Rear Boxes for 159 3.2 JTS Q4

[Ascari32]

Help!

Having finally got a dash display, clear of any alarms - excepting Air bag, which my garage guys are checking out tomorrow, things seem to be coming together. Except!!!!!!!!

These damned rear boxes. The Alfa boxes choke the engine and the Ascaris make her sound like a WWII tank - albeit a very fast one.

It seems they not only generate an awful lot of noise themselves, but they invite the rear of the car to form a duet!

So it seems the quickest fix is to buy some replacements. But, which ones?

I have been considering the Supersprint for a while now, but they aren't cheap. Equally, Ragazzons have come into the frame, a bit cheaper.

What I like about the Ragazzons is, they are 330mm. Long and 188mm. in diameter. My logic leads me to believe the Ragazzons with a perforated straight through pipe, ~ 55mm., have a substantial amount of silencing material around this pipe in all directions. The Supersprint do not, given their cross-section is ovoid.

I have heard the SS are exceptional, but loud. I know nothing about the Ragazzons however, other than anecdotally they are 74 db sound level.

Also, being cylindrical, they are much more rigid than the Ascaris, which have a fatal flaw - it is suggested - insomuch as they are rectangular and have parallel surfaces which not only cause internal resonances - designed - in, this case, to give a particular sound, but unfortunately couple with the Boot Floor and the Spare Wheel Well. It is probably worse than even that as this Acoustic Coupling is probably reflected back again tho the rear boxes which further exacerbates resonance.

Ideas, opinions, advice please.

Cheers, 

[GTV6SA]

I have these on my remapped 3.2 Ti  :-*Awd -Mille Miglia '/Hi Tech  Mufflers SS catback system,good quality ,sounds great and much cheaper than Supertsprint/Reggazon equivalents.

[Ascari32]

Thank you for that GTV6SA, much appreciated.

[Ascari32]

Further to my last, 0815 hrs - car to garage for Airbag Control Module investigation: supplied a spare master module, second hand from Belgrade as the original one is suspected of failing - hence the alarms.

1155am - garage phoned to say "All Done". Air Bag Control Module replaced, passenger - side windscreen washer jet fixed, ECU codes reset and MOT Pass Certificate issued. Advised there is a slight warp of the front discs and cost of replacing - £273 -25p., discs and pads, labour inclusive. They will be done in a week or two.

Clearing ECU files must have reset fuel maps and she is now a lot more "Peppery". Quick, but again below 3000 rpm, dreadful sounding. Torque strong though and she clears traffic quickly - must watch that, not a good idea to be pulled over because of the exhaust racket.

Very pleased and now I can just focus on what to do about these rear boxes. I thought I may strengthen them/reduce vibrations by welding some tie rods through the central "Can", just to see how much they can be dampened down at lower revs. They are as good as useless to me as they are, so it is worth a try before I lay out the cash on new boxes. I have contacted Mille Miglia and await their response. But I shall continue to dig around for more options on what I can do.

In the mean time, light loading of the throttle keeps it tolerable and I need to keep the peace - not least with my wife in the passenger seat!   

[Colin Edwards]

I preferred the Alfa factory exhaust.  Like most factory exhausts, the manufacturer goes to great length to control harmonics and resonance.  Various length stiffening ribs pressed into the material is a common measure.  As is the avoidance of unsupported flat surfaces.

Welding assorted length fins / strips / ribs to the flat surfaces typical of aftermarket mufflers might help.........unlikely to hurt.

[Ascari32]

You're right about strengthening and where possible, avoiding flat surfaces - the very thing my new boxes excel in. I hate the idea of giving up on them, but there is no easy way or short time frame in which to get things done around here. So I think I will have to come back to them, by way of tinkering around.

But I am impatient to finish what appears to be a piffling matter as it really is spoiling the whole project. I found a good company, locally who will make a couple of boxes up for me. But again it will be a matter of too and fro, just wearing.

