Top Tuner's Tip #1: Timing Advanve Curve

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From: twelve_second_vega_REMOVE_460129_THIS_@yahoo.com


Most any engine will respond well to advanced
ignition timing. However, it is important to get the
advance curve correct to avoid pinging and subsequent
engine damage.

It is important to have your
ignition timing set for optimum performance before
selecting power valves/power piston springs (in your
carburetor) because this will greatly influence manifold
vacuum & dictate your final selection.

One of
the first steps in determining the proper advance
curve for your particular engine is to disconnect and
plug the vacuum advance. This allows you to see what
the mechanical advance curve is doing under
acceleration.

The extra advance provided by this
vacuum device is purely a fuel economy feature and it
isn't needed in a performance application. The noted
exception would be at idle with very long duration
camshafts. We will discuss this unique application
later.

Now, connect a timing light and note the rpm when
you first see movement of the timing mark. Regardless
of the advance curve's overall range, you must not
have advance occuring at idle.

Ideally you
want mechanical advance to take place 250-300 rpm
above idle with a manual transmission application and
approximately 150-200 rpm above idle in 'Park' with an
automatic transmission.

When installing an Advance
Curve Kit (small block Chevrolet) be sure to install
the little brass 'Limiter Bushing' on the stop pin.
This will limit the amount of total advance and allow
more initial advance for improved idle & better
acceleration.

Install the weights and springs and check each
combination with your timing light. The ideal advance curve
will be one that comes on a few hundred rpm above idle
and advances smoothly and evenly throughout the rpm
range. Full advance should be seen by 2500-2800 rpm and
no later than 3000 rpm.

Now accelerate the
engine to 3000 rpm and set your timing to 32°-38°. To do
this, you will need a 'Dial Back Timing Light' with the
little dial on the back. Keep your total timing within
this range to avoid problems with pinging and possible
engine damage.

Another method is to hold the
engine at 3000 and advance the timing (pull distributor
toward radiator) until the engine shakes and a popping
misfire can be heard out the exhaust. Now, back the
timing down until the shaking and missing just stop and
check your timing. It will most likely be between 32° &
38° BTDC.

You should see about 14° to 16°
BTDC on the crankshaft at idle with most distributors
and some as high as 20° BTDC. The idea is to have as
much timing at idle as possible without causing hard
starting while never exceeding 38° total advance. You will
be impressed with the performance.

The next
Top Tuner's Tip will discuss ignition timing
requirements with very radical camshafts. I hope you find
these posts informative and enjoyable...Robert Herndon


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