Captain bob

my 408" small block turn out to be a real pleasant installation." too much HP. took a turn for the better with the installation of 275/60/r-15 Nitto drag radials so now i can test the car, i have the new holley 4160 aluminum carb. at 750cfm and i am trying to get it right the idle screws are set with vacuum gauge,float level perfect and .015 clearance in accelerator pump actuator lever squirter is # 31 the jets are 72 and the plugs are "white" not even a tinge of brown, obviously not the desired brown paper bag color.my specs. are all forged bottom end,decked to .005 thousands,75cc AFR. 195 heads totally CNC.6" rods, flat top pistons with 4cc valve relief ,10.5 cr.,rpm air gap,HEI,MSD,34 degrees all in at 2500rpm,total with vacuum advance 52 degrees,hydraulic roller 236/246 lift at 540". my question is what do all you highly experience 400' sbc guys run for primary jet sizes??? i will worry about secondary jets and linkage rods later right now i figure i wanted paper bag color then deal with squirter size and change accelerator cam from green to what ever. the cam is in the number one hole as suggested by holley with 3400 pound 71 vette with 3.55 gears and turbo 400 (700 r-4 on bench) .

bluedawg

I don't quite remeber as I'm at work for another week, but try upping 10 sizes and and re-read the plugs.

Captain bob

thank you i will change from primary jet size 72 to 82 today as a start,like i said bright white not a trace of color on plugs! i would like to add engine runs unbelievably cool .i have a isolated two fan system with first fan on at 180degrees and second fan on at 195 degrees. second fan has never come on yet i guess the four row copper big block radiator has a lot to do with perfect 180 degree under all conditions on one fan.

REELAV8R

Be sure you are reading the plug right. An excellent post on plug reading.

http://honda-tech.com/forced-inducti...ug***-3063102/

MelWff

why would you jump 10 sizes, typically you go 2 at a time. In addition plug color can be deceptive. Not a direct comparison to your carb, but a 3310-1 780 CFM runs 72 in the front and Chevy used 70 in the front for the 780 they used on the LT-1, 1970. What power valve do you have?

74modified

I find today's fuels dont leave plugs as readable as in the past. Each engine is different and each carb should be set up to match. For me, to get a real assessment you need an O2 meter.

Captain bob

back in the day i would normally move 2 or 3 jet sizes but as blue dawg
indicates these 72 are so far off better you move 10 jets up and into "safety zone" and then move down (better a foul plugs then tulip the valves or worse yet put a hole in those pretty custom pistons) at least that how i interpret his post.

Captain bob

here is the new style holley 4160 at 750 cfm.

bluedawg

Being brite white I'd go higher than 2 as a start as two probably won't begin to touch. I got 76's with no power valves front or back on a 400 that's not as big of a cam.

bluedawg

My point exactly.

Captain bob

melwff in answer to your post the manifold vacuum at idle (1000 rpm) and in gear 750 rpm is 12 a little surprised with this roller cam and power valve is 65 ,green cam #1 hole and squirter is 31. the engine loves advance timing now at 18 initial (with vacuum advance connected) 34 mechanical at 2500 and 54 degrees total at 3000 with mach/vacuum advance.

MelWff

think you may have too much vacuum advance, 20 degrees. Should be about 12.