Q: I have a 1973 Chevy K20 truck with an aluminum-head, roller cam 383 stroker. I’ve heard from some of my old-school gearhead friends that a properly tuned Quadrajet is a great off-road carburetor. What are the advantages of the Q-Jet? Are there still service and performance parts available?
A: Your friends aren’t wrong.
Even though the Rochester Quadrajet may not be the first carburetor that comes to mind for performance applications, knowledgeable tuners have modified them with excellent results. One of the attractive features of the Q-Jet is its centrally located fuel bowl, which provides even fuel distribution during extreme off-road maneuvers. Most Quadrajets also have dual-primary boosters. These are very sensitive to low-rpm airflow, providing disciplined off-idle control and response to small throttle inputs. As power demands increase and the smaller primaries can’t meet airflow requirements, the famous large secondaries open, supplying enough air and fuel for your high-performance 383.
JET Performance is the go-to for Quadrajet service and tuning parts, offering complete carburetors, rebuild, tuning, and bushing kits, needle and seat assemblies, metering rods, accelerator pumps, and more.
There are also companies that specialize in used and NOS parts. Setting up the Q-Jet for off-road operation requires float replacement or modification, changes to needle and seat sizing, and extended vent tubes. Additionally, modifying the secondaries to improve transition will help to give you a carb that performs well from idle to wide-open throttle. If all this sounds difficult, don’t worry;
HP Books has you covered with its Rochester Carburetors how-to manual (HPB-HP014). This book is written by Q-Jet specialist Doug Roe, and covers modifications in specific detail, along with fixes for known issues, general performance improvements, and tuning tips. With the use of this book, a little bit of ingenuity, and even some advice from your gearhead buddies, you too will become a Q-Jet believer.
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This is another in a series of weekly Q&A Mailbag sessions with Summit Racing‘s tech department, in which there are hundreds more. Click here to see more.
Love my Quadra jet on my Racecar great throttle response and plenty of airflow for my big block.
By using the excellent technical reference materials listed in the article, you should definitely be able to get your Quadrajet to perform almost as well as a 1450 series Holley with the proper CFM rating for your application. Or you could just take advantage of one of the many holiday sales currently in effect for Holley carbs and do things right from the beginning.
Flogging a dead mule always has the same outcome.
And the beat goes on….
I choose a quadrajet any day over a Holley for extreme off-road use. A quadrajet will run for a couple minutes on it’s side. No chance with a Holley. Keep the Holley’s at the drag strip. That’s the only place they’re useful.
Just be careful, because if you want to put an aftermarket inlet manifold on it later, to get greater performance, you will have limited choices available to you using a spread bore Patten.
Oh No, who is that man in the red suit. Merry Christmas from Aussie, to all.
I always found the Quadrajet was a fine Carb. If set up right there great;;;;;;Lets face it its the only Carb. that when you dump the secondaries it sounds like you sucked the Hood thru the Intake Manifold!!! I’ve used them for 45+ years with no problems.