Unable to find answer to plenum question despite search...
Unable to find answer to plenum question despite search...
(OP)
Before I post this question, i'd like to say that I have serached through the forums using many different keywords to try and get an answer to my question.
I apologise in advance if the answer is somewhere on here and that I have just missed it.
Information preceeding my question:-
My stock Ford Cosworth Turbo inlet plenum has an incredibly restictive elbow.
images:
[IMG]http://img .photobuck et.com/alb ums/v385/C osRush/100 _00921.jpg[/IMG]
[IMG]htt p://img.ph otobucket. com/albums /v385/CosR ush/Inletd esign1.jpg[/IMG]
Whilst this restriction still does not limit the power able to be produced (upto 500Bhp), and improvements to the restriction in its design can only possibly yield better flow i.e. less friction on the air thereby requiring less Turbo boost pressure for the same volume of air.
I hope that makes sense what im trying tosay.
The incoming air does enter the plenum from the underside just off central so does give a relatively equal flow to all inlet runners.
So.....have things moved on since this original design?
Yes they have. In Sweden where the engines have been extensively used for racing a new design plenum was divised (termed a 'swedish plenum').
images:
[IMG]http ://img.pho tobucket.c om/albums/ v385/CosRu sh/101.jpg[/IMG]
[IMG]http ://img.pho tobucket.c om/albums/ v385/CosRu sh/Inletde sign1a.jpg[/IMG]
The inlet was at one end of the chamber at right angles to the inlets.
The volume was tapered to the rear (i believe in order to maintain the velocity of the air to the furthest inlet ports away from the Throttle, by virtue of the taper increasing the airflow velocity)
The plenum volume itself is also increased. Testing has shown that these flow very well on 500Bhp+ engine but show a slight throttle response drop on lesser engines. I put this down to the increase in volume over the standard.
Now my question........
I have here one of the Swedish Plenums, so if any more information is required in the form of measuremments thats not a problem.
However, this plenum is too big for my particular application. I am looking at having a new one made and would like ot know what factors determine the Taper rate from front to rear???
Taking this top view how would I work the taper required???
[IMG]http:/ /img.photo bucket.com /albums/v3 85/CosRush /Inlet.jpg[/IMG]
I realise that perhaps Maths aside, the best solution would be to make a prototype and test it, make adjustments and retest until a satisfactory result was achieved, but this would be very time consuming and also costly (hence why major manufactures spend a vast amount of money on the designs). Ive seen many 'Homemade' ones and some have shown really very good results far better than the stock item, but I will be straight and say that unless the maths are very simple to calulate the taper, no thought was given to any airflow differences between the inlet runners.
I base this on the very uncomplicated design of those ive seen.
Thanks in advance to anybody who can help
I apologise in advance if the answer is somewhere on here and that I have just missed it.
Information preceeding my question:-
My stock Ford Cosworth Turbo inlet plenum has an incredibly restictive elbow.
images:
[IMG]http://img
[IMG]htt
Whilst this restriction still does not limit the power able to be produced (upto 500Bhp), and improvements to the restriction in its design can only possibly yield better flow i.e. less friction on the air thereby requiring less Turbo boost pressure for the same volume of air.
I hope that makes sense what im trying tosay.
The incoming air does enter the plenum from the underside just off central so does give a relatively equal flow to all inlet runners.
So.....have things moved on since this original design?
Yes they have. In Sweden where the engines have been extensively used for racing a new design plenum was divised (termed a 'swedish plenum').
images:
[IMG]http
[IMG]http
The inlet was at one end of the chamber at right angles to the inlets.
The volume was tapered to the rear (i believe in order to maintain the velocity of the air to the furthest inlet ports away from the Throttle, by virtue of the taper increasing the airflow velocity)
The plenum volume itself is also increased. Testing has shown that these flow very well on 500Bhp+ engine but show a slight throttle response drop on lesser engines. I put this down to the increase in volume over the standard.
Now my question........
I have here one of the Swedish Plenums, so if any more information is required in the form of measuremments thats not a problem.
However, this plenum is too big for my particular application. I am looking at having a new one made and would like ot know what factors determine the Taper rate from front to rear???
Taking this top view how would I work the taper required???
