Velocity Stacks

colin Fahrvergnugen

984 posts · joined Mar 2007 · 28 Mar 2008, 11:56 am

#638617

Gday dubbers. Has anyone done any dyno work or research on trumpet style velocity stacks for 48ida carbs?
The yanks seem to use them but are they for looks or do they really increase hp.

Cheers Col

BiX Veteran Volks Folk

2,499 posts · joined Sep 2002 · 28 Mar 2008, 1:19 pm

#638630

From a pure fluid dynamics side, yes they will reduce losses for air entering the carbies. How much on a VW.....🤪

I have no sympathy for my car, only the wallet that pays for it!
Go hard or go home!!!!

dangerous 23 Windows of Awesome

5,901 posts · joined Jan 2005 · 28 Mar 2008, 6:19 pm

#638666

I did some flow tests some years ago.
The various stacks did improve flow through the carbs,
but unless the whole manifold and head combo flows more air then it may just make you feel good.
What could not be tested was how the stack shape and height effected the way the carb draws fuel.

westi wrote:That's mad Alan.

dangerous 23 Windows of Awesome

5,901 posts · joined Jan 2005 · 28 Mar 2008, 6:24 pm

#638669

Sorry no dyno work though.

The biggest revelation was how much restriction a screen on top was.
Best to run a proper air cleaner (K&N), or nothing at all.

westi wrote:That's mad Alan.

OZ Towdster Keen to finish some projects

1,921 posts · joined Dec 2003 · 28 Mar 2008, 6:29 pm

#638671

A little birdy told me you were going to do some more tests soon dave including velocity stacks .

Don't let body work get in the way of real suspension travel

dangerous 23 Windows of Awesome

5,901 posts · joined Jan 2005 · 28 Mar 2008, 6:53 pm

#638675

Yes that is the plan with mine.
Injection though and not carbs.

westi wrote:That's mad Alan.

dangerous 23 Windows of Awesome

5,901 posts · joined Jan 2005 · 28 Mar 2008, 7:25 pm

#638678

Went for 19" from the top of the trumpet, down to the valve seat.
Old set up was 12.5"

westi wrote:That's mad Alan.

rocknrob Insano Dub Head

844 posts · joined Dec 2003 · 28 Mar 2008, 9:30 pm

#638699

inlet stacks and exhaust megaphones are all about taking advantage of the pressure waves caused by each stroke. there was a great book around half a century ago by phil irving which explained it all. supposedly ideally the volume of the inlet tract or the exhaust should be equal to the cylinder volume or a multiple thereof🤓 so the velocity stack would cause a ram effect and the exhaust meg cause an extracting effect😵‍💫 all old hat now since boost 👎

mactaylor Custom Title Time!

1,005 posts · joined Aug 2007 · 29 Mar 2008, 6:29 pm

#638798

those flow charts seems like a fun day! did the longer inlet trumpet move peak torque down in revs?

EVERLAST CONCRETE TANKS
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dangerous 23 Windows of Awesome

5,901 posts · joined Jan 2005 · 29 Mar 2008, 6:36 pm

#638801

From memory the longer stacks on the dyno just increased the torque.
It did not move it down lower..perhaps a little but something like 20ft lbs more@4000.
Hp was down about 1 hp, so well worth the extra 6" or so in runner length.
That is kind of the plan with mine.
We went in steps of 2" at a time till we peaked the torque number.

For IDA's and such, a 1/2" here or there will change very little.
The flow gain may increase power, or the rpm at which it occurs though.

westi wrote:That's mad Alan.

colin Fahrvergnugen

984 posts · joined Mar 2007 · 30 Mar 2008, 2:23 pm

#638888

Thanks for that info dave.

Cheers Col