Zsane Posted February 6, 2004 Share Posted February 6, 2004 Here are a few pictures of some E31 intake port and chamber molds I did. One is of an unmodified port and the other has been opened up a bit at the entrance and cleaned up, the chamber was unshrouded and cleaned up as well. I'm working on others and will post soon. Quote Link to comment Share on other sites More sharing options...
turbobluestreak Posted February 6, 2004 Share Posted February 6, 2004 Zsane, the pics don't work tbs Quote Link to comment Share on other sites More sharing options...
Zsane Posted February 7, 2004 Author Share Posted February 7, 2004 Strange, they were working when I posted this morning, and they weren't a minute ago, but now they're up! Anyway, notice the smooth finish on the modified mold, that port was cleaned up with 80 grit, I didn't remove much except at the entrance, the largest cross section in the stock port is just before the valve to about an inch after the port entrance, you have to view the port from above as well as the side to get an actual idea of port size. The next mold will be of a port that has been opened up to have a slight taper from the entrance to the seat. A word about valve size and the E31, even with the chamber unshrouded to the max for a std. bore L28 with the small 42mm intakes installed, there is only .136 between the valve and chamber wall, and under .100 with the 44mm valves. If you start pumping air through the port this is a large restriction, so even if you lift the valve .500 off the seat, there is still under .100 between the valve head and chamber for about 60deg of the valve head diameter with the 44mm. This is an area where the largest bore possible would allow an improvement and ability to breath by unshrouding this area as much as possible without undercutting the gasket. These are experiments and could result in terrible performance. The plan is to try a differant mod on each of the six intake and exhaust ports and then have them tested on a bench and compare the results. New seats will be installed and variations in seat cuts will also be tried, both small and large valves, there are so many port seat combo's to be tested that this will take quite a bit of time to get optimum results, to be thorough all the differant head castings will need to be tested. Port molds of the differant stock castings will come before any testing. Working 6 days a week doesn't give me much time for fiddling, but I'm trying. Quote Link to comment Share on other sites More sharing options...
technicalninja Posted February 7, 2004 Share Posted February 7, 2004 What material did you use to make your "molds". Is it available to mere mortals-where can it be purchased. Very nice. The difference between as cast and 80 grit is suprising- I saw the pictures before your last post and thought "boy it looks like he overpolished the intake"-many head porters leave intakes between 80 and 120 to improve laminar flow. 80 grit mold surface came out much smoother than I would have thought. Keep us informed of your progress. Threads like this one are the reason HybridZ is IMO the best Z Car technical site. Quote Link to comment Share on other sites More sharing options...
Zsane Posted February 7, 2004 Author Share Posted February 7, 2004 I bought it at Tap Plastics, it's Urethane RTV mold maker, and cost under $30 for two quarts, it's a 1:1 mix and pour, and you need a mold release to keep it from sticking, and patiance to let it set up. These were the first I ever tried, so it's not hard to do. http://www.tapplastics.com/shop/product.php?pid=63& Quote Link to comment Share on other sites More sharing options...
Zsane Posted February 7, 2004 Author Share Posted February 7, 2004 <img src="http://www.hybridz.org/phpBB2/album_pic.php?pic_id=2938"> Quote Link to comment Share on other sites More sharing options...
JMortensen Posted February 7, 2004 Share Posted February 7, 2004 What you are saying about unshrouding the valves is very much correct IME. When I first got my Z running I paid a machinist to put in the larger valves and do a port and polish. He did a really good job in the intake runner just below the seat (the bowl I think it's called), but that was about it. When the front of the crank got screwed up on that motor I decided to build a flat top bottom end and while it was apart I did a lot more head work. My E31 had a rough casting on the short side radius which I cleaned up with my finger and some sandpaper. The real work to be done was in the chambers though. The intake valves were, as you said, VERY CLOSE to the side of the chamber at lift, close enough that I don't think that there was any benefit at all to having a larger valve in there. There probably would have been more airflow around that side of the valve with a smaller valve in place. So I took the dowels that locate the head on the block, stuck them in the head, laid the headgasket on the head and scribed the head where the fire ring was, and took a BUNCH of metal out until I had opened it up right to the edge of the head gasket. I also notched the block as much as I could in the same area. So now there is probably 1/8" or 3/16" of clearance from the valve to the side of the head where there had been maybe 1/32" before. It was really close on my head before. In addition, the area where the seats are supposed to blend into the chamber was really poor. There was a little ring all the way around the valve seats which stuck up a few thou. I can only imagine that this seriously hurt flow at low lift. So I cleaned that up as well. The last thing I did to my head was to clean up the ridge between the valves. This ridge was completely different in every chamber. Some stuck way up, some just barely, some not at all in the area directly between the valves. So I took them all down to nothing. In the wedge shaped areas between the valves there were LARGE bumps which were irregular in shape and had some nice sharp points on them. I can see those same rings, ridges and sharp points on your E31 INTAKE picture. Those were also minimized as much as possible. During this whole process the chambers eventually got polished from all the work. Theoretically this would keep some of the heat reflecting inside the chamber and not allow as much to get into the rest of the head. I did not do as much work in the outer port area near where the manifold bolts to the head, but I feel that I accomplished some huge improvements in the chamber, and some modest improvements in the runners. I'm not a machinist or anything, but I looked long and hard at the pics in the How to Hotrod book, and tried to get my chambers as close as possible to the Gerolamy head in the book. I do not claim to have done quite that good a job, but my machinist expressed his approval of my work and was shocked that I had never done that type of work before. Anyway, it looks like you are doing a GREAT job on your head, and your helping the rest of us while your at it, so I thought I'd share my experience to try and reciprocate. EDIT--I also ground out the spark plug threads that were in the chamber and laid back the area around the plugs a little bit. Jon Quote Link to comment Share on other sites More sharing options...
JMortensen Posted April 7, 2004 Share Posted April 7, 2004 Any news here? Quote Link to comment Share on other sites More sharing options...
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