[IMG]http:/
I realise that perhaps Maths aside, the best solution would be to make a prototype and test it, make adjustments and retest until a satisfactory result was achieved, but this would be very time consuming and also costly (hence why major manufactures spend a vast amount of money on the designs). Ive seen many 'Homemade' ones and some have shown really very good results far better than the stock item, but I will be straight and say that unless the maths are very simple to calulate the taper, no thought was given to any airflow differences between the inlet runners.
I base this on the very uncomplicated design of those ive seen.
Thanks in advance to anybody who can help





RE: Unable to find answer to plenum question despite search...
Some empirical data is no radii less than 10mm. Air chambers I have built as of late is to allow the velocity to slow down by opening the walls (bigger chamber) then based on desired reversion wave create a velocity stack with 1* convergence. If it is not possible to assign individual stacks then just converge into the throttle body.
Go here
http:
http://en.wikipedia.org/wiki/Bernoulli's_equation
I don't know anything but the people that do.
RE: Unable to find answer to plenum question despite search...
Something that should be considered is plenum volume vs engine displacement/RPM. Many plenums, from stock to top level racing, do not have a taper. The smaller the plenum the higher the velocity and the more it must be involved in directing air. A larger plenum will let the air slow for a brief moment before being grabbed by each cylinder.
RE: Unable to find answer to plenum question despite search...
I'll investigate it further.
RE: Unable to find answer to plenum question despite search...
Regards
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: Unable to find answer to plenum question despite search...
Only fabrication issues. There is nothing really complicated about it. It's just a form of a slot distribution pipe as used in some process industries. It just allows an even distribution of airflow across the length of the plenum which ensures each runner gets an equal amount of airflow and helps reduce charge robbing.
The taper should reduce from the throttle body/inlet diameter to zero ideally, though that can only be approximated by a casting. If your fabricating it, just get it tapered down as much as you can. For the slot:
If inlet is 60mm dia, inlet area is ~ 2827mm^2. If length of slot is to be say, 300mm, then slot width is 2827/300 = 9.5mm approx.
With an inlet area to slot area ratio of 1:1, as in the example just mentioned, the airflow will exit the slot at an angle. This angle will depend on the discharge coefficient of the slot and the ratio of areas. The angle is found using the following formula,
COT theta = (Cd*As)/Ad
Where,
Cd - Discharge coefficient of the slot
As - Slot area
Ad - Inlet area
If a Cd of 0.5 is assumed for the example above the air will be comming out of the slot at ~ 60 degrees. The Cd will depend on slot entrance conditions, depth of slot, if the slot walls are parallel, etc. Not something that can be calculated out without driving you nuts, but easier to determine by testing.
Or you could just use CFD...
Personally I like a 1:1 Ad/As ratio for least restriction and just start the slot before the first runner entrance, say 1-2 runner diameters.
RE: Unable to find answer to plenum question despite search...
When I wrote the first post I was unable to see your pictures due to our internet restrictions.
The manifold without the taper will tend to favour no.4 cylinder (at the rear of the engine). This is a manifold with a good taper.
RE: Unable to find answer to plenum question despite search...
Womble,
The Standard plenum actually flows slightly more air to No.3 than all the rest.
The inlet section to the plenum is not actually central but slightly offset towards No.3, and this being the inlet means the shortet path toNo.3 allows for a path of least resistance over the other 3.
This has been extensively tested over many years.
I fully understand that with the throttle inlet at right angles and on the extreme end of the row of inlets as in the Sedish style plenum, on induction you want all the airflow into each cylinder to arrive at the same time since the distance between the throttle and the valve is effectively different (if the plenum was parallel in this instance) therefore leaving No.4 cylinder (furthest away) a greater disntance to travel than that of cylinder No.1 (closest to throttle).
Therefore i can only conclude that the taper serves to increase the velocity of the air further (convergent duct).
Thus hopefully (if designed correctly) to allow all gas flow to arrive at the valves at the same time on the stroke irrespective of the different lengths they have to travel.
Anybody wish to comment on this???
I have tried a search on some free CFD programs but as yet have not found any. If anybody knows where these can be found please let me know.
RE: Unable to find answer to plenum question despite search...
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
RE: Unable to find answer to plenum question despite search...
