CHESTNUTXE 7,260 Posted January 28, 2018 Any idea what the limit would be to mill a 55cc xe head ,like is it possible to take 10cc or more out of it ,im just dabbling with the idea off flat tops instead of 20.5 dish,to get close to 11.1 the head needs around 40cc ,pistons and rings and head gasket ect is gunna be about 500 bucks or mill the head for a cheaper rate but will need shorter pushrods,so cost is about the same but less effort to take the head off. Share this post Link to post Share on other sites
CHESTNUTXE 7,260 Posted January 28, 2018 i just looked at a conversion chart and most seem to think 1cc =0.007inch so it needs about 80 thou off the head to get close to 11.1 is this possible ? Share this post Link to post Share on other sites
ando76 4,354 Posted January 28, 2018 You may want to factor in your piston to valve clearance. Personally I wouldn't hack that much off a crossy head. 1 CHESTNUTXE reacted to this Share this post Link to post Share on other sites
bear351c 10,260 Posted January 28, 2018 11 hours ago, ando76 said: You may want to factor in your piston to valve clearance. Personally I wouldn't hack that much off a crossy head. Yep, what he said. With a high lift cam, etc...may need eyebrows cut in the pistons. 1 CHESTNUTXE reacted to this Share this post Link to post Share on other sites
CHESTNUTXE 7,260 Posted January 28, 2018 what im trying to get around is if flat tops isnt it the same ? reducing the space ? Share this post Link to post Share on other sites
bear351c 10,260 Posted January 28, 2018 Yep, it's basically the same, but, the combustion area is shaped differently, all the combustion with flat tops, is done in the head cavity. Don't know how that would affect a Crossy, Slydog would prob be the best fella to answer this. Obviously pulling the head off would be easier than engine out, and piston swap. 2mm is a fair chunk off alloy to remove, and it's bit harder to put it back. Can use copper head gaskets, (Cometic ? I think) but they're pricey. And any head swap in the future will need the same machining, as the original. 1 CHESTNUTXE reacted to this Share this post Link to post Share on other sites
gerg 10,871 Posted January 28, 2018 Skimming the head on a quench type combustion chamber needs more meat off than an open chamber, as part of the bore area is already flat so is not included in the CC calculation. Every head design is different but for a closed chamber clevo, 5 thou off removes 1CC of chamber. I should imagine crossys to be similar since although the bore is smaller, the quench area is proportionally less than on a clevo.Another very important aspect is quench distance. If your pisons are down the hole, no amount of head machining will fix the poor quench that results, regardless of how high your compression is.Example: If i had my time over again, the clevo would've copped a set of proper zero-deck pistons instead of the Hypertec rebuilders, which sit down the hole too far. Either that or skim the block to get to zero. I ended up taking 0.025" off the heads to get to a bit over 10:1. If I'd have taken the meat off the deck instead, it would have only needed 0.015" to achieve the same cc, with improved quench.Best quench distance is generally said to be 0.040", which happens to be the thickness of a standard head gasket. People do go thinner than this but are pushing the envelope for kissing the head with the piston top.Sent from my CPH1607 using Tapatalk 3 slydog, CHESTNUTXE and stockesp reacted to this Share this post Link to post Share on other sites
CHESTNUTXE 7,260 Posted January 28, 2018 Im at 0.005 deck Share this post Link to post Share on other sites
slydog 7,873 Posted January 29, 2018 Gerg is on the money pretty well. Next thing that may be interesting is my current head has had the chamber opened out a far bit (thanks to previous head porters) and as such quench area is huge but running flat tops with a zero deck helps this along with a low cranking psi. Engines rattle on the torque peak more often then they do @ hp peak. Next thing is my block was decked 45th or so to get zero deck with the slugs use. Next is my cyl head is all but flat on the indicator and as yet both have given me zero issues from doing such. Food for thought. Share this post Link to post Share on other sites
CHESTNUTXE 7,260 Posted January 29, 2018 so yes or no for milling a heap off the head with dish pistons ? while on the subjevt i saw a keith black 1120 piston to suit usa 200 engine,with a smaller dish but the comp height is smaller does anyone no the dish size it says .085 ? Share this post Link to post Share on other sites
ando76 4,354 Posted January 29, 2018 Well I guess the answer to that is, what is your current piston to valve clearance? Minus what you intend to cut off the head and is that going to cause piston to valve issues. 1 CHESTNUTXE reacted to this Share this post Link to post Share on other sites
CHESTNUTXE 7,260 Posted January 29, 2018 i will ask the bloke who did the machine work,what is min 080 ? Share this post Link to post Share on other sites
ando76 4,354 Posted January 29, 2018 Ask old mate. Every engine builder has their own thoughts on this. 1 CHESTNUTXE reacted to this Share this post Link to post Share on other sites
deankxf 20,231 Posted January 29, 2018 one of the negatives would surely be needing new pushrods(custom length?) Share this post Link to post Share on other sites
CHESTNUTXE 7,260 Posted January 29, 2018 i could have had the motor out by now and stripped lol and orderd flatties Share this post Link to post Share on other sites
slydog 7,873 Posted January 29, 2018 8 hours ago, deankdx said: one of the negatives would surely be needing new pushrods(custom length?) Trend Comp and Trik Flow do em in heaps of lengths to suit BBC which is xflow size funny enough 2 gerg and deankxf reacted to this Share this post Link to post Share on other sites
CHESTNUTXE 7,260 Posted January 29, 2018 i have trend in mine Share this post Link to post Share on other sites