what are you running as far as jet size on your Holley 870 cfm (street avenger) on mild 455 ? mine was 78-82 and was kind lean at WOT (bone white plugs) so I just put 80-85 sizes jets ....
Holley doesnt recommend that you increase or decrease more than 2 jet sizes at a time.... a lot of people think that the jet sizes are in thousanths but the number on the side is not the size in thousanths... the holes are drilled in thousanths allright but are not the same as the numbers....[I hope I am making sense here] You need a holley jet size chart to determine the size in thousanth for fine tuning.... If I remember right the numbers are a couple of thousanths for each number increase... You need a small number drill set to be able gage jets with... some jets may have been drilled by some mechanic and not be true to the number size....
I have that exact carb on my convertible (mild cam, mid-13's ET) I didn't change a thing on it. It was perfect, right out of the box. I picked up about .7 off my ET by simply changing my intake to a B4B and my carb to the 870.
