318 Motor, please help
it had a 6.5 power valve on it. i watched a few youtube videos and one said to take the vacuum reading you get when you have the car in drive and divide it in half and if its an even number drop down .5 so for me my reading was 10, so i installed a 4.5. but now i need to start all over since we found the vacuum leak. so i think your right and the number is going to increase, maybe back to an 8.5. im loving my Holley carb and im determined to get it dialed in correctly. thank you very much
These guys are just regurgitating what they heard someone else say. When its repeated enough it becomes beleiveable. But its pseudo-science.
The real engineering is this. The enrichment is needed when the engine is approaching its maximum power for that rpm. An engine with good fuel and air distribution to all cylinders at part throttle and full throttle, and good combustion characteristics under those conditions, can go deeper in the throttle before needing enrichment.
Engines that are focused more on full power, high rpm performance, etc, tend to need enrichment at less throttle. So a those engines tend need PV in the 8.5 to 10.5 opening.
On a real efficient engine like a factory 318 that might just be wasted fuel and less part throttle power. A 5.5 or 6.5 would probably be fine.
Slightly too rich is harder to notice than slightly too lean, especially Seat of Pants.
One observation that will provide a clue as to engine efficiency is the vacuum while cruising.
As you press the throttle (going up hill or accelerating) the vacuum will drop and the car should pull harder.
What is happening as the throttle opens is the fuel mixture is getting leaner and the car is making more power.
There is a point in throttle opening (under load, not in neutral) when the AFR needs to get richer for the engine to continue to make more power.
That's the power valve opening point, or step up, or enrichment vacuum.
https://www.tapatalk.com/groups/rac...tor-afr-characteristics-at-differen-t421.html(if you get a pop up asking you to join TT, just close the popup and read the thread).