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  1. #1
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    Default alloy head for my 308 inboard

    Hi guys,
    since joining this forum just a few months ago, i've been following various performance 308 threads and I've gotta say that I've been bitten by the horsepower bug and I cant wait to get started.

    Like so many others it seems, I already want a bit more power out of my V8 on a limited budget and am looking for ways to go about it.

    From what I can gather, there can be big gains found in a good set of appropriately set up heads. So, here comes my question.......

    Would a set of these alloy VN style heads make much difference to my boat motor and are they even suitable?

    I figure they would be a fair bit lighter so that's a good start already. My current heads are stock cast ones with no porting done that I'm aware of. The rest of the motor is pretty standard too from what I can gather. Maybe a mild cam but that's about it. It's also had a rebuild just 30 hours ago.

    So, whats the verdict? Something I should consider or not? Can I use alloy heads on my boat?

    Here's a link to the ebay page NEW Holden 253 304 308 VN Aluminium Complete Cylinder Heads | eBay

    and a photo

    Cheers

    G

  2. #2
    Do you ever leave? EH179's Avatar
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    A few things to consider before you commit here... Do you currently run VN heads?
    If you don't, you will need to look at manifold, camshaft and exhaust changes as well.
    If you already run VN's, have you thought about modifying them?

    Do some extensive research on the product and the manufacturer, and make an informed decision first and foremost.

    Good luck.

  3. #3
    Do you ever leave? cava454's Avatar
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    Those alloy heads in particular are a piece of shit!!!

  4. #4
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    Forget about those heads, may as well buy magic beans.
    Is your boat a mid mount or a "V" drive ?, your pushing shit uphill (literally) if its a mid mount.
    Get more value from a prop change.

  5. #5
    Do you ever leave? Mickss355's Avatar
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    You can get real good gains from early heads with a pocket port and blending job, mill the heads for some compression, re-work the chambers and a decent hyd cam for very little money - beyond that its gunna cost you some serious coin !
    He who dies with the most toys wins !

  6. #6
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    G'day guys. Thanks for the info so far.

    EH179 - I'm not sure what heads I'm running. I'm pretty new to all of this. Had lots of ski boats but never really worked on them much myself. How do I tell what heads I have?

    CAVA 454 - Yeah I though they might be. Seemed a bit cheap

    HQ 368. It's a mid mount. It goes pretty well now, but you know how it is. Always want just a bit more power. I suspect that never goes away does it? I'm not looking for more top end speed, just a bit more bottom end grunt

    Mickss355. ballpark what would that cost? I'm pulling the motor out next weekend to do a couple of jobs and won't be putting the boat back in the water till Spring so it might be a good time to explore. Would it be a big job to pull the cam out and find out exactly what I have?

  7. #7
    Do you ever leave? Mickss355's Avatar
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    In my experience - if your going to pull the cam out and possibly change it then don't bother wasting time and effort trying to find out what you have unless it is clearly marked.
    I mean if you intend to re use it then you have to make sure that the lifters are kept in order so they can be refitted back in the order they came out.

    380 to 400 hp is very achievable with some port work, enough comp and the right cam.
    At this level you will be getting close to the limits of your stock intake and 650 carbi.
    Hopefully you have a good solid bottom end and don't have to spend any money on it.

    Price - hmm hard to answer - your biggest expense will be the heads, cam and lifters around $400 should cover that.
    You'll have a better idea of direction when you take the heads off and see what kind of pistons you have.
    Last edited by Mickss355; 08-06-2013 at 09:55 PM.
    He who dies with the most toys wins !

  8. #8
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    Mid mount, you'll be doing well to get 60-65 mph and 5000 rpm out of it with a real good set up.
    I think you'll find the a prop a good start if your happy with the rest of it, certainly will lift it out of the water pretty quick and get it on a plane, and throw people out the back of it LOL.
    The Cav plate, if it has one, will also be worth looking at as well.
    You had it on a boat dyno at all ?, probably pick quite a bit up from the tune now thats its on its way to run in and match a prop to suit its graph.
    That was the advice given to me when I started with my first Hallet, best bang for buck I ever spent on a mid mount.

  9. #9
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    Quote Originally Posted by HQ 368 View Post
    Mid mount, you'll be doing well to get 60-65 mph and 5000 rpm out of it with a real good set up.
    I
    The Cav plate, if it has one, will also be worth looking at as well.

    You had it on a boat dyno at all ?,
    50-60mph is all I'd ever want from it. I can bare foot at 40mph so having 10-15mph up my sleeve would be heaps.
    It has a small cav plate where the rudder goes through. It turns down on the side for whatever reason. Not sure how effective it is but I suppose it does a job.
    I haven't had it on a dyno. I'm not sure that there is a boat specific dyno place in Perth or not. Any good dyno place should do eh - if I lift the motor out of the boat?

  10. #10
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    There will be a boat tuner with a dyno there somewhere

  11. #11
    Senior Member Tinman's Avatar
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    Remember it is a boat not a car. Most things you do to the motor to increase the HP will affect you bottom end where you need it with a ski boat. No good if its got nothing until it reaches 2500RPM. Not to mention the dog clutch will not like it either. You need torque not HP. 60mph from a 308 centre mount is a very big ask.
    Cheers Tinman

    Jack of all trades master of none

  12. #12
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    G'day Tinman,
    yeah as I said above somewhere, I'm not after top end speed. Even 45-50mph is enough and i have about that.
    To be perfectly honest, my 4.75m Flightcraft Phantom has all the power it needs for social skiing and even a bit of hooning. It's a freshly built 308 that just needs a bit better tuning.
    For me at the moment it's not about building a race boat or anything like it. It's more about the process of learning about the engine, learning to tune it, learning to fix it and where and if possible learning to extract a few more Hp from it and a bit more torque. "Why?" you might ask. Coz it sounds like fun
    Oh, I've had a faster boat. A Skicraft Interceptor with a 351 Clevland in the back. The "Clevland Express". Went pretty hard but the guy I bought it off was a tight ass and fixed it with the cheapest of cheap. The boat was wired up with cheap crap figure 8 speaker wire. Haha! I sold it back to him. Years ago (way before I had it) it was good for 100mph+ with a worked 351c. I wish I'd had it then

    I've had a couple of nice outboards too....but I'll save that for another day

  13. #13
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    If your engine isn't fresh water cooled, don't even think about alloy heads.
    A dodgey engine swap is not a modified vehicle. The job isn't done till the engineer approves it and the vehicle is registered.

  14. #14
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    Quote Originally Posted by XJS304 View Post
    If your engine isn't fresh water cooled, don't even think about alloy heads.
    Yeah I wondered if that might be an issue. I'm researching prices on converting my boat to closed system cooling. It seems like a good investment

  15. #15
    Senior Member Tinman's Avatar
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    Upward from $1000 and then you have to find somewhere to put it. Generally not much room under the engine cowling.
    Cheers Tinman

    Jack of all trades master of none

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