So, given the expense to date, it will be churlish not to go for Supersprint, Ragazzon of Mille Miglia.

I have been listening and watching a few clips and these three fall into focus. Possibly the Ragazzons, not least because they are cylindrical, 330mm. Long by 188mm. Diameter, with a perforated pipe straight through. Seems they have maximised the space available and are classic absorption types.

They are pretty rigid, have a substantial volume of fill, which is uniformly distributed around the perforated pipe to an equal depth all round. I am also informed, the are 74 db spl, which seems to be a good figure for a straight through box.

However, I continue to cogitate, not wanting to make the same mistake twice,

[Ascari32]

Ok! So I give up! If only!!!!!!!

With Brexit, the agents for Supersprint say, the factory has stock of their rear boxes, but Brexit has created considerable doubt about delivery times. Similarly, Ragazzon have stock, but have to be shipped from E.U. also with issues about delivery.

So, amongst other options, I asked a local exhaust specialist if he could make up a pair of back boxes. Ragazzon publish their dimensions. So, given "Imitation is the finest form of Flattery" I asked them to copy their sizes. Unfortunately it is difficult, I am informed, to get a canister/casing the same size as Ragazzons.

Well I think the Ascari's have had ample opportunity to display their virtues and failed miserably. So on Friday, two new front discs and pads will be fitted as well as the Alfa Boxes.

On Saturday morning, I shall take the Ascari's for butchering/modification. The tips and the inputs will be cut off, the end plates and the separators taken off/out. A new central perforated pipe, wrapped in stainless and packed around with e-glass wadding, as dense as possible; to give good absorbsion, will then be refitted to the Ascari canister. New end plates welded on and both the inlet and tips reconnected.

It may just be an intermediate step, before going into a skip, but it is worth a try. The canister volume is very close to the Ragazzon's so hopefully, they will perform better across the range - given they will be straight through - than they do currently.

For such a size as Ragazzon's, the DBA level should be in the same region, ~74 DBA, but whatever the figure, it has to be better than the Ascari's.

On travelling back along the 14, I gave the Ascari's a chance to show off again - above 3000 rpm and will be so sad to lose that fantastic sound. But, all things in life are a compromise and it is one I shall have to come to terms with.       

[Ascari32]

Much of my time spent on the exhaust system was directed at making the Ascaris work.

Now I accept, they won't! But why?

Well, since the discs were renewed and the Alfa boxes went back on, time has solely been devoted to making them work.

It seems unfortunate that I chose not to devote more time to them before embarking on fitting sports boxes. Looking back, it's now clear, I too was sucked in by all the hype surrounding cat - backs, etc, etc. Certainly, I wanted the exhaust to be as free flowing as possible and came to believe "What was said on the Tin", was factually correct. Not so!

Where the problems lie with the Ascaris are, they are "Compound Structures", an Absorption section, followed by a Central Resonator Cavity and then a second Absorption section before the tail pipe. To complicate matters further, the perforated pipe through the input section, leaves it and directs the gases across the central cavity, towards the perforated pipe through the output section. But they are not on the same axis, being "Off-set" by about 1/3rd to 1/2 their diameter.

It is difficult to explain the consequences of this aspect, but in essence; both acoustically, and in gas flow terms, this introduces an element of non-linearity.

Above ~ 3000 rpm, the gases are flowing too quickly across the central cavity to "Excite" it. So characteristically it is as if it were not there and only the inlet and outlet absorption elements are having an effect upon the nature of the gases. Importantly, they have a "Linear" effect upon them. And as such, the exhaust sound is great, given its character becomes very much related to the engines rpm.

However, below ~3000 rpm, the nonlinearity of the central resonator, has a nonlinear effect upon both the gas flow and the acoustic wave.

Pause for a moment.

Neglecting the restrictive nature of the Alfa Manifold Cats, their central Cat and their Post - Cat Resonator, the standard valve timing of the Alfa camshafts, at low revs, virtually isolates the inlet tract from the exhaust system, by virtue of the exhaust valve closing at 9deg. atdc and the inlet opening at 11.5deg. atdc.

