PuppyDoc

I am going to get a new engine with a street-port... As you all know, a venturi flows more air than a tube of equal diameter... Thus, if I were to get my port done as a venturi rather than just a straight-through port, wouldn't I realize more performance gains? Can I trademark that? "Venturi-ported 13b" just sounds cool!

PuppyDoc

I have a feeling some people don't know what a venturi is...

Ni5mo180SX

I dont know if its as simple as that.

jacobcartmill

iTrader: (6)

what is a venturi bro. i jsut know that they are on carburators

'Vert in Vegas

I believe you will find that a venturi
(a narrowing of a air passage)
will cause the air flow in that area to be at a higher speed.
Not more air.
I don't think you have anything going here.

Jodoolin

A point on your comment that a venturi flows more air than a tube with the same diameter. Not correct if the pressure difference (pressure gradient) across the two are the same.

A venturi (named after the fellow who described it thus: Venturi Effect) is not a tube. It is a constriction in a tube. When the constiction opens to atmosphere the opening is called an orifice. In fluid physics there is this law called the Law of Continuity. It states that unit volume flow through a tube of varing cross sections is the same at each cross section. For that to occur the velocity of the fluid (gas/liquid) passing through the constriction must accellerate and the pressure it exerts will decrease as a result.

Thus, when you place a narrow opening at the end of a tube its velocity will increase as it exits the opening and create a low pressure just outside the opening. If the pressure on the other side of the orifice is greater than the pressure at the orifice then the fluids surrounding the other side will be drawn into the high velocity/low gas and mixing, often violent, will occur. This may have had one of its first applications in steam engines. It is now used in a bazillion applications uncluding carborators.

PuppyDoc

Hence, if I were to use a venturi as my port, the vacuum created by the rotors would draw air in faster, thus increasing volume, especially since my car is turbocharged... I might have to give it a whirl.

RX-7Impreza

you are forgetting something. when the air moves faster it also loses pressure, meaning there isnt as much air in the same space. you gain speed on the air but you lose volume. the air will move faster but it will take longer for the same volume of air to enter the chamber.

the intake burst is only a split second long and the idea is to have readily available air for that burst. this is why some "Cold air intakes" have a large bulge in them, they increase the available air after the MAF.

Good thinking but it is better to have a large opening

Justin

NZConvertible

No, a venturi increases air velocity, not airflow. It is a restriction, so it will actually reduce airflow. This is one of the many reasons carbs suck.

slidingsky

I always wondered about making a twisty<tornado> plug in the lower intake manifold. Like the thing on TV. Woulnt it help disperse fuel better. I have a NA so I dont think it would hurt airflow much.

NZConvertible

Seen on TV, yet never seen in production cars. Wonder why... Nope. You'd be wrong.

banzaitoyota

The venturi idea would work if:

THE ROTARY WAS A STEAM TURBINE!!!!!!!

But since it is not, It wont work.

The venturi (NOZZLE) in a steam turbine exists to speed up the flow of the steam from one turbine stage to the next with a resulting drop in pressure. The turbine is designed with many stages in order to extract energy from the steam as it enters at 500 PSI and exits under 20" of vacuum.(example give is from an S5W Powered Nuclear Submarine). What kind of nozzle (venturi ) where you planning on using? Simple convergent or a convergent-divergent? Remember as Velocity increase pressure will drop with no change in total flow of the system.If you can find a copy of "Principles of Naval Engineering " in your library you will find lots of fascinating reading.

PuppyDoc

Convergent-divergent. Well, how about this theory: Using a venturi between the exhaust ports and the turbo... If a venturi speeds up air, wouldn't it spool the turbo faster? The pressure would remain pretty much the same, as the volume it's going into stays constant (meaning, the volume between the exhaust port and the turbo is constant, the volume of exhaust is constant, so all I am changing is the way the air flows) The stock exhaust manifold looks very inefficient to me...
Either that, or a divergent venturi out of the turbo, to really lower the backpressure... Just bouncing ideas around...

banzaitoyota

You have to maintain an energy balance. With an increase in velocity, you will have a decrese in pressure. Its basic physics. You can break a lot of laws but not the laws of physics.

Good thinking but you have to take your ides back to basic proven scientific fact!. Unless you are marketing electric turbochargers on EBAY.

rxseven

Puppydoc, I think you are thinking on the lines of how a ramjet engine operates. you need to consider the stagnation pressure you create at the narrowest cross-section.

nonameo

Just put a ramjet on your rx-7, then it would work

PuppyDoc

Actually, I am just going to take out everything in my car, build an eight rotor engine, and mount the end of the tranny directly to the differential. Four turbos, eight rotors... what do you think?

HuggyBear

i think youl have a sore bum after your first cruise....

deadRX7Conv

http://ghlin2.greenhills.net/~apatter/wankel.html
Damn those powerplant engineers. Always making things difficult for us simple folk.

Venturi effect: Kinda like the 4-6-4 ports switching. We NA owners already have it. Also, take a look at your AFM and tube going to the TB. While you're at it, look at your TB. Different diameters at the AFM inlet/outlet...........
Turbo guys have twinscroll...... Same idea, playing with opening diameter changes gaseous velocity. There is a fine line where improvements in velocity reduces volume and vice versa.

And, don't forget to tune for each RPM. The actually venturi port will be efficient at one point and a major PITA everywhere else.

Mazda already played with port volume(4-6 ports), intake length(VDI open/close) and spent enough time picking runner length/diameter.....for the engine.

dre_2ooo

"~" denotes AIR moving at normal speed
"+" denots AIR moving at FAST speed

normal :

--------------------------------------
~~~~~~~~~~~~~~~~~~~~~~--->
~~~~~~~~~~~~~~~~~~~~~~--->
--------------------------------------

.

Venturi:

------------------------------------\____/
~~~~~~~~~~~~~~~~~~~'++++++++-->
~~~~~~~~~~~~~~~~~~~~~~____
------------------------------------/..........\

dad: "Ok little johnny, which one passes more air, son?"
Jonny: "um.. the top one daddy, DUH, now give me a hard question"

Sorry to be so negative, but like little Johnny says, DUH!

PuppyDoc

Hey, like I said, just bouncing ideas around...
"Ja, I tink I build engine vis da schpinning rotors, ja."
"Nein, Felix, das vill nefer vork."
"Vell, maybe you tink so, aber, I vill try anyvay."

I'm not trying to solve world hunger or anything here, so if you think my ideas don't work, cool. But if you can expound on it, even better. Everyone here wants more power, and it's easier to bounce ideas off of you guys rather than have my mechanic do it.

RETed

Bernoulli's Principle - this is where the venturi get's its physics from.
As for turbochargers and port sizing, you're ignoring the dynamics of the expanding exhaust gases, which is a whole nother ball of wax.&nbsp The turbo's turbine section already "necks" down the exhaust path to increase velocity - this is the turbine A/R.


-Ted

tesla042

Sure a venturi in the exhaust would increase the velocity, but it would also decrease the pressure... Both velocity and pressure are the energy source that a turbine taps into. Assuming a completely ideal venturi with NO energy loss (not possible), you still have the same amount of energy for the turbine to use...

More than likely, it will end up just being a restriction, and so flowing less exhaust than before. This does NOT break the rule of the same volume passing thru cross-sectional areas --- the volume for the entire system will be decreased because of the restriction.

But hey, it was a neat idea.. don't let anyone discourage you from coming up with more!

-Tesla

'Vert in Vegas

Chevy sells a complete 5.7 liter v8 with fuel injection and computer called the RAMJET.
$4500 and it is yours!