High Flow vs. Standard Power valves
Thread Starter
Racer
Joined: Jun 2002
Posts: 281
Likes: 0
From: Brookfield IL
High Flow vs. Standard Power valves
I have a '69 with the original 350/350 SB and intake manifold. I just rebuilt my Holley 4165 spread bore carb and installed the standard flow 6.5 power valve. The car is running fine but there is a slight initial hesitation when I step on it. So I'm thinking about changing to at least the 8.5 power valve, which I'm thinking would operate a touch sooner on hard acceleration. At least I'll try it and see if it makes a difference. The idle vacuum is 13-14 with the stock cam, so 8.5 shouldn't be interfering at idle.
My main question-- is there any reason not to just get the high flow version? The Holley website doesn't really describe the application difference between the standard and high flow power valves. So I'm naively thinking high flow is better because it has less restriction. But like many things in life, more isn't always better.
Also thanks to those that answered my previous questions. I was able to install a new divorced choke and I also installed the Holley power valve blowout protection with no problem.
Any info on the power valve selection would be greatly appreciated. I will probably eventually get a new carb/intake manifold, but I'd like to get this setup tweaked as best as possible first.
Thanks-
Andy
My main question-- is there any reason not to just get the high flow version? The Holley website doesn't really describe the application difference between the standard and high flow power valves. So I'm naively thinking high flow is better because it has less restriction. But like many things in life, more isn't always better.
Also thanks to those that answered my previous questions. I was able to install a new divorced choke and I also installed the Holley power valve blowout protection with no problem.
Any info on the power valve selection would be greatly appreciated. I will probably eventually get a new carb/intake manifold, but I'd like to get this setup tweaked as best as possible first.
Thanks-
Andy
Race Director
Joined: Mar 2001
Posts: 11,322
Likes: 1
From: Living in the Hartland
Sounds like you have a secondary squirter issue not a pv issue, traditional pv's do not meter fuel they only open and close, metering for the pv fuel is done by the power valve channel restrictor
make sure fuel comes out the squitter as soon as you move the throttle
make sure fuel comes out the squitter as soon as you move the throttle
Drifting
Joined: Sep 2004
Posts: 1,959
Likes: 1
From: North Bend Ohio
If the engine runs fine after the initial bit of hesitation I would look more at the accelerator pump system than the power valve. The accelerator pump was designed to cover up the holes between systems. In other words, there is a spot between idle and part throttle and then between cruise and sudden WOT that the carburetor needs extra fuel to get through. Often times the power valve simply can't react fast enough. The accelerator pump does not have to react like the vacuum operated systems do. If tuned properly, it will operate before there is the possibility of hesitation.
Also, if you change the power valve you may be tipping into it when the engine doesn't need it. This is just a waist of gasoline. Fuel mileage is a part of of your cars performance too.
BigBlockk
Later.....
Also, if you change the power valve you may be tipping into it when the engine doesn't need it. This is just a waist of gasoline. Fuel mileage is a part of of your cars performance too.
BigBlockk
Later.....
Thread Starter
Racer
Joined: Jun 2002
Posts: 281
Likes: 0
From: Brookfield IL
Thanks for that input. I will play around with the accelerator pumps to see if I can get them to squirt a little sooner. The carb is built to factory specs. My 350/350 does have Hooker headers-- would that at all require tweaking of the carb from the factory setup? Just curious. Also to be specific, it doesn't really stumble or badly hesitate like it's running roughly or going to die. It just feels like there's a slight delay between when I punch the gas and it starts to really roar.
On WOT, the engine starts to sputter after maybe 15 seconds. The only thing I could think of was that maybe the vacuum was rising past 6.5, and that sputtering was from the power valve operating and the engine running lean. That's why I thought maybe I should go to a slightly higher value to delay the PV from operating until the vacuum gets a little higher. But maybe the PV has nothing to do with that symptom.
Also when I'm at highway speed and I take my foot off the throttle, I hear a little exhaust popping. Is this indication my idle mixture is too lean? The carb has two idle mixture screws, so I'll go back and make sure I have both of them set correctly tonight.
Thanks
On WOT, the engine starts to sputter after maybe 15 seconds. The only thing I could think of was that maybe the vacuum was rising past 6.5, and that sputtering was from the power valve operating and the engine running lean. That's why I thought maybe I should go to a slightly higher value to delay the PV from operating until the vacuum gets a little higher. But maybe the PV has nothing to do with that symptom.
Also when I'm at highway speed and I take my foot off the throttle, I hear a little exhaust popping. Is this indication my idle mixture is too lean? The carb has two idle mixture screws, so I'll go back and make sure I have both of them set correctly tonight.
Thanks
Last edited by Driftwood; May 16, 2006 at 03:30 PM.
