blow through quadrajet in a box questions....

[shnitzel]

Hello all!

I have been tuning a 73 nova with a stock 350, quadrajet carb in a sealed box with 2 little turbos.  6psi boost max.

it has a boost guage, fuel pressure guage AND AFR meter.  so i can keep a keen eye on whats going on.

It has a full msd system with boost timing control.  And 1:1 boost fuel pressure regulator running from the carb box.

it runs great at 5.5psi of fuel pressure.  it doesnt like more pressure than that at idle.

The car runs excellent, great driveability.  with the small turbos boost hits FAST, no lag whatsoever.

The carb is in very good condition, fresh rebuild kit.  I also have lots of spare carbs for parts to play with.

BUT, it runs very lean......  knocks under boost.  AFR guage reads very lean under boost.

I'd like to know how to richen up the WOT portion of the carb so i can dump fuel down it under boost.  I hope this is possible.

If it is too difficult to richen the WOT of the carb, i may add some cold start injectors that switch under boost to dump extra fuel down there....

shnitzel

[Frank400]

what is the carburetor number and what was done to it ?  Do you know what calibration is in there ?

[carmantx]

Under boost in the box, your secondaries are probably not opening, even if the throttle blades are, the air valves may not be.

[shnitzel]

I expected a night of ridicule about my project before any help.  ha ha ha.

friday night ill be around the car and ill get the #'s from the actual carb.

ive been reading lots about the secondaries.  i will play with those some.

ill let you know specs friday night,

shnitzel

[Frank400]

I expected a night of ridicule about my project before any help.  ha ha ha.

friday night ill be around the car and ill get the #'s from the actual carb.

ive been reading lots about the secondaries.  i will play with those some.

ill let you know specs friday night,

shnitzel

   ...and show us a picture of that set-up !  I had been thinking of doing such a thing as a fun project. 

[A.G.V.chevyfreak]

Can also be that primary needles isn't lifting enough (or on the lean side for the boosted setup) It has pressure from both sides of the piston. And the pressure in the box is a tad more than in the manifold.
 You can check what gm did on the Pontiac ta 301 turbo motors.  The piston is boost referenced. With the later style jet it is easy to reroute a external passage and blocking the manifold side port,Will see if i have any pics of what was done) and with no spring the apt stops it from going fully down if adjusted so not running too lean at cruising.
  I did the same thing to use a jet on 4-71 blower setup that i want to fit on a 250 inline six. Still something i want to build.  ( its a case of too many ideas and not enough cars. )

[Cliff Ruggles]

The power piston requires external boost reference with a check valve from the intake side (manifold vacuum) so it doesn't pressurize under boost.

I much prefer to set them up to run straight off the jets and not use a power piston or primary metering rods for blow-thru applications.

You will need several items to keep things happy with that much power potential.  I high flow N/S assembly, correct jets, MAB's and small tipped secondary metering rods......Cliff

[A.G.V.chevyfreak]

Found them. The port in first pic is normally down into manifold for vacuum, on this carb its external reference.

[Frank400]

looks like a nice set-up.  Any pics with the carb all boxed up ?

[shnitzel]

Thank you very much fro all of your knowledge and advice!  i thought forums were dead, not around here there not!

those pictures are excellent.  and just to clarify, i plug the hole in the bottom of the carb, and i route the vacuum line out of the box and to manifold vacuum.  right?

if im correct with this thinking, ill try that tomorrow night when we work on the car.  and after i will get real carb #'s for you.

after we get it close, im sure well be ordering some parts from you cliff

when we get it out and running decent ill try to get some pics for you.  i dont use phones, or cameras...  so i have to try a little harder than most

shnitzel

[A.G.V.chevyfreak]

[quote author=shnitzel

those pictures are excellent.  and just to clarify, i plug the hole in the bottom of the carb, and i route the vacuum line out of the box and to manifold vacuum.
[/quote]
I found the pics when i was looking on blower mods and ideas.  With the qjet ontop of a blower there is constant vacuum. So should work on manifold side with a blower.   
 pontiac had the carb before the turbo in draw thru, same issue with vacuum as blower.
Havent done turbo setups myself. Just an idea that could be an issue you are having.

On your setup its playing around with tuning to see what works best .
 

[shnitzel]

spent some time tonight rechecking our tune with the carb box open = no boost...  its pretty good.  but its actually lean as NA right now.  even with the secondaries open its a bit lean.

so were working at that first, get the carb running rich at WOT with it NA.

and, VERY sure with the box sealed the secondaries arnt opening.  so we will work on that mod on sunday afternoon.  hopefully fix that issue.  glue the hole and route the line to manifold vacuum.

# on carb is "17058213"

keep you posted as we go!

shnitzel

[shnitzel]

hello again, sorry for the delay.  project went on stand by for a bit.  but last night we played with it some and took pictures for you!

this is a VERY on the cheap budget build.  everything is salvaged / scrounged from friends junkpiles....

last night we attempted to make the secondaries manual.  it worked a bit better, but far from proper.  so its about time we did this right.

i have bought a digital version of cliffs book and read through it a few times so far.  i also have a good general book on quadrajets.  however, im far from a carb guru and more into efi.  but this car is going blow through carb no matter what!   ha ha ha.  we will win this battle!

can you guys help me through this with a little more detail.  im having trouble figuring which port to send out of the box and which port to plug.

and the port that we send out of the box goes further down the intake manifold so increase the pressure differential?

and we will need to open the jets up a bunch as it is running lean even in NA mode.

so attached is pictures of the engine compartment for your amusement, and pictures of the actual carb we are using.  hopefully we can make it go swoosh!

shnitzel

[Cliff Ruggles]

last night we attempted to make the secondaries manual.  it worked a bit better, but far from proper.  so its about time we did this right.

The secondaries are already mechanical (all Quadrajets use mechanical secondaries).

Are you referring to the spring loaded secondary airflaps?......Cliff

[shnitzel]

yes, we made the airflaps mechanical with a rod.  were still far from working properly...

shnitzel