74 LS4-454

If anyone can tell me what are the major differences of the Q-Jet carbs for the 454 from 70 - 74?

1-I imagine the jets and metering rods are different?
2-is the accelerator linkage the same for those years?
3-is the choke linkage the same also?
4-can you interchange Q-Jets from any of those years?
5-what is the difference if any between the MT & AT Q-Jets?

thanks for any info or any source that would have this info....
it is appreciated............................. .....................Tom

eagle275

Alan 71

Hi SS,
I suggest you contact 'Lars', a member of this Forum. He IS the quadra-jet person. I'll bet he can answer your questions!
Regards,
Alan

CCrane65

I only know of a couple of differences;

between the manual and automatic carbs, the auto carbs have specific linkage for transmission kickdown

1970 carbs have a vacuum port on the rear of the carb for TCS in addition to the one on the front.

Lars told me not to use a 1971 carb for my '72 LS-5 as they are too much trouble but a 1973 carb was ok to use.

cc

lars

I haven't heard from him, so the question must not be too important.
Lars

74 LS4-454

thanks for the reply Alan, will do.....

I appreciate the response...learn something new everytime!!!!

busy schedule, sometimes get home to late to get on the puter...
So Lars, will you answer the above questions for me in post #1? and yes it is important
I would like to know more about the 454's besides digging up my old mags, I know there is a wealth of info here on the forum.....as always all responses are appreciated.....

eagle275

74 LS4-454

Lars, you have a PM....thanks.....Tom

lars

I just heard from Tom, so there is real interest in the question. That being the case, I'll put in the effort to provide some technically accurate info:

There were 41 different carbs that Chevy used on Big Blocks from 1970 through 1974....

Here is a listing of all 1970-1974 Chevy Big Block carb numbers:

7040200
7040201
7040204
7040205
7040206
7040221
7040500
7040501
7040504
7040505
7040509
7040521
7041200
7041201
7041204
7041205
7041206
7041209
7042206
7042207
7042216
7042217
7042218
7042219
7043200
7043201
7043207
7043216
7043507
7044201
7044212
7044217
7044221
7044223
7044225
7044227
7044500
7044505
7044512
7044517
7044520

1. All 41 carbs used different jet/rod/air bleed configurations, with primary jet sizes varying across the scale from 69 to 78.

2. All Chevy Q-Jets, whether big block or small block, have the same throttle cable attach point locations, although some carbs use a thru hole while others have a swaged-in stud. Most carbs have 2 attach point locations, with the top location used for most passenger car and truck applications, and the lower point used for Vette/Camaro/Nova with limited pedal travel. Most big block carbs have the lower part of the throttle lever chopped off at the factory to clear the low-riser big block intake.

3. All Chevy divorced choke carbs have the same basic choke rod attach point, but the choke pulloff systems are different. From 1970-72, the usual "early" style plastic pulloff was used. 73-74 used a different pulloff (stamped steel) which incorporated a spring wound around the pulloff lever. This spring caused the choke to snap closed any time the engine was shut off, regardless of engine temp.

4. Any Q-Jet of any year, make and type can be interchanged with little difficulty. Chevy Q-Jets between 70-74 interchange with no modifications, except that small block carbs may need to have the throttle lever cut to fit some big block appllications.

5. AT and MT carbs differ in the throttle lever (AT levers have kickdown cable provisions) and, occasionally, in the number of vacuum ports to accommdate the modulator vacuum line. Some years, jetting is different between the AT and MT carbs as well, with the MT carbs often being jetted richer to prevent a stumble when accelerating and failing to downshift.

Lars

74 LS4-454

Lars, apprecaite the response big time!!!

This is great info, thanks so much for the effort put into this post...
Have saved into my tech folder and also printed out for future reference when needed.
Have never fully understanding the inners of how a carb actually works (meaning all of the technical aspects) I find myself wanting to learn more about them, especially the BB Q-Jet since I have one. I have even bought a few low price Q-Jets just to take them apart and learn about them if for no other reason. Trying to make time to start reading and re-reading the Q-Jet books that I have and the tech info from you (Lars) that I have requested in the past and received. I enjoy read tech articles and tryingto learn about different things.
Again many thanks.................................. ...Tom