17059212 Quadrajet RV application on a 454

[wimpy88]

Thanks for all the great info. SS#72 even made me Google a definition (couldn't get my mind to dredge up 45 yr old info).
I forgot to ask about the needle seat. The needle seat in my kit is a solid piece, vs the one I removed which has a slit in the lower portion. Anyone have an explanation for the difference?


In looking for the choke tube, I'm not finding it online, except as a kit requiring fabrication, so that's the route I'll be taking. Trying to convert to a manual choke & figuring the cable routing & bracketry seems way the hell past my talents.
If memory serves, my carb has the same limited adjustment idle mixture screws Detroit began using in the mid-70s due to EPA regs. Is there a special socket available or do I just order a couple of regular idle mixture screws from QPJ.com?

Again, thanks to each 1 of you for taking the time to provide your expertise. BTW, it would seem somewhat odd to the average person for any one individual to have the number of cars listed by some on this forum...however, I find it very normal.

 

[StreetStock#72]

Fuel dump port, anti starvation. A 454 house at WOT passes a lot of gas.
Those are 'good'.

 

[pontiacgp]

Thanks for all the great info. SS#72 even made me Google a definition (couldn't get my mind to dredge up 45 yr old info).
I forgot to ask about the needle seat. The needle seat in my kit is a solid piece, vs the one I removed which has a slit in the lower portion. Anyone have an explanation for the difference?
View attachment 69554

The windows seat was designed for better fuel control for performance carbs. Some guys will drill a hole in the side of a solid seat. The solid and windowed work the same with the only advantage to the solid one is that it prevents the fuel from draining when the engine is off. Those seats are not marked as far as the size of the inlet so if you are going to change the seat you have to measure the inlet size. If you go with a bigger inlet hole then you have to adjust your float lower to compensate for the increase flow of gas. It would really help you if you bought a book, either Doug Roe or the Cliff Ruggles...

 

[StreetStock#72]

I'm not a Qjet expert, didn't read the book but always looking to learn something. Actually swapped out to more Holley spreadbore double pumpers than I've rebuilt (kitted up) Qjets.
With that said, fuel control is a broad term. If solid and slotted or drilled work the same then why is it done. my understanding is the slot is there if the fuel requirement (at a given float drop) is greater than the amount of volume that can pass between the needle and the seat (on a solid) the slot is a dump (relief) port solves that problem (independent of the inlet size).

Lowering the float height when increasing the inlet size sounds counterintuitive to me if the taper of the needle is the same as a smaller seat hole. I would think (guess) that the float height would remain the same but the drop would be reduced or the tapper of the needle would need to be different.
The other thing I'm not understanding is where would the fuel drain to with the engine off. The fuel level would be lower than the slot and there would be no 'slosh'. It couldn't drain back up the fuel line ...only the bowl vent tube.
Motorhome 454 engines work much harder (and hotter) than even a LS7 in a Chevelle. If percolation/vapor lock (and they do) happens as the engine heats up when turned off then the slotted would be bad for that application if slotted seats cause draining problems.

whow ... my brains hurts after that... LOL

 

[pontiacgp]

The reason, or I should say theory, is that with an opening on the side of the seat there is less pressure built up with the gas entering the bowl. On a street car it wouldn't be noticeable but on a circle track car the power piston and main rods are removed so you'll want as much gas flow as you can get.

I have played with different size of inlet hole on the seat and the difference of a .125 and a .135 is very noticeable. I lowered the float by 1/4" and it was still flooding. It really quit surprising how much .10 can affect the carb. The reason for a larger inlet is the speed at which the gas fills the bowl which can keep the gas flowing to the engines at constant high rpms

 

[StreetStock#72]

I've only run 2GC and 4412 on oval.
In theory (not practice) I think the flooding you had with the larger seat was due to the fact the float height was lowered and the drop was not raised. Again, that would be if the needle taper angle remained constant.

Removing metering rods sounds scary to me... as does running a Qjet on oval.

 

[pontiacgp]

I've only run 2GC and 4412 on oval.
In theory (not practice) I think the flooding you had with the larger seat was due to the fact the float height was lowered and the drop was not raised. Again, that would be if the needle taper angle remained constant.

Removing metering rods sounds scary to me... as does running a Qjet on oval.

the float is adjust by bending the arm at the v notches so the needle is not affected by the adjustment, the reason for the flooding is the gas is coming so fast the float does have time to react to stop the flow. If you are running the engine at high rpm you wouldn't need the float or needle , think about how big a .125 hole is, it's only 1/8", and that has to feed the engine. You only need the float at idle and part throttle operation so the engine does not flood. They sell aftermarket .149 seats which drag cars use if they need it. The smallest seat is .110 which could cause you to run out of fuel on a mild 350.

The reason for removing the power piston and rod it because there is no need for part throttle operation. I don't like a holley on the street but in circle track racing the holley works well. You'll only find a quadrajet on a lower end low budget circle track car

 

[StreetStock#72]

We had (too) many laps under part throttle during caution.
Would been totally 'loaded up' under those conditions... I would suspect.

I laughed at the rulebook but found the 2GC could be tweaked into a pretty good race carb.

Sorry

 

[pontiacgp]

We had (too) many laps under part throttle during caution.
Would been totally 'loaded up' under those conditions... I would suspect.

I laughed at the rulebook but found the 2GC could be tweaked into a pretty good race carb.

sorry

you might find this interesting...

http://classracer.com/classforum/showthread.php?t=13493

me as well.....

 

[airboatgreg]

Ouch eja78,
I am just going by my experience as a driveability master tech having built hundreds and hundreds(Thousands?) of q-jets, owning 3 AC Delco-tech shops and having access to GM training centers. Ya hurt me big guy