q-jet- power piston spring, max range?
Thread Starter
Race Director
Joined: Oct 2000
Posts: 15,048
Likes: 79
From: central FL, near the beach.
q-jet- power piston spring, max range?
Vizard says it works like the holley power valve.
Anyone know how early it can be made to enrich?
(My holley 4165 PV is 13" now, and 14" would be better.)
So, how early can a qjet be modded to start to kick in?.
This is to stop ping on light acceleration with 11:1
Anyone know how early it can be made to enrich?
(My holley 4165 PV is 13" now, and 14" would be better.)
So, how early can a qjet be modded to start to kick in?.
This is to stop ping on light acceleration with 11:1
Tech Contributor
Joined: Aug 1999
Posts: 14,380
Likes: 6,391
From: At my Bar drinking and wrenching in Lafayette Colorado
Matt -
Do you mean how late can you get it to kick in...? Most Q-Jets with factory springs come in pretty early - in the low teens. On a performance engine, you want to delay it down into the single digits due to poor engine vacuum with a bigger cam. The softer the spring, the later it will come in. The stiffer the spring, the sooner the power enrichment occurs. Edelbrock offers springs that seat at 4, 5, 6, and 8 inches of vacuum. You can test your springs using a Q-Jet float bowl core as outlined in my article - it works pretty good. If you want the power enrichment to come in earlier (at 14 instead of 13, for example), you can just drop in a stiffer spring, or you can just "strech out" one you already have. There is no limit to the range you can create for power enrichment.
Do you mean how late can you get it to kick in...? Most Q-Jets with factory springs come in pretty early - in the low teens. On a performance engine, you want to delay it down into the single digits due to poor engine vacuum with a bigger cam. The softer the spring, the later it will come in. The stiffer the spring, the sooner the power enrichment occurs. Edelbrock offers springs that seat at 4, 5, 6, and 8 inches of vacuum. You can test your springs using a Q-Jet float bowl core as outlined in my article - it works pretty good. If you want the power enrichment to come in earlier (at 14 instead of 13, for example), you can just drop in a stiffer spring, or you can just "strech out" one you already have. There is no limit to the range you can create for power enrichment.
Last edited by lars; Nov 28, 2007 at 04:23 PM.
Drifting
Joined: Sep 2004
Posts: 1,959
Likes: 1
From: North Bend Ohio
To say they work the same is a little misleading. Yes, they operate in the same manner, vacuum opens the valve at a preset value but this is where the similarities end. In the Holley the valve is either open or it isn't. Once it unseats you get full fuel flow, the rate being determined by the power valve restriction and the depression in the venturi. The Holley power valve just sorta pours fuel into the engine.
The Quadrajet has a tapered metering rod that regulates fuel flow through the main jets. It actually meters fuel in proportion to the demand of the power system. It actually meters fuel instead of just pouring it in.
I have seen 6 different spring rates over the years. I'm sure there were more.
BigBlockk
Later.....
The Quadrajet has a tapered metering rod that regulates fuel flow through the main jets. It actually meters fuel in proportion to the demand of the power system. It actually meters fuel instead of just pouring it in.
I have seen 6 different spring rates over the years. I'm sure there were more.
BigBlockk
Later.....
Last edited by BigBlockk; Nov 28, 2007 at 11:17 PM.
