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Head resurfacing and comp ratio's 

 

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 Post subject: Head resurfacing and comp ratio's
Posted: Mon Apr 30, 2007 2:11 pm 
Getting Side Ways
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Hey all, This question may be impossible to answer but any opinions are welcome.

I have twice in the history of my engine blown a head gasket and both times the head was resurfaced.

The 2nd time the mechanic mentioned my comp ratio would be up a little..

I know without more info on the state of the head its hard to tell, but any guesses on how much they would have shaved back?

 

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Posted: Mon Apr 30, 2007 8:17 pm 
Parts Gopher
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Depends how bad the head was warped or out of flat. Hopefully any serious corrosion would have been repaired before surface grinding.
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Posted: Mon Apr 30, 2007 8:20 pm 
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would be something between 5 and 20thou

 

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Posted: Mon Apr 30, 2007 8:45 pm 
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What kind of equip is required to measure the comp ratio?

 

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Posted: Mon Apr 30, 2007 8:57 pm 
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Even taking 20thou off will hardly make any significant difference. You will know if it labours using lower grade fuel. You may have to run premium full time to compensate.

 

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Posted: Mon Apr 30, 2007 9:04 pm 
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my ef xr6 that i had used to ping on anything less than 98 octane after i had the head done. the mechanic made the comment that it was quite warped and had to be faced quite a bit.

you could face a similar situation depending on how much its been faced.

 

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Posted: Mon Apr 30, 2007 9:32 pm 
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kwaussiekid wrote:
Even taking 20thou off will hardly make any significant difference. You will know if it labours using lower grade fuel. You may have to run premium full time to compensate.


I always run premium and lpg. I considered putting some regular in to see what happens though.

 

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Posted: Tue May 01, 2007 9:38 pm 
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Bug wrote:
What kind of equip is required to measure the comp ratio?


to do it properly would mean you'd have to take the head off again.

you could have a compression test done and compare it to stock spec.
That would give you a rough idea as to the change. but you probably find all it has done is make up for the lost compression from engine wear

 

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