General Category > Quadrajet Carb Talk and Tips
TV cable to early Quadrajet
Cliff Ruggles:
The main benefit from an early open point would be drag racing a "foot brake" car. The micro second saved when you stomp your foot to the floor to launch the car might show up on your times slip as a little quicker R/T or 60', but it wouldn't be much.
Actually you will enjoy a greater driving experience with most applications by having more of the primaries available without having to get into the secondaries, plus use less fuel for many driving scenarios.
The factory used the higher pivot point on a lot of baseplates not just those found on trucks. Having more of the primary cfm available without getting into the secondaries allows for higher cruising speeds on the primary side of the carb. You can also climb steeper grades in higher gears without having to use the secondaries or downshift to a lower gear, which is advantageous for larger/more powerful engines pushing heavier vehicles, towing, etc.
Not exactly sure what is meant by "manipulating" the linkage. The only adjustments required on any Q-jet baseplate are to make sure that it doesn't hold any of the throttle plates open at idle speed or when they are supposed to be closed, and to make sure the huge secondaries can reach their full open point at WOT........FWIW........
old cars:
Here is a few examples.
I use vernier caliper from the underside of the throttle plates, flat against the butterfly
1970 GTO 7040264 (original 3 point opening secondary linkage)
.300” primary ---- contacts secondary
.400” primary ----.060” secondary opening
.500” primary ----.410” secondary
1968 Chev 7028313 ( original later linkage system/ chevys had already changed )
.360” primary contacts secondary
.400” primary no opening on secondary
.500” primary ---- .250 secondary
1978 Chev Truck 17058213 ( later truck style linkage )
.470” primary ---- contacts secondary
.
.500” primary no opening on secondary
1978 Chev Truck 17058213 – After changes to linkage
.300” primary ---- contacts secondary
.400” primary ---- .070” secondary opening
.500” primary ---- .370” secondary opening
This truck carb I had installed on my 454/500 hp Monte Carlo . Before I made changes to the linkage it was very flat at lower speeds. Too much throttle movement required. After changes it was closer to the ( x ) carb I was used to. I did not see any downside to the changes.
Cliff Ruggles:
Even after all that I don't fully understand the posts.
Are you saying that your engine feels "flat" on the primary side and required the secondaries to make decent power.
It appears that you are adjusting or manipulating the cut-in point and suggesting the earlier the better?........
In any case I'll say this. The 455 in my Ventura is 11.3 to 1 compression, well chose cam, and good flowing heads. It has instant throttle response right off idle, and STRONG power at lower RPM and lower vehicle speeds without getting into the secondaries........and it NEVER feels "flat", sluggish, down on power, etc for any "normal" driving scenarios......
Kenth:
--- Quote from: 77cruiser on April 16, 2022, 08:58:31 AM ---Since they were based off the truck carb, did they have truck secondary linkage or car?
--- End quote ---
Jim, in Cliff´s book page 120 there is a picture of the Edelbrock 1910 secondary linkage (pass. car).
I added pictures of my 1904 and 1910 here:
Cliff Ruggles:
Coincidentally I have one of each in the shop at the moment. The 1904 has a defective casting so it's junk. That's the 3rd or 4th defective Edelbrock Q-jet I've seen to date, so it's not that common but something that needs to be checked when you are working on one.
I fully understand the different secondary linkage and how one allows more throttle angle that the other before it reaches the cut-in point. I've ran/tested many hundreds of samples of both on my engine and never really noticed any difference in performance delaying the cut-in point a little further.
Most likely the factory used the truck or delayed open point to simply allow one to load the engine more for heavy work, towing, etc so you could climb steep grades and such without having to get into the secondaries as soon.......
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