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

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

@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.

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Originally Posted by Bill999

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

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are you running the standard inlet manifold we have built some strong 308s with ported std heads

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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

The air from the snorkel will have to jump quite a gap to get to the air filter!:yaeh am not durnk:

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

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

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

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Originally Posted by csmiffy

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

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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

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Originally Posted by northdude

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

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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

Plop a china turbo on it

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Originally Posted by Tommy

Plop a china turbo on it

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T45 clone with the standard cast manifold but two of the passengers/drivers manifolds depending which side you pick for he turbo and a simple suck thru set up like Buick did 40+ years back would be easy enough with the factory 304 heads and intake

Iv been told the 308 and 304 cast exhaust manifolds are the same so this is very possible that I have most of the pieces needed already.
Buick even used the quadrajet that's currently fitted to my engine. suck thru would simplify the processes by not needing boost compensation/reference power valve too which is nice and I can use the factory 304 intake manifold

Sounds feasible

Using the 304 intake manifold injector holes for methanol injection would be piss easy too and negate the need for an intercooler
Sounds more and more possible the more I think about it

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Originally Posted by Tommy

Plop a china turbo on it

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Surely a VF52 off a subaru would be better than a cheap TD04.

Both would be too small I think
Tdo4s are 1.8l gsr turbos and a subi turbo would be perfect for my 1kz
I'd need to do a twin turbo set up with them to get the 308 cu level of flow required
I had a tdo8 as a teen I can't find that would probably be perfect with a rebuild but I'd say a new Chinese turbo woul be cheaper than bothering and would have the t4 flange which is easy and low cost