Originally Posted by Wolfman3002
Wrench,
Does this airflow limitation have to do w/ either the stock throttlebody or the Air Flow Meter? If I go w/ the Megasquirt system, I'll use the slightly bigger Nissan Throttlebody (60mm vs 55mm for hte stock TB, I believe), and I'm hoping I can eliminate the Air Flow Meter altogether (if that's possible w/ the MS system).
Or, is the flow limitation a matter of valve size? I was also thinking about goping w/ the 2.0l valves to increase the breathing capability of the engine. Do you think that would help?
Randy
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The air flow meter is the biggest limitation. Next would be the cylinder head and then the camshaft, then the intake manifold. But you needn't worry about the intake manifold until you're running a pretty honkin' big cam and only if you already have a very well ported big-valve head.
IMO, the best bang-for-the-buck in terms of building a big valve 1.9 head is to fit 2.2 intake valves (1.77") and 2.0 exhaust valves (1.42"). Opels have very good flowing exhaust ports in the stock configuration, it's the intake side that needs all the work. The nice part about using the factory Opel valves is it minimizes the amount of machine work and therefore $$$. Same size guides and you can use the stock springs and retainers, although for any decent cam you need better springs. Norris Cams has upgraded springs and I believe retainers as well. Simplifies the installation as there's no additional machining other than cutting the seats in the head larger.
You could also go with the tried and true Chevy valve installation, but this requires replacement of all the valvetrain parts and there is subsequently greater labor and machine work involved.
HTH,
Bob