What is the correct secondary metering rod hanger for a '70 Buick Stage I 455? The one carb I have has a "K" metering rod hanger with "AU" metering rods.
Thanks for the info. I've noticed in the rebuild kit instructions, there is a dimension to be set from the top of the metering rods to the top of the air cleaner boss on the air horn. It's set by bending the end of the secondary rod hanger. Makes one wonder why there were so many hangers. They only differ by this dimension, regardless of whether they're K, R, H, or whatever letter.
It would be nice to be able to set the APT and secondary rod height on a test bench similar to what GM used, but not practical for anyone based on the number of Quadrajets being rebuilt today. We all will do with Quadrajets as we do with all other carbs. Rebuild them carefully and tune as needed once on the engine.
It's impossible to "bench" tune them for a variety of reasons. First and foremost, very few folks are using any sort of "standard" engine build. They choose different heads, compression ratios, cams, intakes, exhaust systems, etc, etc. The nice thing about using a Q-jet vs aftermarket carburetors, is that they are much more sensitive at low engine speeds. This has them typically working pretty well on most set-ups without a lot of jet and rod changes. Helps even more if the builder knows how to provide a "basic" calibration and has the carb set up with the APT system functional (early Buick units). The APT feature allows for external tuning of the part throttle system. Using the correct jets and metering rods, the tuner will have full control of the A/F ratio across the load/speed range at cruise or light throttle driving, where the vehicle will spend most of it's time. Another great feature is being able to tune the secondaries in seconds without taking the carb apart. This makes the q-jet the most user friendly carb out there, being rivaled only by the Thermoquad, and to a lesser extent by the AVS. Unless anyone hasn't been paying attention, Edelbrock brought back the AVS (Thunder Series) carburetors. Still an old/outdated and inefficient design, but LIGHT YEARS better than their AFB clones. I've tested ALL of the aftermarket carburetors currently available, street, dyno, and at the track. The two best carbs that have ever been on my engine are my 1977 Pontiac Q-jet and Holley 850 dp. The Q-jet won the dyno testing by 2hp and track testing by .02 seconds and .30mph. Runner up was a custom built/tuned 4781-2 Holley 850 DP carb. Built by myself with DIRECT help from an engineer that used to work at Holley. It is an older model with the downleg boosters. I have a much newer Holley carb with the huge annualar boosters. It's just a tad better for "normal" driving than the old 850, but the huge boosters cut off some airflow at high rpm's, so it runs just a tad slower at the track and gave up a few HP on the dyno. To this day it amazes me than a 1977 Pontiac q-jet, that's never had a grinder or sanding roll touch it, flows enough air to sustain an engine making over 550hp, and it comes up with better power and track numbers than aftermarket carbs that were designed strictly for "high performance" use and never had to meet any sort of emission standards. I also did some extensive street testing with all the carbs we dyno/track tested. The best I could do with any of the Holley's or Holley clones was about 180miles per tank of fuel (14.2-14.4 gallons). Most never got past about 160 miles. My 1977 Q-jet would go 200-230 miles on the same amount of fuel every single time we tested it. It's only 20 mpg's or so more per tank, but one has to ask themselves "where did all that extra fuel go with the aftermarket carburetors?". As good as my Q-jet did during the testing, it lost in one catagory. Sustained high speed/aggressive driving. The big Holleys won this catagory hands down. I was not able to compete with the Q-jet without getting into the huge secondaries. The small primaries wouldn't even come close to sustaining my 455cid engine for "aggressive" street driving on the primary side only. I'll leave you folks with this, a recent email from a customer who carried his new 455 to a dyno shop that built/raced, lived/breathed Big Block Chevy's: "Hi Cliff, I thought you might like a picture of one of your beautiful carbs sitting on this nasty 468. Twas the night before the dyno session and all thru the house, not a creature was stirring... And the next day on the last and best two pulls, peak tq. was 604 ft.lbs.at 3900 rpm, and the best hp pull was 552 at 5500 rpm. SD ported KRE heads flowing around 297 cfm, RPM intake, SD Old Faithful cam, 10.5:1 cr., crank scraper, 30 degrees total timing, and Cliff's 800 cfm q-jet. There were a couple of other brand boys there that were so shocked, I thought we were going to have to dial 911. The dyno guy walked out into the shop and says...604 ft. lbs. with a Q-Jet, can you believe it ???!!! The only thing we had to do to the carb was adjust the idle speed and lean the APT 1/4 turn! Thanks Cliff!!!" Yes guys, the other brands can make great power with the parts we currently have available to them, and use many stock components along the way. We just finished up a project with the owner of an early Chevelle. He refused to go aftermarket with his heads, intake and carb. They just about laughed him out of the shop he carried his engine to when he showed up with the stock "flat" intake and q-jet sitting on top of it. Under the stock parts were a long rod 454cid engine with 10 to1 compression, very well prepared original heads, and custom hydraulic roller camshaft (our contribution to the project along with his Q-jet). He commenced to crank out over 500hp and 600ft lbs torque just like the Pontiac engine in the email above. Once again, he had just about everyone, including the shop owner headed for the emergency exits!........Cliff
Great info, Cliff. Thanks for sharing your experiences with us. It will be awhile before I know the results of these Stage I Buick Quadrajets I just finished. I was very careful when re-installing the secondary throttle plates in the bases. On one carb, there is no visible light around the edges when the base is held in front of a light source. One another, after switching the throttle plates around and trying different ones, there is a very slight amount of light visible around the edges. If these carbs are as sensitive as the end carbs on Tripower setups, I would anticipate idle problems with any visible gaps. What's been your experience with this. Some guys use DAG 213 on the secondary throttle plates on Quadrajets. Have you ever had to do this? By the way, your book is very well-written and informative. Thanks.
Great info, Cliff. Thanks for sharing your experiences with us. It will be awhile before I know the results of these Stage I Buick Quadrajets I just finished. I was very careful when re-installing the secondary throttle plates in the bases. On one carb, there is no visible light around the edges when the base is held in front of a light source. One another, after switching the throttle plates around and trying different ones, there is a very slight amount of light visible around the edges. If these carbs are as sensitive as the end carbs on Tripower setups, I would anticipate idle problems with any visible gaps. What's been your experience with this. Some guys use DAG 213 on the secondary throttle plates on Quadrajets. Have you ever had to do this? By the way, your book is very well-written and informative. Thanks.
Great info, Cliff. Thanks for sharing your experiences with us. It will be awhile before I know the results of these Stage I Buick Quadrajets I just finished. I was very careful when re-installing the secondary throttle plates in the bases. On one carb, there is no visible light around the edges when the base is held in front of a light source. One another, after switching the throttle plates around and trying different ones, there is a very slight amount of light visible around the edges. If these carbs are as sensitive as the end carbs on Tripower setups, I would anticipate idle problems with any visible gaps. What's been your experience with this. Some guys use DAG 213 on the secondary throttle plates on Quadrajets. Have you ever had to do this? By the way, your book is very well-written and informative. Thanks.
Thanks. A very slight amount of light around the secondary throttle plates is OK, but it should be equal on both sides, and just on the edged, not fore/aft. This insures that the throttle shaft isn't twisted slightly, and that each time the huge secondary plates close, they fully close to the same position.....Cliff
