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On 1 Sep 2002, at 23:03, Martinez, Leon wrote: > The Mexican head is about 25 to 30 degrees cooler than the > MOFOCO head (1 and 2)making it over 100 degrees cooler > than the old MOFOCO head it replaced on cyl 3 and 4. > So when cyl 1 and 2 is at 250 degrees then 3 and 4 is at > 220 degrees and so forth. I CERTAINLY don't want to be seen as defending MoFoCo, but what are the chances that the point where you are measuring the temp is hotter because there is a better heat flow path out of the head to your measuring point? It's often hard to keep in mind that the temp we're really interested in is really in the internal regions of the head where we can't actually measure the temp, so we measure the temp outside and make an inference about the inside temp. If I design a head that has better heat flow paths from inside to out, but the same (to simplify the example) outside airflow and surface area, then its outside surfaces will run HOTTER, because that's what they MUST do to shed heat better. Consider this example: Take 2 alum rods, 1/8" dia and 1" dia, both 4" long. Stand each one on end in a dish 1" deep with water. Take an Acetylene torch and try to melt the upper end of each of them. The thin one will heat up and melt right away, but the thick one never will. The water at the base of the thick one will eventually boil. It's clear that the thin one is hotter on the top, but the thick one is hotter on the bottom. If you were just measuring the temp on the bottom you would be tempted to choose the thin one, but that would be the wrong choice. The thick one is hotter on the bottom BECAUSE it is doing a better job of removing the heat from the heat source. Along similar lines, I realized in a conversation with Keith Park at Parma that the same temp reading on a hot and cold day meant that the inside of the head was actually running hotter on the cold day. Leon, Your data is VERY interesting. I certainly don't want to discourage your efforts, but I just want to make sure we all understand the limitations we are working with. I'd love to see one of these MoFoCo heads sometime. They often show up here at shows, and I'm sure I've looked at these heads, but not as carefully as I'd like, and not with all your interesting data in mind. Remind me again where you are taking your temp measurements. If you look at this area on each head style can you tell if the MoFoCo head might have a better heat flow path to this position than the OE or Mexican head? - ******************************* Jim Adney, jadney@vwtype3.org Madison, Wisconsin, USA ******************************* ------------------------------------------------ To unsubscribe, E-mail to: <type3-off@vwtype3.org> For more help, see http://vwtype3.org/list/