[SPLIT] Compression Ratio

TheHood

TheHood

Member
Won't the higher CR of theses rods / pistons cause knock issues unless the ECU's up to the job of controlling ignition timing precisely enough? notsure.gif
 
OAKMERE

OAKMERE

Regular Member
Re: My Z22SE Engine Build

I will be interested to see if the standard ECU can deal with the extra CR as skimming the head by 1mm would be an easy way to gain a little power on the standard piston rod setup. I seem to remember the ECU can retard ignition but not advance to take advantage of higher octane fuel. dunno..

Cheers Oakmere
 
ATOM X

ATOM X

Senior Member
Re: My Z22SE Engine Build

OAKMERE said:
I will be interested to see if the standard ECU can deal with the extra CR as skimming the head by 1mm would be an easy way to gain a little power on the standard piston rod setup. I seem to remember the ECU can retard ignition but not advance to take advantage of higher octane fuel. dunno..

Cheers Oakmere
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Dear Oakmere
How much do you believe 1mm will raise CR by?
 
OAKMERE

OAKMERE

Regular Member
Re: My Z22SE Engine Build

I think it has been worked out that 1.5mm skim would give a 11:1 C/R and a 1mm skim would give just over 10.5:1 CR. Also some of the upgraded valves give a higher compression ratio.

Cheers Oakmere
 
ATOM X

ATOM X

Senior Member
Re: My Z22SE Engine Build

OAKMERE said:
I think it has been worked out that 1.5mm skim would give a 11:1 C/R and a 1mm skim would give just over 10.5:1 CR. Also some of the ungraded valves give a higher compression ratio.

Cheers Oakmere
Click to expand...
The reason I asked is that I looked like you were suggesting on an earlier post that
removing 1mm would have equaled the same CR as the YH

Irrespective

20thou (0.5mm) will increase the 2.2 by 1/2 cycle raising from 10:1 upto 10.5:1
40thou (1mm) will increase the 2.2 by one cycle raising from 10:1 upto 11:1
60thou (1.5mm) will increase the 2.2 by one and 1/2 cycle raising from 10:1 upto 1!.5:1

60 thou is the max from the head any more and the oiljet is compromised
for additional increase in CR can be acheived through skimming
upto 60 thou from the block face

I am assuming you meant custom pistons not upgraded valves?
 
A

alanoo

Senior Member
Re: My Z22SE Engine Build

Nop valves
The SiValves some of us use are slightly less dished, those give ~0.25 more CR per side (0.5 for exh + inlets)
 
ATOM X

ATOM X

Senior Member
Re: My Z22SE Engine Build

alanoo said:
Nop valves
The SiValves some of us use are slightly less dished, those give ~0.25 more CR per side (0.5 for exh + inlets)
Click to expand...
do you honestly beleive that
that is 3.2cc per cylinder
they must be bloody big valves
because as the math's does not stack up
 
A

alanoo

Senior Member
Re: My Z22SE Engine Build

Didn't check myself

I cc'ed myself the 0.97mm skim for 1 point of CR, but haven't check the valves.
They are definitely are less dished, guess I'll cc some spares asap
 
OAKMERE

OAKMERE

Regular Member
Re: My Z22SE Engine Build

Has anyone taken as much as 1mm off the head with the standard ECU? (I will be getting it mapped after the work is complete) My engine mods will not be untill next year but if I am taking the head off to port and have 1mm+ valves fitted I just thought I might as well get it skimmed as well.

Cheers Oakmere
 
ATOM X

ATOM X

Senior Member
Re: My Z22SE Engine Build

OAKMERE said:
Has anyone taken as much as 1mm off the head with the standard ECU? (I will be getting it mapped after the work is complete) My engine mods will not be untill next year but if I am taking the head off to port and have 1mm+ valves fitted I just thought I might as well get it skimmed as well.

Cheers Oakmere
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Yes I have several times
 
OAKMERE

OAKMERE

Regular Member
Re: My Z22SE Engine Build

ATOM X said:
The whole of page three of this post is a hijack

OAKMERE said:
Has anyone taken as much as 1mm off the head with the standard ECU? (I will be getting it mapped after the work is complete) My engine mods will not be untill next year but if I am taking the head off to port and have 1mm+ valves fitted I just thought I might as well get it skimmed as well.

Cheers Oakmere
Click to expand...


Yes I have several times
Click to expand...

Good to here you didn't have issues. I thought the same about the hijack sorry. I think we should blame The Hood for starting it. :LOL:
 
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