Venturi tubes

[mndude07]

Does anyone have experience with a venturi tube/s on the exhaust right after the collector?

Did you see any gains? Losses? Thoughts, comments?

[mndude07]

Bump

I think one after the collector would enhance my air velocity and reduce backpressure, especially considering the size that my exhaust is going to be....but does anyone have anything to back this up?

[93F22A6]

Have any pics of what your talking about? If it's what I think your talking about, I don't think it would really help any. But I've been wrong plenty of times before, so who knows.

[mndude07]

http://store.summitracing.com/partde...5&autoview=sku

[93F22A6]

Something like that should increase backpressure, but some backpressure is good.

[mndude07]

Something like that should increase backpressure, but some backpressure is good.

Wouldn't it decrease backpressure? Air after the venturi moves at a higher velocity than before, and thus the pressure must decrease because of the law of conservation of energy.

I could be wrong, but I see this as a cheaper, yet effective alternative to a true merge collector as seen on a header like bisimoto's.

[NAiL05]

It moves a higher velocity after the restriction. I see it as a bigger benefit in intake design. The exhaust there are easier ways such as bigger piping or mandrel bends. I can see where your coming from but I dont see it as a benefit on the exit side.

[cp[mike]]

i was going to say the same, AFTER the restriction its at a higher velocity and lower density. before it gets the opposite. though i cant say im fully read up on the physics behind a venturi tube, it doesnt sound beneficial to me

[mndude07]

It moves a higher velocity after the restriction. I see it as a bigger benefit in intake design. The exhaust there are easier ways such as bigger piping or mandrel bends. I can see where your coming from but I dont see it as a benefit on the exit side.

Thats a good point. I will have mandrel bends and bigger(2.5") piping on a N/A setup.

My thinking was that I am going to be running a very long resonator, probably about a 22" or 24" body, and then a 5x11x22 muffler. That resonator is going to slow air flow, so why not speed up the air before it gets to the resonator?

>>>"The Venturi effect is the reduction in fluid pressure that results when a fluid flows through a constricted section of pipe. The fluid velocity must increase through the constriction to satisfy the equation of continuity, while its pressure must decrease due to conservation of energy: the gain in kinetic energy is balanced by a drop in pressure or a pressure gradient force. An equation for the drop in pressure due to venturi effect may be derived from a combination of Bernoulli's principle and the equation of continuity.

The limiting case of the Venturi effect is when a fluid reaches the state of choked flow, where the fluid velocity approaches the local speed of sound. In choked flow the mass flow rate will not increase with a further decrease in the downstream pressure environment."<<<

Its not a huge issue, as I'll have an e-cut out, but i still want to get the most out of this.

Nail, I think I remember reading in a post of yours a long time ago that you have two resonators? If so, what are the dimensions and where are they located?

[wed3k]

id pair that with a 3" exhaust. running the right merge collector and that "venturi tube", one will be able to run a much larger exhaust setup to not only increase flow but doesnt hurt the velocity.

[d112crzy]

Most high dollar headers use something like this. They won't exactly go from big to small and back to big, but just one size and then they will cone to a bigger size, usually after the collector.


And whomever mentioned back pressure, quit thinking in the olden days. You don't EVER want back pressure. What you want is an exhaust that has no restriction and has optimal flow for the powerband you want.

[NAiL05]

The high dollar headers use an anti reversion chamber or something of that nature. It absorbs the pressure waves thrown at the exhaust not much of a venturi IMO. If they do I see little effect in it but thats just me. Its just there to dampen and smooth out the exhaust flow exiting the header. There is also another exhaust design higher dollar headers and carse use such as ferrari and so on use from the factory. Its something like bisi's designs. A lot of higher dollar drag cars and so on use this but I will post up whenever I remember what it is...Brain is kinda overworked at the moment.

I had two resonators welded together. They were after cat and it toned down the exhaust a lot. If you can find a large resonator itself then that would be a good compromise. I had two 18" welded together.

[d112crzy]

Those anti reversion chambers are called "steps". They go from absolutely one size right to the next. They use those in the primaries/secondaries.

The venturis are usually used after the collector.

[bcjammerx]

...this just looks like a kink in the pipe...it's going to be low velocity right before the bend and high pressure as the exhaust bottle necks.

If it were tapered from the original pipe to larger maybe...or if it enlarged from size AA.AA to size BB.BB then went back to size AA.AA.

But I don't see how this could help exhaust flow.

Back pressure...you want the exhaust to flow out...and not get air backing up at all...if you don't have a header or pipes at all then you'll bend valves as a result of the cool air hitting the valves but as long as you run a header you don't need to worry about that...still possible in certain circumstances...anyhoo back pressure isn't something we need to worry about.

[CB7Man]

Burnt valves are from no backpressure...
Then again depends on what your doing
Stock Idleing engine with no backpressure will burn valves (not moving enough air)
However WOT it might be a better thing in the high RPM range, however it sacrifces low end torque.
I had a 3" flowmaster on my car then I switched to a OEM EX and theres a high difference in torque. However now high end has suffered.
I take gas saving torque anyday