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decomping a 4L 

 

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 Post subject: decomping a 4L
Posted: Tue May 15, 2007 7:44 pm 
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im turboing my ef and im trying to decompess it with out using a plate or getting specially ground forgies. ive been down to my local performance shop and has recommended that i hav a bit meat taken out of the pistons itself (because there only 6 months old) and to use a thicker mls headgasket. has anyone ever heard of grounding out the bowl in the tops of pistons for decompressing???
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Posted: Tue May 15, 2007 9:20 pm 
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you'd be far better off removing metal from the chambers in the head.
you can pick a some flow while you're at it to.

basic unshrouding of the valves and releaving the chamber back where it gets close to the valves wiill pick some low lift flow and lower the compression at the same time.

I used to have a pic to explain what i'm talking about but i can't seem to find it. if some one has a pic of a chamber without the swirl ridged i'll draw on what i'm talking about

 

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 Post subject: Re: decomping a 4L
Posted: Tue May 15, 2007 9:49 pm 
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Last edited by dynowog on Mon May 21, 2007 9:22 pm, edited 1 time in total.

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Posted: Wed May 16, 2007 12:55 am 
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Its timing control you requre, something thats boost refrenced...
http://www.msdignition.com/ignition_7_6462.htm
Maybe ???
Timing is 90% the cause of detonation....

 

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Posted: Sun May 20, 2007 9:06 pm 
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yeah thanks, everyone says to take it out of the head aswell. turn it into sort of a hemisphere. dunno about the timing tho, retarding it wud lose power wudnt i (well if u dnt hav a vernier cam gear) , i'll stick with lowering the comp ratio and upping the boost, mite even get it ported a bit more while its there.

thanks lads
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Posted: Sun May 20, 2007 9:09 pm 
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and no i dnt kno about shaving meat of pistons but the performance shop i went to which has top fuel drag cars does mate. but yeah thanks, the head is the go.
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Posted: Mon May 21, 2007 11:38 am 
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Last edited by dynowog on Mon May 21, 2007 9:23 pm, edited 1 time in total.

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Posted: Mon May 21, 2007 12:21 pm 
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Never touch the pistons if you can help it, the head is where I've removed metal from, and DON'T use a thicker gasket unless your going copper and o-ringing, these things blow gaskets as is. If you want something that won't blow easily without going to copper and still want close to standard gasket thickness use two of the steel shim style AU gaskets, which is what I've done. My compression is around the 8.6 or 8.7:1 mark.
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Posted: Mon May 21, 2007 2:18 pm 
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hey mate i was just asking for advice. and there acl race series, not just standard pistons, which also has a thicker crown then standard. also it will hav proper egine managment! what u think im gonna run boost thru it without sum sort of aftermarket ecu attatched to it. next time can u get ur facts straight before u start hating dynowog!!!




Can anyone who is just gonna hate on ppl which hav next to f**k all advice not bother posting please. eg. dynowog
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Posted: Mon May 21, 2007 4:16 pm 
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Last edited by dynowog on Mon May 21, 2007 9:24 pm, edited 1 time in total.

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Posted: Mon May 21, 2007 6:49 pm 
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yeah cant b helped by ppl like you, which has no advice at all, except to b negative for no reason at all. ive done nothing to u at all mate i come to fordmods looking for advice and have ppl like u giving me a hard time. and how were u caring???? i think im a little lost here. sarcastic bullsh*t is caring???
and thats the thing mate u were no help at all. telling me to slap a turbo on a high compression engine, very smart.


id like to thank everyone else who posted for there useful advice.
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Posted: Mon May 21, 2007 8:25 pm 
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you don't need to remove that much from the chamber as to turn it into a sort of hemispherical head.
only a small amount of metal needs to be removed. But if you are getting a shop to do it they would 'CC' the chambers to get the exact size you need (though i would double check with them aswell).

They should also remove the metal to the most benifit to you.
eg: unshrouding the valves and laying back any chamber wall the is 'too close' to the valves (again i would double check with them on that aswell).

You should also be left with a head that has no sharp edges in the chambers.


the biggest problem with decking the pistons, is that you open the the squish/quench clearence (the clearence between the the piston top and the head face at TDC), that can lead to a premature onset of detonation.
you should be aiming for between 35 and 45thou 35thou being ideal.

 

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Posted: Mon May 21, 2007 8:49 pm 
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cool yeah. ive had it ported, but i think its just had the edges smoothed out, its not realy bigger.

thanks heaps
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Posted: Sat May 26, 2007 9:10 pm 
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my acl's were dished out a little, the head was cc'd as well. it's running at 8:1 has been no problem so far. 350rwkw
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Posted: Sun May 27, 2007 2:16 pm 
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i have .135" squish clearance...

 

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