I have a 400/512 with trickflow 270 heads, 10.6:1 comp., trickflow cam with .640 total lift at the valves, a tunnel ram with 2 650 Brawler mech. secondary carb.s. First question... Im assuming that all four jets per carb. need to be the same....What is a good starting size jet? Id like to start on the fat side and work my way leaner. Does anyone run a combo like this? What are you running? Second question.... I believe that all engines have one cylinder per bank that tends to be the leanest running.. Im running zoomies and would like to put an AFR bung in one of the tubes per side for a dual AFR gauge. Which cylinders tend to run the leanest on these engines?

 

Looks like you had better brush up on reading spark plugs.

 

Just my 2 cents !!!! If your going to go rich and work back to lean...
Carbs: I would just Square up the carbs.. 4 Small Squirters (25's) >> 65 Jet Square >>>> Block off plugs for the power valves for now anyway >>>> Make sure all the Air Bleeds are the same numbers for there (Idle, Mid, High) areas in the carb, and make sure these are tight and not loose. Make sure the Throttle Plates are synced as well as the accelerator pumps and that you have a vertical throttle plate at full throttle. Hope you have the tuning kits for this, it makes it easier than getting everything individually...
This should get you started....

Exhaust: With running the zoomies, something 2 channel is not going to get you where you want to go... But to answer your question... Cylinders 7&8 normally run leaner because these two cylinders run hotter simply because these are the farthest from the radiator.. (IN SIMPLE TERMS) "Hope I don't get trashed for saying that !!!"
8 Channels will be the way to go, One prob for each cylinder and that will not steer you wrong... Other than that.... Yep, like Iowan said, going to need to get good at reading spark plugs...

Good Luck with the Project.....
If you need some reading to look at.... Check over at For A Bodies Only... Dominic dose a good job with Small Blocks and Dual Carb set ups. I forget his screen name over there. But I think it may be Thumper or Thumper Dart ????

 

I guess with a tunnel ram and 2" spacers the mixture should be pretty consistent across the cylinders. 7&8 would definitely be the easiest and cleanest locations. Just not sure they are the leanest typically.

 

I agree with Bob that you’re going to need a eight channel. I believe with the two channel you are just pissing into the wind.
As far as the carbs go I would be tempted to install them right out of the box and see how it ran and drove, then change one thing at a time.