Has any one actually done any of the modifications to a q-jet as suggested from Doug Roe's "Rochester Carburetors" book. Any mods such as drilling the secondary fuel feed tubes. enlarging the holes that replenish the secondary fuel wells.I am just curious as too how much modifying the q-jet some of you have done for street/strip use. Does any one else know of any other good q-jet books on the market also. Sure would be interesting to read some of your replies.
I've done most of the mods in the book, haven't tried the oversize accelerator pump trick yet. I'm afraid I don't have any hard data to show the improvements, but seat-of-the-pants testing says the mods help. If you can find the older version of the book, it's full of even more good info. The book is twice as thick and has a multicolored cover. Devon
There is a brand new book on qjets just out. A little more in depth for performance work. I have it and it is a good book. Cannot think of name right now. Just check Amazon and do search. Has a yellow cover.
Years ago after buying the first Roe book I modified a 72 800 carb. Followed the Performance guidelines pretty much from A to Z he suggested in the book. Drilling out internal passages, the works. And that carb ran beautiful. I did back to back comparisons with a good Holley 850 DP carb (4781) which had the air horn milled off. Both carbs were optimized for that engine. They were almost identical in performance, with the Holley just eeking out slightly better numbers in et and mph, as measured in the hundreth's, not tenths. But the QJ got appreciably better mileage, by about 3 mpg (from 13 to 16). And since this car was also my daily driver, I left the QJ on it. Throttle response was instant and the kick in the pants when the secondaries opened was just the more reason to stand on it at every opportunity. I since lent it to someone to try and I guess they liked it so much I never got it back.......and I can't remember now who I lent it to ou:
the q-jet had to meet emmission standards and was typically lean in the idle and transfer circuits. i would get both books, each has it's good points, and one or two practice carbs. once you know the circuits and how they work, do modifications in small incriments. a couple places sell the replacement tubes and bushings the book talks about. good luck, have fun.
I've done the mods including the 2bbl accel pump. ET and HP not affected much between my modified carb and a basically stock carb with same jetting. Both are 71 800 cfm carbs. If you read into it I think most of those mods were for road racing cars, not drag cars. Just my $.02. If you have the right secondary rods most of the Q-jet's 1/4 mile capability will be realized, as long as you can keep the bowl full and the transition circuit allows a hard launch.
I've done some of the mods, still can't get enough fuel at idle (79 emissions quadrajet) Tried other carbs, they didn't drive as nice as the quadrajet
