I am looking at buying a 800cfm quadrajet. I found an older style (the all silver one below) and a newer style for sale (one with cadnium plated parts below). Any advantage of one versus the other? What is the main difference in the 2 carbs?
Re: What is the difference between the older and newer (75+?) quadrajet? Any advanta What are the numbers on the carbs? During a rebuild what is the ID of any parts they changed? Neither have a stock exterior finish.
Re: What is the difference between the older and newer (75+?) quadrajet? Any advanta Buy a carb from a Q jet pro: http://www.everyday-performance.com/
Re: What is the difference between the older and newer (75+?) quadrajet? Any advanta There's no way to tell the difference just by looking at these pictures. Both are re-manufactured, and if not done by a reputable shop, chances are neither one is any good. They may look nice, but they won't ever operate correctly. Even since the Q-Jet went out of production in the 80s, the shops that re-manufacture the cores end up tearing out all of the specific pieces and parts which allowed each model Q-Jet to be precisely tuned for a particular vehicle. Instead, all of the rebuilt carbs end up having a generic setting for about 200 engines...while properly operating on none of them. The only thing they do correctly is pass emissions testing. Most shops can't put back what the remanufacturer tore out without considerable cost, so there's no way to get them back to the original state. The remanufactured Q-Jets are pretty much ruined once they've been through this mill. There are many threads on the board which cover this topic...best bet is to get a correct, unmolested core for your engine and rebuild it yourself.
Re: What is the difference between the older and newer (75+?) quadrajet? Any advanta Ok all, I figured out the answer....sorry....I should have been more specific with what I was looking for in my original post. The newer one on top (aka M4M) has a few features the older style (aka 4M) does not have. http://www.cliffshighperformance.com/tech_qjet_history_4.html 1. APT: adjustable part throttle. Allows for part throttle adjustment of mixture by 3 to 4 jet sizes. 2. Casting is thicker to try and prevent warp age seen on some earlier models. 3. Smaller float for increased fuel bowl capacity. I have rebuilt and tuned multiple earlier style q jets.....just never messed with this later style. I was having trouble finding a really good early style 800cfm buick builder plus I am really pressed for time lately, so decided to try SMI induction. I bought the newer style carb from them. (The top one in the pic). I will post and let you all know how the carb is. I will say I was thoroughly impressed with the amount of info they asked about my engine and drivetrain set up when I ordered......everything from cam profiles to heads and specific head work to stall speed to gear ratios. They say that their intent is to build a custom q jet that performs perfectly out of the box. I will check the carb performance with a wide band a/f meter and also my trusty vacuum gauge. Will let you all know what I think.
Re: What is the difference between the older and newer (75+?) quadrajet? Any advanta Ok, I am back. I received the carb from SMI induction last month. $425 including shipping. I checked the build with my wideband air fuel monitor. The build was close, but I did have to swap out the secondary rods from CV to CC. WOT is now perfect 12:5-12:9ish. I also spent WAY too much time trying to chase down an idle and right off idle miss that I thought was coming from the carb but FINAllY figured out I had a bad distributor cap! Once I replaced that stupid accel crossfire cap it smoothed right out, no miss. I have never had a miss that was due to ignition only present at low rpm and then smooth out above 1500. I like the APT feature for ease of tuning. Ended up with 76 jets on the primaries, which at first freaked me out due to the size - I am used to running 71 or 72 on the earlier style carbs on the 455s. After some Internet research I determined this is normal for these carbs. I will be interested to see what kind of gas mileage I get. I do find that this carb runs leaner than the older style at right off idle at cruise - maybe 1000 to 1700 rpm. (17:1 ish). If I richen it up enough to correct it is too rich at higher rpm. I read another post describing this same symptom with these carbs. Car seems to run fine, no surging or heat issues even though that lean.....so I think I will leave it. So, bottom line, I would buy one of these carbs and use this company again.
