Quote:
Originally posted by car9fan
iam trying to get the right power valve i put the gague on the bottom of my carb. port it reads 5-6 what size p.w. dp i need .you can see what carb, and motor i have at rons.mustangii.net 
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Nice looking car.
Numbers indicate when the valve would open. 6 means at 6 inches of vacuum and 8.5 means 8.5 inches of vacuum and so on.
Are you sure the numbers don't read like this 6.5?????
This means the power valve will open at 6.5h.g of vacuum.
Most carbs have this size from the factory.
On a car with a loose converter I like to have the power valve # to be about 2H.G less then the engine vacuum at idle. If it was a tight converter or a stick I go to put in a power valve that was 1/2 of engine vacuum.
Example: if you pulled lets say 10inches of vacuum.
5-speed, or a tight converter... put in a #5,6 power valve.
A loose converter (3,000* or more) put in a 7,8 power valve.
These are examples only.. and ALL ENGINES DO VARY!
This is just a good starting points..
* = Actuall slippage not what the converter is rated at...
Of course this means that you would need to rejet the carb and reset the mixtures screws.
Good luck