jetting
Safety Car
Joined: Aug 2000
Posts: 3,711
Likes: 43
From: San Antonio TX
Re: jetting (sweet79corvette)
A Holley double-pumper and it's a four-barrel. Really? :)
The metering on double pumpers tend to be on the fat side since these are intended for the track. Leave the installed jets in it and do some testing. The best way to do it is to run it on the eighth or quarter and change jets in skip incriments until the point where your mile per hour drops off. The natural inclination is to start by going leaner but you have to be careful since if you're lean now, you could burn a piston. So go rich and if the mph doesn't improve after one change, start going leaner.
You could read the plugs as to where the firing ring is occuring on the porcelan but this is more of a practiced art and is very difficult to do with any accuracy and it really only works well on the track after a full-throttle run, so you're kind of on the track anyway.
You could also just play around with it on the street but this method really only works when trying to go leaner. Essentially you do the skip jets until you notice a lean misfire and go two to four jet sizes larger from the point of lean misfire.
There is also the scientific method which uses a wide-band O2 sensor which is overall the most accurate for a street engine and is about the only method to use when setting up the fuel maps in an alpha N electronic injection system. If you have the bucks to spend and you appreciate technology, this is worthy of consideration.
It's hard to do a one size fits all when it comes to jetting but by all means go with what Holley put in the carb as your baseline.
The metering on double pumpers tend to be on the fat side since these are intended for the track. Leave the installed jets in it and do some testing. The best way to do it is to run it on the eighth or quarter and change jets in skip incriments until the point where your mile per hour drops off. The natural inclination is to start by going leaner but you have to be careful since if you're lean now, you could burn a piston. So go rich and if the mph doesn't improve after one change, start going leaner.
You could read the plugs as to where the firing ring is occuring on the porcelan but this is more of a practiced art and is very difficult to do with any accuracy and it really only works well on the track after a full-throttle run, so you're kind of on the track anyway.
You could also just play around with it on the street but this method really only works when trying to go leaner. Essentially you do the skip jets until you notice a lean misfire and go two to four jet sizes larger from the point of lean misfire.
There is also the scientific method which uses a wide-band O2 sensor which is overall the most accurate for a street engine and is about the only method to use when setting up the fuel maps in an alpha N electronic injection system. If you have the bucks to spend and you appreciate technology, this is worthy of consideration.
It's hard to do a one size fits all when it comes to jetting but by all means go with what Holley put in the carb as your baseline.
Intermediate
Joined: Feb 2002
Posts: 36
Likes: 0
From: belleville wi
Re: jetting (sweet79corvette)
i was wondering why you went with a holley? I just got my ZZ4 and was going to use the Q-jet and just change to CE rods.
tom :jester
[Modified by silver 80, 4:34 AM 12/26/2002]
tom :jester
[Modified by silver 80, 4:34 AM 12/26/2002]