I also pondered over buying a 'Swedish Style' plenum, but then thought that there may be better designs, one of the guys earlier mentioned a WRC type of plenum, this is one on a Focus WRC car:
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I would really love to know what the slot passage like in between the inlet pipe and plenum, does it look like this perhaps?
htt
htt
htt
What about this one for equalizing the flow?
http://i
Looks ideal, unless the pipes come into the plenum from a bend, that may mess things up a bit.....
Just some food for thought.........
RE: Unable to find answer to plenum question despite search...
The 1st and 2nd pictures you have linked are exactly what i'd been considering making.
Here is a picture of one a friend of mine made.........
It worked out very well and looks awesome considering he made it by hand.
http:
And here it is welded up and polished.
http:
And quite simple to make too.
He told me he had done some comprehensive maths to work out what was needed but in all honesty I'd suspect a simple flow bench would yield results easier.
You only need equal flow/pressure to each runner.......
RE: Unable to find answer to plenum question despite search...
(add599d2.jpg, 442372fd.jpg, 723e51c4.jpg) I can see trying to equalize the flow, but wouldn't this slot be restrictive? If they were trying to minimize the effective plenum volume that could have been done other ways.
RE: Unable to find answer to plenum question despite search...
RE: Unable to find answer to plenum question despite search...
Where did you obtain your plenum body pieces from??? were they custom made???
I see you have been looking at the Ford Sierra Cosworth inlet plenum.
Is that because you were intending using it or modifying it in some way.
It is indeed the original 2wd inlet plenum you have pictures of that I have, but am trying to replace with a better flowing one (the restriction in the elbow section).
Any information you have regarding the designs, the source of any parts for custom fabrication greatfully received
Find me on www.Passionford.com
RE: Unable to find answer to plenum question despite search...
What is the purpose of the slot in Deltona's second manifold?
(add599d2.jpg, 442372fd.jpg, 723e51c4.jpg) I can see trying to equalize the flow, but wouldn't this slot be restrictive? If they were trying to minimize the effective plenum volume that could have been done other ways. "
"CosRush (Aerospace) Wrote:
I would suggest that instead of a slot, the whole interface of the plenum body and the inlet be opened up to increase maximum possibly flow. "
The way I see it (theory:unproven) is this:
To get equal flow to each runner from an end feed plenum is very difficult, to address this the manufacturers of my plenum have cut a slot, this equalizes the flow, BUT, as you point out, this upsets the flow and causes a restriction, loose this restriction and loose the equal flow to each runner. It's a case of not being able to have your cake and eating it.....
This is why we need some pics of the INSIDE of your friends home made plenum (which looks very good BTW)
I just wish I was where I am now (design wise) when I saw the Focus WRC plenum, photos weren't allowed as it was in the MSport facility, but I could have blagged a look i'm sure If I had known, It would have given us some ideas...
RE: Unable to find answer to plenum question despite search...
As for the Cosworth manifold my hunch is that it is open. The momentum of the air is deflected by the taper in the inlet section. Plus the air has to make two 90 deg turns to get into the intake runners. I find it interesting that the inlet tube opens up to the plenum right at the #1 runner - I wonder if this was done on purpose to balance the flow OR were they space limited. My first inclination would be to start the opening about 2" farther forward so the air for #1 doesn't have to go back towards the front.
As for balancing flow I would first consider an air splitter or deflectors inside of the plenum. This type of thing is done on the 70's Trans Am style of cross-ram manifolds with the large flat plenums. They had lots of problems with air and fuel distribution.
RE: Unable to find answer to plenum question despite search...
One thing I really need to know: Does constantly highly pressurised air in a boosted engines intake pipes/plenum behave differently to that in a normally atmospherically pressurised engine? In my mind they behave differently, am I wrong?
RE: Unable to find answer to plenum question despite search...
Not talking about anyone here - but one of my pet peeves is people who think that turbo's trump all evils. That there is no need to consider intake restrictions, port the heads, etc. They think that it doesn't matter with boost. I see this especially with diesel people who are used to being air rich anyway. But if you increase the intake efficiency you just increased the engines efficiency. BTW - Gale Banks has been preaching this message for years.
RE: Unable to find answer to plenum question despite search...
