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| bradders |
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The 3.9's engines actually have a bigger bore than the 4L's but the 4's have a longer stroke. As both engines are almost identical, why don't i use a 4L head and crank and have the 3.9L pistons and barrels? surely that would give higher compression and turn a 3.9/4L hybrid into a 4.2L @ ~10.5:1 compression.
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| Southy |
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ppl are already doing this
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| bradders |
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darn, so it can be done!? Awesome, i was expecting a whole ppl to give me s**t n say its impossible and i'm stupid lol. Any ideas what sort of compressions i'm looking at? What the added Kw's are? how easy/hard is it to do? and any other crutial info i might need to know. Will the standard ECU s**t itself?
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| Southy |
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most people didnt do it for the Change in compression, They just belive the EF/EL/AU heads flow alot better
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| bradders |
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yeah i'm not really talking about the heads. I'm talking about using the crank and con rods from a 4L in a 3.9L and just using the 4L heads because they are better. Really there should'nt be any change in compression from the 3.9L-4L heads. but i'm expecting a larger cc and higher compression by changing the con rods and crank. i just wanted to know if it was possible and can be done. I hav'nt crunched the numbers and i'm hoping someone else has because i don't want to. Maybe a change in crank and con rods could cause a compression of 20:1 which is useless. Or maybe bring it up between 10-11 who knows. maybe not at all. but there should be an increase in cubic capacity and imagine it, lumpy cam effectivly "stroked" 3.9 >>> 4.2 along with pacies and lukey that'll cain!
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| bradders |
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I'd probably use an AU (i guess series III) head if any head or an EB II head. I belive they are the strongest, and VCT is pretty handy too. I belive the EB II is better cast than any of the others although it is a fair bit older now. chances are, if i was serious i would get it ported any way.
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| stockstandard |
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...or just use 40 thou over pistons when you rebuild the 4.0 and take a few thou of the head.
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| jim3964 |
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If around 10.5 would be ideal LPG motor, couldnt run ulp unless you used premium and even that compression might be too high, might ping a bit and the ecu would retard it, so you wouldnt get any power benefit...... well thats if theory anyway
_________________ 98 AU Falcon Futura I6 ABS & Cruise stock (The Wifes car
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| MARK.TANIA |
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there is a bloke here in orange he has done it it is the ea/ed block bored 60 thu ef crank /rods all balanced /tic head /full port job/big cam.it is in his speedway car .and the fcker screams.
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| bradders |
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i bet
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| opto |
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bradders wrote: The 3.9's engines actually have a bigger bore than the 4L's but the 4's have a longer stroke. As both engines are almost identical, why don't i use a 4L head and crank and have the 3.9L pistons and barrels? surely that would give higher compression and turn a 3.9/4L hybrid into a 4.2L @ ~10.5:1 compression.
Wouldn't it be cheaper just to get the head ported and shaved to get a higher compression ????
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| bradders |
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a good port n polish is pretty expensive. a longer stroke (4L stroke) with a wider bore (3.9L) would not only crank up teh comression, but it would increase the cc. i'm guessing to 4.2
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| stockstandard |
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bradders wrote: a good port n polish is pretty expensive. a longer stroke (4L stroke) with a wider bore (3.9L) would not only crank up teh comression, but it would increase the cc. i'm guessing to 4.2
The increase in bore width is bugger all - most rebuilt 4.0's would be running the same size. The small increase is capacity will hardly be noticable. A port and polish is about $400-500
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| bradders |
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the but the four litres have a smaller bore. you really think it'll be that small?
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| stockstandard |
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bradders wrote: the but the four litres have a smaller bore. you really think it'll be that small?
Thought that this didnt sound right. Just checking the numbers - 3.9 bore is 91.9 and stroke is 99.3 4.0 bore is 92.3 and stroke is 99.3
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