[HeadDoctor]

Brian

Here's what happens - When you nail the throttle the vacuum drops to 3.2" HG or less, so if you have a 35 PV in there it won't open untill the vacuum gets below 3.5"HG

In oval track with a 390 carb and 9 to 1 engine we put a 45 PV in there so it will close when the vacuum returns to close the PV and lean the motor down. In a drag car you generally want low number PV's because you're always at WOT. That way the PV is closed unless you're "On the Gas"

In your case I would suggest that you get a series of PV's from 35 to 65 in every increment and find the best one for your application. Remember that you have to be 10 jets smaller when you run PV's so a #70 jet should be sufficient. Get smaller and smaller with the main jet until you can tell that its running to lean with a 35 or 45 PV. At normal cruse RPM.

With the 65 or 85 PV it's going to open as soon as the engine sees that vacuum signal. The best way to determine this is to have a friend ride with you while the vacuum gage is hooked up and let them watch and write down the various Numbers as you increase and decrease the throttle, based on the RPM of the engine. Then you will have a chart to go by and you can tune the motor with the PV system and still have a lean main jet. I don't recomend that you do the next part by yourself without "Do-Dilligence" - You can drill out the PV fuel passage to get more fuel if its absolutely necessary.

You can also stagger the PV's front to rear to get the thing even more manageble.

Mike Urich's Holley book is probably the best on this and he goes into great detail about tuning with the PV system.

Denny@JDS Induction Products