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you state in your book that the stock exhaust vavles fo the 2liter.. is to large,, this will cause over scavenging.... with this thought in mand..if i use 11 mm cams on both side.. doe's this cause the same problem?? iap and centerlind here in the states see a 11 mm intake cam to be used with the stock 9.5 mm exhaust came for the bosch fi....what is your thoughts on this? thanks
 

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The subject of calculating valve sizes is a complex one, so we can benefit from what the rest of the world is doing...sort of a survey. If we look at what the different manufacturers are doing in similar size engines, you will not find ONE to use such big exhaust valves! In fact, some recent BMW engines have 47mm intakes with 38mm exhaust valves!! And these are engines with very respectable specific power output. Another factor to consider is CR. The higher the CR is, the smaller the exhaust valve can be, as the higher cylinder gas pressure is more than adequate to expell spent gases out.
Another very important factor is exhaust manifold efficiency and the rpm this exhaust system is tuned for. Usually, we design headers after first fixing the type of cams to be used. Seems you would have to work backwards and see what type of exhaust cam is a good match for your headers! What I'm getting at, is that only through experimentation you will arrive at the best cam/performance combination for your particular needs.
Sorry I can't come up with a plain black and white answer, but I hope to have explained why!
Jim K.
 
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