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| newxr |
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Hi All
A few weeks ago I suggested a Venturii Exhaust Assist device - essentially an air sccop under the car that passes air through a narrow tube to increase its speed and then the fast airflow is directed behind the tail pipe to reduce the pressure behind the tail pipe to assist exhaust evacuation. Well I built and mounted one and tested it using my G-TECH 3 Runs without the device - mean 138.6kw (best run = 139.4kw) 2 Runs with device - mean 144.5kw (both runs over 143kw) 
All runs within 1 hour of each other on the same track Car = BA XR6 N/A with T-snorkal and 2nd XR8 Type CAI
_________________ <b>XR6NA with T Snorkal in Silhouette with Lux Pack + 2nd CAI XR8 Snorkel, Pacemaker Headers, High Flow Cat, Redback Exhaust with Twin Tailpipes - 149kw (G-Tech)</b>, Lower Grill, Side Air Bags, Power Pedals, Boot Lid Carpet, Boot Liner, Rear Sun Screen, Mats, Spats, Scuffs, Tint, Gold Plated Badges |
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| 4.9 EF Futura |
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Thats actually a brilliant idea.... i guess the faster you go, the more effective?
What about exhaust outlet facing sidewards... http://www.halfbakery.com/idea/Venturi- ... t_20System
_________________ I promise..... I will never die. |
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| newxr |
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4.9 EF Futura wrote: Thats actually a brilliant idea.... i guess the faster you go, the more effective?
What about exhaust outlet facing sidewards... http://www.halfbakery.com/idea/Venturi- ... t_20System Yes the faster you go the greater the reduction in air pressure Sideway tail pipe - no but a downward tailpipe yes - older F1 cars had exhaust tailpipe close to the ground because pressure is reduced due to the air rushing under the car however not practical as you would need the tailpipe only a couple of centimeters above the ground.
_________________ <b>XR6NA with T Snorkal in Silhouette with Lux Pack + 2nd CAI XR8 Snorkel, Pacemaker Headers, High Flow Cat, Redback Exhaust with Twin Tailpipes - 149kw (G-Tech)</b>, Lower Grill, Side Air Bags, Power Pedals, Boot Lid Carpet, Boot Liner, Rear Sun Screen, Mats, Spats, Scuffs, Tint, Gold Plated Badges |
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| twr7cx |
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Excus my retardedness, but does this mean your exhaust goes from one dimension to another smaller? E.g. your exhaust might be 2 1/2", but goes to 2 1/4" at the tail pipe?
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| gravelrash |
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mate ya lost me..........
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| ItchiOne |
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Similar principle are used by a wing to hold 747's up and F1 cars pressed to the road.
I thinks its Bernoulies (sp?) principle, but then again it has been many years since i last studied fluid dynamics 
I guess the difficulty is to know what size ducting needs to be placed around the exhaust to get the desired effect and whether it will upset under car airflow enough to adversly reduce download (or increase upload, as is the case for most cars). Newxr, was the car less stable after adding the ducting ? Cheers |
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| chunkz |
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ItchiOne wrote: I thinks its Bernoulies (sp?) principle,
i dont know about the spelling but yeh thats the right principle mate
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| chunkz |
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gravelrash wrote: mate ya lost me..........
im not positive i have read what he has said like 5 times so im trying to understand theres a scoop underneath his car... that picks up air (unless your in reverse  )
because when the car goes forward air goes into the scooop connected to the scoop is a pipe... the air rushes through the pipe and it comes out at the end the air thats picked up in the scoop... pushes air away from the back of the exhaust, so your exhaust fumes can come out easier... which i dunno how it works... but makes car more powerfull.... i dont know how but i think its absolutly brilliant if you can figure it out.. and not make it look so ugly :S
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| EF 4.9 |
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Unreal idea, using a smaller pipe would increase velocity at a lower speed but it would reach maximum effect at a lower speed than a larger pipe.
Would it be more efficient if the exhaust pipe exited to the side and the duct was straight?? There is a lot of variables to play around with... Hmm the possibilities. for those that dont understand, its the same effect as the old 1940's pump type fly spray uses, and lots of other things
_________________ They say people don't believe in heroes anymore. Well damn them! You and me, Max, we're gonna give them back their heroes! |
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| chunkz |
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i can get my physics teacher to work this s**t out...
must people would want max at 80km/h? those who wanty street legal s**t... (not talking about off road drags) edit: more thinking.... well you'll need a bigger opening (scoop) then a small pipe.... if its same pipe all the way through obviously the velocity will be same as the car... well actually say speed caus velocity is a vecta 
(holy s**t i do listen in physics :O ) ummm i forget wht i was gunna say... if you have say a 3" pipe all the way to the end but have like a 1" tip on it.. if your welding is good... and not alot of pressure is on it... any one know the acg speed of exhaust out goings? caus going on the theory it isnt faster then 60km/h then should woork fine
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| newxr |
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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
_________________ <b>XR6NA with T Snorkal in Silhouette with Lux Pack + 2nd CAI XR8 Snorkel, Pacemaker Headers, High Flow Cat, Redback Exhaust with Twin Tailpipes - 149kw (G-Tech)</b>, Lower Grill, Side Air Bags, Power Pedals, Boot Lid Carpet, Boot Liner, Rear Sun Screen, Mats, Spats, Scuffs, Tint, Gold Plated Badges |
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| tomcolahan |
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What are the 'seat of your pants' results like?
_________________ We'll keep our cow s**t in the country, you keep your bull s**t in the city. |
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| twr7cx |
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So does the back of your car look like it's got two exhaust pipes, one curled?
Any chance of a picture showing the entire back of the car pelase? Just otu of itnerest. Last edited by twr7cx on Sat May 14, 2005 5:39 pm, edited 1 time in total. |
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| chunkz |
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yeh like in the picture....
im trying to think of other ways you can make it look (coming up from the bottom?)
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| jonbays |
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Really not to sure about all this at all.
Some good underlying areodynmaics theory but not well tied to the cause and effect of improving the engine efficiency. I doubt it works at all. Well it will probably keep the back of the car cleaner and assist the exhaust gasses to escape the exhuast faster but is it going to help scavenge the cylinders any better on exhaust stroke I think not or is it going to draw in any more A/F mixture on intake stroke NO WAY. Why not put a super charger on the exhaust and see waht happens. No its a joke right? |
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