This stymieing of the air flow; the "Alfa Romeo Staccato Effect", means the MAF has a lot of work to do, in a short space of time to generate an output voltage for the ECU to calculate the required fuel, particularly given the piston in now 11.5deg. into  its induction stroke.

So the MAF Element must have a sharp rise in voltage/Kg. flow rate. And because the influence of exhaust gas flow has been checked by the NVO, the MAF output voltage will be pretty accurate.

Pause for a second moment.

However, with the changes made to my engine, three more important factors come into play.

1) The high flow exhaust manifolds.

2) The high flow Sports Cat and their Siamese inputs from the front and rear banks: Siamesed at the input rather than hitherto with the Alfa Cat - the output! Plus the Stainless Steel high flow Centre Section.

3) The 23.5degree PVO of the C.B. Cams. Only their duration has increased, the lift remains the same.

Pause for a third moment.

The Autodelta Manifolds, the Supersprint Sports Cat and the Centre Section are "Linear" - they have a substantially "Neutral Effect" on the exhaust gases. Regardless of whether the engine is turning at 750 rpm or 7000 rpm, they appear "Dynamically Constant".

The combination of the manifolds, the cat, the central section and the Colombo Bariani PVO, essentially creates a transparency between the inlet tract, where the MAF sits, and the tail boxes.

So, attempting to combine a "Nonlinear Element" with a device which has a very fast changing rate, ie, the Ascaris back boxes with a MAF with a very fast changing rate of output voltage for a small change in flow rate is extremely difficult and virtually impossible to ensure constant results.

These are the principal reasons why it was essential to replace the Alfa MAF with a device which has a less acute Voltage out/airflow change, (dy/dt characteristic). Even with a Porsche 055 element it is still too acute for the exhaust system, a principle effect the CB cams create. However, this element can be "Desensitised - the dy/dt slope cannot be reduced except by internal re-alignment, but it's "Turn - on" threshold moved.

However, despite the Transfer Characteristic of the 055 Insert, and four other brand new devices - all of which have their responses published in the Bosch Data Sheets, I have found it impossible to align the exhaust system/engine characteristics with the Ascari back boxes. It seems the absorption elements of the Ascaris are too small to counter the reactive nature of the nonlinear cavity at their centre.

They may well work with valve timing such as Alfa's standard 3.2 JTS, but they cannot work under the conditions my modifications have created.

I referred to this in some of the very first discussions I had with numerous exhaust specialists - which to a man, they failed to acknowledge

The Alfa boxes however, can and do! Being Absorptive and certainly more restrictive, they reduce any reactive components within the system, creating a predictable response across the RPM Range.

It was an unusual conundrum! It was only by studying the apparently lack of performance of the Alfa's, that the failings of the Ascaris came into focus.

[Ascari32]

And Finally! - Comes the recognition that the Alfa MAF is no longer ideal for the engine given all the modifications done to it.

I now understand; despite this, the ECU has been set up such that it marries with its: Alfa's, chosen MAF Transfer Characteristic.

So the output voltage for any given  airflow, is such that the ECU would select a specific Fuel quantity to inject, across the range of a "Standard, Unmodified 3.2 JTS Engine", for the specific AFR/Lambda, when the Alfa MAF element fitted.

This being the case, the engine performs well and the exhaust system in now relatively very quiet than hitherto. And it is only the lack of handling ability of the Alfa Back Boxes that catch it out when pressing on hard. Acceleration is really good, with no "progression holes" - no flat spots from tick-over to very high revs. Torque at low revs -1100 ish rpm is good in fifth gear and she will pull well without any indications of "Pinging"

Despite this, she seems to have lost a bit of pulling power - grunt if one likes, in the mid range, compared to when the Porsche element 055 is fitted. Still good, but clearly lacking when comparing the two. And the sparkle is missing as the revs climb on hard acceleration. Seems a fair bit more civilized, nice but the 055 has spoilt me for what it offers!

