Re:GT 1600 Jr. M tuning procedure (longish)

[digest@xxxxxxxxx]

> Hi, Jacob
>>Does the fact that the valves are tight have much influence on the
>>emissions? What happens when the valvetrain wears - do the gaps get
>>smaller or larger normally?
>
> Yes tight valves have a profound impact on emissions.  It is the came as
> having a cam with longer duration, the valves are open longer so the
> intake and exhaust flow need inertia and wave action to keep them moving
> in the right direction, but its not there till the engine is at a higher
> RPM, so at lower RPM you get more exhaust reversion up the intake and
> more unburned fuel out the exhaust valve before it closes.  You can't
> tune a carb till the valve timing is right.
>
> Valve train wear depends on what you call wear.  Wear in its classic
> since would open the clearance, valve seats being banged down by a lack
> of lead on a soft seat causes them to close.  The first ALFA engine I saw
> with hard valve seats was the first Motronic spider (1989?), before that
> exhaust seat recession was common.
>

Hi Chris.

Thanks for your advice.

I figured the duration issue out too, but wasn't sure what the impact
would be on the emissions/running of the engine. I have always run the car
on 98 LRP gasoline though I am informed that it should be able to take
unleaded. Valve seat recession shouldn't be an issue in my turn of
ownership.

Consequently I figure a valve shimming session is in order. Is it
advicable to go to the more open end of the spec or the closed? The spec
is something like .51 - .55 (off the top of my head but for example
purposes) for the exhaust. Should I then rather go to .55 say or to .51?

I'll change the oil and filter too to make sure things are nice and clean
in that department.

Regards

Jacob Haagerup
'75 GT 1600 Jr. M 1.8
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