Set Timing on Chevy V8's
Get Peak Performance
BY: Lars Grimsrud
How to Set Your Timing for Peak Performance
by Lars Grimsrud
SVE Automotive Restoration
Musclecar, Collector & Exotic Auto Repair & Restoration
Rev. B 4-18-01
This tech paper will discuss setting the timing on a Chevy V8.
This procedure also applies to other GM V8s.
The procedure outlined here differs from the Service Manual, and
is based on my years of experience doing this work in the
quickest, least painful, most economical way while keeping the
level of quality high. It is recognized that other people will
have different methods of doing things, and may disagree with
specific methods and procedures that I use.
How to Set the Timing
When you think about it, setting the timing at idle speed makes
no sense at all: You don’t operate your car at idle, and timing
changes as the rpm changes. Fact is, the timing spec at idle
speed is provided as a simple way for most people to set the
timing, and is not a good procedure for optimum performance.
Small block Chevys (and most other GM performance V8 engines)
perform best when the total timing (full centrifugal advance
plus the initial timing setting with vacuum advance
disconnected) is all in by 2,500 – 2,800 rpm and is set to 36 –
38 degrees. If you have an adjustable timing light, this is
very easy to check. If you don’t, you need to scribe a 36-
degree mark on your harmonic balancer. Here’s how:
Measure the circumference of your harmonic balancer using a
sewing tape measure (or other flexible tape measure). Get it as
accurate as you can. Take this measurement and divide by 10.
The number you get is the distance to 36 degrees. Measure this
distance CLOCKWISE from your existing harmonic balancer timing
mark and place a clear mark on the balancer. Remove your
distributor cap and rotor. Remove the 2 centrifugal advance
springs. Install the rotor and the cap (without the springs).
Disconnect the vacuum advance.
NOTE: This procedure cannot be used on the HEI ignition
systems. Removal of the springs will cause an artificially over-
advanced condition that will never be achieved with the springs
in place. You can use the basic technique described in this
paper with the HEI units (setting timing up to 36 degrees), but
to check total timing, you must install a set of soft springs.
You cannot remove the springs altogether. With the soft springs
in place, rev the engine until the centrifugal advance is pegged
out. Adjust for 36 degrees total. Then re-install your original
Start the engine. It may kick back a little due to the advance
coming in immediately without the springs. If you’re using an
adjustable timing light, set the light to 36 degrees advanced.
Now rev the engine just a little while observing the timing
marks with the light. It shouldn’t take much rpm to peg out the
advance without the springs installed. With an adjustable light
set at 36 degrees, align the stock timing marks with “0” when
the timing is “pegged out.” With the non-adjustable light,
align your new 36-degree mark with “0.” Rev the engine a little
to make sure the timing will not advance any further. Shut it
Pop the cap and rotor and re-install the springs. Put
everything back together, but leave the vacuum disconnected.
Start it up. For future reference, make a note of the timing
setting at idle. This is your new curb idle timing spec. Now
give the engine a few quick rev’s past 3,000 rpm and verify that
the full timing (36 degrees) is coming in. If it’s not, you
need to change to a softer set of springs until you get full 36-
degree advance before 3000 rpm. (NOTE: A stock set of springs
will usually not allow full centrifugal advance to come in
before redline rpm. If you have stock springs installed, don’t
rev the engine beyond its limits to try to force full advance
Shut it down and hook up the vacuum. Now do a road test.
The 36-degree 2500 rpm advance curve is optimum for performance,
but may require premium fuel. Lug the car around, and punch the
throttle at low rpm while listening for detonation (“engine
knock”). If you’re getting any audible knock, you MUST retard
the timing. Retard the timing in 2-degree increments until
engine knock stops. Engine knock will seriously damage engine
components if not corrected. If you get no knock, you may see
slightly improved performance at 38 degrees total timing. This
is particularly true if you’re running at high altitude.
If you have no engine knock under acceleration, but the
car “chugs” or “jerks” at cruising speed (light throttle
application), you are getting too much vacuum advance on top of
the mechanical advance. You may need to change out the vacuum
advance diaphragm with an adjustable unit available from
aftermarket sources. Adjust these units so that you get the
most vacuum advance possible without any “chugging” or “jerking”
at cruise speed.
Your timing is now set for best possible performance. Make note
of the new setting, and use this for your future tune-up
Questions, Comments & Technical Assistance
If you have questions or comments regarding this article, or if
you notice any errors that need to be corrected (which is quite
possible since I’m writing this from memory), please feel free
to drop me an e-mail.
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