What the stock 75 TS Motronic can and cannot do. - Alfa Romeo Bulletin Board & Forums

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post #1 of 815 (permalink) Old 01-06-2012, 06:04 PM Thread Starter
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What the stock 75 TS Motronic can and cannot do.

The first eight of these posts were made by several people regarding this subject. However they were located in Engine Conversions under the title of "Twin Spark head on 2L Nord Block".

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post #2 of 815 (permalink) Old 01-06-2012, 06:05 PM Thread Starter
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One important detail most people overlook when 'carbing' the std TS engine, is the intake timing variator (ITV for short) which most of the time is -unfortunately- removed. The std TS intake cam has 12mm lift and a duration of 300*-definitely not what you'd call 'road spec'.. By moving it around ~30* we can have both good low speed tractability and high end power. If the device is removed, we are left with a pig of an engine! It will either work well low down or high up, depending on where you have timed it, but not both! The VIT device operates by taking load and rpm info from the ecu. Load info is lost with carbs. A simple throttle switch won't do. One practical way to restore this operation is to employ both a throttle pot and an rpm signal. These two inputs are fed into a comparator cct and they dictate when cam shift will occur. The cct will have two trimpots which will allow you to adjust the point at which the cam solenoid is powered, ie throttle angle and rpm. I have done just that in a similar mod and it transformed the car. If however you choose to install Godzilla cams, the VIT can't operate as you'll have definite (and fatal) v/p contact. Cam sellers are careful to point out that VIT must be disabled.
Jim K.

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post #3 of 815 (permalink) Old 01-06-2012, 06:07 PM Thread Starter
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Quote:
Originally Posted by Jim K.
The std TS intake cam has 12mm lift and a duration of 300*-definitely not what you'd call 'road spec'.. By moving it around ~30* we can have both good low speed tractability and high end power.
I assume that is 30 crankshaft degrees = 15 camshaft degrees.

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.....The VIT device operates by taking load and rpm info from the ecu. Load info is lost with carbs. A simple throttle switch won't do. One practical way to restore this operation is to employ both a throttle pot and an rpm signal. These two inputs are fed into a comparator cct and they dictate when cam shift will occur.
What's a "comparator cct"?

Can you outline what the algorithm is to compute when to energize the ITV as a function of rpm and % throttle position? I know the precise formula would depend on the engine's state of tune, but in general, how are the two inputs combined to produce a step function in ITV solenoid voltage?
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post #4 of 815 (permalink) Old 01-06-2012, 06:07 PM Thread Starter
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Can someone verify what the increase on the compression ratio - assuming the head hasn't been milled - would be by using nord rods? I (thought I) read where it would then be 11:00 to 1. I'm going to have Spruell modify a set of their TS pistons to come up with 10:3 to 1.

Jim K. yes, I too have both of your 4-cylinder Alfa books. When I read in a Bosh manual what the mid 80's Motronic does to meet numerous driving/running scenarios - whereas frequently the fuel and both the ignition and cam timing are affected, I'm thinking that not even a good aftermarket EFI system would be nearly this 'efficient'. And using carbs, oh why would one do that?

Is the stock inlet cam timing set-up the ideal setting? I'm referring to the initial setting of the inlet cam during a rebuild.

Sorry to do a bit of hijacking here.

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post #5 of 815 (permalink) Old 01-06-2012, 06:08 PM Thread Starter
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Std TS timing: open between 29-22* BTDC, close between 90-97* ABDC (hi rpm).
Open between 61-54* BTDC, close 58-65* ABDC (low rpm).
No fancy stuff like algorithms etc for setting rpm and throttle angle switch points, just trial and error by searching where the best all-around performance is obtained by driving the car in all kinds of traffic conditions. The owner/driver is the final judge of where the cam will switch!
Rather than explain the comparator lets consider it as something easier, a black little box with 2 changing inputs and one output. The output is enabled when the two inputs reach the preset points (chosen throttle angle and rpm) which can be set with two trimpots on the pc board.
For such carb conversions, when no VIT is present, it would probably be advantageous to regring the intake cam to some other spec with less duration to improve low speed tractability.
There is no ideal cam setting, you can't have the best of both worlds with this profile.
As for Bosch ecu's vs aftermarket, I don't think anyone is naive enough to believe any private company has enough resources to refine their product in a better way -for road use. The same is true for competition; what I mean, is if Bosch decides to specially map a high-end racer, it will most probably have better all-around performance than anything offered by other specialty ecu makers. If you argue 'it ain't so', it will take names like Zytek to compete -and at what cost?
Jim K.

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post #6 of 815 (permalink) Old 01-06-2012, 06:09 PM Thread Starter
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Jim:

Thanks for the explanation.

I think what you are saying is that a home-brewed algorithm could be as simple as "turn on the IVT when both of these conditions have been met: throttle position exceeds X% and engine speed exceeds Y rpm".

But that Bosch might be using something more complicated, perhaps using engine temp. or the product of throttle position and RPM as a parameter.
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post #7 of 815 (permalink) Old 01-06-2012, 06:09 PM Thread Starter
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Not wanting to hijack the original idea of this thread, so will move it to a separate thread if this 'area' continues.