My sentiments exactly.............
It matters not whether the engine is N/A or boosted, at the end of the day the N/A engine still gets 1 bar of atmospheric pressure where as a boosted engine might get 1.5bar.
Any restriction to flow in design i.e. unsmooth casting lines in manifolds/plenums, tight radius' all effect the gas flow by the same amount.
It matters not the whether thats at 1,2 or 3 bar.
What people in the Turbo world often seem to believe is that because the intake is pressurised above atmospheric pressure this overcomes any small losses, which whilst it is true also means that both the turbo and intake system are working harder than they need to.
Gas flowing to any of the intake system on both N/A and Turbo engine will yield improvements in gas flow and in a turbo engine this has shown itself as producing the same power for less pressure.
or producing more power with the same boost.
Effecient flow is the key to reducing friction to the gas flow and this ultimately affects the velocity,pressure and temperature of the gas.
Its here that the velocity is reduced and the temperature increased as friction is caused by the gas flow through a lesser efficient intake, both of which you want to avoid as much as possible.
RE: Unable to find answer to plenum question despite search...
Ive also seen custom plenums with the addition of balance tubes between the inlet and the runner area, such that the pressure in the inlet as it enters the plenum is split so as to provide additional air directly to the runners in a similar way (but in reverse obviously) to an 4-1 exhuast manifold and help equalise the pressure difference between them. Worked very well too.
RE: Unable to find answer to plenum question despite search...
Also note that the first generation Olds Quad4 intake manifold was an exhaust header in reverse. They replaced it after 2 or 3 years with a traditional cast AL intake - which kept max hp the same but improved torque. I imagine that it was too expensive for mass production.
RE: Unable to find answer to plenum question despite search...
I'm thinking more about the the behaviour of pressurised air, in my head I can see the first wave of charged air behaving totally different to when the whole system is pressurised.
Difficult to explain, but I can see the initial burst (when you come on boost) being like a wave of water
washing along a dry river bed, it favours then easiest route (down the furthest port in the plenum, if you're not careful), but what about afterwards when the whole system is constantly pressurised? I can visualise it being like a full balloon, no matter where you put a hole in it you will get air squirting out. Will these differences in behaviour (if they exist) disrupt any flow bench testing that we may do to show equal port sharing?
Picking up on what you say about using a header in reverse for an intake manifold; Why do we have a plenum on the intake of a high performance car, what purpose does it serve? Why don't we just split the intake into however many cylinders we have and have a pipe to each one straight from the intercooler?
RE: Unable to find answer to plenum question despite search...
As an example on mine at 4000rpm when the engine produces full boost, the inlet valve is opening 33 times a second.........
I feel that in order to test a new plenum design you would also need the inlet section too and measure from the outlet of the inlet (to the head port).
Hope that makes sense..........
I suspect its down to a combination of cost for manufacture in mass production cars and perhaps little gains v's complicated design/space issues over a standard plenum in modified cars.
RE: Unable to find answer to plenum question despite search...
As an example on mine at 4000rpm when the engine produces full boost, the inlet valve is opening 33 times a second.........
I feel that in order to test a new plenum design you would also need the inlet section too and measure from the outlet of the inlet (to the head port).
Hope that makes sense.......... "
Sure, it makes sense, but I'm talking about testing the plenum here on a flowbench for equal runner sharing, If you can't replicate real life situations it would warp your results, a flow bench works with only a light vacuum pulling through the ports.
What I would suggest is a small curved piece of metal halfway around the far side of each runner mouth within the end feed plenum to catch the bypassing air and encourage it to go down each port equally by altering its height, angle, or doing away with it etc, you could set these up on a flow bench (If my theory is wrong about boosted air behaviour) before hand, or even full baffles/deflector plates. You could also try out different degrees of taper on the tapered plenums to find out the optimum angle.
Quote:
"Picking up on what you say about using a header in reverse for an intake manifold; Why do we have a plenum on the intake of a high performance car, what purpose does it serve? Why don't we just split the intake into however many cylinders we have and have a pipe to each one straight from the intercooler?"
I suspect its down to a combination of cost for manufacture in mass production cars and perhaps little gains v's complicated design/space issues over a standard plenum in modified cars.
