MatraSport Forum

I  was lucky enough to recently acquire a complete Vortex Exhaust system for a 2.2 Murena which I plan on fitting soon.

I intend to carry out before and after power runs on my local rolling road, to see how effective it is and to see if it actually does what it says on the packet? Which is to increase exhaust gas velocity, create a vacuum to scavenge the exhaust gases out faster and thus increase bhp and torque by up to 15%. Plus better fuel economy etc....  :-\

I thought this might be of general interest to you all and wondered if anyone actually has some experience of these systems.
(Other than my best mate who sold it to me.  ;) )

For further sounds too good to be true information see:-

http://www.vortexexhausts.thermashieldenergy.com.au/index.html

http://www.vortex-performance-exhausts.co.uk/

I do very much hope it is all true and will keep you posted.

Cheers,

GP

Hard to believe, indeed.
I'm very curious, so, keep us informed about your experiences.

That exhaust looks like it is going to be LOUD. :o

It exits on the right rear of the car, not the left as the standard Murena exhaust. You will have to cut the fiberglass to make space for the the pipe.

But it does look interesting and I am also curious, as to what you find from your rolling road tests.

I always thought there should be "some" back pressure for an engine to perform its best. The Vortex looks like it is almost wide open and will have very little.

Yes, engine needs the back pressure from exhaust and if it isn't there, it doesn't work properly, because part of unburned fuel leaves the cylinder too early. That's why cars with damaged exhaust lose the power... and it's also the reason why 2 engines of my Murena went broken (before I bought it), because somebody put there an 4-1 exhaust and leaved the original carburetors, so the result was that the engined was running on very poor mixture which means higher working temperature and damaging of the engine is "comming soon" ;D So using the 4-1 pipe, or exhaust system like this could be fine, but it's necessary to rich up the inlet side too - bigger carburetors, fuel injection, etc.  ;)

PS: this seems to be "home made" piece, so first questions are - why the seller have sold it, how it is prooven and which systeme of "feeding" it had.

It was sold as part of a package of complete engine, gearbox and gear linkage, as the owner had replaced the complete package with a different engine and gearbox.

I don't know how it was proven, other than it was being driven around the U.K. and trips to Europe on a regular basis, with no problems as far as I am aware.

It was running on 2 x 40mm Solex sidedraught carburettors.

I will be very cautious and have to admit to all the concerns mentioned above. But I will go about this is a planned manner and hopefully come to a definitive conclusion to this “Vortex” technology.

GP

I have to correct your terminology there Michal - there's no 'back pressure' needed to 'hold in' the fuel on a four stroke engine: The valves are shut during the combustion phase, and during most of the intake phase too. You are correct, however, that the exhaust design can change the way the engine performs, and may also require rejetting of the carburettor, but this is more complex than just 'back pressure' and involves parameters like cam overlap, lift, carburettor type, and the actual construction of the manifold: Is it a 4-1 or a 4-2-1 exhaust. The length of the runners is also important as it is used to tune the exhaust to maximise torque at specific RPM, becasue at resonance frequencies, the exhaust gasses passes more easily through the manifold runners.

/Anders

Funny you should mention that. My first thought when I saw the Vortex exhaust, was that it was a resonance tuned exhaust. By tuning it just right you can effect the RPM at which the engine delivers max torque or HP.

I think that there is a smal phase, when inlet valve is opening at the same moment when exhaust one is closing for rinse out the rest of the burnt gas... isn't it?

Indeed, that's the overlap. The S cam has about 50 degrees overlap, but on the Holbay cam as much as 76 degrees. The standard cam only 32 degrees.

At low rpm, the overlap can allow a bit of unburned fuel/air mixture to pass directly into the exhaust, but as rpm increases, the overlap ensures that the low pressure, which exist in the combustion chamber during the last phase of the exhaust stroke  can aid in accelerating the fuel/air misture even before the piston starts its pumping effect. This is because the "bubble" of exhaust gasses has been accelerated and is still moving inside the exhaust as the piston slows down its upward going movement: The inertia of the bubble now starts working like a pump and by keeping both inlet and exhaust valves open at the same time (overlapping), the pump works on the inlet.

On a 2-valve engine, this is very useful because you need high airspeeds around the valves, so they generally like overlap. 4-valve engines don't benefit as much from it since breathing is a lot less restricted than on the 2-valve engine.

That's very interesting Anders, I didn't knew all these details... Why the Hollbay cam has it so long? To clean the chamber better?