The Porsche has alarm bells ringing in my head as I start to run out of road, when she is only starting to open - up. It's a missile at 4500 rpm and it unnerves me to say the least! Brakes will have to be uprated!

But the 055 element runs the car rich and that is even when it is tamed by 793 ohms in series with the output to the ECU. It can't be too far out as too rich and power would fall off. But over-rich by modern standards perhaps. And 793 ohms is pretty much the limit before the AST/Hill Start/VDC/Fuel gauge fails.

It seems clear now that whatever element is ultimately decided upon, an ECU recalibration needs to be done to optimise performance. My preference is for 055 because it is startlingly good at both acceleration and has a very broad, elevated torque level, across the revs. Stunning really!

But it is a very grey area for me. It is a question of whether the 055 can be aligned correctly without losing performance, or if the 159 bona fide element can step up its performance when re-aligned.

No more can be done until the issue of back boxes is resolved and hopefully a pair of equal - length sections to go between the Autodelta's and the Sports Cat.

However, I know now just how good "Best Rich Torque" can be. With the Porsche element, it must be pretty close as I have no black smoke, with the proper Alfa element coming in at somewhere leaner, perhaps at around Stoichiometric. Clearly economy with the 055 element will not be as good as with the Alfa element, but I will gladly forgo that, if the Porsche element can be adjusted properly.

I am absolutely delighted to find myself in this position. I can well see, I shall have to do two dynamometer runs, to properly compare the MAF Elements But hell, that's no hardship and I am licking my lips at the prospect. 

[Ascari32]

Hi Nigel,

Just keeping you posted. I resorted to buying a completely new Alfa MAF, element and housing as it was getting to the point where I did not know what to believe was correct and what was not. Two of the elements I bought, although new, were not manufactured by Bosch and I have seen various plots of the characteristics of so – called equivalents which did not even come close to the Bosch transfer characteristics.



So I thought it a good idea to start again with a bench mark I could trust.



As can be seen from the attached Dyno, the AFR of my 159 is not bad – slightly more rich as one would expect of an Alfa. However, with the increased airflow through the manifold now, and the greater fill, I expected further enrichment. This was where it was getting all too confusing. And looking back, my brand new 3.0 GTV MAF element gave pretty good results. But I could not get the MAF element I gave you to work very well at all. So, possibly it was not the correct element for the JTS or it is down on performance.



So since those initial tests I have been working with the Porsche 911 Turbo 3.8/4.0L MAF element. That is way over the top rich. And lo and behold, the element I appear to have bought is not a pukker Bosch. But, attenuating the Element output with a resistor of 793 ohms in line to the ECU worked well.



But it is right on the cusp. Apparently, the CAN bus allocates inputs which links together certain functions on a common port. In this instance, VDC/ASR/Hillstart/Handbrake/Petrol Gauge are all common to a single CAN bus port. So a failure of anyone of these will bring up a common fail on all!



However, just before the cusp, the fuel gauge will fall to zero, without bringing up a common fail of all these. So I have been using this to gauge to what point I can reduce the MAF output voltage before the fuel gauge falls to zero. It is a pretty effective tool, hence the 793 ohms resistor. On fitting a resistor, progressively the fuel injected at tick over is reduced and with it the noise level from the exhaust. And 793 ohms was as much as the Pseudo Porsche element could take.



With the Alfa boxes back on, this has made a tremendous difference to noise levels but clearly these boxes are far too restrictive, although still making good power, probably a little reduced.



It was at this point I decided to buy the new Alfa MAF unit – complete. Out of sheer frustration, I took the resistor out of the MAF o/p feed to the ECU and made a straight connection, then plugged in the Alfa insert. Bingo! Boxes still struggling to cope under load, but much, much better. Good performance, no flat spots anywhere and linear progression over the rpm. But definitely leaner, and a fair bit at that. It is said, water droplets from the exhaust is evidence that the cat is working – ignoring the times when there may be other problems. So, not only is the engine ticking over quietly, she is quieter generally, with good torque at urban speeds. But it does not have the sparkle the Porsche element brings to the performance.



