Pipemax 101 - Pipemax Program discussion

[jfholm]

Does this carb run power valves in it? Check and see what number you have if it does have power valves. 750 cfm is on the bigger size for your engine. I noticed that the vacuum went to "0" on launch and stayed there for the whole run. The power valve opens when it is below the number stamped on it. So if it was a 65 power valve then it would be open and enrichening your mixture anytime the engine vacuum was below 6.5" of vacuum. Seeing how you are at 0 the whole run that may be why you are overly rich. If you take out the power valves and block the holes you usually need to up you jets 6 - 8 steps. Then you could work backwards until you are at 12.5 or so at launch.

The high speed air bleeds usually have a tendancy to affect the higher rpm fuel mixture so making them larger I do not feel would help.

John

[johno]

You can also restrict/ control power valve feed (if the jets are to big) by placing a 'W' shaped peice of thin wire into the PVRC. But a W.O.T. vacuum of 0 indicates a carburettor thats too big for that motor, or the main venturi needs downsizing ( if they are removable)! :;):

[200cfm]

Went into the carb today. Primary was at 74 and secondary was at 83. So I dropped it two steps 72/81. I see a 4 and a 5 on the power valve so I assume it is a 4.5. I left it alone. I notice the 0 reading on gauge at WOT you mentioned. What vacumn would you want showing? Maybe the gauge is not sensitive enough to detect the carb pressure drop. Has to be drop across it or else the fuel would never flow. Why would it go faster on mph if carb was too big? It made a gain over the 4010 carb which is at 600 cfm rating. Hoping to retest this Friday and see if improves or disapproves.

[Flash]

[johno]

Four barrel holley carbs are tested at 1.5" mercury. At this pressure the carburettor is seeing its full flow. When the pressure is reduced below 1.5", the carburettor no longer flows its full amount, it flows less due to the lower pressure drop its seeing. To calculate carb flow at lower pressures use; carb cfm (at 1.5" Hg) divided by the square root of (1.5" divided by 'new pressure drop'). So if you had a carburettor rated at 600 cfm @ 1.5", but only have 0.5" at W.O.T. then the carburettor will only be flowing 346.42cfm!! :;):

[200cfm]

Good teaching point. I understand this better. Does this mean the carb rating is like a PTS calibration plate rating? Certain delta pressure drop gives X flow. The carb rating is acting perhaps like an orfice plate reference. I looked at the early video with the 600 cfm 4010. Can't detect any needle movement toward a Hg drop measurement. Just don't think the gauge has that much sensitivity. Perhaps an on board wc manometer or some super sensitive sensor chip. Then one could know the carb Hg drop and then use that formula to calculate the cfm. Then back math to calculate the engine cfm efficiency. Just brain storming here. Pipemax has a drop down menu for carb cfm. At 6000 rpm a 600 cfm is adequate. The 750 carb is adequate for up to 8000. I realize it is over carb but I like the time slip.

[Flash]

[Flash]

[jfholm]

[johno]

[Flash]

[larrycavan]

[larrycavan]

This pic is a dyno run with predicted results from another engine performance analyzer application.

From 6000 on up it's pretty darn close.

The CFM is dead nuts.

[larrycavan]

Let's try this again. I cropped the pic. Hopefully this time the numbers can be read

[larrycavan]

Rest of the screen. Hopefully this works out for size and readability.

NOTE: the A/F was rich. 11.9 - 12.1



Edited By larrycavan on 1251594633