FIAT 124 Spider
Engine Maintenance + Modification
71
There are two methods you can use to set the initial ignition timing. One is “by the
book,” meaning you set it just like FIAT tells you to and lock it down. The second is to
set the ignition timing by ear. There are advantages to both methods – your goal needs
to be to set your engine to the point where it runs best, which may be “by the book”
and may be “by ear.”
The “by the book” method is to take the ignition advance information from the black
metal plate inside your hood (if it isn’t there then use the information in table 10 above).
FIAT varied the timing data (to meet emissions regulations) enough that you want to rely
on your car’s data plaque if you can. Using a timing light on the #1 plug wire, start the
engine and point the light at the crankshaft position marker. Rotate the distributor so
that the timing is set per the crankshaft marker (see Figure 43). The engine speed may
increase or decrease while setting the timing; adjust the carburetor idle speed screw
accordingly to maintain the correct engine speed.
The “by the ear” method disposes of the need for a timing light. Once your engine is
set to zero degrees BTDC you will advance the distributor to the point at which the
engine speed is no longer increasing. Advancing the distributor improves combustion,
resulting in increased engine speed, but at some point it is too much and a reduction
occurs. Once the reduction begins retard the ignition until the engine speed is at the
highest point without missing or puffing. Set the idle speed to the appropriate RPM.
In both cases you want to drive the vehicle and check what you’ve done. If you’ve tuned
by the book you need to check the timing again with a light. If you’ve tuned by ear then
make sure engine operation through acceleration and deceleration is nice and smooth.
The ignition may be advanced too much (remember, the distributor further advances
once it gets moving) and require you to retard it a few more degrees to get it all correct.
There is a third method – where you tune to the desired maximum advance. Richard
Ridge submitted the following on my queries about ignition timing:
[What is optimum timing?] It is the timing that allows the car to start readily and smoothly accelerate
while also delivering the highest peak torque possible under full load. And of course it also has to meet
whatever emissions limits are required. It is not a single number, rather it is a curve, a smooth timing
advance progression from a few hundred rpm to the rpm at peak torque.
The actual numbers depend on cam timing, compression, head work, induction and exhaust
configuration. Accuracy requires dyno work or trial and error on the street. Looking at the factory curves
for different engine configurations is a good way to start.
For a race engine that has no real starting, drivability or emissions restrictions, the answer does boil
down to a single number. Others have suggested that for TC engines in typical competition trim, the
number is in the 35-38 degree BTDC range.
Given this information, if you want to seek out a specific degree of maximum advance
you need to determine the maximum advance of your distributor, do a little math, and
figure out your initial timing. If you want 35 degrees of advance and have a distributor
with 30 degrees of total advance, your initial timing will be 5 degrees. Sounds simple,
right? Trial, error, and patience will pay off if this kind of accuracy interests you.
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