Their are a lot of people on here who want to add some more performance to their car by playing with the carb, but have no clue where to start. So post your car/motor specs then your carb specs. Then just a quick sentance about how the setup is working for you. Motor- 1969 350 Comp- 9:1 Mods- 1969 GS 350 TA C110 cam Poston Intake 750cfm QJET 1in 4-hole Spacer TA Headders Crane Electronic Ignition Custom 2 1/4 exhaust MagnaFlow Mufflers Rear Gears- 3:23 Carb 1973 750 cfm qjet. It has 068 jets, and 45B primary rods, with AY secondary rods, and a M hanger. This carb setup isnt working the best with my car, so i dont recommend it.
The Quadrajet book by Ruggles has a ton of good information but has recipes for small block engines and states that "big blocks will be different" and leaves us hanging. The best carb and timming specs come from our guys who have wide band A/F meters and dyno's or years of drag racing. Lets hear from some of these guys based on Ruggles recipes. USE THE ORDER AND STEPS OF HIS RECIPES if you can. Lets make a good STICKY for this Q-jet location. Try to include notes on those who combines RICH AFR with lots of timing vs LEAN AFR and low ign timing. (Seperate 750 & 800 spec's) Calling for Jim Weise, Dave Hemker, Gessler, ETC. PLEASE and THANKYOU, Gary B.
Motor- 1970 BBB, 462 CID Comp- 10.42:1 Mods- TA Aluminum Stage1SE (Flow 313/225@.550) 1970 GS455 Stage1 KB MKC118 cam TA SP1 Intake untouched 7042240 1972 800cfm QJET MT Headers Dr. Gas X Pipe (3" X 2 1/2") MSD Digital6 with Dave Ray Distributor GSCA 2 1/2" Exhaust with Walker 17749 mufflers 1967 BT Switch Pitch 400 with 3200/1800 TSP converter rear gear 3.73 Gear Vendors Overdrive. John Osborne Q-jet, .076 jets, 46B rods, BG Secondary rods (.0397) on G hanger. I use full manifold vacuum to the distributor with 6* of vacuum advance. I have my Transmission Governor set to shift automatically at 5500 (1-2), and 5400 (2-3). I've used total timing from 34 -39* at the track and these aluminum heads seem to like a lot of timing. Some guys in the know have advised me that the motor doesn't like that much timing over 5000 RPM, so I will use the high speed retard feature of my MSD to pull some timing out at 5000 RPM next time it goes down the track.
Thanks Larry for your info. Hey 69GS350 If you have a Big Block carb you may not need to change a whole lot. If you have a 350 carb, get Ruggles book and read the formulas as they are primarily for small block engines and the 1st recipe or 2nd recipe should be on target for what you need. His book will tell you what jets, rods, hangers, holes to drill, air valve setting, float level, etc. Also in the text he describes what size cam and vacuum readings you can relate to the recipes and modifications offered. From your info, I already see some jet and metering rod changes comming. Be sure to blueprint your distributor FIRST and cut a 30 degree mark on your damper for timming settings. If the distributor is off, all will be in vain. It is complicated stuff, so read the first chapters and highlight all the parts and locations, etc. Then change only the things that requlire no drilling until you have the tools and knowledge. You CAN make important improvements without drilling anyway. Some of the guys hopefully will be giving their input here and helping us out as I have some questions myself while currently working on my 800 BBB q-jet. I'm now close to matching the 2nd recipe and ready to start fine tuning.
Motor -70 462 ci comp- 9.70 ported iron stage 1 heads mkc 118 cam iron intake 7040240 Q jet iron exhaust manifolds 2 1/2" exhaust w/X pipe and walker muffs 3000 rpm converter 3.42 original posi Q jet modified by me, 70 jet in passenger side,72 jet in driver side,42B metering rods, one coil cut from power piston spring,AU secondary metering rods on G hanger,.125" needle and seat,total timing 30* all in by 2500rpms,no vacuum advance just mechanical.stock distributor w/unilite conversion. Governor modified to shift at 5200 rpms,carb works great and is crisp. Installed on Sandys "X" and runs 12.78 with sticky tires and 13.1 on poly glass,weighs 3800lbs. gary
The best way is to have a good Air/Fuel metering kit on your car. It tells your everything. What the carb is doing on launch, max RPM, at gear changes, idle, cruise ect. IT really helps you fine tune a race engine and even more so for a street engine, as you are looking for Max HP and good cruise effiency (MPG) I sell many of Innovate LM1 kits from my website, I use it myself on several cars and feel it is the best for the price. http://www.gesslerheadporting.com/members/gesslerheadporting/ghp.nsf/top-menu-items/ghp05 I think every carb needs to be tailored to each vehicle. There are so many variables thats important to tune the car just right. I use a 800 Q-jet on my Black GS that I race in the F.A.S.T. class. I make custom sized primary jets as my car usually wants a primary jet of approx. .089" or larger. I use a larger throttle bore size and the primary venturies have been modified for increased air flow. Another reason for the Air/Fuel ratio gauge is that Q-jets came with different air bleed sizes, and they react differently to the same primary jet size.
Greg, I think the A/F meeter is a great idea and will try to buy one from you after Christmas. How does the meter indicate if it is time for an air bleed change VS jet change?? Do you recomend a max limit on air valve opening (eg. 80 degrees OR 1.270")? Thanks Greg, for all the help you have contributed to everyone and have a great New Year.
Gary, The LM1 A/F Meter shows A/F ratio's and also RPM's when ordered with RPM capability. Not exactly sure sure if one can Identify if air bleed or jet needs to be changed. Maybe a carb expert can shed some light on this. On secondary air valve opening, I like the flap to be 90 degrees for max. flow potential.
