I have looked everywhere I know to look and I haven't found the limit of the std power valve. What size PVCRs need the Hi-flow? Thanks!

don't think I have ever used a high flow. if I did it was by accident.

My last two carbs came with Hi Flow units and I was told by both suppliers to keep using the Hi Flow units when I changed sizes. They were Promax and Quick Fuel carbs. Maybe one of them can help determine why they are used.

Anything with a pvcr of .090 or larger requires a hi flow "window" style power valve.There are also standard "window" style power valves,that a lot of people refer to as high flow.

I am really surprised that this info is not readily avaliable. I checked and the Hi-flows are in stock at a lot of suppliers, so there must be some demand for them. I have looked in Emanuel's Holley book, but it shows the old Holley std flow PV that had the little holes. And he did not say at what PVCR size the Hi-flow PVs become necessary. I'll save you all the long story here, but I think I need the Hi-flow PVs. I would like to know at what point they become necessary before I go to the trouble of ordering them and changing them.

I just looked at a book I have that shows over .060,use the window type,and over .090,hi flow window type.It states that most 3310's and all double pumpers should be .060 or larger,for what it is worth.

Thank you!!!!

Just found another article that states small picture window pv good for pvcr of .065 to .095,large picture window pv good up to .120 pvcr.So it would seem to be pretty close to the other article.

Thank you for the folow-up.

What are the dimensions(measurements) of the standard window versus the hi flow window?maybe we have all been using the hi flows without knowing what they looked like

I just got my hands on a new-in-the-package Hi-flow PV. At first glance, I don't see that the windows look any bigger. It will be tomorrow evening before I can pull the a PV out of my carb. When I do, I will try to post some side-by-side pics.

I couldn't wait, so here is a pic of a standard and a hi-flow, side-by-side (hi-flow is on the right). The windows measure the same. And except for the hi-flow having a darker finish, I can't see a difference. The only thing I can figure is maybe the opening on the threaded end, but I'm not going to tear it up to measure it. Hopefully, I can get the hi-flow in this week, and see if I can richen up my A/F.

i might be wrong ...but im going with "Snake oil" .








Kinda like the fancy "Hi Flow" air filter i just tested at the track.

0 gain over a $3 O'Reilly filter.

Quick Fuel's version of the high flow has 4 doors.

The bore of the housing is slightly larger on the hi-flow casting.

the valve stem has more "wiggle", that is it deflects more on the hi-flow .

Like others have stated, not needed unless pvcr is larger than .090"

It has been a while since I have bought any so my information might be out of date. As I remember holley only offered the highflow in 2 sizes I always used the 6.5 but I think there was 10.5 also. I didn't go with the size of the window to identify them but instead used the amount of side to side play as the indicator. with a standard flow and a high flow in hand you will notice that the high flow has much more room for the needle to move in relation to the seat. If you use the standard PV instead of the high flow it can make the engine very lean. (ask me how I know) But using a high flow instead of a standard flow will not change the tune, unless you need something other than a 6.5 PV, Good luck.

You're right! There is a lot more deflection to the shaft of the Hi-flow. I like the looks of that 4 window PV. I have .092 PVCRs and could not get it to richen up any more with the 80 mains that the cruise likes. It was plenty rich with 88 mains.
Holley offers the Hi-flows in several openings from about 3.5 to 9.5, give or take.
Now I can get back to tuning. Thanks to everyone for the help on this!