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VT V6 head work gains?

TI3VOM

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Hi there guys and gals I went to get a price for my heads to get ported and polished+shaved the guy that I spoke to said that it's not worth the money and there will be not much of a gain and the other bloke there said that the manifold would not match up after shaving the heads.

So my question is who has had there heads Ported polished and shaved and what gains have you yielded plus did your intake manifold match up ok and if not what did you do to fix it.
Cheers Glenn.
 

chargedvx6

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The heads will only perform as well as the next restriction in the chain will allow. If you have a F/I engine that rule becomes a little less important.
 

TI3VOM

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Has anybody done it and had gains? I am asking this question as I know there will be another restriction somewhere along the lines within the engine. All I need is twin cats and I'll have all the bolt on mods that I can get for a VT V6 to breath so now I need to open up the engine to see more gains.
 
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bandidoben

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doing that on its own will do F all mate unless you upgrade the cam or rockers. id be doing these things first then the head work.
 

0081

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I think you will find there are gains to be had but the costs to carry out this mod will be a fair bit, as you are not up only for the head work but all the head bolts, gaskets and sealent to refit the heads.

I would look at cam and or rockers, valave springs and a double row timing chain first.
 

Dr Goggles

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if you shave the heads you will have a poorer fit with the intake manifold, as the inlet face will move down and away from the manifold. You'll get bigger gains with a bigger or twin throttle body. A port job on it's own won't give you much....a shave on it's own will give you grief.......
 

Tsunamix

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v6 Heads are over-ported from the factory. You see the ports are shaped around the american bunch of bananas manifold, and the junction between head and manifold is the area in which the air stream turns from a vertical up and down type flow, into the back of the valve.

In essence - the port doesn't cut straight across the designed air path, but at a diagonal.

Holden australia re-worked the Inlet manifold to build torque - quite successfully I might add. No Alloytec has ever had the torque of the ecotech.

In the re-work, the existing port ended up too big for new air path. which as long as you don't machine out the manifold, doesn't affect airflow much, and seems to impart a bit of tumble which helps atomisation at the injector.

If you machine out the manifold to match the port, you end up with a dirty big chamber at the end of the manifold runner, that is almost twice the cross sectional area of the inlet runner. What this does is slow down the airflow, reducing torque.

From what I have been able to test, there actually looks to be some gains available (as much as 25kw) from welding up the ports in the head, and grinding them back to match the manifold. It seems if you add some material to the floor of the port in the head, flattening out the curve in the floor, and match it up to the inlet runner, you get a much much better flow velocity.

I've been doing some flow bench work and at 26inHG the flow figure goes from 121 CFM up to 138CFM and airspeed 88% of inlet to 104% on inlet - inother words flow is increasing and air is accelerating as it travels down the runner instead of slowing.

But atomisation is reduced due to less tumble. Careful shaping may see me able to add some swirl back in though. Lots more work to do yet.
 

TI3VOM

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Cheers Tsunamix that's a lot of good info there I will speak to a few guys that deal with heads and see what they can do or suggest.
 

TI3VOM

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Right at this moment I am comparing prices between the manifold spacer, plenum spacer, larger throttle body as opposed to a twin throttle body setup.
Either way by the time I get the heads done if I do now I would have a larger T/B+more or a twin T/B setup.
 
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