power valve block off question

[74360duster]

do i need to raise the jet sizes of my primary jets after installing the holley power valve block off?the reason for installation is that last year at the drag strip my car began to load up idling and when i go on it,it seemed to lean out.was popping like not getting enough fuel.so i figured maybe the power valve is bad.that is why i bought the block off.

 

[lead69]

Yes,if you block the power valve then you need to go up in jets-I go up two jet sizes or four numericaly-(80 to 84 as an example) to compensate for the lack of power valve.I would not reccomend getting rid of a primary side power valve if its street driven at all,its not nearly as efficient or driver friendly and if you have the correct power valve there really wouldnt be any noticeable gains in performance.I usually block the secondaries on a double pumper.

 

[74360duster]

its a 750 double pumper.i drag race only with the car.figured i would block off the power valve and eliminate any future problems.

 

[340mopar]

If it's a drag car only block off the power valve and jet the carb were it needs to be. Power valves are for part throttle, lower vacuum, higher engine load enrichment. A drag car carb really has two settings, throttle closed (idle) and wide open throttle (racing) so you don't need the enrichment at part throttle. I do not run power valves in my 660's and it is the way to go. Plus not all power valves flow the same amount of fuel so if you change a power valve you may have to change you jetting a little. I have seen some power valves with big square holes and some with little round holes.


I have a saying "parts left out don't fail" so if you don't need a part in your car don't run it. It's one less thing that could cause you to lose a race.

Chuck

 

[2shelbys]

See if Holley can give you flow numbers for the valve you have an go up enough jet sizes to compensate. I have seen recommendations of up to 8 sizes larger. When using a only a primary power valve you also need to have this difference between the primary and secondary jets or your primaries and secondaries will be operating at different air/fuel ratios which will cause problems, especially as the secondaries first open.