Venturii Exhaust Assist - Works (g-tech)

[Guest Rota_Motor]

sounds like it works, although I reckon take it to the track to see if it really does

if it is working, that means you have a heap of air blowing under the car, which isnt best for roadholding, or so I hear.

also by my thinking, at speed, there should already be a low pressure area behind the car, especially at the lower edge of the bumper, which from memory is almost a diffuser in design.

[newxr]

  Rota_Motor said:

sounds like it works, although I reckon take it to the track to see if it really does

if it is working, that means you have a heap of air blowing under the car, which isnt best for roadholding, or so I hear.

also by my thinking, at speed, there should already be a low pressure area behind the car, especially at the lower edge of the bumper, which from memory is almost a diffuser in design.

<{POST_SNAPBACK}>

There does not need to be air blowing under the car - the movement of the car itself forces air into the intake at the speed of the car so the vacuum created is related to the speed of the car - faster the car moves the greater the vacuum created.

As for track - I can't see it improving times much - a 4-5kw gain is not really going to show up on the track. Also, track times are very much driver dependent so I can't see any point.

Pointing exhausts down - not really as the tailpipe is very high above the ground - to take advantage of the low air pressure the tailpipe would have to be no more than 3cm of the ground - poor clearance. This was the problem that forced F1 cars to abandon the concept.

[Grass]

  newxr said:

  XXXR6T said:

So it basically creates an area of low air pressure directly behind the tailpipe and hence causing the high pressure air in the exhaust (hot air) to escape more quickly lowering the high speed back pressure created by the exhast... is that how it's working?

Very interesting concept...

The exhaust is normally of lower pressure than the atmosphere however it can escape due to its speed however by lowering the resistance behind the tail pipe this just helps it along.

My set up has a 3.5" intake with a 1.5" exit so at 60km/h the air is exiting the device at over 240km/h and significantly reducing the presuure behind the tailpipe. Older F1 cars had the exhaust pointing down as the air rushing below the car reduced the pressure and the exhaust flow was improved.

But does the air increase in speed ? Perhaps it increases in pressure instead of accelerating, perhaps it does a bit of both.

P + 1/2 ρv2 = a constant

Hence it could be an increase in pressure or an increase in velocity of the air.. or both

[Mr66]

I'm wondering at what point the drag created by a 3.5" funnel would negate any potential kW gains.....?

[newxr]

  Grass said:

  newxr said:

  XXXR6T said:

So it basically creates an area of low air pressure directly behind the tailpipe and hence causing the high pressure air in the exhaust (hot air) to escape more quickly lowering the high speed back pressure created by the exhast... is that how it's working?

Very interesting concept...

<{POST_SNAPBACK}>

The exhaust is normally of lower pressure than the atmosphere however it can escape due to its speed however by lowering the resistance behind the tail pipe this just helps it along.

My set up has a 3.5" intake with a 1.5" exit so at 60km/h the air is exiting the device at over 240km/h and significantly reducing the presuure behind the tailpipe. Older F1 cars had the exhaust pointing down as the air rushing below the car reduced the pressure and the exhaust flow was improved.

<{POST_SNAPBACK}>

But does the air increase in speed ? Perhaps it increases in pressure instead of accelerating, perhaps it does a bit of both.

P + 1/2 ρv2 = a constant

Hence it could be an increase in pressure or an increase in velocity of the air.. or both

<{POST_SNAPBACK}>

Correct indeed - while in the device the pressure of the air increases however as soon as it is released at very high velocity into the open air it causes the air pressure in the vicinity to drop. Try holding a piece of paper to your mouth a blow over it - the paper actually rises as the blowing action reduces air pressure just above the paper so the air below the paper forces the paper to rise.

In order to achieve a meaningful reduction in pressure you really need to accelerate the air to very high speed and this is what the device achieves by creating a venturi type funnel to acclerate the air immediatly behind the tailpipe.

[XtRmn8]

The exhaust on my car points down at the rear.

[newxr]

  Mr66 said:

I'm wondering at what point the drag created by a 3.5" funnel would negate any potential kW gains.....?

<{POST_SNAPBACK}>

Unkown - however I have installed the scoop so that it is behind the first mufler as you do not need air to forced into the scoop the simple movement of the car does this.

[newxr]

OK

A quick review - it is a combination of the Venturii and Bernoulli principals. The sccop under the car has a large opening which then passes into a smaller tube. Due to the reduction in tube diameter and the continuing inflow from the scoop the gas has to increase in speed to escape out the other end = Venturi Principal. Now the accelerated gas is passed directly behind the tailpipe. A fast moving gas will reduce the pressure in the local vicinity = Bernoulli principal. The reduced pressure behind the tailpipe means the exhaust gases are able to exit much more easily. This is the same as say having a larger exhaust system. The only problem is that in order to achieve an adequate reduction in pressure you need to accelerate the air to very high velocities and thiat is why the venturri setup is required. With my set up of a 3.5" scoop and a 1.6" exit at 60km/h the estimated exit air speed is about 240km/h giving a 10% reduction in air pressure behind the tailpipe.

Various permutations and combinations are possible - there are numerous online calculators that will give you rough velocity and pressure outputs for various input velocities