Re: Holley question
 

I was told decades ago to remove the power valves on Holley carbs being used for all-out drag racing and simply jet the carb up 3 or 4 jet sizes. The rationale I was given (and it seems to make sense) is that power valves are devices that provide part throttle enrichment (i.e. they open when you depress the accelerator and vacuum drops to their approximate opening point), and drag race engines spend the entire run at WOT.

Re: Holley question
 

The picking a power valve method of idling in drive makes no sense. The PV has no part in idling, so why idle in drive to pick a PV? If your PV is opening or effected by idle vacum something is wrong. Wrong PV could close at WOT if vacum rises. Not worth having a PV in a race engine.

Re: Holley question
 

Rod, I suggested the Daytona Sensors because you stated you wanted a good unit to use in the future in other projects.

Therefore, if cost is the issue, I would recommend the NGK unit. It works great and very affordable.

I can assure you there are many that have been disappointed with the LM-2 units due to issues and not being reliable.

Re: Holley question
 

My problem with the LM-2 was with rpm. It would not display, record, or playback anything over 2K rpm. I tried multiple work arounds as per their tech support. After a year of playing around with it, I accepted the fact it didn't work as advertised. AFR displays ok.

Re: Holley question
 

The amount of jet change needed when blocking off the power valve is determined by the PVCR (power valve channel restriction) - the 2 little holes under the power valve in the metering body. That can be as high as 10. But I never used the formula.

As for using the vacuum reading "at idle, in gear", it's just a reference to make sure that the power valve you start with isn't opening at idle, in gear. If the reading is 7" of vacuum, you'll need a power valve below that to avoid a constant over-rich condition - i.e.: 6.5, 5.5, etc.). It's simply an on/off switch. But as mentioned, it's often eliminated in a race application with success. It's more important in a street application that spends more time idling.