| [ Total Views: 720 | Total Replies: 10 | Thread Id: 68271 ] |
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 colin
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| posted on March 28th, 2008 at 11:56 AM |
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Velocity Stacks
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
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BiX
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| posted on March 28th, 2008 at 01:19 PM |
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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!!!!
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dangerous
A.k.a.: Dave Butler Muffin Man
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| posted on March 28th, 2008 at 06:19 PM |
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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.
| Quote: | Originally
posted by westi
That's mad Alan.
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dangerous
A.k.a.: Dave Butler Muffin Man
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| posted on March 28th, 2008 at 06:24 PM |
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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.
| Quote: | Originally
posted by westi
That's mad Alan.
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OZ Towdster
A.k.a.: Andrew Westwood
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| posted on March 28th, 2008 at 06:29 PM |
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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
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dangerous
A.k.a.: Dave Butler Muffin Man
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| posted on March 28th, 2008 at 06:53 PM |
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Yes that is the plan with mine.
Injection though and not carbs.
| Quote: | Originally
posted by westi
That's mad Alan.
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dangerous
A.k.a.: Dave Butler Muffin Man
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| posted on March 28th, 2008 at 07:25 PM |
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Went for 19" from the top of the trumpet, down to the valve seat.
Old set up was 12.5"
| Quote: | Originally
posted by westi
That's mad Alan.
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rocknrob
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| posted on March 28th, 2008 at 09:30 PM |
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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 
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mactaylor
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| posted on March 29th, 2008 at 06:29 PM |
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those flow charts seems like a fun day! did the longer inlet trumpet move peak torque down in revs?
EVERLAST CONCRETE TANKS
1800 552 123
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dangerous
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| posted on March 29th, 2008 at 06:36 PM |
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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.
| Quote: | Originally
posted by westi
That's mad Alan.
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colin
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| posted on March 30th, 2008 at 02:23 PM |
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Thanks for that info dave.
Cheers Col
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