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GT40 all the things!
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Discussion Starter #1
I've searched but can't really find what I am looking for. How much can you take off the head? I am looking for 11.5-12:1 CR, but then I'll use an SVT gasket to drop it back down a half point. Can this be accoplished with just the head? I am hoping to not have to purchase high compression pistons, or touch the block.

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Hatch Nation #136
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I know that the block is a zero deck block, so you definitely don't want to mess with that.
 

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You will need pistons for that kind of CR by milling you may see .3
 

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GT40 all the things!
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Discussion Starter #4
I'm sure I can mill off more than .03"

I remember reading a thread a year or 2 ago where Pete (illinipo) gave some good info, but dammed if I can find it now.
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I'm sure I can mill off more than .03"

I remember reading a thread a year or 2 ago where Pete (illinipo) gave some good info, but dammed if I can find it now.
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Yes you can mill more than that what I was trying to say I dont think you will raise your CR more than .3 by milling it.
 

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GT40 all the things!
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Discussion Starter #6
Thats the first I've heard that.
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I may be wrong though
 

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Shot me 3 deer!!!
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well, to get to your target, you MAY need the pistons. i'm not sure how far you can go. but i dont even think .080" gets you to 11:1 on the zetec. after that, the piston valve reliefs will be a problem or could be. i don't know if anyone has done the measurements. but for that kind of compression on a stock block, i just don't know if you'll have the clearance.
 

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GT40 all the things!
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Discussion Starter #9
The problem is, is if I swap 9:1 pistons onto my SVT rods I'll gain .040" which is good, but I am wanting to leave the block in the car while building it. If I swap pistons, I'll want to bore it over. I am hoping to save the cash on pistons if at all possible since I won't NEED them for the power I'll be making.

I've heard of people decking the block .010" though. That might be more trouble than its worth.
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GT40 all the things!
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Discussion Starter #10
Sorry I worded that wrong. SVT rods are .040" longer.

But that got me thinking. I may be able to swap my stock pistons onto the SVT rods and gain that .040". Then use a cosmetic gasket to clear piston/head contact.
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If you mill the head much, your valves WILL be seeing some pistons. You have a little bit or clearance, but not much.

FYI, my block is 11.75:1 and I needed custom pistons.
Unless you want to run race gas 100% of the time, you'll need to stay BELOW 12:1 IF you have cams, with stock cams, you'll need to stay below 11.5:1
 

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Discussion Starter #12
ZX2 cams and E85. I'm shooting for 11.5:1, but if I can get closer to 12 that would be better. 11:1 is the minimum. I plan on running an SVT gasket at first and if there is no problems, then swap to a standard Zetec gasket.
 

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C2H5OH
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The compression limitations don't apply to him as much as it does for you guys.

The zetec head can be milled up to 0.125" and the SVT head can be milled up to 0.073" by my measurements.


And I posted the milling vs compression thread, which might be why you couldn't find it --> http://www.focusfanatics.com/forum/showthread.php?t=199568
 

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Discussion Starter #14
Thanks Jon. Glad you chimed in here. Does that include valve/piston contact, or is that just where the head is no longer usable?
 

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C2H5OH
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That is shaved to the valve seat.
I don't know where the valve contacts the piston. But the ZX2 guys have shaved a ton and not bent valves. Sure the engine is interference, but as long at it's in time you'll be fine.

For instance I'm shaved 0.045" and have 60* on the cam where I don't contact the piston. So I can't imagine a smaller stock zetec valve and less lift being that big of an issue.
 

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GT40 all the things!
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Discussion Starter #16
Right on. Looks like I need to experiment with some clay on the pistons. Thanks.
 

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C2H5OH
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My #'s are metric, his are standard ... keep that in mind. Along with mine being math based only.

The "Every .0075" is one tenth of a point of compression (.1)." I believe was just a ballpark figure from the hotrodder days. It may not be accurate for all engines simply because the shape of the CC is different on each, and when you shave material off the total CC volume will vary.
 

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I milled my FR head .050. Im pretty sure iv seen some one mill theirs .080 with out problems.
 

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I prefer to just change pistons that way I cant screw up and bend a bunch of valves [giddy]
 
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