2eighTZ4me Posted April 21, 2009 Share Posted April 21, 2009 Building a turbo motor that I hope to see 20psi + boost. F54 block, p90 head with mild port work. Stock crank. - I have 240Z 9mm rods at 133mm in length that I will be using. - Stock 280 rods are 130.35mm, leaving a difference of 2.65mm. - Stock pin height = 38.1mm. - 38.1mm - 2.65mm = 35.45mm pin height. - I am going to be ordering a set of forged slugs. - I am also going to be running MS for engine mgmt. This means I am going to have to order pistons with a +/-35.45mm pin height. Now here's the dilemma. Turbo pistons are dished with a 10.6cc dish. Would I be better off getting dished pistons and a 35.45mm pin height OR get flat tops and have them make the pin height an even 35mm? (or less) Advantages / disadvantages of one route over the other? Don't want terribly high compression due to boost, but was thinking that either of these two methods may/may not be equally effective. Two methods to "skin the cat" so to speak..... Dished pistons with proper pin height would traverse the entire bore. Flat tops with a lower pin height would traverse "most" of the bore, but would stop short of the actual block deck by a hair or two. Am I off my rocker for even thinking like this? (Don't ask my wife!!) Thoughts? Quote Link to comment Share on other sites More sharing options...
1 fast z Posted April 21, 2009 Share Posted April 21, 2009 YOu need to Have .025" piston to head clearence. Order your pistons extra thick in the domes. Then when you get them, you need to find out where the exact mirror image is of EACH combustion chamber, usually by putting prussion blue on the head, and bumping the head, with no head gasket with the pistons installed in the bore, and on rods and on the crank. Then mark the outline of the CC with a scribe. Then go to your mill and dish the correct amount, but do NOT go outside of that scribe line. Then once you have them all dished, go back on the inside and lighten them up, since you ordered them extra thick, and make it about .200' thick everywhere in the dome. Hope that made sense. Quote Link to comment Share on other sites More sharing options...
2eighTZ4me Posted April 21, 2009 Author Share Posted April 21, 2009 "go to your mill" -- That's funny!! Sorry Bryan - what you say does make sense, but I don't have any machining equipment (other than a die grinder!). I'm just trying to find if either situation (as it sits) is going to be more beneficial over another. I haven't ordered pistons yet, so I'm trying to determine which route to go. I'm not going for a 500hp motor, I guess I'm just trying to find out what type of piston to order to match the rods. Flats with a lower pin height, or dished with a higher pin height. I don't want to make this any more complicated than it probably is already! I do value your input though - and thank you for the reply - I'm not loaded with $$$ or technical expertise on engine building - that's why I'm asking you guys. I just want to order a set of pistons and be done with it. Quote Link to comment Share on other sites More sharing options...
1 fast z Posted April 21, 2009 Share Posted April 21, 2009 It all boils down to what you want to run for fuel then. You will get detonation problems at a certain boost, but all dependent on fuels. I would Do As I am saying, and take the pistons to a machinest, and they will charge you around 2-300 bux to do it RIGHT. Quote Link to comment Share on other sites More sharing options...
Brad-ManQ45 Posted April 22, 2009 Share Posted April 22, 2009 Dish or no - the pin height will be the same - take a look at the dished pistons - they have a raised edge all the way around. This is actually a rather poor way to dish the piston (cuts down on quench area). You'd be better off getting pistons w/a dish under the combustion chamber rather than the whole top of the piston (minus the rim of course) - take a look at the pics of the combustion chamber and you'll see what I mean. Quote Link to comment Share on other sites More sharing options...
attworth Posted April 22, 2009 Share Posted April 22, 2009 This is what they're referring to, sort of. This is a SBC piston. You basically want to copy the combustion chamber into the piston. If you haven't read this, do. It's a good thread that gets pretty in depth with squish. http://forums.hybridz.org/showthread.php?t=129940&highlight=squish Quote Link to comment Share on other sites More sharing options...
Daeron Posted April 23, 2009 Share Posted April 23, 2009 YOu need to Have .025" piston to head clearence. Order your pistons extra thick in the domes. Then when you get them, you need to find out where the exact mirror image is of EACH combustion chamber, usually by putting prussion blue on the head, and bumping the head, with no head gasket with the pistons installed in the bore, and on rods and on the crank. Then mark the outline of the CC with a scribe. Then go to your mill and dish the correct amount, but do NOT go outside of that scribe line. Then once you have them all dished, go back on the inside and lighten them up, since you ordered them extra thick, and make it about .200' thick everywhere in the dome. Hope that made sense. Post of the month.. Brian, I just might quote this post directly rather than rehash the ideas myself in the future. Would you mind? Whatever the specific numbers and tolerances any individual decides to build to, this is "How you choose custom piston specs when you start mucking about with rod lengths and closed chamber heads." Quote Link to comment Share on other sites More sharing options...
1 fast z Posted April 23, 2009 Share Posted April 23, 2009 You can only quote it, if you fix any grammer mistakes! Quote Link to comment Share on other sites More sharing options...
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