Copyright © 2002-2003 Dave Resch
All rights reserved.
This page explains how you can improve the power output of a
engine, with the stock cam and stock low-compression pistons,
2150 2V carburetor, and stock DuraSpark II ignition. If you
don’t have money
to spend on major performance upgrades, or maybe you just have
an old engine
with a lot of miles and you can’t justify spending the money to
soup it up,
this section is for you.
Now, we have to get down to some brass tacks here. I can’t tell
you how many
vehicles I’ve seen with a hideous mess under the hood — spark
plug wires swollen
from soaking up the oil leaking from the valve cover gaskets,
in sludge and varnish, and so many missing and/or broken
components it was a
miracle the engine could run at all.
As obvious as it should be, I have to say that the starting
point of any
performance improvement is tuning up your engine and getting it
up to at least
factory specs for performance.
Even though factory power ratings were only in the 150hp
ballpark for most 351M
engines, if your engine has been neglected for a while or is in
dire need of a
tune up, it could well be down to 100hp or less. In that case,
just getting it back
up to factory spec would be a huge improvement.
If you’re starting from scratch, with a neglected engine in
need of a tune up,
here’s what I recommend you start with:
Basic M-Block Tune-Up Procedure
Clean the engine.
Steam clean or thoroughly de-grease the engine. It’s a lot
(and way more fun) to work on a clean engine.
Check the ignition system.
Start at the spark plugs, and work your way back to the
If it’s been a while, you may as well replace all the
(spark plugs, spark plug wires, distributor cap, and rotor).
Appearance of the spark plugs tells a story. If you don’t
get at least a Haynes or Chilton manual with the page of
color illustrations. Read the manual about what different
plug conditions mean and what you might need to do to
Overhaul the carburetor.
Remove it, clean it, and rebuild it. Even if you’ve never
worked on a
carburetor before, you can probably overhaul a Motorcraft
carb — they are that easy.
All you need is an aptitude for reading the exploded view
come with the rebuild kits, some patience for working with
a clean workspace where you won’t lose any of those
teeny-weeny parts, and
a sense of adventure. Follow the choke and accelerator pump
instructions in the carburetor rebuild kit.
If you’re not so adventuresome, maybe you’ll be motivated by
the desire to
save the $200 (or more) it will cost for a rebuilt carb at
the parts store.
Note: I'm including a carburetor overhaul in this
because many problems are caused by dirty or maladjusted
carburetors, and fixing
everything else but leaving the carburetor untouched is not a
recipe for success.
For detailed information on overhauling and tuning the
carburetor, check out
Change all the filters.
Air filter element
Install a new PCV valve.
Just to be sure, especially if you haven't done it recently.
PCV valve can cause horrible driveability problems.
Change the oil.
Old motor oil can adversely affect the engine's performance
Check all vacuum hose routing.
Make sure all vacuum hoses are connected properly. Check the
of all hoses, connectors, and vacuum diaphragms. This is
eliminating vacuum leaks — a major, and surprisingly common,
If you don’t have an engine calibration label with a vacuum
the best option is to look for another vehicle similar to
yours that has
one and refer to it.
The ProjectBronco web site has a calibration label posted
for a 1979 Bronco,
351M with automatic transmission,
Set the ignition base timing.
Set the base timing according to the specification on your
label. If you don’t have one, start with 4 degrees BTDC.
You can look up some general '77 to '82 M-block truck timing
Once you have the engine in a good, basic state of tune, you
can consider moving
beyond the factory specifications.
Tweaking your stock M-Block