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Thread: holden 308 VN head conversion

  1. #1
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    holden 308 VN head conversion

    Im toying with the idea of building a second 308 motor up
    I have a early 80s hilux surf with one fitted to it and yesterday I have had a pair of VN heads dropped in my lap

    the two things keeping me from being fully convinced is current factory low compression ratio standard bottom end, Is there any way to up the compression ratio apart from replacing the pistons? decking the block? planing the head?
    how much am I sabotaging the effort If i just run it with the current factory compression?
    im trying to keep it as low cost as I can, the cost of the valley cover inlet manifold is the next hurdle at around a grand for the edelbrock or redline
    Im toying with the idea of chopping the top off a 304 intake and converting it to a top carb set up But I dont have one handy to see if this is possible

    Im semi hoping someone had a miss spent youth tuning these old iron blocks

  2. #2
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    No idea on these specifically, but stroker crank another option for changing compression. Probably least cheap option on the list.

    What's the objective?

    Definitely quad carb down-draught the thing.
    Seem to remember they don't flow that great so a port and polish will help making ponies.
    Quote Originally Posted by 308
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  3. #3
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    yeah stroker kits take them to 355 or higher which is great but that is big $$ territory

    my current motor is running a quadrajet which is 750-800cmf so pretty happy with that flow wise


    I have no objectives mate I just like messing with old junk and making something sort of useful
    and instead of messing with my current fitted motor I was thinking a second one that slots in its place when ready
    I dont "Need" more power in the surf but it will be a good test bed seeing as it will slot straight in


    you are spot on with the poor flowing ability of the 308, hence the head swap as it goes straight on but you need the intake manifold to suit and extractors/exhaust and a cam to match
    the VN heads standard in the 304 flow better than a extremely ported 308 head
    so with a little tickle up the vn heads should be pretty cool old and hopefully cheep engine improvement

  4. #4
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    Low height head gasket (high compression head gasket)?

  5. #5
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    No no, I meant quad carb = Four carbs. Fuel that bitch!
    And it simplifies the plumbing/intake manifold requirements, assuming firing order is sensible.

    and a Supercharger, obviously...

    Muffler shop in town cnr clyde st, does/did reasonable work at reasonable prices if you need extractors and can't/wont weld em yourself.

    Sounds like you've done the numbers... surely there's a forum out there where people have hotted em, should be able to find out how much HPs the big end will take stock.
    Quote Originally Posted by 308
    not smart enough to be useful
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    @Bill999 Can do it yourself!?

    If it was me, I'd positive pressure it! Build a box for the Quadrajet, get 2 cheap turbo's and gates (2nd hand Jap or cheap Chinese) do some plumbing and you could DIY if for FA.
    Tommy and Russian 22. like this.

  7. #7
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    Quote Originally Posted by Bill999 View Post
    yeah stroker kits take them to 355 or higher which is great but that is big $$ territory

    my current motor is running a quadrajet which is 750-800cmf so pretty happy with that flow wise


    I have no objectives mate I just like messing with old junk and making something sort of useful
    and instead of messing with my current fitted motor I was thinking a second one that slots in its place when ready
    I dont "Need" more power in the surf but it will be a good test bed seeing as it will slot straight in


    you are spot on with the poor flowing ability of the 308, hence the head swap as it goes straight on but you need the intake manifold to suit and extractors/exhaust and a cam to match
    the VN heads standard in the 304 flow better than a extremely ported 308 head
    so with a little tickle up the vn heads should be pretty cool old and hopefully cheep engine improvement
    are you running the standard inlet manifold we have built some strong 308s with ported std heads
    22 hornets and most things 6.5

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    It's rough as guts but bit by bit I'm tidying it up
    Electronic ignition conversion has made it run like a gem
    It's had some very questionable running repairs which is a shame as it was certed for the v8 conversion before it was let lapse
    All very standard currently with a quadrajet carb

  9. #9
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    The air from the snorkel will have to jump quite a gap to get to the air filter!
    ‘Many of my bullets have died in vain’

  10. #10
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    yeah my favorite mod is the wood wedge that is acting like a belt tensioner for the power steering pump

  11. #11
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    Would it not be a shit ton easier to find a short block for the VN heads and rebuild that?
    Trans bolt patterns the same?
    I do realise you would have a spare motor then.
    What is so hard about higher comp pistons? A lot less work then some of the stuff you have mentioned but I suppose they dont require mucking around with the engine in the chassis onto speak.
    Did the same years ago. Put closed chamber 302 clevo heads on my 400. Good for nearly a point of comp and better for pinging too apparently

  12. #12
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    Surely a fresh std 308 would have more than enough power for a hilux

  13. #13
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    Quote Originally Posted by csmiffy View Post
    Would it not be a shit ton easier to find a short block for the VN heads and rebuild that?
    Trans bolt patterns the same?
    I do realise you would have a spare motor then.
    What is so hard about higher comp pistons? A lot less work then some of the stuff you have mentioned but I suppose they dont require mucking around with the engine in the chassis onto speak.
    Did the same years ago. Put closed chamber 302 clevo heads on my 400. Good for nearly a point of comp and better for pinging too apparently
    that is my plan if I can find a low cost 308 kicking around, rebuild on a stand then swap them over once it is up and running, Im ok with a spare motor and a mate has a friend with a few to choose from, there was a short block and complete engine a few weeks back that I missed out on for 400 locally, but now nobody can seem to find it. so likely missed out

    the only problem with Hi comp pistons is they cost lots and im trying not to spend a ton on it
    csmiffy likes this.

  14. #14
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    Quote Originally Posted by northdude View Post
    Surely a fresh std 308 would have more than enough power for a hilux
    yeah but why not? my girlfriend already wont ride in it because it frightens her
    could be the rusty roof and lack of working seatbelts
    mostly this is me wanting to mess with a motor and get some enjoyment out of a power increasing build.
    if it goes as well as im hoping it will ill plonk a std 308 in its place and find a better shell(probably commie) to put the hotted up motor in

  15. #15
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    Plop a china turbo on it
    Bill999 likes this.
    Identify your target beyond all doubt

 

 

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