In actual fact, with the Porsche element acceleration is stunning! Torque across a wide spread is "Massive".



Quote C.B.



Alfa Romeo : 159 - Brera - Spider 3200 24v JTS


The road profiles offer a good compromise between the various daily use needs of an automotive engine: regular minimum. "good torque at a low rpm, low exhaust emissions and a significant increase in maximum power."

Some of the parameters on which action is taken to improve the performance of an internal combustion engine through camshafts with a new profile are the increase in the lift of the valves, "the increase in the crossing values of the exhaust and intake valves and the duration of the cylinder filling phase." Through a correct design of a profile from the correct mix of these parameters, an improvement of the engine performance in relation to its use is obtained.

specific note for the product
Made on request



It needs a little more time to digest, but I would say it is clear the Alfa MAF is unsuitable when so many changes are made to the exhaust system in conjunction with these camshafts. Physical inspection of both the Pseudo Porsche element and the Alfa one shows the Air – flow window of the Alfa's is smaller by a considerable margin, as is the sensor element within the window. So regardless of any fuel map re-adjustment, the limiting factor is how much air can be metered through the Alfa Sensor Window!!!



Ultimately, this factor will dictate what power can be extracted from the engine with all these improvements.



However, with the Porsche element, clearly, it is capable of metering much greater volumes of air and the ECU can be adjusted to re – balance the AFR. These findings are borne out by the Bosch Transfer Characteristics of which only the lowest flow - rate element was not tested. With so little to go on, there was no alternative but to determine which element would be most suitable, by experimentation.



So future Alignment will be done with a New Genuine Porsche 280 – 218 – 055, alias 98660612501. All other elements are henceforth to be discounted.

[Ascari32]

Hi Nigel,

Just keeping you posted. I resorted to buying a completely new Alfa MAF, element and housing as it was getting to the point where I did not know what to believe was correct and what was not. Two of the elements I bought, although new, were not manufactured by Bosch and I have seen various plots of the characteristics of so – called equivalents which did not even come close to the Bosch transfer characteristics.



So I thought it a good idea to start again with a bench mark I could trust.



As can be seen from the attached Dyno, the AFR of my 159 is not bad – slightly more rich as one would expect of an Alfa. However, with the increased airflow through the manifold now, and the greater fill, I expected further enrichment. This was where it was getting all too confusing. And looking back, my brand new 3.0 GTV MAF element gave pretty good results. But I could not get the MAF element I gave you to work very well at all. So, possibly it was not the correct element for the JTS or it is down on performance.



So since those initial tests I have been working with the Porsche 911 Turbo 3.8/4.0L MAF element. That is way over the top rich. And lo and behold, the element I appear to have bought is not a pukker Bosch. But, attenuating the Element output with a resistor of 793 ohms in line to the ECU worked well.



But it is right on the cusp. Apparently, the CAN bus allocates inputs which links together certain functions on a common port. In this instance, VDC/ASR/Hillstart/Handbrake/Petrol Gauge are all common to a single CAN bus port. So a failure of anyone of these will bring up a common fail on all!



However, just before the cusp, the fuel gauge will fall to zero, without bringing up a common fail of all these. So I have been using this to gauge to what point I can reduce the MAF output voltage before the fuel gauge falls to zero. It is a pretty effective tool, hence the 793 ohms resistor. On fitting a resistor, progressively the fuel injected at tick over is reduced and with it the noise level from the exhaust. And 793 ohms was as much as the Pseudo Porsche element could take.



With the Alfa boxes back on, this has made a tremendous difference to noise levels but clearly these boxes are far too restrictive, although still making good power, probably a little reduced.



