#1  
Old 10-17-2020, 10:34 PM
oethel's Avatar
oethel oethel is offline
Senior Member
 
Join Date: Jan 2015
Location: west ky
Posts: 100
Default Carb help

Did a test run today at 9lbs of boost and was happy with the run.My afr in my Holley was right in the 11.5 range.Would like to step up to maybe 12lbs boost.My main jets are 71 square and my pvcr's are .062 four total. Two in the front two in the rear.My question is,can I main jet up enough to stay in my afr range or do I leave my main jet alone and just play with pvcr's depending on boost or maybe adjust sizes with both?How much can a main jet air bleed change afr?I know how much fuel it takes to get my afr correct at 9lbs.So can I calculate how much fuel it would take to run 12lbs and the correct afr?

  #2  
Old 10-18-2020, 11:54 AM
Tom Vaught's Avatar
Tom Vaught Tom Vaught is offline
Boost Engineer
 
Join Date: Dec 2001
Location: The United States of America
Posts: 31,294
Default

Play with the PVCRs as that is the common way boosted carb calibrations are done.
Some people actually have 6 PVCRs in each metering block. Usually not all the same size.
Two are large, two more are to get the fuel close, and the last two are fine tuning of the calibration for each metering block to get the exact A/F they want.

This way for a boost increase you typically only need to replace two PVCRs with a different size. The big ones do not change much, the smallest ones take care of the fuel balance to both main wells and the medium ones adjust for the boost change.

Tom V.

__________________
"Engineers do stuff for reasons" Tom Vaught

Despite small distractions, there are those who will go Forward, Learning, Sharing Knowledge, Doing what they can to help others move forward.
  #3  
Old 10-18-2020, 12:22 PM
70 bird's Avatar
70 bird 70 bird is offline
Chief Ponti-yacker
 
Join Date: Feb 2005
Location: Taylor Mi.
Posts: 973
Default

Unfortunately blow thru carbs are trial and error. I would up the rear jets and see what happens you can always change them back.... its hard to un-drill a hole.

Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT -4. The time now is 11:33 AM.

 

About Us

The PY Online Forums is the largest online gathering of Pontiac enthusiasts anywhere in the world. Founded in 1991, it was also the first online forum for people to gather and talk about their Pontiacs. Since then, it has become the mecca of Pontiac technical data and knowledge that no other place can surpass.

 




Copyright © 2017