Author Topic: Fact or Fiction - you tell me!  (Read 390 times)

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Fact or Fiction - you tell me!
« on: October 22, 2021, 08:09:15 PM »
After all the travails surrounding my Modified 3.2 JTS Q4, I finally bought a pair of Supersprint rear boxes.

I did not want to throw good money after bad; Ascaris, so I have tried every which way to make them work. But it was painful to acknowledge they probably never would. Even more painful that the Supersprints would cost me 814 delivered.

I communicated as much as possible, the information which came out of my various attempts to make them work, to Supersprint. The response was both very quick and the information freely given was very revealing. They had already provided me with a great deal of information about the shortcomings of the Alfa Twin Cat - which I had already decided would be binned.

In frustration, at one point I said I would be more inclined to leave the tail boxes off altogether than suffer the unholy racket they make, if I thought I could get away with it!

In my attempts to make them work I had them strengthened and that seemed to work, reducing vibrations transmitted into the bodywork. But the partial blockage input to output, across the central empty cavity was insurmountable as it causes reflections back towards the engine, vibrating the stainless steel centre section and generating noise inside the cabin.

I was able to mitigate this to a degree, by experimenting with MAF elements and also the quiescent output to the ECU. One aspect of this was very successful insofar as I realised the Standard JTS MAF element was wholly unsuitable with the modified engine, causing over - richness at low rpm and lean running at the top end.

Eventually a 3.8/4.0L Porsche 911 Turbo MAF insert was bought and it seemed ideally suited. However, the system was still too noisy and with the Alfa boxes, restricted the exhaust gases drastically. So it seemed it was a case of "Damned if you do and Damned if you don't". I left the 270 ohm resistor in series between the MAF output and the ECU input in place however.

After my remarks to Supersprint with regard to leaving the back boxes off altogether, they responded by saying: -

"Our rear silencers are like having an open pipe. They have exceptional aural damping characteristics, without restricting gas flow velocity". They went further than that, but I feel it would be unfair to disclose information given in confidence as to why this should be the case!

So, on the 18th Oct the Supersprint rear boxes were fitted. Immediately there was a big reduction in sound level, and the engine spooled up even more quickly than before. With the Alfa boxes, although overall the engine response is vastly superior to that of standard, it is nothing anywhere like as fast as with the SS's.

The Ascaris are much less restrictive than the Alfa's but the reflections cause a god damned awful racket through the body work and the central section and cat until 3000rpm and above.

However, with the SS's there is a uniformity in the sound, completely free of any resonances anywhere across the rpm range. What I did notice however, was a slight metallic "Tinkle", which I communicated to Supersprint, thinking it was coming from the region of the stainless steel centre section/sports - cat. It was however, not irritating and only appeared to occur when stabbing the throttle.

After two days, and only just becoming accustomed to the way the car had changed - aurally and in character - throttle response superb: able to balance the car on the throttle so delicately, it was even more noticeable how on lift - off approaching a bend, the car would run - on much more, would need to touch the brakes where hitherto I didn't need to.

I rationalised this was further affirmation of reduced engine drag/inertia. The recourse was to lift off the throttle earlier before the bend to give the car a chance to loose speed, rather that touch the brakes.

However, there was still the issue of valve timing being set up, when the engine is cold, to provoke fast light - off temperatures in the cat. This fundamentally causes excessive noise in the exhaust system for about a minute, before it settles back to a tolerable idle.

It was at this point I remembered the 270 ohm resistor fitted to the MAF. Logic; deduction from experiments had indicated this resistor had reduced noise within the exhaust system. So, did I need to "adjust the value"? It seemed that I was going to have to start from scratch again. I was reluctant to touch it just yet as my wife was in hospital for an operation on her knee - split it clean in two when she fell on the sharp edge of our concrete drive. So I left it untouched, two-ing and fro-ing the 16 miles between us and the hospital. It is amazing how subtle things draw your attention when your mind is elsewhere - worrying about my wife and the impending operation on an otherwise healthy 72 year old type 1 diabetic.

Now she is home and now I am playing mother. However, mobile phone at hand, I decided to look again at the Porche MAF element. Deciding to press reset and go back to basics, I removed the 270 ohm resistor and connected the MAF up as standard.

Net Result: -

Exhaust system sound has dropped to a level suggesting sportiness but not dramatically loud. And the "Metallic Tinkle" has disappeared!

Conclusions on that are, whereas hitherto the 270 ohms corrected over - richness at tick-over/low rpm, it was now, with the Supersprint back boxes, causing leanness at the top end. It will take the ECU some time to normalise to the new MAF conditions but it is getting there.

In the mean time the off throttle over - run is delightful - better again than with the Alfa boxes. Engine drag has significantly reduced further too! So much so that, whereas 5th or even 6th gear in bends on country roads was fine given the engines flexibility in high gears, yet low on revs was acceptable, now with so little speed being pulled off the car, fourth gear has become de rigour. It seems 5th & 6th are now back to functioning on major roads/motorways and fourth is more than adequate for lesser roads.

In fourth, the dramatic improvement in throttle response and the massive reduction in pumping losses has resulted in sublime through - bend balance on the pedal, with exquisite over - run emanating from the tail pipes. There is a tightness, almost a link between the foot and the way the engine responds to the lightest of touches by the foot. I swear the car seems no heavier than my 3.0 GTV, the way it shrugs off its weight.

The MAF/ECU relationship is still not normalised and just occasionally I get a misfire when the engine is not quite hot enough and I am too enthusiastic with the throttle, but that will sort itself out over a few more miles. I had been suffering from intermittent EML's, appearing, then clearing. However, on fitting the Supersprints, the standing EML cleared as I left the garage and has remained so!

There is so much one can learn about engines - so many eminent engineering studies to learn from. Which makes it seem so perverse, given exhaust systems remain a "Black Art", and yet modern - day enthusiasts of this marque are more inclined to tamper with their exhaust systems, rather than the one thing that makes all Alfas special - their engines.

My advice is - Study the engines and leave the exhausts to genuine experts. When Adam unpacked my rear boxes, without looking he said - "They are still going to be Loud". Then he said, "These are Supersprints, the best there is! - do you mind telling me how much".

More to the point, after he fitted them, he hit the throttle and it all fell into place. The pedal was like a trigger and the response was like a gun firing - instantaneous!




ps. I need bigger brakes now and better shocks and springs as the driver is lucky - he has the wheel to brace him. Passengers sway left and right on even the most modest of bends, at speeds which hitherto the body would never roll at!                   


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Re: Fact or Fiction - you tell me!
« Reply #1 on: October 24, 2021, 11:32:53 AM »
Good to hear. The brembo brakes of the 3.2 awd jts ti with some ebc yellow stuff or blue stuff is more than enough for street driving. Get some michellin ps4 and that will be enough. Don't need bigger aftermarket brakes.
159 3.2 JTS TI

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