I'm not talking about mass production, but specially designed one-offs like ours, people still follow the same principles using plenum chambers, I have many pictures, but why?
I fancy it will be something about reverse pulses and equal distribution of constantly boosted air, maybe it will be hard to split the one pipe into multiples equally as it will perform differently at different levels of air pressure?
RE: Unable to find answer to plenum question despite search...
There are pulsations and constant flow situations going on due to the turbo pumping air fairly smoothly and the inlet valves opening and closing in each port.
Inertia from the air will tend to flow more air to the end cylinder, especially if the plenum curves into the last cylinder.
To stop this, design a straight pipe that is fed from one end and is parallel to the head and goes past all 4 ports then hits a dead end at the other end, say 3" past the last port. Have each runner perpendicular to this pipe and have a bell mouth at the entrance to each runner. That will minimise variations due to inertia effect.
Larger volume of this plenum makes more power, but smaller volume reduces turbo lag. The optimum volume is a compromise between these to conflicts. Only you can decide where that optimum compromise is for your application.
Regards
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: Unable to find answer to plenum question despite search...
1. The turbo can only spool up so fast - so I don't see the tidal surge happening. But throw this out the window if you have a poorly designed blow-off that goes full open or closed. Then you will get some momentary unpredictable pressure waves - unless you want to spend the next month doing complex CFD analysis!
2. As for the intake header, most of the time higher rpm's are used to get higher hp numbers with non-diesels. This points towards shorter runners which would be difficult to fabricate into a proper header while still providing equal flow and minimal restriction. The Quad4 was gutless below 3500rpm and needed all the help it could get.
3. The vast majority of plenums I have seen are as PatP describes. Constant cross section extending past the last cylinder. I would think if the tapered plenum gave a significant advantage we would see it more. It's probably something the race boys do because of space constraints or to get that last 1.5hp. You might see better transient behaviour because the plenum holds less volum but it is much more design sensitive.
4. Your set-up appears to use a two piece plenum. If you have the time/money/inclination you could design two different covers and see which works best.
RE: Unable to find answer to plenum question despite search...
http://
Im very interested to see the results of any design and testing you carry out.
I hope you keep us updated on any progress.
I would suspect the best enviroment for testing though would be 'in use', therefore you would probably be looking at a custom exhaust manifold too since the design of this affects the inlet air too, and if you have a cast manifold you'll struggle to get probes fitted and would need a Wideband lambda sensor on each exh header and also and Egt probe, best optimised if you have mapping software via a laptop. That itself would add upto a lot of money in itself.
Once you were satisfied that you had the airflow right for your own useage you could remove the probes and make use of it.
I cannot see any other way of accurately measuring the airflow in its normal enviroment...........
jbthiel
I suspect you are right, but most I have seen are infact tapered, and only some of the older designed ones are still parallel. This suggests to me some development improvements both in mass production engines and in motorsport.
Probably as a result of the latter (in the same way that F1 benefits from Aerospace design).
RE: Unable to find answer to plenum question despite search...
In the end this is like almost every other engineeing question - DEPENDS!! There are so many competing variables that you will never have a perfect design. We all have to live with good enough. :)
RE: Unable to find answer to plenum question despite search...
Ive already shown this to Deltona, but it does make a good representation of the difficulties.
This is the final Ferrari F430 inlet plenum test results, and it clearly shows that despite Ferrari's design,testing and very large budget they did not achieve totally equal balance to all runners.
http:
The only way IMO is testing testing testing......
RE: Unable to find answer to plenum question despite search...
I'm just curious since a lot of analysis programs automatically scale the colours to span the range of numbers, whether it's 1 unit or 1,000,000 units.
Thanks for sharing that pic.
Bob
RE: Unable to find answer to plenum question despite search...
RE: Unable to find answer to plenum question despite search...
Regards
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RE: Unable to find answer to plenum question despite search...
RE: Unable to find answer to plenum question despite search...
If you are going to use the Swedish style plenum then consider the angle at which the throttle body presents itself to the plenum, you can angle it so that it blows towards the first few runners rather than straight in, see here:
http://s
This engine is a 2 litre and is pushing out some serious power (in excess of 700bhp)
RE: Unable to find answer to plenum question despite search...
