Old 07-08-2020, 06:19 PM
ponchorob ponchorob is offline
Senior Member
Join Date: Aug 2007
Posts: 218
Default Low vacuum powerpiston spring cutting

Running rich...so maybe powervalve open at idle....engine 421 with ramair 4 cam...with 65 tripower th400 Stall conv. Is Nearly stock.... 13hg vacuum at 780 rpm without vacuum advance ...connecting vacuumadvance illhave 15-16hg slightly higher rpm.. Initial 10 degrees Plus 17 degree vacuum 27degree total at idle but when going from Park to drive vacuum Drops to 10hg....so powervalve should be open i guess.... 2 questions ....can i improve or reduce the big drop from Park going to drive.....

Other question how Many coil should i cut off the Spring read between 3 to 8 coils with 041 crane ...so not clear.....also at which end of the spring should i cut cause the the coils going to the airhornside Are more compressed then the other end going to the powervalve direction....

Old 07-11-2020, 03:06 PM
Dick Boneske's Avatar
Dick Boneske Dick Boneske is offline
Ultimate Warrior
Join Date: Mar 2004
Location: Winneconne, Wisconsin
Posts: 5,030

Cut four coils off the end of the spring. Cut them on the end that contacts the poser valve (bottom of the rod). Stock spring pressure is about 210 grams to move the rod upward. A RAIV cam should work better with about 150-170 grams of spring pressure. I use a postal scale to measure.

To be safe, just uncoil four turns off the rod. Measure the pressure. Uncoil or recoil turns until you get the desired change. In that way, you don't destroy the spring if cutting too many coils off.


'64 GTO Tripower Hardtop (Wife's Car)
'64 GTO Tripower Post Coupe (My Car)
'08 Grand Prix GXP LS4 V8 (Wife's Car)
'09 Pontiac G8 GT 6.0 V8

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 05:42 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.


Cold Case Radiators

Cold Case Radiators is a Max Performance company that produces high end aluminum performance radiators at a price point that won't break the bank. Polished and stamped tanks. 2 rows of 1" tubes. Lifetime Warranty.


GTOG8TA.com is a Max Performance company that manufacturers parts for the 04-06 GTO, 08-09 G8, and 93-02 Firebird/Trans Am platforms.

Copyright © 2017