carburator power valves
10-10-2005, 11:58 AM
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carburator power valves
what is the best size carburator power valve to use for a holley 850 4 barrel duel pumper on a built up 454 HO with a 8 lb procharger set up. running 8 to 1 compression, and 92 primary and 103 secondary jets. , .130 vitron needle and seat. does anyone have a idea what size come stock in a 850 Holley
10-10-2005, 12:21 PM
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Re: carburator power valves
I have always used the starting point of choosing power valve size based on 1/2 of manifold vacuum @ idle. If manifold vacuum is 15in at idle, then I would start with a 7.5 power valve and then tune from there. Also remember that as you change power valve sizes, you will more than likely need to change squirter sizes to compensate for any hesitation.
Hope that helps!
Hope that helps!
10-10-2005, 03:52 PM
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Re: carburator power valves
I had about the same set up, I will look and get back to you but I think I was running 5.0 or 5.5 and the jets were around 88 pri and 92 secondary. the motors have been running 5 years now trouble free.
10-10-2005, 05:10 PM
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Re: carburator power valves
Most come with a 6.5.
It depends on the vacume of the motor now.
It depends on the vacume of the motor now.
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10-10-2005, 05:58 PM
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Re: carburator power valves
This is a procharged motor with a blow thru carb, not a N/A engine. The power valve reads the difference between the pressure in the box on top of the carb & the pressure/vacuum in the manifold. At cruise with a big prop the motor could be at 0" of vacuum with 3.5 lbs of pressure in the box. The power valve sees this as 7" of vacuum.
10-11-2005, 08:38 AM
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Re: carburator power valves
Originally Posted by Turbojack
This is a procharged motor with a blow thru carb, not a N/A engine. The power valve reads the difference between the pressure in the box on top of the carb & the pressure/vacuum in the manifold. At cruise with a big prop the motor could be at 0" of vacuum with 3.5 lbs of pressure in the box. The power valve sees this as 7" of vacuum.
10-11-2005, 09:05 AM
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Re: carburator power valves
Wouldn't it be better to not run power valves in this type application. Maybe get Nickerson to set up the carbs?
10-11-2005, 05:58 PM
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Re: carburator power valves
A blow thru system is harder to get jetted correctly compared to carb on a regular roots blower. On a roots blower the air going thru the carb at any given time is close to the same from idle to WOT. In a roots blower setup you are able to boost reference the PV so it sees what the motor load really is & give the motor more fuel when it really needs it. In a blow thru system the air density changes as the boost/rpm goes up making it harder to get the correct A/F ratio. The power valve helps to get the correct points at all speeds & throttle settings as long as you install the correct one. Seems like Nickerson has done his homework & figured out the formula for a blow thru system.
10-11-2005, 10:59 PM
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Re: carburator power valves
So tell me this, since it is DP and I assume it has progressive linkage, would you not want to jet the secondaries for WOT operation? And if that is the case, why would you not want to plug the power valves in the secondaries and jet the secondaries for WOT a/f ratio, and just run power valves on the primaries where part throttle and idle characteristics are more important?