That said, I'm glad to hear that I'm correct regarding the sophistication of even mid 80's Bosch EFI technology.

The 75 TS shop manual treats the installation of the cams the same as if they're nord cams. Yes, being a bit lazy but has anyone made lists of what happens - or more precisely, what benefits are there - if the inlet cam is slightly retarded or advanced? I'm assuming the exhaust cam remains in the stock position, though that might not be the case.

Also...assuming I go to 10.3 to 1 pistons is there any likelihood of cam/piston interference when trying retard and advance positions for the inlet cam?

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post #8 of 815 (permalink) Old 01-06-2012, 06:11 PM Thread Starter
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Starting with the last question, I don't recall what v/p clearance there is in the TS engine on overlap.
Altering intake cam timing is a bit involved in the TS, as its not like the exhaust cam (which follows normal Alfa tradition). You need a couple of huge wrenches to loosen the big-a$$ mechanism and then you can play with 60 little teeth, which connect the front part to the rear. Therefore you have 60 teeth of leeway. Well, thats 6* /tooth -cam degrees. If you also count the number of chain gear teeth, you can vary timing in smaller increments. Blaaaah! Performance cams usually have the same gear sprocket as the exhaust so life becomes easier (however, no VIT). I personally haven't played with timing these cams back and forth, nor have any of my cronies here. I guess that on efi engines, people tend to change eprom chips rather than playing with cams. One possible reason is the fact that they're afraid it'll require costly mapping every time, for perfect results.
I built an engine recently with 12.5:1 pistons from P.Spruell, 47mm valves and Godzilla cams from Alfaholics. V/p clearance is a huge 4.5-5mm so I suppose there's plenty room to play (don't ask, the engine is not in the car yet).
Jim K.

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post #9 of 815 (permalink) Old 01-06-2012, 06:12 PM Thread Starter
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Quote:
Originally Posted by Biba69
That said, I'm glad to hear that I'm correct regarding the sophistication of even mid 80's Bosch EFI technology.
I've just fitted a modified 25 year old Delco (GM) ECU to a nord engine, and it's certainly very sophistocated compared to the aftermarket ECUs that I've looked at.
There's over 500 tuneable parameters in the firmware, not counting map cells
This ECU would have no problem driving the IVT, there's a couple of PWM outputs that can be mapped to things like engine load.

One area that this ECU shows it's age though is lack of sequential injection, and that's a hardware limitation so can't be overcome with a firmware change.

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post #10 of 815 (permalink) Old 01-06-2012, 07:17 PM Thread Starter
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Jim, if you've made the transition... What kind of gas/petrol/benzina do they have in Greece that you can use 12.5:1 pistons? I'm aware that some automotive manufacturers are upping the compression ratio fairly high - I assume it is more efficient - but you can't even use a knock sensor on a TS or nord. Although I'm sure the fuel in Greece (or anywhere outside the US) isn't spiked with corn gas.

I should know their names but there are 75 TS Motronic chip guys in both the UK and the Netherlands. I've exchanged emails with the fellow in the Netherlands and he implied that his Motronic chip would have no problem handling higher compression and 'larger' injectors - though suggested I bring my Alfetta GT by his place and put it on his dyno so he could make a custom chip. That's a long drive from SoCal.

I've been following the "Programmable Ignition" thread in Engine Management and the consensus seemed to be that dual MirelliPlex or MSD units would work fine on a TS. Any opinions on this?

I'll throw this into the mix but I've found only one thread regarding NGK's Iridium spark plugs. I've been using their BPR6EIX plugs for a couple of months and am very impressed with them. Interestingly the part # for the 75 TS is BKR6EIX.

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post #11 of 815 (permalink) Old 01-06-2012, 07:28 PM
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Why do you say you can't you use a knock sensor on a nord? Because of the cam chain noise?


--------------------------------------------------------------------
fast forward a few weeks and a couple hundred posts:
We've made significant progress with understanding the
ML4.1 ECU - both what it does, and how to modify/tune the system.

For newcomers to this thread who want to jump straight to the
details rather than read the whole thread, there's an index to some
of the more interesting technical information here.
---------------------------------------------------------------------

Last edited by festy; 01-23-2013 at 09:18 PM.
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post #12 of 815 (permalink) Old 01-06-2012, 07:43 PM Thread Starter
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I've just been told/read that the nord and TS 'make too much noise/vibration? (in general?)' for a knock sensor to be effective. However, I'd love for this to be proven wrong.

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post #13 of 815 (permalink) Old 01-06-2012, 08:12 PM
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I'm (slowly) working on making a digital knock filter for my nord, using DSP and RPM derived gain to separate knocks from the noise floor.
Running the knock sensor on the back of the engine gives a better signal than the front, and although the valvetrain still produces a fair bit of noise, the knocks occur in a very specific frequency range (around 6.8KHz from memory for a 2L nord) so a bandpass filter on the input stage *should* clean most of the background noise up.
Windowing would really help a lot too, but I haven't worked out an easy way to get the necessary signal to trigger that from my ancient ECU yet...

