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Compression Ratio 

 

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 Post subject: Compression Ratio
Posted: Wed Jan 14, 2009 10:59 am 
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By how much can the CR be increased by shaving the head on my '00 AU Ghia?

 

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Posted: Wed Jan 14, 2009 11:08 am 
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how long is a piece of string?

how much are you going to shave it?

 

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 Post subject: CR
Posted: Wed Jan 14, 2009 1:07 pm 
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Gee, Thanks mate, that's a great help..........!

 

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Posted: Wed Jan 14, 2009 2:17 pm 
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well as preveously asked how much are you planing to take off the head??
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Posted: Wed Jan 14, 2009 2:18 pm 
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Shaving the head isn't a good way to gain compression. If you take off any decent amount you won't have any left for if you do a head gasket and warp it, not to mention messing with your timing (although you can overcome this).

There is a line on your head that shows the most that can be taken off it.

 

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Posted: Wed Jan 14, 2009 2:32 pm 
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Well when I rebuilt the motor in my ef, by both shaving the head AND having the block decked aswell as using an au head gasket, the comp went from 9.3-1 up to around 10.5-1.
At a rough guess, I would think that about .1 per 10 thou of the head??? Any one more knowledgable able/care to comment?? I would ring a head reconditioning place/ engine builder in your area to get some advice. try H.S.D in Moorabbin on 9553 2517 and speak to Eddie or Rodney.

 

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 Post subject: Compression Ratio
Posted: Wed Jan 14, 2009 3:22 pm 
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skidder wrote:
Shaving the head isn't a good way to gain compression. If you take off any decent amount you won't have any left for if you do a head gasket and warp it, not to mention messing with your timing (although you can overcome this).

There is a line on your head that shows the most that can be taken off it.


Thank you my friend. Your response is indeed food for thought and I would now agree that taking metal away from the head may not be an astute move and I certainly would not want to invite engine reliability problems such as warping and failed Head Gaskets.
My reason for posing the question is that I intend to have my car converted to run on Liquid Injected LPG and I have read that, to take best advantage of the precisely timed and measured injection of this fuel, the CR may be increased to a figure approaching 13:1. Immediately I set to cogitating on the prospect of achieving such a figure by the simplest and most economical means however you have certainly given me good reason to tread warily and I thank you for your advice.
I wonder has anyone any anecdotes to share w.r.t. this course of action?

 

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 Post subject: Compression Ratio
Posted: Wed Jan 14, 2009 3:37 pm 
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grub73 wrote:
Well when I rebuilt the motor in my ef, by both shaving the head AND having the block decked aswell as using an au head gasket, the comp went from 9.3-1 up to around 10.5-1.
At a rough guess, I would think that about .1 per 10 thou of the head??? Any one more knowledgable able/care to comment?? I would ring a head reconditioning place/ engine builder in your area to get some advice. try H.S.D in Moorabbin on 9553 2517 and speak to Eddie or Rodney.


Thank you sir, your response is just what I was hoping for. Your friends at H.S.D. may know what is the maximum that may be removed from a stock head and what that may achieve although the gain may not be substantial using your figures as a guidel.

 

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Posted: Wed Jan 14, 2009 9:24 pm 
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Condor60 wrote:
Gee, Thanks mate, that's a great help..........!


at least it's an honest answer.

best thing you can do is pull the head and cc it. measure the thickness of it, work out how much YOUR head can be shaved and then cc it again to that level. Then you will know how long your piece of string is.


grub73 wrote:
At a rough guess, I would think that about .1 per 10 thou of the head??? Any one more knowledgable able/care to comment?


You can't put a number to it. The because of the shape of the chamber, the amount of reduction in CC is reduced at each point.
the first 10thou removed will have more effect then the second 10thou and so on.

 

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Last edited by tickford_6 on Thu Jan 15, 2009 2:27 pm, edited 1 time in total.

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Posted: Thu Jan 15, 2009 5:55 am 
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tickford_6 wrote:
Condor60 wrote:
Gee, Thanks mate, that's a great help..........!


at least it's an honest answer. No! It is neither!
best thing you can do is pull the head and cc it. measure the thickness of it, work out how much YOUR head can be shaved and then cc it again to that level. Then you will know how long your piece of string is.


grub73 wrote:
At a rough guess, I would think that about .1 per 10 thou of the head??? Any one more knowledgable able/care to comment?


You can put a number to it. The because of the shape of the chamber, the amount of reduction in CC is reduced at each point.
the first 10thou removed will have more effect then the second 10thou and so on.

 

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Posted: Thu Jan 15, 2009 11:34 am 
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^^ he means the shape of the chamber is roughly hemispherical, meaning the cross sectional area as you go furher up is smaller. ie an example being it could be 4in across at the bottom of the chamber, then 50thou up it could be 3.5in etc etc (i just made these numbers up as an example).

 

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EVL098 wrote:
Cramping in the hand from having it on your Wang for an excessive period of time is a definate con.
Seriously do people google "f**k up modifications for Fords owned by Jews" and get linked straight to this site nowadays?

AU,factory fitted tickford kit/IRS, t5,Sports ryder/KYB: gone.

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Posted: Fri Jan 16, 2009 2:59 pm 
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skidder wrote:
^^ he means the shape of the chamber is roughly hemispherical, meaning the cross sectional area as you go furher up is smaller. ie an example being it could be 4in across at the bottom of the chamber, then 50thou up it could be 3.5in etc etc (i just made these numbers up as an example).


Thank you, I figured that was what was meant.

 

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