Gre3D
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| posted on 1/2/17 at 12:14 AM |
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st170 compression boost
hi guys, as explained in my build diary my 4age Toyota has blown to bits and i'm building a 2l st170 at the moment,
i just ported and polished the head somewhat, and tomorrow i'l take it to my engine guy to have the valve seats cut and the head skimmed,
now i'd like to know how much i can skim off the head?
using std. psitons, std camshaft,
i'll be using a megasquirt & itb's and the vvt controller from triggerwheels.
i've got all bolts inside the engine from arp to make sure it doesn't let go like the 4age did 
i've read one guy who says you can skim i t 1mm ( 0,0393701 inch ) without problems but i'd like some people to conform that for me
pleae?
thanks!
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Nickp
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| posted on 1/2/17 at 07:06 AM |
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Few things to consider-
How much are you going to gain from increasing the CR with STD cams?
How will you be 'correcting' the cam timing? With verniers?
Will this decrease your V-P clearance to the point you can't fit hotter cams in future?
What's the CR as STD?
Are you going to calculate (by measuring the chamber volume) how much to remove or rely on interweb 'experts' 
In the past I've decked the block to achieve the desired CR rather than skimming a valuable head within an inch of its life.
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perksy
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| posted on 1/2/17 at 08:23 PM |
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Wot Nickp says above
To be fair if your going to build a nice engine up and want to skim the head it needs the compression ratio calculating
The internet might say '30 thou is fine' but you need to know what you have before you start and also check clearances
Drove a 7 once with a Zetec in it that somebody had "skimmed the head to give it more compression mate" and it pinked and drove
horrible
Ended up with trip to the rollers to get the ignition mapped, Really it should have had the head off and a thicker gasket fitted..
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snapper
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| posted on 1/2/17 at 09:40 PM |
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You can use a thinner head gasket which will cost a little less than a head skim and if you don't like it you can just go back to a standard
gasket
I eat to survive
I drink to forget
I breath to pi55 my ex wife off (and now my ex partner)
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Gre3D
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| posted on 3/2/17 at 09:46 AM |
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ok, thanks guys.
tuner sais he'd take off no more then 0,5mm so i should be fine 
if it would be pinging i think i can just use higher octane fuel or edit the spark map in the megasquirt
but i dont expect to see any problem with a 0,5mm skim
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