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Blue smoke is oil burning. The cat when hot burns most of it off, when you replace that with a bypass or premuffler, you will notice the oil burning out of the exhaust.
The difference of smoking noticed between the different chips seems to occur mostly on the older 84-86 Carreras. My theory is that because the new chip updates the idle specifications from the 84-86 spec to the 87-89 spec, from 800 to 880 rpm, in addition to advancing the base idle ignition timing from 2.5 degrees ATDC to 3.5 BTDC, increases the intake vacuum enough to suck oil past marginal valve guides that previously was just borderline. The solution besides rebuilding the top end may be to reduce the oil level in the motor, lower the idle speed and/or backdate the idle specs.
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