what is the top screw on this dump valve for?
 

Blitz Dump Valve on eBay, also Other Performance Parts, Performance Tuning Parts, Car Tuning Styling, Cars, Parts Vehicles (end time 03-Oct-08 22:20:43 BST)

same as this one, fitted it last night, altohugh mine has more of a trumpet on it.

what is the bolt / thread on the top in the middle for, and what does adjusting it do?

cant really hear the valve at the mo, but it does seem to imporve through gears accelerating.

as above, what is it there for, and what might tightening/ loosening it off do?

thanks

David

it is used for adjusting the spring tension on the valve. I think With the type shown (and certainly for my greddy type s), undo the 10mm nut and turn the centre shaft (is there an allen key in the top of it?) clockwise to increase spring tension and vice versa. lock the shaft again with the 10mm nut once finished.

ok, sorry for sounding stupid, but what implications does this have either loosening, or tightening the spring?

i assumed that it would only release pressure, once your take four foot off the revvs, or change gear at high revs etc

long post i know..sorry..

in free air ( off the car )The bov will be normally shut by the pressure of the spring only.

when installed on your car you connect a hose from the top of the valve to the manifold and the other side of the valve is in the charge pipe. ( 3rd side vented to atmosphere)

when you snap the throttle closed, the hose on the top connected to the manifold is now under vacuum, where as the charge pipe is still under pressure. It's this difference that causes the air to dump from the charge pipe out through the valve. When equilibrium is established, the valve will be shut again under its own spring pressure.

reasons to increase spring tension
hold more boost / dump less air on gear changes / avoid rich afr issue on in gear over run / change dump valve sound.

reasons to decrease tension
Dump all available air on gear changes / change dump valve sound / ???


there are probably other reasons too but off the top of my head i cant think of any more.

was long, but necessary i feel, is a good explaination cheers :thumbup:

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