Sorry to have an undertone of sarcasim. The truth is the level of perfection required is beyond most of us here. In that aspect,
HillbillyHellcat's post on Fri Jun 18, 2004 9:50 pm
Quadrajets are a special GM carburetor made by Holley. Let me point this out:
THEY ARE JUNK
is party right. Except the RP made them, and they are junk if you are not prepared to follow 38 years of US experience.
The truth on how to make a Qjet get out and hunt is out there.
For most people its easier to fluff around with Holleys.
Ever enjoyed working on 4300G Autolites, Varaible Venturi carbs on Capris or Lincoln Marks, or had the pleasure of making an 1100 idle? Or sort out a Holley 5200 , 4150 or 2300 with a blown power valve?. There are plenty worse carbs around.
The Q'Jet is in fact the best carb ever made, in my opinion. It's got the best float bowl, best zinc oxide casting, best fuel delivery, and the best booster system ever made.It's also the hardest to tune of any carb, and has the most issues with carby base warping. These last two items have been cured by the late John Ligenfelter, and by, funnily enough, the Impco boffins in Ceritos, Cal. Regarding the key four modifications any Qjet fanatic needs, You must:-
a) blue-print the throttle linkage so the secondaries open at the right degrees of primary throttle location,
b) get the hanger and
c) metering rods exactly right for the application. There are 32 good metring rods for V8's, 9 of which are used by GM guys on 231 to 454 cube engines with sucess. Most of them are now obsolete. In addition they can be bent to deliver the correct cc per minute from the jets. Simply, this is the most adjustable system of any carb in the world, greater variance than even an SU carb. It's the main reason foolish people say you get good and bad Quadrajet 4M's. You don't. The key is that production variances on Rochester Productions were pretty wide, but get any of the basic stuff out of spec to the middle of the line process control, and it may work better of worse, depending on the application.
d) The only way to do the above blueprinting is by stealing info from the GM guys. Many have had dyno running to the GM Test 3 300 hour runs, and can pin-point issues of concern.
In Australia, the small Qjets gave 462 hp net at 6700 rpm on the 5 liter Holden Commodore Group A racers. Same carb that gave only 164 hp at 4400 rpm on the stock production car. From only 725 cfm on the later 4MV model. Show me any carb which can triple the peak power delivery with nothing but metring rods, hanger and blueprinting. There were a host of publications by Mal Wood and Larry Perkins in Oz in the late 90's about how to make 'em haul. These guys were ace car sorters who said nothing else even got a look in after setting them up. Even Ivan Walker, a Ford engine builder, used Qjets on 351C's because the stock Autolites and Holleys were junk in comparison!
This concludes "information on the four Noble corner stones of Q Jet Kabala".
