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Head Shave for more compression Straight Gas EF 

 

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 Post subject: Head Shave for more compression Straight Gas EF
Posted: Tue Jan 01, 2008 7:30 pm 
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How much can you take off EF cylinder heads? Is 2mm ok?
I am about to replace my head gasket (Genuine Ford AU gasket & bolts). I would like to machine some off the head to raise the compression. I'm running straight gas & I would like at least 10.5:1.

Does anybody know how much they usually charge for just machining the head gasket surface?

My car has done 250,000km and it's leaking coolant out the side of the head gasket under the header.
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Posted: Tue Jan 01, 2008 8:21 pm 
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2mm you might be able to run diesel instead of LPG. A skim should not set you back much (<$100) and the AU gasket will add a few points to the compression as well.

 

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Posted: Tue Jan 01, 2008 8:45 pm 
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Ask the shop you get to do the work, but remember that when you up compression you will put strain on the rest of the 250,000km motor, probably blow rings :(

 

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Posted: Tue Jan 01, 2008 9:06 pm 
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E-Gas engines have 10.7:1 stock.
I just want to run about the same.
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Posted: Tue Jan 01, 2008 9:08 pm 
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twason wrote:
the AU gasket will add a few points to the compression as well.


can you be more specific?? how much does it change it by exactly?
What is the difference in thickness between the stock ef-el gasket & the genuine AU?
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Posted: Tue Jan 01, 2008 11:32 pm 
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luke111 wrote:
twason wrote:
the AU gasket will add a few points to the compression as well.


can you be more specific?? how much does it change it by exactly?
What is the difference in thickness between the stock ef-el gasket & the genuine AU?
do the calcs,measure the head dome in ccs,gasket and swept bore,piston to deck.then you can shave head,or plan something different.to get my vn to 10.5/1 comp. i had to change pistons,take 2mm off the block,both banks, then 1mm off the heads=3mm,the heads cant take more than 1mm,thats how i got it----8.5 to 10.5/1,do your home work.doing 302 heads now.

 

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Posted: Fri Jan 04, 2008 1:48 pm 
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I once bought a vehicle with a 350chev that was built for straight gas but it had a pinging problem and i think the compression was too high, though i never found out for sure. It might have been say 12 or 13:1, but i really don't know. I somehow did heaps of cheap kays with it and it was great but the pinging was a curse.

It wasn't getting hot, the timing and ignition curve was fiddled with heaps, etc, etc, but the pinging came in and out, often seemingly due to LPG quality. Wind back the timing to stop all pinging and it wasn't very powerful. It ran very efficiently though, i was told it had low CO2, or was that O2, i can't remember.

 

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Posted: Wed Jan 09, 2008 5:58 pm 
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whats a suitable amount to take off a straight gas head i want to do this to my au gas as it only has 9:7:1 or something same as petrol engine.
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Posted: Wed Feb 13, 2008 8:46 pm 
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Can anyone please help me out?
Im pulling the head off this weekend.
Is 2mm ok to take off??
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Posted: Thu Feb 14, 2008 8:40 am 
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you will have chain probs if you take too much off, the tensioner can only take up so much slack.
If you want more compression, then your far better off using a 3.9 head, or different pistons.
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Posted: Thu Feb 14, 2008 9:13 am 
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luke111 wrote:
Can anyone please help me out?
Im pulling the head off this weekend.
Is 2mm ok to take off??


do you know if the head has been machined before?
2mm is a lot to take off.
thats about 80 thou.
plus the difference of the gasket thickness..
i wouldnt take more than 1mm off
and you dont know how much alloy has coroded inside the water jackets
then you also have to worrie about keeping the tension on the cam chain..as 66coupe said
there could be problems??

also we are talking about a used engine and you might be able to raise the comp a bit but if the bottom end has a few kms on it you may just cause it to create more compression blow bye.

otherwise hunt down a 3.9 head use your cam and that may give you a similar result and you wont have to worrie about clearence differences and then you shouldnt have to worrie about the cam chain tension..
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Posted: Wed Feb 20, 2008 11:13 pm 
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how much will comp go up with the 3.9L head?

sounds like a good idea.
is the combustion chamber smaller in the 3.9l head?
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Posted: Wed Feb 20, 2008 11:33 pm 
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sorry to hijack the thread,

my ED had the head shaved 55 thou due to being warped from head gasket failure, plus an AU gasket has been put in.

what would my Comp Ratio be around?

rest of motor is standard.

 

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Posted: Thu Feb 21, 2008 9:03 am 
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luke111 wrote:
how much will comp go up with the 3.9L head?

sounds like a good idea.
is the combustion chamber smaller in the 3.9l head?


afaik the 3.9 head has a significantly smaller chamber and also has a swirl ridge that the other heads dont have which also takes up chamber space..

its hard to say how much it will raise the compression unless you can measure the cc of the 3.9 head and chamber..

a mate of mine put a 3.9 head on his nc fairlane but we never measured the compression it was just a head we through on to get the car going after blown head gasket..

and it did go better after the change how much was questionable but noticable.. it never really had any probs with pinging or anything so i would say it probably raised the comp but it didnt raise it to the point of detonation...
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