Quadrajet Tuning link...

[Green79Scottsdale]

Hopefully the link works properly. 32 page PDF document by a Corvette guy in the UK. Any Qjet guys on here that can comment on how good this article is? I can read it and understand it, but I have no idea how accurate the info is.

http://www.corvetteclub.org.uk/files/downloads/how_to_tune_a_qjet.pdf

 

[350runner]

Yes it's good info. I read that some years back. Very detailed and correct. Nice download pdf

Sent from the dust in front of you!

 

[Green79Scottsdale]

Thanks for the confirmation! Come spring time I am going to borrow my buddies A/F meter and do some tuning on my truck.

 

[MadOgre]

I was to bored to read the whole thing there is one issue I found how ever and that is that the power piston has nothing to do with ineffective idle mixture screws.

He says that too stiff of a power piston spring will result in ineffective idle mixture screws. This is incorrect. Ineffective idle mixture screws are a result of Manifold vacuum being too low at idle to sufficiently draw fuel through the idle system so then the idle speed screw is adjusted to allow sufficient idle. What this does is open the throttle plate enough to now engage the off idle system which disengages the idle system which the idle mixture screws control

The Idle system is bypassed at off idle this is what makes them ineffective.

If you had a stiff power piston spring it would allow more fuel to enter the idle circuit which would ultimately be controlled by the idle mixture screws. The problem with low vacuum at idle produced by cams with over lap is that the tubes that supply the idle mixture screws are to narrow to deliver sufficient fuel at lower vacuum. So a stiff power piston spring that is now supplying more fuel should theoretically help the situation. The problem however is that the idle tubes are to narrow to allow sufficient fuel at low vacuum.

A modified quadrajet for use with lopey low vacuum cams has enlarged idle tubes and bleeds to enable sufficient fuel flow at lower vacuum.

So that was just one thing that popped out at me. Who knows maybe the rest is correct maybe not.

 

[350runner]

The idle circuit and primaries are in unison at part throttle. They So they are both working for a split sec.

Sent from the dust in front of you!

 

[MadOgre]

What does that even mean?

 

[350runner]

Lol

Sent from the dust in front of you!

 

[MadOgre]

lol

 

[Quadrajet Power]

I've read that before and I agree with others, it has some good information. Over the years, I take an article like that and add it to the knowledge bank so to speak. Lots of sources for good info.