yo2001 Posted August 8, 2002 Share Posted August 8, 2002 Okay, it's really a general piston question. How much metal do you need on top of the piston for turbo application? Is more metal better or less metal better? Reason why I'm asking is that I got a set of JE pistons that have domes. (.140" dome to be exact) I need to get them shaved for compression reason. I've measured the pistons and the dome and I found out that I would end up with .100" of metal after I shave the dome off. What do you guys think? Quote Link to comment Share on other sites More sharing options...
Lockjaw Posted August 9, 2002 Share Posted August 9, 2002 That is not much. I have some forged pistons here that came out of a turbo engine Hesco built if you want to measure them. One has a hole in it, so it shouldn't be hard. For that matter, we can cut it in half if you want. What about cutting less off and using the thicker HKS gasket? I would do whatever I had to do to keep the top thick, even running less boost. You could coat the tops with a thermal barrier, that may help. Let me know about the piston. Quote Link to comment Share on other sites More sharing options...
yo2001 Posted August 9, 2002 Author Share Posted August 9, 2002 Well, stroking it with LD crank is not helping me with the compression. 8.36:1 with 2mm gasket I guess I can keep about .020 more that's about it I think before 8:5 to one. 0.120" is 3mm so that might be okay I think. Ira told me to be careful about shaving the top of pistons. He might know the masic number. I think alternative way is to unshroud the valves a lot. run like 60cc head Anyway, I like to measure your piston. I'm going to get in touch with you tomorrow. May be we'll tinker with your slow sixty Z too. Quote Link to comment Share on other sites More sharing options...
Lockjaw Posted August 9, 2002 Share Posted August 9, 2002 I got the stainless line on drivers side front, and put the brake shims in the caliper, and have all that back together. While I had the wheel off, I thought replacing the worn out end link bushings with urathane ones would be a good idea, but I have to loosen the other side so I can move the sway bar. I got to say, those Toyo calipers look nice on there, especially with the stainless lines. I think I am going to put my stainless clutch line on too. At some point, I need to run out to Dave;s house and get Ricks engine hoist so the engine can come out, and get Dave's engine stand. Then I need to grind out my turbo exhaust manifold to free up some HP when I get a turbo for it. Call me. Quote Link to comment Share on other sites More sharing options...
jeffp Posted August 9, 2002 Share Posted August 9, 2002 shaving the top of a piston that was not made for a turbo application is not recommended. First, .100 thick on the top is about 1/3 the thickness it needs to be, so you will end up blowing a hole in the top. Also the piston does act like a heat sink so that thin on the top will just melt. Then there is the issue of the pressure that will be produced by compressing the air, and then the combustion, to thin, way to thin. Quote Link to comment Share on other sites More sharing options...
yo2001 Posted August 9, 2002 Author Share Posted August 9, 2002 Originally posted by jeffp:shaving the top of a piston that was not made for a turbo application is not recommended. First, .100 thick on the top is about 1/3 the thickness it needs to be, so you will end up blowing a hole in the top. Also the piston does act like a heat sink so that thin on the top will just melt. Then there is the issue of the pressure that will be produced by compressing the air, and then the combustion, to thin, way to thin. Well, the pistons is made for turbo application. There cut for RB26DETT by JE. There is .240" of metal on top of the pistons uncut. Forged pistons too. Do you think I can't coat the pistons and get away with .100" to "140 of metal? Quote Link to comment Share on other sites More sharing options...
blueovalz Posted August 9, 2002 Share Posted August 9, 2002 I had some tall domed pistons for a N/A motor cut down to about .200" minimum thickness, which according to an experienced race engine builder, was about the thinnest I should go. This was a N/A motor. Originally the face thickness roughly followed the contour of the dome, and the minimum thickness was about .300" on small quarter sized place at the valve reliefs. I removed about .340" off the top of the dome, but it did not get into this thinner part of the piston face until the very end of the milling process (thus the thinner part of the face was not effected as much as the rest of it was), so check the piston carefully at different places to verify where and how thick the thinnest place is. Quote Link to comment Share on other sites More sharing options...
Lockjaw Posted August 9, 2002 Share Posted August 9, 2002 Maybe you can have Hesco weld some extra metal in the piston to reinforce it. They actually told me they weld pistons all the time. I had a forged one with a hole in it from a dropped valve, and they said for me to bring it down and they would weld it up. Quote Link to comment Share on other sites More sharing options...
Lockjaw Posted August 9, 2002 Share Posted August 9, 2002 Why don't you just adjust the rod length or the stoke to drop the piston down in the bore a little? Then you can keep your crown thickness, and get your compression. Mine sat down in the bore 1mm or so. Ran good too. Of course when the oil ring failed and it had to come apart, I had the block decked to shorten the gap. Quote Link to comment Share on other sites More sharing options...
jeffp Posted August 10, 2002 Share Posted August 10, 2002 >Well, the pistons is made for turbo application. There cut for RB26DETT by JE. There is .240" of metal on top of the pistons uncut. Forged pistons too. Do you think I can't coat the pistons and get away with .100" to "140 of metal?< You might be able to get by on .250 thick, but man it is taking a chance. With this case the issue becomes the heat sink capabilities of the top of the piston. You need to dissipate the heat and you need a X amount of material that will accept the heat, dissipate and distribute the heat without getting so hot that the aluminum gets soft or even molten. One thing I have noted about all of these coatings is that they work well, but they are short lived relatively speaking when you want to run the car say 100k or along those lines. I almost got that poly/molly coating on the piston skirts when I did my engine, but decided against it when I found out it would last only about 50K or so and that was not in a race engine. The cost was to much in my opinion. You know, David at Malvern Racing would probably have some good insight on the minimum thickness of the piston tops. He is a prety smart guy and I like to run stuff by him I cant make up my mind on just for a different perspective. One thing I have learned is that it is never stupid to get more opinions, the more information you can get the better off you will be in making an intelligent informed decision. Quote Link to comment Share on other sites More sharing options...
Lockjaw Posted August 10, 2002 Share Posted August 10, 2002 Well Yo came by last night and we cut one of my old forged pistons so we could mic it, and they were only .2 inch thick!!!! But they had some raised reinforcement ribs on the underside of the piston crown. Now I want to say this. These were made by Ross Racing in the early 80's, and they are not a turbo piston. I would say they are pretty much a copy of the stock Nissan NA piston. They had about 80k miles on them, so I am sure they were well punished. The 300ZXTT has a piston coating on the skirts and it is gone by 100k miles. Quote Link to comment Share on other sites More sharing options...
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