It was at this point I decided to buy the new Alfa MAF unit – complete. Out of sheer frustration, I took the resistor out of the MAF o/p feed to the ECU and made a straight connection, then plugged in the Alfa insert. Bingo! Boxes still struggling to cope under load, but much, much better. Good performance, no flat spots anywhere and linear progression over the rpm. But definitely leaner, and a fair bit at that. It is said, water droplets from the exhaust is evidence that the cat is working – ignoring the times when there may be other problems. So, not only is the engine ticking over quietly, she is quieter generally, with good torque at urban speeds. But it does not have the sparkle the Porsche element brings to the performance.



In actual fact, with the Porsche element acceleration is stunning! Torque across a wide spread is "Massive".



Quote C.B.



Alfa Romeo : 159 - Brera - Spider 3200 24v JTS


The road profiles offer a good compromise between the various daily use needs of an automotive engine: regular minimum. "good torque at a low rpm, low exhaust emissions and a significant increase in maximum power."

Some of the parameters on which action is taken to improve the performance of an internal combustion engine through camshafts with a new profile are the increase in the lift of the valves, "the increase in the crossing values of the exhaust and intake valves and the duration of the cylinder filling phase." Through a correct design of a profile from the correct mix of these parameters, an improvement of the engine performance in relation to its use is obtained.

specific note for the product
Made on request



It needs a little more time to digest, but I would say it is clear the Alfa MAF is unsuitable when so many changes are made to the exhaust system in conjunction with these camshafts. Physical inspection of both the Pseudo Porsche element and the Alfa one shows the Air – flow window of the Alfa's is smaller by a considerable margin, as is the sensor element within the window. So regardless of any fuel map re-adjustment, the limiting factor is how much air can be metered through the Alfa Sensor Window!!!



Ultimately, this factor will dictate what power can be extracted from the engine with all these improvements.



However, with the Porsche element, clearly, it is capable of metering much greater volumes of air and the ECU can be adjusted to re – balance the AFR. These findings are borne out by the Bosch Transfer Characteristics of which only the lowest flow - rate element was not tested. With so little to go on, there was no alternative but to determine which element would be most suitable, by experimentation.



So future Alignment will be done with a New Genuine Porsche 280 – 218 – 055, alias 98660612501. All other elements are henceforth to be discounted.

I believe I may be getting somewhere. And once again, it draws me to mutual influences between MAF and exhaust system - specifically rear boxes. I am not sure there is a solution which is going to be wholly satisfactory.

Someone posted the Alfa 3.2 JTS MAF has a low maximum flow rate. This seems to be borne out in my findings. I believe, it is because of the NVO of 2.5deg., before the inlet valve opens at 11.5deg ATDC. It has a very sharp rise in output voltage for a relatively low increase in flow rate. This I believe is to compensate for the shortened time it has to produce the correct AFR given the lateness of the inlet valve opening.

The peculiar thing about the JTS MAF; Bosch 280 218 182 is, it has a Venturi, within which the MAF sensor sits, which is enclosed within the main Venturi body - ie. a double Venturi system. However, the MAF element within the inner Venturi is close - coupled and the downstream screen is very obstructive - held up to the light it is virtually impossible to see light through it.

Judging by its design it directs a very linear flow of air across the MAF sensor, the "Target Window", which is much smaller than any I have inspected. The sensor element within the target window is also considerably smaller than all the others I have tested.

I think this aids both low revs and an even tick-over, despite the standard valve timing promoting lean - burn.

The problem comes when valve timing generates a massive element of scavenging, resulting in a very rich mixture at low revs. The torque under such circumstances is extremely strong and tests have shown the engine does not labour when in sixth gear at 1100 RPM. But the richness promotes very sooty tailpipes - yet no lambda codes.

However, by comparison to the Porsche 055 element, Bosch Element 98660612501, top end acceleration is "Mundane".

Cruising in urban environments is silky smooth and the engine and exhaust system is extremely quiet, only becoming raucous with enthusiastic application of the throttle. Still it is a lot better than hitherto. And given traffic conditions today, 90% of the time is spent on roads at low speed - 40 to 50 tops. Even so, at 70 she is very civilised with little intrusive noise in the cabin.

