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[Albatross]

On the subject of manifolds I would say it needs someone who knows what they are doing to get the best out of them, but anything would probably be an improvement.

The standard manifold is untuned, in that the exhaust ports for each cylinder just terminate into a common plenum with the pipe connected to one end.

The big advantage of a tubular manifold is that you can tune the lengths of the primary pipes to scavenge the cylinders more effectively and isolate the effects of adjacent cylinders. The length of these pipes depends on the engine speed at which you want them to work (there will be speeds where they are poor and speeds where they work well), and the exhaust valve timing.

Kevin

Does that mean that I could even see a drop in performance at certain engine speeds?

I don't want that, I want to retain the same smooth power curve, only higher up on the graph. I may supercharge this in the Spring when my bonus comes through so I want it to be breathing as well as it can to make the most out of the SC.

[Kevin Wood]

Does that mean that I could even see a drop in performance at certain engine speeds?

I don't want that, I want to retain the same smooth power curve, only higher up on the graph. I may supercharge this in the Spring when my bonus comes through so I want it to be breathing as well as it can to make the most out of the SC.

You'll undoubtedly see an "undulation" in the torque curve as the pipes go in and out of resonance, and they are normally tuned to resonate at the maximum torque RPM for road cars. Whether at any point you'll get less torque than with the standard setup I don't know.

If you are contemplating forced induction then, although the same principles apply to getting the engine breathing well, an expensive exhaust modification might not be the most cost effective route. It would drop lower on the list of priorities, IMHO, because you'll be limited by the compression ratio and a good exhaust will just slightly reduce the boost pressure you need.

Kevin

[Albatross]

Does that mean that I could even see a drop in performance at certain engine speeds?

I don't want that, I want to retain the same smooth power curve, only higher up on the graph. I may supercharge this in the Spring when my bonus comes through so I want it to be breathing as well as it can to make the most out of the SC.

You'll undoubtedly see an "undulation" in the torque curve as the pipes go in and out of resonance, and they are normally tuned to resonate at the maximum torque RPM for road cars. Whether at any point you'll get less torque than with the standard setup I don't know.

If you are contemplating forced induction then, although the same principles apply to getting the engine breathing well, an expensive exhaust modification might not be the most cost effective route. It would drop lower on the list of priorities, IMHO, because you'll be limited by the compression ratio and a good exhaust will just slightly reduce the boost pressure you need.

Kevin

So are you saying that for road use (with or without an SC) that manifolds are not that good a path to go down?

What would be higher on the list of priorities?

BTW: What about this 3.0 pre-facelift mid-section question? An ABS member has offered me a set for free.

[Kevin Wood]

So are you saying that for road use (with or without an SC) that manifolds are not that good a path to go down?

What would be higher on the list of priorities?

BTW: What about this 3.0 pre-facelift mid-section question? An ABS member has offered me a set for free.

I think you'd have to try hard to make things worse than the standard manifold. What I am saying is that if the exhaust is tuned there will inevitably be peaks and troughs but overall the car will be faster. You could always get a tubular manifold made up with short primaries which will flow better but not give you much in the way of resonance effects and you will retain a flat torque curve.

I don't know if the pre-facelift cats would fit or if they are more free flowing but if they're free it might be worth a try.

Kevin

[Albatross]

So are you saying that for road use (with or without an SC) that manifolds are not that good a path to go down?

What would be higher on the list of priorities?

BTW: What about this 3.0 pre-facelift mid-section question? An ABS member has offered me a set for free.

I think you'd have to try hard to make things worse than the standard manifold. What I am saying is that if the exhaust is tuned there will inevitably be peaks and troughs but overall the car will be faster. You could always get a tubular manifold made up with short primaries which will flow better but not give you much in the way of resonance effects and you will retain a flat torque curve.

I don't know if the pre-facelift cats would fit or if they are more free flowing but if they're free it might be worth a try.

Kevin

I've been speaking with a company who is making up a set of tubular manifolds for another ABS member. He indicated to me that the primaries would be around 10" long which is quite short. The main reason for this is the lack of space. Would that be OK and give me a more level behaviour?

What would you do rather (or as well as) manifolds in preparation for an SC if you had the opportunity?

[Kevin Wood]

10" is well short of being tuned at the kind of speeds the V6 runs at, so it will just be a better flowing version of what you have, really.

The point I was making about supercharging is that, if you go that route, you will easily be able to get more volumetric efficiency out of the engine and the limit will be the standard compression ratio, assuming you're not going to lower it.

With a naturally aspirated engine you have to work at the inlet and exhaust to get more VE. With a supercharger you will be able to get as much VE as it will handle regardless of the exhaust. Having an efficient exhaust will give you a more efficient engine, of course, but won't necessarily limit power as it would with a naturally aspirated engine.

Kevin

[Albatross]

10" is well short of being tuned at the kind of speeds the V6 runs at, so it will just be a better flowing version of what you have, really.

The point I was making about supercharging is that, if you go that route, you will easily be able to get more volumetric efficiency out of the engine and the limit will be the standard compression ratio, assuming you're not going to lower it.

With a naturally aspirated engine you have to work at the inlet and exhaust to get more VE. With a supercharger you will be able to get as much VE as it will handle regardless of the exhaust. Having an efficient exhaust will give you a more efficient engine, of course, but won't necessarily limit power as it would with a naturally aspirated engine.