I'll let you know if it works when it's finished
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post #14 of 815 (permalink) Old 01-07-2012, 11:05 AM
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In all our $hitty predicament here in Greeceland, we at least have good pump fuel, the well-known (in Europe) BP-Ultimate, Shell V-power Racing and many other brands, all claiming around 98-99ron and the cost is ~1.70€/liter. There is definite performance difference between these and the 'normal' 95ron, going for ~1.58€/liter.
The particular TS, has 12.5:1 cr, and 300* intake, so I don't anticipate any problems. As another indication, consider that my 'road' 1.8T has 8:1 (up from 7.5:1) and I run 1.3bar (19psi) with a 10548... intake cam. So, fuel is good!
The 1.8T has a knock sensor as std so I wouldn't worry about the feasibility of putting it on the TS or any other Nord. It is fixed on a stud between cyls 2-3 on the lower side of the intake manifold. Here's how it works: when it detects knock, it retards advance (all cyls) by 2* at a time until knocking disappears. If the max of 8* retard is exceeded, it signals the famous Pierburg solenoid valve which opens the wastegate! Very effective -remember now, this is a 1985 design! As a matter of fact, if you try to increase static advance to greatly improve low speed tractability (from 8* to ~15* BTDC) the engine won't boost at all -ask me how I know
I've also talked with Stephan Lenior (Squadra Chips, Holland) and he usually insists on people taking their cars to him if its anything other than a std engine. He is right as only on the dyno he can tailor-make a proper map. Fortunately, we have several people here who can do the same -mapping of a std ecu runs ~400€.
Few years ago, I made a knock sensor cct for a friend who maps cars. The display is a series of LED's; he says its a great help in properly mapping an engine on the road. Now, if I could only design an ignition to fire a plug just before the verge of detonation....Maybe in the next lifetime...
Jim K.
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post #15 of 815 (permalink) Old 01-07-2012, 05:15 PM
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This is an excellent idea for a thread topic.
I'll add a couple of thing here that based on research but aren't necessarily Bosch specific.

Some/most older engine management systems stop listening to the knock sensor after a set engine speed. This is because the noise filtration circuits couldn't cope with the sheer amount of racket and that racket could cause false knock signal causing the computer to do what it does to deal with knock. Whether that's what Bosch were doing back in the day, I don't know.
Higher processing speed computers and better (digital) noise filtering systems would help a lot here.

Narrow band exhaust gas oxygen sensors can only supply a very limited amount of information. They obviously help during low load (cruising down the road at anything upto highway speeds), normal operating temperature condition to keep the engine around stoichiometric air/fuel ratios. The ratio where catalytic converters work the best. This is not best for fuel economy.
The other advantage the EGO sensor give to digital engine management systems is to allow the computer to help deal with wear in the fuel system that accumulates over time. What tends to be called long term fuel trim(s). As pumps get older, their pressure may drop a small amount. Injector flow characteristics can change and the fuel pressure regulator may also start to get old and not hold correct pressure over all of the pressure range it needs to work. The feedback from the EGO sensor allows the computer to calculate an overall correction to injector pulse width and apply it to just about all operating condition.
What needs to be understood is that there is a real limitation to this. It can only be learned during close loop conditions (the computer won't know if your engine is running stupid rich or lean at high loads) and is probably an overall percentage of change applied to injector open time. I don't know how much capacity for this the older systems had, but the earlier systems were built with simple processors (compared with wht's used now) and small memory, so I would be reluctant to try and expect them to deal with injectors flow changes (up or down) past 15% (experiments would need to be done to get real answers about any self learning of the ECU).
Engine management systems using narrow band EGO sensors don't look at the signal from the EGO at high load. It doesn't have enough meaningful information in it do be useful.

Imagine this:
You've modified the engine to make significantly more power. More than what the factory computer can tolerate in terms of fuel delivery, anyway. So you figure (measured and calculated) that the engine needs 20% more fuel flow at full power. So you manage to get this by cranking in extra fuel pressure via an adjustable rate fuel pressure regulator. Now as you cruise down the road, the engine doesn't need to make more power to do that job, and is getting 20% more fuel than it needs at anything other than full load. At full load, it's running sweet (good AFR on a wide band meter).
Lets say that the ECU can deal with 20% extra fuel in a cruise condition and starts to 'learn' what correction it needs to apply to get injector open times back to a point where the computer can again go into proper close loop during cruise. After a while (hours/days), the long term fuel trim applies an overall correction of 20%. It's only doing what the engineers designed it to do but it doesn't know that the extra 20% of fuel you added was needed at full power. And that correction is applied EVERYWHERE because that learning is used to allow for wear and tear and small production variations.
After the ECU learns that correction, you may well stick your boot into it and have your engine run dangerously lean. 20% lean or there abouts........

Slowly Progressing Vortech Supercharged 1990 Alfa Romeo 75 Potenziata. Out of Action Twin-Charged 1988 AW11 MR2. Current Daily Driver, The Glorified Taxi 2006 BF FPV F6 Typhoon.

Last edited by Duk; 01-07-2012 at 05:30 PM.
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