However, when the Porsche element is fitted, the airflow within the inner Venturi is such that there is considerable exhaust system noise. Hence, to tone it down a 733 - 793 fixed value resistor has to be fitted in series with the MAF output and the ECU input. Although noise levels are generally higher, it is the performance of the engine at higher revs which is remarkable. It is really powerful and the car accelerates very, very quickly. Exhaust deposits are much reduced too! But, although better than a Standard 3.2 JTS at low revs - very tractable - it is not as good as when the 182 element is fitted.

I don't think there is a solution to this. To fit the Porsche Body and element, will introduce more turbulence in the inlet tract as the 055 element just sits in a single Venturi pipe and the inlet tract is not really long enough; after the air filter, to linearize the airflow by eliminating turbulence. So I think; although I have not tested the theory, with 23.5deg. POV, the tick - over would become much more unstable - lumpy.

I need to put this to bed and return when more information is available for a permanent solution. So I intend to run with two MAF  elements. They are quickly interchangeable in any case.

So, for the kind of day to day driving I shall be doing, ie. 90% urban/small country roads, I plan to leave the Bona Fide JTS element insitu.

But for long journeys on high speed roads, the Porsche element - a new 98660612501 will be fitted. To create swift interchangeability between the two, the cover of the Bosch element will be removed and a resistive element fitted inside: PCB to Pin (5) will be disconnected and a small Ceramic ~ 750 ohm resistor fitted. then outwardly, there will be no obvious supplementary network in - line between the MAF connector and the ECU wiring harness.

The value of the resistor may well differ in the final analysis as there could be some difference when I get the genuine Bosch Element, as opposed to the one I have been using for my tests - ie. some unknown manufacturers would - be equivalent.             

[Ascari32]

The Ascari Back boxes have dropped out of the equation - Hurrah! Sold them for 200 quid, despite pointing out all of my issues with them. The guy has a standard 3.2 JTS and doesn't intend to modify his car, but simply wanted a different "Sound". Should work better than they did on mine. But if they are anything like mine above 3000 he will be happy. That's 200 quid towards my Supersprints,  or whatever.

However, in anticipation of getting a genuine Bosch 98660612501 element, I saw no harm in experimenting with my "New but not genuine" 280218 008. This element - well the genuine article - sits above the 019 & 531 elements, but below the 98660612501 and runs out of steam at 850kg/hr - well above a 3.2 N/A engine's needs. But the output voltage is higher than 2501, giving me more to play with in bringing it back down to a figure that my ECU input is happy with.

Also, if I wrecked it in the attempt, it's not going to be too painful as it will just gather dust amongst other redundant parts cluttering up my garage.

Anyway, Pin (5) output connection was separated internally from the PCB motherboard and a 820 ohm, 1/4watt resistor fitted in place. I had tried a 1k ohm but the engine was a bit rough although perhaps I should have allowed it more time to auto - adjust. But living in a village it is our only means of transport and I did not simply want to go back to fitting the 280 218 182, the original engine MAF element. That remains my "Reference element" and will only do A/B comparisons when I believe I am close to where the performance of the engine should be.

Well, after another test run and allowing it more time to auto - adjust noise levels crept up a shade more than with 182. Better than 182 with acceleration noticeably quicker.

I didn't make a bad job of soldering the 820 ohm resistor under the cover - in fact quite neat really given my eyes are shot to bits at close distances, even with glasses. So today I will pull the cover off the Pseudo 055/2501 element and do a similar exercise. The 055/2501 when fitted with the 793 ohm resistor is quieter than the 008 element with 820 ohms, but I think the 008 may just be a bit sharper at low revs.   

[Ascari32]

Attached picture is of the modified 280 - 218 - 008 element now fitted to my Q4. It was seen as both a practical exercise and an interim experiment until I get my hands on a genuine 98660612501 insert, but wasn't intended to be other than a practice run for the final modification to the 2501.

