Questions about Qjet powerband like performance

[Johnheck69@gmail.com]

I tried to post this question here before but had trouble creating a post.  My question is about a powerband like response I would get on a 65 Old's Cutlass I had in the late 60's.   The car was originally a 4 speed with a 330 motor.  I changed it to a 67 400 that I believe had a qjet carb.  When gradually depressing the gas pedal at some point I would get a powerband like effect.  This would happen long before fully opening the secondaries.   When starting out I would do this and then shift to the next gear and could repeat it in each gear.  I'm certain the carb was a qjet because a friend and I rebuilt it later on.   I know we often remember things differently but this is not that.  The car definitely had the effect that I mention.  I had the car for several years.  I'm not confusing this effect with the secondaries fully opening.  Often I would be in first or second and gradually depress the gas pedal until that effect happened and then mash the pedal for a fully opened secondary response.  Some people I spoke with think there was something binding causing the air valve to snap open while others thought I might have used the 4gc carb from the 330 because they claim that carb had a powerband like effect.  Any ideas?  Could this have been a faulty part like a spring or an adjustment.   I now have a 65 Cutlass with a 455, a qjet and 4 speed.  The car is running good but the qjet operates like most claim they should with even acceleration. 

[Cliff Ruggles]

1965-1966 Qjets have several very poor features and the weighted air door is one of them.

Instead of using the choke pull-off to dampen the secondaries they had a rod and weight.  This is a very poor design and even with the adjustment spring to help with the opening rate the weighted air door just doesn't work well.

Those carburetors also had the plunger valve/bypass set-up to keep the bowl full, another horrible idea that went away in 1967.

The 1965-66 units are a BIG reason the Q-jet got a very poor reputation early on, which was difficult to shake off.  They early units worked poorly on the secondaries, bottom plugs leaked, fuel inlet threads stripped out easily, and the weighted air door arrangement and fuel inlet valve was HOPELESS.

The aftermarket answered the plunger/bypass fuel valve set-up with a plug and standard type N/S assembly.  This still didn't help them much as the inlet seats have a tiny hole in them and combined with the early hinge pin arrangement they were next to impossible to keep full in a high HP application.......Cliff

[Johnheck69@gmail.com]

Cliff,

Is it possible to adjust or modify the quadrajet to create a powerband or passing gear like effect before fully opening the secondaries?

Thanks,
John
386-492-4875

[Cliff Ruggles]

No modifications needed.  Keep in mind that you have limited cfm on the primary side with all spread bore designs. 

So basically you can not achieve nearly the engine power or vehicle speed as you could with a larger square flange type carb on the primary side alone.

Q-jets and Thermoquads are both very similar in power characteristics and when set up correctly they will provide a "seamless" power curve from idle to the shift point.

Folks seem to expect some sort of "rush" of power with 4bbl carburetors which is actually a loss in performance if you have noticeable transition. 

Since the Q-jet provides air to the engine based on demand, set up correctly you will not feel any "rush" of power going into the secondaries.  Since you don't feel any "hit" or transition the body will evaluate the performance as less than a carb that feels like you just hit the nitrous button! 

So when set up correctly you will end up with a broad/flat power curve with no noticeable transition anyplace.  The "boring" power curve for sure will be thought a loss in power performance if evaluated by "the seat of your pants".

I've tested more carburetors back to back at the track than most who will read this.  One event in particular we tested 8 carburetors on two very fast cars in one day.  One big Holley, one big Edelbrock Thunder series AVS, and 6 Q-jets.  The carburetor that is on my car currently won all testing, 60', ET and MPH at every point.  It did this on both vehicles.  With that said if you raced the car with the Q-jet in place, then the big Holley double pumper we tested, you'd very quickly say that the big Holley would win out in every area.  This simply happens because the Holley provided a HUGE "rush" in power when you got into the secondaries, the Q-jet was "seamless" clear across the load/speed range.

Here is a clip of my car a the track in full street trim.  Notice how smooth the power comes on and stays in the power clear down the track.  No big "rush", no lunge, no noticeable transition anyplace......Cliff

https://www.youtube.com/watch?v=6zVdoLR-VzM