I have a few questions I need help with. What is the best size powervalve to run in a Holley on a stock 429 motor its a 72 model I have a holley 1850 I know they come with 6.5 but is that best? Also what size jets are best ,it has stock 66 jets.

 

I can't answer your question directly because I don't know how stock your engine is , how heavy you typiclly load your truck or how fast you drive or what altitude you live at. From the factory the carb is set as close as possible based on it being a stock truck.

The power valve richens the fuel mixture when the engine vacumn drops below the number stamped on the valve. The best way to determine which power valve to use is to temporarily attach a vacumn gage to the engine with the vacumn hose routed into the cab. Load the truck as you typically do and drive it on the highway. You will want a powervalve number about two numbers down from what you read. This will keep the power valve closed for crusing.

There are three ways to select jets, trial and error (change only one sizes at a time), read the spark plugs (difficult without experience) or install a air/fuel meter. Trial and error does works, you can feel the difference.

By measuring acceleration between to fixed points you can which jet is best for maximum power. By using a welding tip cleaner you can enlarge the power circuit fuel orifices located beneath the fuel side of the power valve. By placing a small wire (cut from this welding tip cleaner) in these orifices, you can effectively make them smaller.

Before starting, if you have any evidence of fuel boiling in the carborator float bowls, add a holley aluminum plate heat shield. It will require some triming to fit. Also get some bowl gaskets and transfer tube o-rings. Use diswhashing soap to lube the gaskets and grease for the o-rings. That way they can be reused many times over.

The secondary side is adusted only by changing jets. The powervalve (if equipped) will be open any time the secondarys open so there is no need to change it. A good place to start is to increase or decrease these jets in proportion to the primary side jets. Holley make a spring kit for opening the vacumn secondaries sooner.

Remember you are starting from a decent point of tune. Therefore you can stop anywhere along the way with no ill effects...or go farther than described above.

 

The rule to picking a power valve is to measure the engine vacuum at an idle in gear (is an Auto trans). Then divide that by 2. So if you have about 18" of vacuum, i would use a 8.5 power valve.
If it's a manual trans, then divide idle vacuum by 2 in neutral.

 

thanks its pretty stock, a 72-429 but instead of the d2 heads i used d3's and the only mods really are dual 2.5 exhaust and a 1" 4-hole carb spacer, I added it for a little extra torque.thanks.

 

All ya need is a vacuum gauge to figure out the correct one.