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You can make a strong engine out of a B20 without much loss of driveability. Just don't get too wild with the cam, for a street engine I would say the F-cam is the maximum (300 degrees, not much overlap, pulls strong from 2500-7000). If you do this you should also swap your d-jet for carbs (Weber DCOE 40 or 45's). If you want to keep the d-jet I suggest you keep the D or K-cam. I know that there exist tweaked D-jets that can have fueling set in 10 percent increments but the major drawback is that the you get 10 percent richer or leaner over the whole range which isn't good at all (if low end power and consumption is good than top end suffers and vice versa). You could port the head but you need to know exactly what you are doing or the result will be disapointing. The maximum size for the valves is 46mm intake and 38.5mm exhaust with normal guides and 46 mm in and 40 mm out with offset guides. If you get bigger valves be sure to enlarge the combustion chamber around the intake valve to unshroud the valves otherwise it won't give you extra power. Get a header with big tubing, not the skinny pipes. On the dyno it became obvious that almost all 4/1 headers loose much power in the low and midrange and only give about 3 hp gain over a stock two pipe manifold (this was with the carburettors rejetted and ignition reset to optimal for each header and on the same engine). A big tubed 4/2/1 with the cyl 2 and 3 tubes on the outside of cyl 1 and 4 tubing gives much better low and midrange and comparable top end.
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