72 455 carb, 7042240, 800 CFM. Engine is a true 10.1 to 1 455 with stock heads and manifolds, and GSCA 220-230 camshaft, automatic. I know its a fairly small cam for that kind of compression, but I am also at 3500 feet with density altitudes often up to 5500 feet, so trying to fill those cylinders. Anyway, stock jets in this carb were 73, and stock primary rods were 48B (yes, 48!! All my manuals say 44 rods but both 72 carbs here have 73's and 48B's). What kind of iniitial setup should I run for this engine?? 73 and 48's will be too lean I am sure.....I have a set of 75 jets that might work ok with the 48B rods... Not worried about secondaries at this point. rebuilding carb and would like to try and avoid going back in once its together... Thanks!! later Tim
I've used 73/44 on both of my fairly-mild 455s Settled on that with a lot of both track and street tuning.
Tim, I have that same carb on my GS, from John Osborne. He put 76 jets, and 46B rods, and BG secondary rods (.0397 tip). I would imagine, you would need leaner for altitude. E-mail John, and ask his opinion, JOP455@aol.com
48B withCT seconds I just went through a 7042240 carb with 48B primarys with 73 seats, CT seconds. fired the BEHEMOUTH up and it sounds awesome. I cant get out on the road due to weather, I will though. Whats wrong with the 48's. I have some 44's and I have some BZ seconds should I use one or the other? what, if any is the advantage? Also how do I get in touch with john O. thanks Jerry :3gears: :3gears:
Jerry, there is nothing wrong at all with 48B rods. I just thought it was funny that all my books and informations says 44B rods so was surprised to find 48B's in both carbs. What I hear a lot is that the jets minus the rods should be about .030, so if you have 73 jets you should be close to 43 rods. This would be .030" the 44 rods would be .029". But with the 48 rods you are now down to .025" For a stock 72 455 that is probably fine but with higher compression and bigger cam I would think its gonna lean out and give you surging at crusie speeds. Not totally sure though, especially with our altitude so thats why I asked... Later Tim
Here is a zipped spreadsheet I made for myself a number of years back when I was comparing jets and rods I had scavenged from boneyards or had found in my own car. You might find it usefull - you can even add your own data. I like the secondary metering rod chart - really gives a good impression of relative mixture between rods. My current primary setup is about one hundredth too rich.
455 .30 over Staged mild cam headers. Any suggestions on rods. I dont know much about carbs. My opinion is... carbs suck :laugh:
I'd go 3 or 4 primary jet sizes richer (probably 3 - 2 for the headers and 1 for the cam as long as it is hotter than stock). You need to maintain close to the factory part-throttle jet:rod ratio. In other words, the part throttle opening with the rod in the jet should be very close if not exactly stock.
General rule of thumb for Q-jets. For every 3 jet sizes you go up, go up 1 rod size. The 70 Stage1 carb had 68 jets and 42B rods. If you go to 71 jets, you need a 43B rod. 74 jets 44B rod etc.
so you say richer... so you say richer... what does that mean to me. do I need to change the jets or rods or both. I have no idea what to do. I am a carb idiot amungst other things o No: I have only a 73 jets,but i have the 44 rods and some 48b rods
Cool!!! Well thanks alot, that verifies what ive been readng. The next thing I noticed was the butterfly on top of the seconds was sticking... it looks like it was snapping back for thirty years and it had cut a groove in the little tang that stops it from opening too much while at idle. I took it down again filed the groove out and seems to operate fine.