Kevin

Sorry Kevin,

I'm a bit thick on things like this and don't understand much of the above really at all.

Would I be right in thinking that in essence what you're saying is:

That the 10" tubed manifold would be OK, smoother (less undulated), but not overall as good as longer pipes? What's more it would be beneficial if naturally aspirated, but a bit of an unnecessary waste of cash if I were to fit a supercharger?

[Essex_Andy]

I think the point being made is that for forced induction (supercharger or turbo or combi of both) the scavaging of exhausts gases through a specifically tuned exhaust system is lower on the list.


In essence the forced inlet charge pushes a lot of the waste gas out. Less need for the exhaust system to draw the waste gases out. Tuning equal lenghts for primary tubes so each pulse of exhaust gas can slot in turn with the next one. Then the decision/benefit of a cross pipe for V engine set ups etc


Trying to cast my mind back re long primaries v short ones v torque on motorbike builds and the benefit of primaries joing en-masse or going 4 into 2 into 1 etc

[feeutfo]

my 2 pence, for whats its worth, i had always presumed any forced air induction, turbo or sc, would over power any effect gained by scavenging cylinders with a "tuned" exhaust. For instance a turbo exhaust takes little notice of pipe length and just takes the easiest route to where ever the turbo is positioned for convenience.

 I would think you need to decide which route you want to go down. Forced induction or a free flowing exhaust.

In my experience, a longer downpipe gives a more rev happy "powerband" and basically moves the power further up the rev range,in effect gaineing on one hand and taking on the other in relation to the current curve.
 I wonder if vx made the manifold that way to achieve a flat torque curve(shortest possible outlet pipes or plenum in this case), the opposite of peaky powerband delivery(longer downpipes) ? That would imply, if you want more of whats already there, a super charger would be more appropriate? If you like that sort of thing...

Alot of assumptions in there. Maybe a more experienced member can confirm?
KEVIIIIN...!

[Albatross]

I like my car the way it behaves, so would not want to change the characteristics of the power curve, but I would like to see if I can increase the power overall. I wouldn't want a revvy engine; hence the thought of a small supercharger rather than turbo.

I just want a more powerful car overall that's all.

To put this all into context of what else is going on at the moment here. I'm also just about to fit an LSD which will change the ratio from 3.9:1 to 3.7:1. I'll also be changing the tyre rolling radius on the tyres by going from 235x35x19 to 255x35x19 which will compensate the ratio change a small amount.

[nabsim]

I know the big problem with tubular manifolds on the V6 vec was getting equal length headers to fit, there just is no room. The vec is transverse though where the mig is inline, do you still have the same problems with space on them?

[Essex_Andy]

If you want more power it really depends on how big your wallet is.

How much is the blower set up costing you?

How much would an over bore with race spec cams, ported and polished heads with uprated fuel pump and injectors cost compared to a blower project?

[Kevin Wood]

Also depends how much of the work you're doing yourself against having it done, and whether you're after making the best of what you've got or a serious power hike.

Tuning is not something that's best done piecemeal, IMHO. Better to decide what you want to achieve and then to do what you need to do to achieve it, following one well trodden path / proven combination of mods from a single source rather than mixing and matching.

In a lot of cases, the sensible answer, IMHO, is that you shouldn't have started with a V6 Omega, but life doesn't always have to be sensible, of course.

Kevin

[Albatross]

Also depends how much of the work you're doing yourself against having it done, and whether you're after making the best of what you've got or a serious power hike.

Tuning is not something that's best done piecemeal, IMHO. Better to decide what you want to achieve and then to do what you need to do to achieve it, following one well trodden path / proven combination of mods from a single source rather than mixing and matching.

In a lot of cases, the sensible answer, IMHO, is that you shouldn't have started with a V6 Omega, but life doesn't always have to be sensible, of course.

Kevin

Kevin, very wise words; to set out the stall:

I "started with a V6 Omega" because I love it and I am not trying to build a racing car. I do not want to compromise what the best of the car is at all and simply want to make subtle modifications; I'm "after making the best of what you've I've got".

Boring out the engine is too much, perhaps even fitting a blower is too much. I'm exploring the idea of the manifolds, but am open to dissuasion.

I have done little bits and pieces and will be exploring the brakes too, but I repeat; I am not trying to build a rocket-ship out of a barn.

I suppose that the thread started in a discussion about manifolds & cats and then, perhaps understandably, it got diverted onto the "bigger picture". Now that I have clarified my "bigger picture" may I take us back to the question about manifolds?

I'd value your thoughts on manifolds with short(ish) pipes & sports cats on an otherwise unmodified 3.2 V6 Omega.

The man who makes them indicates that the gain may be as much at 20%, but you have concerned me about smoothness of the power curve.

[feeutfo]

an interesting read, esp the bit about emissions. All manufacturers suffer with this compromise, as im sure you know, and some very nice improvements can be had by returning the motor to how Mr Vx intended, not some eco Nazi tosspot behind a desk.

http://www.courtenaysport.co.uk/index.php?act=viewDoc&docId=21

Ps i know nothing about the companys reputation, but i have seen negative remarks from other members, but i think the info is along the right lines and maybe a phone call would give the answers you need to the torque curve question, bearing in mind they will probably need the work at the moment and will most likely say what you want to hear.