FIAT 124 Spider
Engine Maintenance + Modification
84
Another option is adjustable camshaft wheels. These allow you to independently change
the timing of each camshaft to match your requirements. This compensation allows for
fine tuning of your engine to a degree not possible with stock components. Some of
these wheels require modification of the cylinder head; check with your supplier.
Adjustable camshaft wheels will add something new to your engine – complexity.
Consider that factor and speak to people who use them before installation.
11.1.7 Big Valves
Many suppliers sell big valves and/or peformance heads (meaning a stock head that has
been cut to fit big valves and ported for better airflow). Simply buying the big valves and
cutting the head to accommodate them or buying a performance head will not result in
any huge performance increase. The fuel delivery system has to be capable of bringing
more air and fuel into the combustion chamber. Big valve heads that are ported and
matched to a ported intake manifold will allow more air and fuel into the engine. A larger
carburetor will also be required on most engines.
11.2 Intake Manifolds
A variety of intake manifolds were installed on the carbureted Spiders. They followed
two basic designs as described earlier in this book, dual-plane and single-plane. To
recap, a dual plane manifold has two chambers inside of it, one is small and the other is
large. The larger one is the primary plenum and services the main throttle of the
carburetor. The smaller one is the secondary plenum and services the secondary
throttle. Dual plane manifolds are designed for optimal operation of the secondary
throttle of pneumatically-operated carburetors. Single-plane manifolds have one interior
space. Fuel and air from both throttles is delivered from this one large space into the
intake runners and then the combustion chambers.
With the exception of the 2000 series all of the manifolds are quite good. On the 2000
Spider the intake manifold should be used with the ADHA (stock) carburetor only. The
casting is such that the secondary throttle opening is too small for any other carburetor.
For pneumatic carburetors fitted to the earlier Spiders you should plan to use the stock
manifold for the model year and carburetor, for example, use the 1608/1592 manifold
with the 28/36 DHSA carburetor.
In all cases it is realistic to block off all of the ports except for the brake booster inlet.
Keep in mind that if you plan to keep emissions control devices that rely on manifold
pressure you can’t block off their ports.
11.3 Ignition
Running with points? There are a few decisions that need to be made about your
ignition system if you are looking to improve things. Improvement can often be made by
simply making sure your entire ignition system is working properly. Thad Kirk, a long
time respected FIAT owner, has articles on points ignitions on www.mirafiori.com
. He
notes that a well tuned points distributor provides reliability and performance right up
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