also tried to explain what increases and decreases exhaust gas speed.
Drifting
Joined: Oct 2006
Posts: 1,934
Likes: 3
From: Citrus Heights California
Venturi effect is used in spray cans, carburetors, etc.
It has nothing to do with exhaust scavenging.
Exhaust scavenging is caused by exhaust pulses carrying momentum creating a slight suction. It doesn't happen in steady state flow. Scavenging and VE can be increased by tuning primary length to catch negative wave reflections from a previous exhaust stroke during the next exhaust valve event.
Venturi effect can occur in steady state flow, exhaust scavenging does not.
It has nothing to do with exhaust scavenging.
Exhaust scavenging is caused by exhaust pulses carrying momentum creating a slight suction. It doesn't happen in steady state flow. Scavenging and VE can be increased by tuning primary length to catch negative wave reflections from a previous exhaust stroke during the next exhaust valve event.
Venturi effect can occur in steady state flow, exhaust scavenging does not.
This is a quote from your vey next post" I'll throw you a bone though, in that some header collectors can use a venturi effect to increase scavenging on the other cylinders."
Last edited by Kool88vette; Apr 8, 2007 at 07:48 PM.