Well first of all the Holbay is a 296 degree cam whereas the S cam is only 279. Longer inlet/exhaust periods necessitates more overlap "to fit". In this way it's actually more like the Sodemo Gr.4 cam, which I think is similar to the 160 hp cam that Politecnic offers. However, the lift of the Holbay is only 7.06 mm whereas the S cam lifts 7.4 mm. This may seem a small difference, but it does mean a big difference in inlet cross sectional area. The Sodemo cam lifts as much as 7.75 mm. The standard cam 6.5

Because the Holbay is relatively low lift cam (but still more than the standard cam), the inlet pulses on the carburettors have less amplitude, but the overlap and long periods ensure that the pulses are a lot longer. This is probably the reason it works so well on the standard carburettor which it's long narrow intake runners - you don't even need to re-jet it.

Roy has told me the Holbay guys had a lot of experience  with this engine (in the smaller 1.6 and 2.0 trims), so they probably knew exactly what they were doing, but why they ended on these numbers, I don't know. It's a pity the company has closed their cam profiling section.

/Anders

15%!  More like 1.5% I suspect, unless the exhaust was particularly restrictive in the first place. :-)

There is far more to exhausts than realised by many.  You get a pulse wave that travels down the exhaust and when it gets to the end (of the tailpipe) reverses back to the valves.  If it reaches the valves on the negative pulse of the wave it will aid extraction and improve the power.  If however, it arrives on the positive pulse it will obstruct the gases exit and power.  So lengths are critical.  (Formula 1 teams at one time used to start with a certain length and then cut them back until they got the best figures, such was the crude way then!  It will all be done on computers these days)

A secondary thing do to with this pulse wave, is that on long exhaust systems, you want to position the exhaust hanging points where the wave crosses from positive to negative or vice versa (in other words where there is least vibration) and the exhaust rubber mounting will last well.  If you hang it where the wave is at a peak, the mounting will break far more often.

With our short exhausts and the way they are mounted I doubt this mounting feature will be a factor, but it shows just why you cannot just choose any lengths or mounting points at random and expect to get the best.

To answer another point, on a naturally aspirated engine, more overlap can help improve combustion chamber filling and therefore more power, but as the overlap increases, the emissions will get worse as some air/fuel goes straight out from inlet to exhaust.  This is why you now have variable valve timing on modern engines.  No overlap at idle to keep emissions low, and more overlap as revs rise to give you the power you need (no overlap at higher revs and throttle would seriously restrict power).

Roy

I wonder... is there such a thing as a sensor that can detect this reverst wave ? If so it might be possible to make an automatic pipe length tuning, that made sure the wave always arived at the valves at the negative pulse, regardless of the rpm.

When we are speaking about engine tuning... is there somebody who has more than 150PS from 2,2 engine?

I am sure an exhaust system can be designed to get the wave back at the valve, at the moment the next wave is coming. But only at one specific RPM??

You can compare it with resonance. If the resonance frequency of an object is 20 hertz, you can get the object vibrating big time when applying a small amount of energy of 20 hz. When applying any other amount of hertz, the object will not get into resonance.
When not in resonance, the object is easyer to vibrate when the object is as light as possible.

Apply this to exhaust.
An exhaust tuned to resonate at 6000 RPM, will give a big advantage at 6000RPM, but at any other RPM it will not do anything.  For any other RPM it helps to have as less restriction as possible.

As we are not allways running our engine's at one speficik RPM, it is better to forget about tuning the exhaust system, and focus on restriction.

DISCLAIMER,
I am NOT an exhaust expert. This is my personal opinion. It is likely to be wrong.

I plan to get there with my ported cylinder head etc.


It *is* a resonance effect. It's like an organ pipe or flute only wanting to play one note - at that note, the air flows through more easily than at others, where the waves die out and energy is lost.

It pays to consider this resonance effect because it's there and it makes a considerable difference whether you want it or not. And if you think of it, a muffler far down in the exhaust system is probably not "felt" by the engine as even if it restricts the exhaust a little, it also opens up the exhaust and allows the pressure waves to die out instead of coming out of the exhaust outlet. That applies to the inlet as well. So a well designed and damped muffler can be seen as an open outlet from the engine.

So exhaust resonance tuning is a good tool to increase and/or moves the max torque point of the engine to the most RPM.

The other effect is that of the vacuum on the back of the exhaust bubble. To benefit from that you need vacuum, which you won't have in a completely open or restrictionless exhaust system. So there's a point where there will be too little restriction! Now, the vacuum on the back of the exhaust bubble is distributed back to the other cylinders from the place where the runners are joined, where the (low pressure) wave will travel (at the speed of sound) back. Depending on the exhaust design and engine RPM, it will either aid the scavenging of the cylinder (as in a short manifold where cylinders are joined by pair, as in the Murena 2.2 cast-iron manifold), or starting the early suction of air/fuel mixture into the cylinder during the cam overlap when both inlet and exhaust valves are open (as on the 4-in-1 manifold with its longer runners). Or both!

