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Discussion Starter · #1 ·
Hey guys i recently picked up a set of
JE .20 pistons,
JE rings
CROWER rods

I have a 2.0mm hks headgasket on there and the head has already been ported and polished.
would it be advised that I change my 2.0 to a 1.0 for higher compression?

The guy at the machine shop syas that he wants to get around 9.5:1 compression from the car and the 1.0 will help and he plans to deck the block aswell.
the stock compression i belive is 8.5:1
How likely is it that i will detonate?

I just thought I'd get some opinions on the situation before i went ahead with it all.

Thanks guys
 

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you wont be able to run as much boost on pump gas as before but you will ahve faster spool times and better power before boost

to max your turbo your gonna need race gas 100 ocatne or better

Bill
 

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why would you want to increase cr? with upgraded pistons and rods, lower the cr and cram more air in...
 

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As MotoFool sad, you would have better response but will be limited to maximun pressure that you can run.
Unless you would use AEM PEMS or other standalone with knock detection I would go with the stock compression or lower.
To play with CR like that you better be able to control timing good =)
 

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Well, there are differing opinions of course, but I am of the opinion that you should not use headgaskets to change CR. Headgaskets should be selected that give you the proper squish or quench area. Deck height, piston pin location, rod length, piston dish, head cc, etc. are things that s/b changed if a lower CR is desired.

Dale H
87T
 
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What kind of turbo are you going to run? Stock rods are good for 500+rwhp, so how much power do you plan on making?

Like it has been stated before, I wouldnt go fucking around with the compression ratio too much...
 

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use an online compression calculator to calculate your compression ratio. make sure it takes into account all aspects of the engine, not just general measurements. Good luck!
 

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the 2.0mm headgasket is way thicker then stock

the better gasket would be the 1.0mm gasket

if you not going above 600horse which i doubt the compression ratio and detonation should not be *that* big a deal

i would recomend looking into a j&s safeguard system..

Bill

if your going higher compression i would not mill more then 40thou total head and block with the 1.0mm gasket.

unless you like replaceing valves
 

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Faded87T said:
Well, there are differing opinions of course, but I am of the opinion that you should not use headgaskets to change CR. Headgaskets should be selected that give you the proper squish or quench area. Deck height, piston pin location, rod length, piston dish, head cc, etc. are things that s/b changed if a lower CR is desired.

Dale H
87T
Agreed.
 

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I would take some measurements and see where you are. Every engine will be different. Depending on the how far the crank sits in the block, how the rods fit to the crank, general production differences in rods, pistons, blocks, etc. etc. etc. etc., will all give each engine its own unique measurements. There are a few key measurements you need to know, to properly build an engine. One is deck height. Assemble your engine and measure the distance from the piston at TDC to the block deck. This is your deck height and can either be positive or negative (the piston can either sit above or below the deck). This figure + the thickness of your HG will give you your quench or squish area. Generally speaking, a squish of .04 is on the "tight" side and nearing the danger zone (i.e., piston smacking the head at high rpms), and anything much over .06 and the benefits of squish (squish helps to prevent detonation) get reduced significantly. So depending on your deck height and the amount of squish you want to run will determine what thickness HG you should use.

Once a HG is selected, determine the CC of your head and piston and do the math to determine your CR. If it is not what you want, then you can change other things the get the CR you want (headwork for more CC, a headgasket w/ a different diameter, piston pin location, piston dish, rod length, etc. etc.).

This is just one backyard mechanic's opinion.

Good Luck
 

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Discussion Starter · #13 ·
Faded87T said:
Well, there are differing opinions of course, but I am of the opinion that you should not use headgaskets to change CR. Headgaskets should be selected that give you the proper squish or quench area. Deck height, piston pin location, rod length, piston dish, head cc, etc. are things that s/b changed if a lower CR is desired.

Dale H
87T
Well the head has been ported and polished, the blcok will be decked

so hes dodint hat to lower the compression
but he still reccomends the 1.0mm gasket

i guess what im kinda asking is that if it woudl be "safe" for me to ahve a comprssion liek 9.5:1

Engraged- are you saying i should keep compresion low and run more boost??
 

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Naw, 9.5:1 is even too crazy for me. My current setup is at 9.4:1 and i'm pretty much maxxing out the stock ct at 15~ psi

Put in a 1.5mm GReddy HG, should get your C/R down to 9.1:1 or so.

Then it will be fun.
 

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there is not much difference between 9.0:1 and 9.5:1 maybe .5 psi? that you couldn't run?

if your car has a afc and you can tune it or anything better then a afc then you should have no worries..

id suggest some type of boost retard or j&s safe guard system though

Bill

btw decking the block DOES NOT LOWER COMPRESSION it Raises it!
 

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Faded87T said:
I would take some measurements and see where you are. Every engine will be different. Depending on the how far the crank sits in the block, how the rods fit to the crank, general production differences in rods, pistons, blocks, etc. etc. etc. etc., will all give each engine its own unique measurements. There are a few key measurements you need to know, to properly build an engine. One is deck height. Assemble your engine and measure the distance from the piston at TDC to the block deck. This is your deck height and can either be positive or negative (the piston can either sit above or below the deck). This figure + the thickness of your HG will give you your quench or squish area. Generally speaking, a squish of .04 is on the "tight" side and nearing the danger zone (i.e., piston smacking the head at high rpms), and anything much over .06 and the benefits of squish (squish helps to prevent detonation) get reduced significantly. So depending on your deck height and the amount of squish you want to run will determine what thickness HG you should use.

Once a HG is selected, determine the CC of your head and piston and do the math to determine your CR. If it is not what you want, then you can change other things the get the CR you want (headwork for more CC, a headgasket w/ a different diameter, piston pin location, piston dish, rod length, etc. etc.).

This is just one backyard mechanic's opinion.

Good Luck
I couldnt agree more. 1mm will make a big difference in calculation, especially when considering that the bore of a MHG is bigger than that of a stock HG. Take the time, do the measurements, do it right.
 

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U should keep the same ratio.. I'm a little higher then 8.5:1 due to the hks 1.2 mm gasket and my head being milled.
 
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