K
Ken73
Guest
I seem to remember a few years ago that someone had mentioned offset jetting their carburetor.... if you're unfamiliar with that term, maybe an explanation would be in order.
I have a '73, which I've installed an Edelbrock Performer (NOT the RPM model) intake on. I've owned a flowbench before, and out of curiosity inspected this manifold and performed a flowtest. There are two planes on the intake - one "small" and one "large" .. I believe the idea was to offset the manifold enough that it would run fairly well at idle and fairly well at the top end. Sort of a "compromise" intake if you will. I found that the "small" side only flowed about 230CFM per runner, and the "large" side flowed closer to 280CFM per runner (these numbers are approximate.. I've since lost my notes!)
Now, that being said, a carburetor with equal jetting would produce either a lean condition on one side, or a rich condition on one side, or innacurate metering for both, entirely. However, a carburetor with *offset* jetting would produce the proper mixture ratios for each plane, resulting in more power AND better mileage. The real trick was to use oxygen sensors (small) in the header on the #5 and #7 cylinders - these are the two that run the leanest, and are on the two different intake planes.
I can't remember the gentleman's name that had tried this and had good success with it - with any luck he's on here and will pipe up? Has anyone else tried this?
I have a '73, which I've installed an Edelbrock Performer (NOT the RPM model) intake on. I've owned a flowbench before, and out of curiosity inspected this manifold and performed a flowtest. There are two planes on the intake - one "small" and one "large" .. I believe the idea was to offset the manifold enough that it would run fairly well at idle and fairly well at the top end. Sort of a "compromise" intake if you will. I found that the "small" side only flowed about 230CFM per runner, and the "large" side flowed closer to 280CFM per runner (these numbers are approximate.. I've since lost my notes!)
Now, that being said, a carburetor with equal jetting would produce either a lean condition on one side, or a rich condition on one side, or innacurate metering for both, entirely. However, a carburetor with *offset* jetting would produce the proper mixture ratios for each plane, resulting in more power AND better mileage. The real trick was to use oxygen sensors (small) in the header on the #5 and #7 cylinders - these are the two that run the leanest, and are on the two different intake planes.
I can't remember the gentleman's name that had tried this and had good success with it - with any luck he's on here and will pipe up? Has anyone else tried this?
