davidburns

Hi i just won this manafold on ebay for 75bucks, its a dual plain alloy intake to suit oldschool pre efi heads, does anyone know if it flows better then the 4brl standed manifold? anyinfo would be great, here is a pic of the mani in question.

ayios

It has the single hole drilled in the middle.
This means its been used on the very early 253 / 308 heads.
If your putting it on later model heads you will have to drill some new holes.
Later model meaning. Commodore VB or even WB onwards. Some one else might want to clear that up.

davidburns

yeah its cool, i got a vh (oringaly blue motor) but i got a red 308 in her now so should be no probem, but i was just wondering on the performance of this manifold?

VAN454

Looks like an aftermarket version of an L34 manifold. You can see that the plenum is open instead of having 4 holes under the carb. This similar to what they did on the early Brock Commodores. It would be a slight improvemnet over a stock manifold.

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THERE'S NO SUBSTITUTE FOR CUBIC INCHES........EXCEPT FOR RACE POWER!!

VAN454

Give it a good clean up and port match it.

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THERE'S NO SUBSTITUTE FOR CUBIC INCHES........EXCEPT FOR RACE POWER!!

davidburns

When you say clean up how do you mean?

Something i was thinking of doing was smoothing all the walls in the plenum and runners cause it has a rough surface from casting and wondering if there is no reason i cant make it all smooth so it flows easyer???

ayios

Have fun smoothing them out!!!
NOt as easy as you would think!!
Believe me I have tried it.

11nos

leaving the walls of intake runners with a textured finish promotes air turblance. This holds the fuel in the air and doesn't let it stick to the walls like in highly polished situations.

davidburns

Ayios: its an alloy manifold so it wont be to hard and i got heaps of time to waste.

11nos: So smooth the walls inside the plenum but not in the runners?

VAN454

No don't smooth the walls at all, unless you are on striaght gas. No I meant just for cosmetics, the port match is what will inprove flow. The other thing you can do is either drill a hole (about 5mm) in the wall dividing the plenum or even remove this wall completely. This increases the efective size of the plenum, but keep in mind that you will lose some bottom end power but get an increase in mid to top end. This is a mod that people used to do before single plane manifolds were available. The effect is similar to a single plane but not quite as extreme.

__________________
THERE'S NO SUBSTITUTE FOR CUBIC INCHES........EXCEPT FOR RACE POWER!!

ayios

I know its alloy mate.
Get a tungsten carbide burr stick it on a dremel and have a go.
See if you still think its easy!

wabbit

it's a piece of piss, ayios

you just need a wire brush to run the bit on every now and then. cleans it up good

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Move along, please

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fat block 253

Never remove the plenum divider in a dual plane. That's one way to stuff a manifold. Don't even even try to grind the runners because to port match a manifold properly , you need to sit the heads on the block, sit the manifold on , then the transfer the head port to the manifold etc. Don't smooth out runners- they need to retain the rough finish. Bolt it on unmodified. The precision manifold works well in applications that call for a dual plane manifold, up to about 5500 6000. It should also have provision to be drilled to suit later heads.

markjcshz

smoothing out manifolds is a no no .the runners and a bit of roughness help keep fuel and air mixed you wombats, and port matching should only be done by some one with a clew . to many idiots think getting better flow is done with a bur on the end of adrill all youl end up with is a piece of scrap alloy better to buy a good manifold than **** your motor with a shonky one

wabbit

port matching manifolds isn't exactly rocket science

__________________
Nothing to see, here


Move along, please

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