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Lower Compression for Turbo 

 

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 Post subject: Lower Compression for Turbo
Posted: Tue Apr 18, 2006 2:04 pm 
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hey guys, got a couple of question on turbo-ing for those in the know. as far as turbo-ing an EB I6 (not after huge power figures) do i need to lower the compression? or more to the point, at what boost/figures would people recomend the compression be lowered, and to what?

then the next question is how to go about it? i'm trying to do this on the cheap so i'd like to avoid changing rods and pistons and try for a decompression plate (if such a thing exists for the falcons). then does the decompression plate need a head gasket either side of it, on one side or not at all? prices for such as thing would be appreciated 8-)

thanks guys

 

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Posted: Tue Apr 18, 2006 8:44 pm 
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the EB only had 8.8:1 compression, there is no real need to lower it any further.

infact if your only after a mild setup it might pay off to raise it a little up to 9:1 higher compression will bring the power up everywhere and should be more feul efficient........

an AU headgasket and i light skim to get the head flat should see you there.

 

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Posted: Wed Apr 19, 2006 12:42 am 
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i thought it was only the 3.9 that had 8.8 comp, arent the 4l 9.2??

 

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Posted: Wed Apr 19, 2006 12:46 am 
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just put a thicker head gasket on......... duno how much it will lower it tho
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Posted: Wed Apr 19, 2006 2:12 am 
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ebs_4l wrote:
i thought it was only the 3.9 that had 8.8 comp, arent the 4l 9.2??


All pre-EF non-XR's have 8.8

 

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Posted: Wed Apr 19, 2006 2:49 am 
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and here i was thinking i had 9.0:1

i think i may have blown a head gasket yesterday but getting water thru my engine (funny story) so if i have to replace it then i'll use an AU one for sure...

 

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Posted: Wed Apr 19, 2006 10:34 pm 
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Just leave it stock if your not chasing big power... no point making extra work for whats going to be a big job anyway.
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Posted: Wed Apr 19, 2006 11:30 pm 
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Slabz wrote:
and here i was thinking i had 9.0:1

i think i may have blown a head gasket yesterday but getting water thru my engine (funny story) so if i have to replace it then i'll use an AU one for sure...




if you have to take the head off to fix an already blown gasket, you have a little thinking to do.

being an EB you posibly have the head with the swirl ridge (detonation ridge)

not sure when ford stoped using that. if you do and the head is comming off i'd recomend having the machine shop remove the ridge completly and while he's there have him de-shroud the valves.

that will drop your compression and improve flow straight away as well as lessening the chances of knock. though it may drop the compression to much.
when you put the head back on use an AU gasket as it will stand up to boost better and bring the head closser to the pistons this will give tighter squish and again lessen the chances of knock.

it all comes down to what you want out of this engine,
remember anyone can shove a bit of boost in and make some power, but the guy who sits down works out exactly what he wants and plans for it will get a better end result

 

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Posted: Thu Apr 20, 2006 2:44 am 
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can you explain the swuirl ridge or give some pics because i've already had the head off once and if i do it again i wanna know what to look for...

 

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Posted: Fri Apr 21, 2006 10:40 pm 
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That swirl ridge was on 3.9 engines...Up to EB 1...

 

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Last edited by EBXR8380 on Sun Jul 02, 2006 2:47 am, edited 1 time in total.

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Posted: Sat Apr 22, 2006 11:44 am 
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this is the swirl ridge

 

 

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Posted: Sat Apr 22, 2006 9:01 pm 
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thanks falcon 6... from memory (which may or may not be reliable) i'm pretty sure i dont have it...

 

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Posted: Sat Apr 29, 2006 12:56 am 
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what is the point of that swirl ridge thing?..
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Posted: Sat Apr 29, 2006 12:52 pm 
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at a random guess, i'd say it is meant to help "swirl" the gases to get more complete combustion or possibly to help gases enter or exit the chamber...

 

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Posted: Sat Apr 29, 2006 1:41 pm 
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tickford_6 wrote:
this is the swirl ridge


yay, my cylinder head is famous. :)

 

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