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[sev]

I've just aquired a set of 3L cams and hydraulic lifters and a 3L lower manifold - thanks Mark  

MY question is this - in order to fit the 3.0L lower manifold onto a 2.5 head I take it that the ports on the head are smaller than the 3.0L engine's inlet ports and thus the head would need porting work.

Surely the lower manifold won't just drop straight on and everything'll be rosy ?!

I'm not being thick am I? :-/

[Martin_1962]

Yes the heads will need a bit of porting, I have one ported and one o port 2.6 heads in the shed!

[sev]

Yes the heads will need a bit of porting, I have one ported and one o port 2.6 heads in the shed!

So that being the case Martin, is there really any benefit to fitting 3.0L cams into the 2.5 if the charge is insufficient?

Then again, I suppose most engines can really do with bigger inlet valves as the all run on the lean side for emissions.

Have most people who have done this conversion opted to do porting work to their heads?, I had rather hoped that I could avoid the whole cylinder head off business as if I was going to do that I'd rather just go out and buy a 3.0L engine or better still the whole car!

[amba]

I have 3.0 cams fitted in my 2.5 and it does make a noticeable difference.
When I did them never replaced the lower divider ,but intend replacing it in the next week or so when do a breather and seal replacement on plenum as have slight air leak,so will let you know if I can tell any difference with the replaced inlet manifold, or not.

[MV6Matt]

I'm a fan of the 3 litre cams mod (thanks Mark too).
I did change the manifold divider for one of Courrtneys enlarged ones for the 2.5 V6.
Yes it does make a difference.
Remap, modded/performance air filter and box (for gods sake dont go the K&N Cone route - not unless you want loads of warm air sucked up of course) and stainless Exhaust will add even more.

Be interested to know how you get on!

Matthew

[Martin_1962]

Yes the heads will need a bit of porting, I have one ported and one o port 2.6 heads in the shed!

So that being the case Martin, is there really any benefit to fitting 3.0L cams into the 2.5 if the charge is insufficient?

Then again, I suppose most engines can really do with bigger inlet valves as the all run on the lean side for emissions.

Have most people who have done this conversion opted to do porting work to their heads?, I had rather hoped that I could avoid the whole cylinder head off business as if I was going to do that I'd rather just go out and buy a 3.0L engine or better still the whole car!

Don't bother with the divider then - this just matches the 3.0 divider to the smaller heads

[amba]

Is there much difference between the 2.5 and 3.0 lower inlet manifold then in sizes,as I had assumed that the opening would be considerably larger for the 3.0.
If you are staying with standard unported 2.5 heads will the 3.0 manifold do any good then ?

[MutantCav]

Am I completely wrong in thinking that porting 2.5 heads to make the opening the same size as the 3.0 heads means they are then in fact the same as the 3.0 heads?? I thought putting 3.0 heads on a 2.5 bottom end was not advised due to the low compression you achieve??

In reality putting a 3.0 lower divider on cant hurt as far as I can see, and adds increased flow even if its very very marginal...surely changing the upper divider (the bit the injectors slot into) would also make a slight difference as surely the 2.5 ones also have smaller holes?? The extra flow is surely only for the length of the 3.0 parts put on which if its just the lower divider would be VERY short and then the 2.5 upper divider would restrict it back again...

[amba]

Yes I see where you are going now with this.So it really seems that whilst the cams from a 3.0 do make a difference as they increase the distance the valves open,the volume of air is then resticted by the 2.5,s narrower inlet system,and if it was replaced in total by that on a 3.0 the extra air would so negligable as to improve much.
This is really quite confusing,as most thoughts suggest that the lower manifold should be replaced when doing a camshaft upgrade.

[sev]

Yes I see where you are going now with this.So it really seems that whilst the cams from a 3.0 do make a difference as they increase the distance the valves open,the volume of air is then resticted by the 2.5,s narrower inlet system,and if it was replaced in total by that on a 3.0 the extra air would so negligable as to improve much.
This is really quite confusing,as most thoughts suggest that the lower manifold should be replaced when doing a camshaft upgrade.

Exactly amba,

Until I do the work I won't be able to see for myself.

Having done light flowing work to a head before, (nothing drastic, just blueing up the surfaces, fitting the gasket and removing all superfluous material and casting imperfections ) my thinking was that the lower divider will have different divider port - head inlet port sizes than the 2.5L

This being said, with proper attention could be blended or have the material removed in order to make the charge passage easier and less turbulent, and if made larger would allow a greater volume of charge to pass.

So this being the case, would it not just be better to have the original 2.5 lower divider since the port sizes will be matched - alternatively perhaps it's more to do with the shape of the entry port rather than a dimensional difference?

The problem is, that if you end up putting a step in the inlet tract, you haven't achieved anything as the fule charge cant pass through into the compbustion chamber easily as it trips over itself with turbulent flow.

MutantCav, I agree on the swapping heads, also I believe that it's a different bore as well as stroke.

But, given the location of the injectors, I wonder if the length differences of the upper divider are more to do with the tuned lengths of the air inlet tracts as that can have a massive effect on an engine's characteristics depending on what power/torque characteristics you want to achieve.

MV6 Matt, was the courteney lower divider just larger on the plenum or engine inlet port side or both?

I know it's all swings and roundabouts really, but it's just nice knowing these things.  

[amba]

Sev

The trouble is without having both a 2.5 and a 3.0 side by side to compare we are all just guessing...and unless you pull it all to bits you cannot tell.Would be really usefull if somebody could get a close up photo of both sizes and also if they could do the respective head sizes aswell
It has always been stated that if you upgrade the cams you should do the lower inlet,perhaps it is just "snake oil".

[sev]

Amba you're right, and when I get my bits, that's what i'll do - a side by side comparison.

The only thing I won't be able to do is the port size on the 3.0 head, so perhaps if I get the rest done, and post the measurements and template the area then perhaps other members can fill in the gaps  

[Martin_1962]

Differences between heads

Very late 2.5 is same as 2.6

3.0 and 3.2 have bigger bowls so are lower CR on smaller V6s

ports are smaller on 2.x so the gas flow would be quicker.

The dividers - well on the 2.6 heads you file out the bottom corners by abou 1.5 to 2mm and the top round bit by about 1mm.

Mikes car has 3.0 cams and matched ports to 3.0 divider and that goes well.

During the bank holiday week I hope to fit flowed heads with 3.0 cams to my 2.6

Inlet manifolds AFAIK they are all the same.

[NiallyV6CDX]

So I'm guessing that because the ports in the 3.0 divider flange are slightly larger than the 2.5, that the whole boar of the rest of the intake manifold is also slightly larger too? :-?

If so, would it not be ideal to fit the 3.0 plenum and manifolds too, and then file out the head ports to match the divider flange, that way the whole intake system would be larger and without any steps from large to small or vice versa?

Anyone got any info on the 3.0 manifolds versus the 2.5s

[tmx]

how does the veccy GSi get 192bhp out of a 2.5/6 then i know it has 3.0 cams but it must have other little porting mods??