Thanks for that
Ive decided though for the time being to use the standard plenum until such a time that I have available time and money and tooling to design a better plenum for my engine.
I personally would not be happy until I knew the airflow was as good as (but preferably better than) the original, and unfortunately I have run out of time to get involved now, so on the 'back burner' for the time being.
I hope you make some progress with yours however, keep us posted of any progress, especially with respect to any results you find
RE: Unable to find answer to plenum question despite search...
RE: Unable to find answer to plenum question despite search...
The changing pressure, and therefore the changing temperature in a turbo application makes pulse tuning to difficult to bother with.
Regards
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RE: Unable to find answer to plenum question despite search...
Granted you can go to the nth degree in design detail... But for DIY I don't think it's that hard. If you go for a front entrance plenum design that has the volume you require, tapering down to a minimum height above #4 runner (1.5xrunner_id minimum)you should get very good runner to runner distribution - bare in mind OEMs may allow up to 5% variation between runners. OEMs do use steady state flow bench testing for validation also, so if you have a tuner near you that has a flow bench you can ask if they can flow test it for you. Guy Croft Racing Engines has a flow bench if you get stuck.
RE: Unable to find answer to plenum question despite search...
You can then easily experiment with volume by using spacers at the split line.
You can read the plugs, measure exhaust gas temperature or even run oxygen sensors on each exhaust pipe to determine cylinder to cylinder variations. As the plenum splits, you an access the bell-mouth of each runner to rework it. Then rework the bell-mouth on each runner inlet to get the maximum charge you can get with uniform distribution. Resist the urge to lower the good cylinders to the lowest common denominator and try to improve the rest to equal the best.
While flow benches can be a useful tool, they are constant flow and therefore do not tell the full story, like variations in adjacent cylinders due to charge robbing due to firing order. They also do not give any help re plenum volume so long as the plenum CSA is enough to supply steady state flow to the furthest cylinder. Flow benches do not help predict the effect of pulses in the manifold and do not help in predicting the effect of volume on the magnitude of these pulses or oscillations.
Regards
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RE: Unable to find answer to plenum question despite search...
If you want to get the most bang for the least money - modify your existing cover by milling off the throttle body mount and welding the hole shut. Then mill a long slot and weld on a tapered inlet section. You can reuse the throttle mount cutting off the flange and welding it onto this section.
I also like the dual inlet idea you showed - if you have the room for it. This takes a lot of the equal flow problems out of the equasion.
http://i
------------------------------------
An off subject item - how do add the quote box in your reply? If looked and can't find how to do this.
Thanks. IceStationZebra
RE: Unable to find answer to plenum question despite search...
You can then easily experiment with volume by using spacers at the split line.[/quote]
This has been done for about 2 years now, but nobody has any decent testing information with regards to the overall effects, other than to say it improved throttle response........
I also agree with pat over this very important issue Pulse induction tuning.
In the standard plenum you can see how the pulse length is equal between the cylinders by virtue of the plenum face being at right angles to it, im sure Cosworth tested the pulse range and adjusted the plenum face to add the induction pulse at around the turbo on spool area for added torque.
However, utilising a tapered plenum the face is in a different region for each runner, so I can only assume the pulse tuning would be not only unequal, but you could find that the pulse of one runner matched the frequency at an unsuitable time and caused that partiular cylinder to go lean.......
I too have my own ideas of how I would design the plenum, but ultimately it still boils down to lots of fabrication of individual sections and joining them in a way the same as for the final piece, testing adjusting, more fabrication etc etc. Which if you have access to Time, Spare materials and tooling would not be too much of a problem. But now I myself am out of the Aerospace business, I do not have such facilities, therefore all of the above would have to be paid for by me
As an example (I realise it need not be.....) but the Swedish style inlet plenum I had here until recently which was built deasinged and tested on HP cars (upto 700BHP) was made from stainless steel, hence it cost of £350.
Aluminium is obviously much cheaper in the form of materials, but still requires Tig welding (something which seems to be expensive in itself).
Add this to the addtional equipment needed for any testing as I stated previuosly (Egt probes,WB Lambda etc) an it does work out expensive IMO.
Certainly for me at this time
RE: Unable to find answer to plenum question despite search...