As a secondary exercise I plotted the response of this element, with 820 ohm fitted, against the "Pseudo" 2501 fitted with 733 ohms fitted. In essence, they; for all intents and purposes are identical, although the 008 does not extend beyond 850 kg/hr.

Having allowed the 008 to auto - adjust, it has now settled down to provide exceptional performance. True, the engine is running a little rich by modern standards, but it must be somewhere close to best mean torque because it lacks nothing, in any gear, pulling very hard and fast from low revs. The only issue being the restriction of the Alfa boxes causing and increase in sound level due to "Throttle - induced fuel enrichment." But the levels are considerably lower than hitherto.

However, achieving "Drone Free Performance", particularly at 70 mph, circa 2500 rpm was fast becoming a Pipe - dream, a Utopian Goal, never to be realised. I never dreamed the car could be so quiet at seventy - it's like another car!!!

I am still absorbing just how things have changed. It is sublime, pulling strongly with very, very low acoustics coming from the exhaust system and when accelerating hard in lower gears, the engine is so melodic.

Believing I had identified where the problem lay, particularly given only the Alfa boxes remain, it has been a massive exercise in trial and error, whilst trying to rationalise all factors involved, not least the MAF suffering from the non linearity of the Ascari Boxes because of the new exhaust system's transparency.

Having sold the Ascari's, the cash from which will go towards my new boxes, I have considerably more confidence that this thing can be tamed, without having to sacrifice performance due to exhaust system restriction. I have not made my mind up about which to go for, Supersprint's or Ragazzon's, the former being more expensive. However, it is a question of how long it is going to take to get them on my car. I would also like to get a pair of equal length sections for between the Autodelta's and the Cat. But I'm no further forward with that.

In conclusion:-

Understanding better the relationship of the MAF to the ECU has been a real eye - opener. I expect that when I finally do get the rear boxes, I will again need to optimise the MAF element by way of modifying it's operating threshold. But this exercise has demonstrated the clear link between AFR and exhaust noise, exacerbated by Non - Linearity in the first instance; such that the Ascari's introduced, and Back - Pressure caused by over - restrictive absorbsion boxes such as Alfa's.

But I am starting to view the modification of the MAF element as akin to changing the Jets or Venturi Tubes of carburettors. Logic; well mine anyway, seems to suggest there is nothing I can do about the threshold level the ECU needs in terms of lowest MAF output voltage. So that element will need to be addressed by software modification.

However, my original Dynamometer plot indicated over richness: 13.3/5:1~ 3000 - 5000 rpm - Lean Best Torque, to 11.5:1 Rich Best Torque above 5000 rpm. So it would seem, my exhaust was always going to be on the sooty side.

So I am happy for it to remain thus until this exercise is finished. I am becoming quite adept at picking up on small changes in performance as result of the changes I  make to the MAF. And to be rewarded by the elimination of any droning and indeed virtually all exhaust noise in the cabin when cruising at motorway speeds - notably 70 MPH is, for me - a real triumph.

I would not say it was akin to "Tuning a Piano by Ear". But hey! it comes close when for so many weeks, it seemed I could never resolve the problems this revised exhaust system created. However, I never reached the point of despair where I thought I had made a mistake in buying the Autodelta's, the Supersprint 100 CPI Sports Cat and Stainless Steel centre section. Or for that matter, the Colombo Bariani Camshafts.

But that; I think, is a function of my background as a Prototype Engineer. Always believe you are doing something wrong and re - test. And re - test again, and again -------------- and again. Eventually meaningful changes, sometimes very small ones, can be the difference between success and failure.

I'm not there yet. but the end is in sight!

     

[Ascari32]

Sorry,

For some reason, although I thought I attached the MAF Sensor, it wasn't sent!

I couldn't wait for Farnell to deliver the ceramic resistors I ordered, so I squeezed a "normal - Vintage" component. Fitted just right and cover goes back on nicely.