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V8 Engine Discussion 6.2L LS3/L99 V8 | Exhaust | Ignition | Induction | Intakes

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post #11 of 31 Old 06-28-2014, 02:47 PM
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Originally Posted by RedRockLS3 View Post
First post....yay.

Fluid dynamics supports the concept, albeit the effect would be dependent on other variables to determine how effective this would be given it's particular application.

The attached image gives a generalized idea to the Venturi effect and how it works.
True that venturi will convert static pressure to velocity pressure, IF the inlet included angle (minimum 20* I believe), outlet included angle (6* I believe) and the throat diameter (smaller = more velocity pressure) are correct. From what I've seen of the ported throttle bodies they don't even come close to replicating a true venturi. Hence, I would question that a negative pressure is created in the ported throttle body. I have one on my car because it was cheap and I'm not in a position to prove or disprove their value. I did not notice any difference from the stock throttle body on the street or at the track, but I left it on the car because it didn't slow the car down and it was more trouble than it was worth to remove it.
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post #12 of 31 Old 06-28-2014, 04:24 PM
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True that venturi will convert static pressure to velocity pressure, IF the inlet included angle (minimum 20* I believe), outlet included angle (6* I believe) and the throat diameter (smaller = more velocity pressure) are correct. From what I've seen of the ported throttle bodies they don't even come close to replicating a true venturi. Hence, I would question that a negative pressure is created in the ported throttle body. I have one on my car because it was cheap and I'm not in a position to prove or disprove their value. I did not notice any difference from the stock throttle body on the street or at the track, but I left it on the car because it didn't slow the car down and it was more trouble than it was worth to remove it.
I am not the best at noticing things with subtle differences but I put a power wedge, VMAX TB, and CAI CAI on all at the same time and I thought there was a dramatic difference ... the throttle response and slightly deeper sound especially ...

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post #13 of 31 Old 06-28-2014, 04:32 PM
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I'm not trying to say that it is a true Venturi at all. Just attempting to illustrate how there is a correlation within it's concept that folks try to capitalize on.

In just about all throttle body applications I've seen that claim a horsepower increase, tests show a marginal or even negligible difference in overall power changes - whether it goes up or down. On the Mustang side if the fence, I remember some folks talking about how the BBK throttle bodies increased throttle response. Upon investigation, it appears that the internal gearing of the throttle body was different from stock allowing it to open just a hair faster than normal, giving it it's perceived throttle increase - in conjunction with it's larger diameter. I'm not saying that's the case here but, I suspect that opening up the throttle body just before the butterfly would allow a larger volume of air to collect before being taken into the intake manifold. That in of itself may give a perceived increase of throttle response and even an increase in power so long as all the other variables are in line, too.

I have seen more extreme examples of folks utilizing a Venturi on vehicle applications. It looks awfully impractical and for the effort involved, doesn't substantiate time and effort investment.

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post #14 of 31 Old 06-28-2014, 08:48 PM
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Originally Posted by RedRockLS3 View Post
I'm not trying to say that it is a true Venturi at all. Just attempting to illustrate how there is a correlation within it's concept that folks try to capitalize on.

In just about all throttle body applications I've seen that claim a horsepower increase, tests show a marginal or even negligible difference in overall power changes - whether it goes up or down. On the Mustang side if the fence, I remember some folks talking about how the BBK throttle bodies increased throttle response. Upon investigation, it appears that the internal gearing of the throttle body was different from stock allowing it to open just a hair faster than normal, giving it it's perceived throttle increase - in conjunction with it's larger diameter. I'm not saying that's the case here but, I suspect that opening up the throttle body just before the butterfly would allow a larger volume of air to collect before being taken into the intake manifold. That in of itself may give a perceived increase of throttle response and even an increase in power so long as all the other variables are in line, too.

I have seen more extreme examples of folks utilizing a Venturi on vehicle applications. It looks awfully impractical and for the effort involved, doesn't substantiate time and effort investment.
Agreed. A marketing/sales ploy for sure. A "venturi effect" is a meaningless/dimensionless play on words. The pressure drop across a true venturi makes them very inefficient.
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post #15 of 31 Old 06-30-2014, 01:35 AM
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I'm not claiming to know anything about Venturi effect or anything else, but replacing just a throttle body without replacing the intake to go with it is pointless.

The funnel reference was a good example.
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post #16 of 31 Old 06-30-2014, 09:50 AM
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How do you guys explain the gains that have been seen with the V-Max then? I get what you're saying. But real world gains are real world gains. And it has been proven since the LS3 became available in the Corvette and even before that.

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post #17 of 31 Old 06-30-2014, 02:45 PM
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How do you guys explain the gains that have been seen with the V-Max then? I get what you're saying. But real world gains are real world gains. And it has been proven since the LS3 became available in the Corvette and even before that.
I don't really know how to explain the dyno differences, other than to surmise that it might be within the normal margin of error or something else changed. All I'm saying is that there is no venturi effect and that my butt dyno did not notice a difference.
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post #18 of 31 Old 06-30-2014, 02:58 PM
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Originally Posted by rdemarce View Post
I'm not claiming to know anything about Venturi effect or anything else, but replacing just a throttle body without replacing the intake to go with it is pointless.

The funnel reference was a good example.
I'm not certain the funnel reference is a good example. Water is a non-compressible fluid, whereas air is a compressible fluid, and the physics of the two are quite different. That being said, if the top section of the funnel 1 held more water than the top section of funnel 2, and both had the same diameter outlet, funnel 1 would empty at a greater rate because there is more head forcing the water through the outlet. The same would be true for an orifice in an air line, the more pressure or vacuum I had the more air I could pass through the same diameter orifice.

Since in a naturally aspirated motor we're dealing with vacuum at the inlet manifold to suck air into the intake, the larger the opening of the throttle body the more air will pass through it provided there are no restrictions somewhere upstream or downstream. Most likely there will be restrictions in the intake manifold, cylinder heads, exhaust manifold, etc., so all the pieces of the puzzle need to be compatible for maximum gains.
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post #19 of 31 Old 06-30-2014, 03:26 PM
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Some of your comparisons directly conflict with long established data. Because by your statements, if what you're saying is true, then a cold air intake would not make the increases in HP/TQ that they do. A good CAI will increase hp and tq by approx 15 hp/tq even tho the TB, intake manifold, heads, cam, and exhaust remain unchanged. So if a cold air intake can do this, why is it hard to believe that a ported TB can do the same?

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post #20 of 31 Old 06-30-2014, 05:37 PM
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Some of your comparisons directly conflict with long established data. Because by your statements, if what you're saying is true, then a cold air intake would not make the increases in HP/TQ that they do. A good CAI will increase hp and tq by approx 15 hp/tq even tho the TB, intake manifold, heads, cam, and exhaust remain unchanged. So if a cold air intake can do this, why is it hard to believe that a ported TB can do the same?
I think you are misunderstanding my statements. The reason some CAIs increase air flow (and HP) is because they have lower total pressure drop and less heat soak than the stock CAI. You can lower Delta P with a bigger diameter pipe, less restrictions, fewer bends, etc. With a given vacuum, airflow will increase with less Delta P, this is why a dirty air filter starves a motor. it raises the Delta P. Oversimplified, more air allows more atomized fuel which translates into more HP.

Personally, I have not seen any dyno data that shows a HP increase with a PTB. Most sellers, at least over at Camaro5 say no performance gains, only improved throttle response. That statement is somewhat contradictory to me, since if I get my car to respond to the throttle quicker I ought to get where I'm going quicker.

Difficult in this performance world to find two "experts", which I am NOT, that agree on everything.
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