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On 16 Jan 2002, at 9:13, Brian Schlepp wrote: > This is an old debate that goes deeper than just the VW world and will > probably never go away. Was it 1966 or 1967 that the factory went to > dual ports and dual carbs and the horsepower went up about 5hp? But > what else changed? It was 67, and the only things that changed (which affect this question) were the dual ports in the heads and the split manifolds which were needed to match up to the new heads. The cam did not change. Those 2 things made a lot of difference between the 66 and 67 dual port engines, as the single port engine start to fall off at 3000-3500 RPM. The dual port heads were one of the best things that VW ever added to their engines, those plus the type 3 dual carbs. > Port velocity has alot to do with effeciency. Efficiency is a pretty broad term to use here, so I'm not sure exactly which things you're thinking about. If everything else remains equal, volumetric efficiency will go down with increased velocity because increased velocity can only come at the expense of larger pressure drop. I admit that this ignores ram air effects, and those are going to be very RPM dependent, as well as cam dependent, as you said. OTOH, if the velocity falls too low, the air won't pick up fuel in the carbs. This is one of the reasons that FI works so well for HP applications, since you can still get the right fuel/air ratio at low velocity and high volumetric efficiency. > My point in my email was a normal 1965 motor with single port and single side > draft was fine for the intention it was built for. By increasing the > displacement by only 6%, but improving the cam, would infact improve the > power of the whole package. I certainly agree that adding those things would be bound to bring improvements, so we agree. I just didn't think that it made much sense to build an engine like this and try to sell it as something special when something based on later stock parts would probably be better. My guess is that a stock cam, dual port, dual carb 1600 would do better. We should also keep in mind that the single port, single carb engine was only ever sold as a 1500, so the upgrade to a 1700 is really a 13% displacement increase. Did he mention a "hot" cam? If so, I missed that. > Suck water lightly through a big straw and you will need to suck longer. > Suck water lightly through a little straw and you will be fine. No matter how I look at this it seems to me that I'll always get more air thru the bigger straw (all other things being equal, of course.) I can always do things to make up for the little straw, like sucking for a longer time, but if I did the same things with the big straw I'd come out ahead, assuming that I don't let the flow rate fall below what the carbs will handle. > Suck really hard and the big straw wins. Little suckers (stock) only need > little straws, but the big suckers (strokers,big cam,big pistons) need big > straws. Here we agree again, and my whole point was that it made little sense to combine the big pistons (and special cam) with the little straw. I certainly don't have any problem with someone who would want to make the nicest single port, single carb engine they can. I was just troubled by the idea of going this route if you were setting out to make a high performance engine. - Jim Adney jadney@vwtype3.org Madison, WI 53711-3054 USA ------------------------------------------------------------------- Too much? Digest! mailto:type3-d-request@vwtype3.org Subj=subscribe