Hey Johnny Hunkins, ZEX plugs+carb & vac advance tuning = even better

Johnny,
Love the Sweeper Chevelle, especially the bbc.  The ZEX plugs product test caught my attention with the mention of your plug fouling problems.  I had been putting up with sooty plugs for 20+ years on my BBC 67 camaro, 'till I bought a Innovate Wide Band meter system.  I spent most of last summer reading the Innovate forum, and tuning my then new BG 1000 race demon.  I thought that carb ran great out of the box, but didn't know how fat it was until I got the wide band.  Main jetting was good, I tuned them at the track, but it was fat everywhere else.  Explained why I only got 11 mpg even with a TKO od, plus the plugs were always black and sooty.  Long story short, after the carb tuning, and lots of tuning of the vacuum advance (mallory unilite with a adj adv can set to min vac, but I limited the can's stroke to prevent over-advancing), the plugs are clean even after 4000 miles so far this year, and now I'm getting 16-17mpg on the highway (4.33 gears, 2700 rpm at 75ish mph).  Before the extensive tuning, the motor only pulled about 5-6 inches vac at idle (1200 rpm), and the needle on the vac gage was always bouncing around.  Now it pulls 9.5 inches at a 1100rpm idle, and the vac gage is dead stable.  The motor is really smooth now.  Anyone can make them run wide open, it's alot harder to make a nasty motor drive slow and easy.

 My motor is basically the same as the Pile Driver on pg70 of the nov '09 issue, but in .070 over 454 form,an off-the-shelf comp xr292 solid roller cam, team g intake, and the previously mentioned bg carb; same TFS heads, same c.r.

Those multi-ground electrode plugs work differently than alot of people think.  Most people I've talked to think they get 2 or 3 or 4 sparks, depending on the number of grounds.  But in reality, the spark jumps to whichever electrode is closest, then when that one erodes back, the spark jumps to the next one until it erodes back, and so on.

Glad the plugs helped you out, but I bet if you really dug into that carb with a wide band, and nailed the vac advance setup, the beast would be even better.  It would make a great tech article that would help out alot of guys, but the carb tuning is quite in depth.  An article on vac advance setup would be helpful, as very little has been written on it, and nailing that down really tamed the big cam I'm running.

The adjustable vac advance cans are designed backwards in my opinion.  Turn the screw one direction, and it limits the amount of vac advance provided, but at the same time it raises the amount of vacuum needed to get the thing to move.  Turn the screw the other way, and the opposite happens (way too much advance added, and lower vacuum needed to move the timing).  Big cam motors need exactly the opposite - they don't have much vacuum at idle so the advance can needs to start adding advance at low levels, like 6-7" or so; and big cam motors usually need alot of inital advance, like 18-20 degrees at idle (no vac advance included), so if the vac can adds 25 or 30 degrees of advance then you have way too much at highway speeds (assuming you're near or over 2500 rpm on the highway, and all of your centrifugal timing is in by 2500).  

What I did was drill a hole for a roll pin in the vac can's actuating rod, and put washers between the roll pin and the vac can to limit the amount of travel, then I could adjust the screw to get the advance to start working at a low vacuum level, without over-advancing the timing at highway speeds.  This worked great, really tamed the motor for around town driving, pulled 10 degrees out of my water temperature, and picked up ~1.5mpg on the highway.  Sourcing the vacuum from manifold, instead of the ported source on the carb, was much better as it adds some advance at idle, as in about 5-7 degrees, and helps keep the plugs cleaner.

The great thing about vac advance is when your puting around or cruising down the highway, vacuum is high which pulls in the extra advance.  Then as you crowd the throttle, or stand on it, the vac drops and pulls the timing back out.  All without a computer - although computer controlled would be lots easier than the freaking roll pin and washer trick.

Gotta go, great mag, keep up the good work.
Mark.