huxley309 0 Posted July 12, 2006 (edited) Well we all know the mi16 is a cracking bit of design but ive been doing a fair bit of reading and it's made me think hmm what can i do to improve on what is already a good engine design... Well pistons.....now we all know a good squish gives an even and clean burn right but mine are anything but standard and looking at them i got to thinking what if the high piston crown would cause problems causing the mixture to more to the sides of the wall rather then sit in the centre of the combustion chamber Here is the aforementioned piston Now the roof of the chamber is pentroof but! is it possible to make the exhaust canted improving inlet flow and also on the inlets would a flatbacked tulip valve be a wise choice for say someone wishing to retain std valve size? Now as for the roof itself would machining a bit of metal around the spark plug area again improve the burn by pushing the mixture right into the roof? I await the answers with batited breath Edited July 12, 2006 by huxley309 Share this post Link to post Share on other sites
PumaRacing 2 Posted July 13, 2006 That piston looks a bit of a nightmare for gas flow and burn cleanliness. Sharp edges everywhere, a redundant raised bit on each side between the valves and very small radii in the corner of the valve seat cutouts. The bit you won't have noticed is that the gudgeon pin bore has been abrasive honed rather than roller burnished to size. That tends to be the sign of a small volume player without the ideal big OE equipment. Roller burnishing polishes and compresses the skin of the aluminium to give a very precisely sized and hard wearing surface and is de facto production technique on all OE or big volume aftermarket pistons. Look at the pin bores on any OE piston and you'll see they are mirror smooth rather than cross-hatched. I used to design and make pistons though so these things stand out like a sore thumb to me and no one else will notice I guess. The skirt design is also a bit old fashioned compared to state of the art forged stuff these days. I'm intrigued to know where these came from. I'll guess that at least they were cheap. Share this post Link to post Share on other sites
Sandy 191 Posted July 13, 2006 Matching the cutouts and crown height to the necessary valve clearance is preferable, but uncommon with off the shelf pistons on fast road engines! Share this post Link to post Share on other sites
petert 587 Posted July 13, 2006 The pistons I get made by Wiseco have less dome, shallower pockets and thus less sharp bits, as suggested by DB. Certainly not the most expensive or best piston available, but excellent value for money for fixing worn liners. I prefer to push a more flat top piston closer towards the head, increasing CR and decreasing squish height. You also have quite deep valve pockets, by necessity for off the shelf applications, but less than desireable. I prefer to start with less rather than more pocket depth, milling to suit the cam lift and lifter type. A deep pocket means more crown height is needed to restore CR, which means ...... a vicious circle. If they were mine, I'd consider decking the block and liners, take a corresponding amount off the piston crown/dome and clean up/remove all the sharp edges. I'd be aiming for 0.028-0.030" squish height, then calculating other clearances from there. I assume you're aiming for around 12:1 CR? Probably not the suggestions you were looking for, but you did ask! Share this post Link to post Share on other sites
huxley309 0 Posted July 13, 2006 (edited) lol no doesn't bother me in the slightest anyway bit difficult now as those pistons are in my engine afterall And running well might i add, the only time ive seen a raised crown so extreme are on the hemi head where it needs the raised crown to improve the squish and cr Maybe a similar thing is going on here where by je were allowing cutouts to take bigger valves thus saving having to machine 2 types of piston but the crown had to be raised to increase cr Peter, yes the car did make 12:1cr but was deemed unsuitable for a road/track car so was dropped to 11.6:1cr and runs fine on sul will be in for a full remap week tuesday all being good Mind they can rattle a bit so do have more clearance than a std piston but not that bad when i had the head off Afaik je are the only company that do off the shelf 85mm pistons for the 1.9mi unless you know of any others? I wonder how much a one off set would cost Im not 100% sure now but i think mattsav reckoned the pistons were very close to the valves but i can be doing taking the head off again and check the clearances Edited July 13, 2006 by huxley309 Share this post Link to post Share on other sites
