Q for Holley carb owners

[SportZ2]

Does anyone have a holley carb on their V8 conversion that live at 5000ft (give or take a 1000ft)?

 

If so how are you jetting your carbs. I have a 4011 (650 cfm) and the jets that came with it are .060 for both primary and secondary. I know that I should go down one number for every 2000ft and that two numbers down is good for 5000ft.

 

Should I keep the jetting consistant or can I run smaller jets in the front and bigger jets in the rear? I'm hoping to get some ideas of a good starting point and knowing what people are already running would help. Also, what if any advantages or disadvantages have you found by jetting this way.

[dr_hunt]

I'm not familiar with the 4011. I have 3 holley DP carbs, all run at 5K or higher elevation regularly. Mine are all DP carbs and I jet square since all the venturi's are the same size and airflow. You can run smaller jets in the primaries and larger jets in the secondaries, but it depends on whether or not you run power valves in either metering block. I run power valves in my 750DP only. If you don't run power valves, then you have to jet up 6 to 8 sizes to compensate for the fuel loss attributed to the power valve being removed.

 

Also there are different flowing power valves, 2 stage, 2 window, 2 window high flow and 4 window ultra flow.

 

You also have to pay attention to the needle and seats, there are several different sizes of those as well and they need to match your HP potential of the engine to keep the bowls full and not lean out the engine on the top end.

 

.060 is a really small jet. 650 DP carbs usually have .068 jets stock in my experience. In my 750DP I run .074's and 4.5 two window power valves for 8000 ft elevation on a 406, it has 7 inches of vacuum at idle on that engine.

 

The main thing is that you have to read the plugs, flow distribution problems in your intake system can require staggered jets or a 6 jet/8 jet conversion carb. This is the reason that EFI is really so much better IMO, cause you can meter fuel to each cylinder more precisely, at least in the MPFI.