All that said, I don't think there's a design rationale behind the 4-in-1 manifold on Murena - and I don't think anyone will have the inclination or money to spend on trying out different designs. Except GP perhaps? ;) However, it looks and performs well!

/Anders

One thing I want to try on my 4in1 exhaust, is to wrap it in insulation. I have seen kits with insulation tape and straps.

I am thinking that it could help on the wave and at very least help reduce the heat generated in the engine compartment.

Also, my 4in1 is not stainless and ugly rusted, so it will make it look better. :D

Yes me.

I am hoping next week to book a day at the rolling road to find out out the definitive conclusion to the Vortex exhaust technology mystery??? Will keep you posted.

P.S. To answer Jon's question also, I currently have fitted a 4 x branch stainless steel exhaust manifold wrapped in Thermo-Tec COOL IT exhaust insulation. This does considerably reduce the heat in the engine compartment and I can only presume it assists with the performance output, along with the gas flowed head, 2 x 45 Weber DCOE carburettors and 150Cv Politechnic Camshaft, as the graph attached below seems to confirm.

http://www.thermotec.com/technology/10-how-does-it-work.html

GP

How much?

I don't think it helps. It may even do damage since the heat is kept in the exhaust, potentially causing damage to the manifold and - worse - to the cylinder head. The Murena's engine bay cooling is well designed by the airflow around the engine and under the trunk, plus the carbs and inlet is on the "cold" side of the engine, so as long as you have a good supply of fresh air into your carbs, heat radiated from the exhaust will not affect the inlet side at all.

Further, the other argument presented by Thermo-Tec is wrong. To aid scavenging and overlap, you want the exhaust gasses to cool down as they travel down the manifold. Cold air has lower pressure than hot, and it's low pressure you want transmitted back to the exhaust valves in either case.

/Anders

158.2 bhp /66321 rpm (160.4 PS)
136.8 lbft / 4804 rpm   (18.9 kgf/m)

Looking at my 4 into 1 exhaust manifold and looking at pictures of the Politeknic stainless version, it looks like, on both, the tubes do not have the same length from the head to the common point.

That concerns me, since I plan to convert to an injection manifold and use a MegaSquirt controll box. I planned on mounting the wide-band Lambda probe at the common point of the exhaust manifold. But if the pipe length is not identical, then it seems like the exhaust pulses could throw off the MegaSquirt. I assume it adjusts timing based on the pulses and oxygen mix at the sensor and if they do not arrive with the same delay, will the MegaSquirt be able to adapt quickly enough? ???

Do anyone you have experience in such matters?

It's not a problem. Megasquirt doesn't adjust mixture one cylinder at a time, but all four. Unless something is very wrong with the engine, they will always require the same mixture. It may time the firing of the injectors individually based on the crank sensor, though that should not be necessary.

Why do you think they are not identical length? Looking at Politecnics photo, I think they are roughly equal:

(http://www.politecnic.com/img-matos/photosmatra/collecteurmur.jpg)

Roughly is right,  ;) If we call the rightmost pipe cylinder 1 and the left most cylinder 4, then looking at the pipe to cylinder 1 and comparing it to cylinder 2 they start with the same bend from the junction and then cylinder 2 angles off to the left, thus needing a longer pipe to reach the head. The same goes for 3 and 4. It is hard to tell if there is a difference between 1 and 3 or 2 and 4.

But for a perfectionist like me it just don't look quite right.  :D I think you would agree, that for optimal performance and tuning, all four tubes should be exactly the same length, as they are in serious racing  applications. ;D

The Vortex might not fit on this Porche.

http://ekstrabladet.dk/biler/bil_nyheder/article1377812.ece

But what a radical engine swap. I would like to put that in my Murena.  ;D

365 BHP + 949NM torque :o

The Murena has now been on a rolling road for a power run first with the old exhaust, followed by a power run with the new "Vortex" exhaust.

Old Power: 157.4 BHP / 6640 1/min   ---------    New Power: 161.5 BHP / 6711 1/min
Old Torque: 141.0 lbft / 4044 1/min   ---------    New Torque: 139.0lbft / 5626 1/min

So an increase of 4.1 BHP or +2.6% was achieved with a -1.4% loss of Torque.

See attached power/ exhaust  graphs printout for further information.

Conclusion: It does not achieve what it claims in any way!

The noise is also quite unbelievable. I have just driven the car home 27 miles, I have a splitting headache and cannot hear a thing. I received a phone call  en-route and was asked if I was inside a Spitfire or something similar?  :-[

Tomorrow the “Vortex” exhaust is coming off. Ah well, win some, lose some!  ;D