250 GTO Exhaust

mhanson · Jan 30, 2009

The exhaust tips on a 250 GTO are called "Snap" tips. I'm wondering why? Is it the mfg, or is there something meaningful about the name? They have an odd shape - a double cylinder with slits cut around the outside. What purpose does this serve? Back-pressure relief?

Thanks,

Mike

El Wayne · Jan 30, 2009

Some info here:

http://www.ferrarichat.com/forum/showthread.php?t=9011

http://www.ferrarichat.com/forum/showthread.php?t=164937

Most accurate response is probably this one:

http://www.ferrarichat.com/forum/showpost.php?p=136605&postcount=14

Kare said:

Snap...

--------------------------------------------------------------------------------

I think it is a little naiive to think that Italian engineers would equip an exhaust system of a racing car with a useless piece of decoration. This is *NOT* the case.

Putting a huge amount of exhaust fumes out at high revs introduces a few special problems. At high speeds a Ferrari 250 engine will put out 200 litres of exhaust fumes per second. That's about 50 litres per second per exhaust pipe.

At headers the exhaust fumes are very hot and they cool significantly running through the long exhaust pipe. When they cool, the volume decreases. As the volume decreases, flow speed (=kinetic energy of the fumes) decreases too***. This effect creates "an invisible choke" at the end of the tailpipe, which must be broken. Exhaust flow can be improved in various ways; on standard cars the end is usually cut at an angle or slightly bent. This way the outside flow will improve the exhaust flow. Adding a device like snap is more efficient; with a snap you can blend fresh air into the fumes as they are exiting and also create a vacuum by adding a shroud around the pipe end. Note especially that the diameter of the tailpipe end may not increase; that would slow the fumes even further and amplify the "invisible choke" effect.

So the effect of a Snap won't show on a standard dynamometer because the thing does not work at stand still; you would need to integrate a wind tunnel into your dynamometer to see what it does.

Best wishes, Kare

*** In the ideal world the exhaust pipe would be a cone getting smaller and smaller in diameter towards the rear... It is interesting that when people design exhaust systems from the top of their head (for motorcycles mainly) they tend to do exactly the opposite...
Click to expand...

planktom · Jun 2, 2015

and...what i didn`t find in the links :
afaik : S.N.A.P. stands for : Scarico Negativo Aria Pressione
=> E.N.A.P.> Exhaust Negative Air Pressure ;-)

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