Q-Jet Power Piston Spring Selection
Thread Starter
Racer
Joined: Sep 2019
Posts: 349
Likes: 44
From: Spokane, WA
Q-Jet Power Piston Spring Selection
I have read Lars paper in which he describes selecting a power piston spring that is 1.5" - 2" less than your manifold vacuum in drive (or neutral in my case). My manifold vacuum is 15" with the current cam I am running. This would mean a spring that starts to enrich the circuit around 13" of vac. The heaviest spring I have is 8-12" of vac. However, I was under the impression that when you have less manifold vacuum, you want less spring tension so that the rods don't pop up and enriched your idle circuit when not needed. So, I am confused. It seems like GM ran springs that were stock for my car had a tip in around 8" vac...roughly half of manifold vac. Hopefully somebody can set me straight.
In the car currently is a 8-12" vac spring. Its the same spring that was in the car when I had the base 350/300HP cam making good manifold vacuum (20").
Do I need a lighter spring?
In the car currently is a 8-12" vac spring. Its the same spring that was in the car when I had the base 350/300HP cam making good manifold vacuum (20").
Do I need a lighter spring?
Race Director
Joined: May 2006
Posts: 18,692
Likes: 2,572
Read this link and the description of 8 to 12, starts to open at 12 and fully open at 8. So with 15 that is the correct spring. The factory choice is based on many factors including emissions and economy.
https://quadrajetparts.com/quadrajet...ode-p-210.html
https://quadrajetparts.com/quadrajet...ode-p-210.html
Last edited by MelWff; Aug 16, 2020 at 11:27 AM.
