Grand Haven Rd.
Spring Lake, MI 49456
UNDER THE SCOOP
On this Fourth of July when we
are all celebrating our
Independence and all that goes along with it, we are also reminded that
there are many independent thinkers in this society as well. My
Great Grandfathers were both the second and the sixth Presidents of
these United States (John Adams and John Quincy Adams) and I have read
many books about their lives. Now my Grandfather John Adams had a
cousin named Samuel Adams (yes the beer guy) and both were in politics
and had completely different ideas on how to setup and run this
business we call America. They bitterly disagreed
on many subjects but ultimately they both agreed on one
thing and they both signed the Declaration of Independence
and the country was born.
With that in mind, recently a very talented engine tuner was
explaining how he never changed his Holley carburetor on his
vehicle. He stated the carb requires very little or no tuning or
jet changing after you get it set and that works for his program.
The guy wins races.
I couldn't disagree more. All of the testing and tuning I
have performed has consistently shown that for maximum performance you
need to stay on top of the air conditions and data the computer kicks
out (or your spark plug reading tool) and adjust accordingly.
There are many theories to tuning carburetors. In the average
application, typically what you're going to find for
our designs is that for every 1300 feet of corrected
density you will be required to remove one jet or 1-2 percent of fuel
from the booster. Another thing you have to definitely keep an eye on
is that fact that as the air heats up and the humidity rises you need
to increase your idle air bleeds and intermediates (if equipped)
otherwise the engine will get real fat and lazy. This requires it to
clean the plugs up on the first part of the run and your performance
really falls off.
On my own favorite personal race car, I increase the idle air bleeds
about .006 and the intermediates about .008 when the density gets about
3200 feet and take one jet out of it. Otherwise it really falls off in
the 330's and isn't fond of restarting when its hot. But if
you try to keep that tuneup in it for the cold Michigan races in the
fall (1200 feet or less), it hesitates like a monster and will be off 2
mph or more from the gain you should've received from the better air.
So you richen it back up when it gets to those low density altitude
numbers and the air fuel ratios on the computer and the time slips sing
a happy song. Most gasoline powered cars will move up and down a tenth
or so from good air to bad air. A passenger car is typically not going
to notice a 10 hp loss. A bracket racer sure will.
I rented the track one day for testing (there was no wind and the air
was very stable) and made 13 passes in a row inside .017. The car is
deadly at 13:1 on the meter, but if it starts creeping toward 12.7 the
330's move around over .01 and it really sounds thick at the far end of
the track. So you take the fuel out and it
runs the number again.
Keeping in mind that this is tuning on a higher level than the average
weekend driver may even need to do, but bracket racing these days is
even more critical than NHRA pro stock. If you're off by .02 in NHRA
you can go a couple of rounds and take a few guys out. If you're off by
.02 in bracket racing, the trailer door is down before you make the
turn off road. Ever notice guys adding/removing 5 lbs from their car in
staging lanes. Its that critical.
Which brings us back to the point. When you're walking your
sparkplugs around the pits asking opinions, realize that there are many
talented folks out there, but each has a slightly different way of
doing things. Everyone wants to achieve similar goals, your job,
whether you are voting in an election or tuning a vehicle is to work
with all the parties, take in the data, analyze it for application to
your program and choose the path that best fits your beliefs.
Everyone you talk to may think slightly different, but they all want to
achieve the same goals. Remember Grandpa John and Sam didn't
agree on politics on many subjects but both agreed and signed the
Declaration of Independence.
Thanks for reading.