which power valve

[original72]

OK since i had a few good backfires thru the carb figured i should replace the power valve.... question is with which one.... was thinking 8.5 but not sure.... it is a 440 with 9 to 1 comp..... 488 lift crane cam.... 2200 stall converter...... thorley 1 3/4 into 2 1/2 collectors..... and a holley 750 cfm model 3310

Thanks in advance
Bill

[Charger4404spd]

You will need to take a vacuum reading at idle to determine the correct one. For example, if you are pulling 14" of vacuum, you will divide that number by half, which is 7. Go to the nearest valve below that number. For this example, you would need a 6.5" pv.

[Ghoste]

I thought it was supposed to be 1.5 to 2.0 below your in idle vacuum reading?

[firefighter3931]

I thought it was supposed to be 1.5 to 2.0 below your in idle vacuum reading?

That's how i size them. The tip in from idle circuit to main circuit is smoother from my experience using this method....less chance of Bog.

Ron

[Chryco Psycho]

Make Sure you take the vacuum reading at idle IN GEAR if it is an automatic

[Ghoste]

What's the deal with two stage power valves and how do you choose those if or when you need them?

[firefighter3931]

Make Sure you take the vacuum reading at idle IN GEAR if it is an automatic

Yep, that is very important. If you size the PV too large it will be running on the main circuit at idle and be rich.

Ghoste, haven't used a 2 stage PV....the std PV seems to work well for me and allways has.

Ron

[Ghoste]

Here's another question for you then.  How come the 4150 uses two power valves but the conversion kit for a 4160 leaves it as single power valve unit? 

[Runner]

most 4150s only use a front power valve, infact most dont even have a provision for one in the rear metering block.


      most newer holleys come with a power valve blowout protection biult into them.   the power valve is alot tuffer than people give them credit for.

[Ghoste]

Okay.  I was under the impression that all the 4150's had two.  Thanks.