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madmax
Fordmods - Getting Side Ways
Age:45
Posts: 3748
Joined: 18 Nov 2004
Location: Skye VIC, Australia
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 Posted: Sun Feb 06, 2005 6:16 pm Post subject: |
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| Lukieman wrote: | Are the engine blocks for the 3.9 and 4 litres the same!?!??! If so, then the head on a 4 litre is bigger (the extra 100cc) then wouldn't that decrease the compression ratio...
Once agian, it is to my understanding that the engine volume is taken by the displacement in the block and not the head. |
As said capacity is measured in the block bore x stroke, the head has nothing to do with capacity, as you pointed out it does have everything to do with compression. By the way it not 100cc more like 35cc. The 3.9 is about 3.930(rounded down to 3.9) the 4.0 is about 3.965 rounded up to 4.0. These figures may not be exact but they are close. (personally I think this is Ford playing with maketing figures).
Hope this clears it up for you |
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Epitome
Fordmods Stock as a Rock
Age:36
Posts: 196
Joined: 05 Nov 2004
Location: Manjimup WA, Australia
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| Posted: Sun Feb 06, 2005 6:37 pm Post subject: |
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| Lukieman wrote: | Are the engine blocks for the 3.9 and 4 litres the same!?!??! If so, then the head on a 4 litre is bigger (the extra 100cc) then wouldn't that decrease the compression ratio...
Once agian, it is to my understanding that the engine volume is taken by the displacement in the block and not the head. |
Yes. the displacement is from the bore and stroke. The head chamber volume is not a factor in that calculation. It is a factor when calculating comp ratio, though.
The 4.0 has 35cc more than the 3.9 (3984cc compared to 3949cc), but this is nothing to do with the head. The bore is a "hair" larger. |
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madmax
Fordmods - Getting Side Ways
Age:45
Posts: 3748
Joined: 18 Nov 2004
Location: Skye VIC, Australia
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| Posted: Sun Feb 06, 2005 6:41 pm Post subject: |
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| Epitome wrote: | | The 4.0 has 35cc more than the 3.9 (3984cc compared to 3949cc), but this is nothing to do with the head. The bore is a "hair" larger. |
Thanks for clearing up the capacities, I knew it was only 35cc, just couldn't remember the exact sizes for each. (I was close) |
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madmax
Fordmods - Getting Side Ways
Age:45
Posts: 3748
Joined: 18 Nov 2004
Location: Skye VIC, Australia
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| Posted: Sun Feb 06, 2005 6:42 pm Post subject: |
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| Quote: | | 3984cc compared to 3949cc |
I was close! |
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Defective
Fordmods Newbie
Age:24
Posts: 13
Joined: 27 Nov 2004
Location: Melbourne VIC, Australia
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| Posted: Mon Feb 07, 2005 12:33 am Post subject: |
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Go have a talk to a head specialist, because the ones I’ve talked too all seem to think the extra 84cc comes from the head. As far as I know the blocks are similar but there is a difference in pistons and in water jacket. I’ve also been told that you can not put a 4L head onto a 3.9L block due to the difference in pistons and compression as it ends up being too high, but so far only one mechanic (not head specialist) has told me that so I'm not too sure, never looked into it as I have a 4L block. Right now I’m only as good as the information I’ve been told, and if I’m wrong I’m wrong.
Now we are getting off subject here anyways, the original post was about fitting a 4L EF/EL head to a 4L EB II block and what would the compression be like. As far as I know the difference in compression came from the head between those models. I have fitted an EF head to my EB II block and ill tell you what it was worth the cost. I did have a little extra done to the head and if you’re not planing on going all out wild with head work then the EF head is a great base head to start with. |
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madmax
Fordmods - Getting Side Ways
Age:45
Posts: 3748
Joined: 18 Nov 2004
Location: Skye VIC, Australia
View User Gallery (10)
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| Posted: Mon Feb 07, 2005 9:07 am Post subject: |
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| Defective wrote: | Go have a talk to a head specialist, because the ones I’ve talked too all seem to think the extra 84cc comes from the head. As far as I know the blocks are similar but there is a difference in pistons and in water jacket. I’ve also been told that you can not put a 4L head onto a 3.9L block due to the difference in pistons and compression as it ends up being too high, but so far only one mechanic (not head specialist) has told me that so I'm not too sure, never looked into it as I have a 4L block. Right now I’m only as good as the information I’ve been told, and if I’m wrong I’m wrong.
Now we are getting off subject here anyways, the original post was about fitting a 4L EF/EL head to a 4L EB II block and what would the compression be like. As far as I know the difference in compression came from the head between those models. I have fitted an EF head to my EB II block and ill tell you what it was worth the cost. I did have a little extra done to the head and if you’re not planing on going all out wild with head work then the EF head is a great base head to start with. |
Capacity always comes from the block, bore and stroke.
The head specialist may have been refering to where the extra power gains came from, as most of the improvements where in the head and induction area. The 4.0lt engine was slightly bored out, but only by 35cc not 84
As for putting a 3.9 head on a 4.0 block, you may be right, you may end up with too higher compression. The only way to tell is to cc the head ie measure the capacity of the combustion chamber and work out the compression ratio from there. |
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