Hi Torque starter motor

[lowact]

Has anyone ever measured crankshaft torque of a reassembled V12 engine after fitting new (std) bearings, seals, rings? I measure 67 Nm (<50 lb.ft) with the engine nicely lub’d and without sparkplugs or any peripherals, not even a water pump. Is this reasonable?

Trouble is that the OEM starter can barely turn it over. My geared starter does better but still not good enough imo, i.e., with a powerful jump starter initially 12 – 13 V:


Marek, I have 29 mm diameter pinion with 134 tooth flywheel. My interpretation is that you have a 25 mm dia starter pinion with 160 tooth flywheel (engine number is >7000), in which case you would have 20% more SM torque than me. Of all the V12 variants, I have the one that had the weakest starting arrangement.
Also, your fuel rail pressure will be much lower than the 30 bar pressure of my LPi (liquid propane injection), so you do not have the issue that I am facing. I will need good voltage when starting, to enable the injectors to open against 30 bar fuel pressure. If starting voltage is too low, the injectors may not be able open against 30 bar, no fuel, no start.
This is a real issue (not just with LPi) that gets airplay on ecu forums due to it is frequently misdiagnosed. I.e., switch straight to start, it just cranks. Switch off & try again, this time the car starts. Could be a need to fine tune the initial fuel settings. Or it could be the injectors did not open, because volts are too low when the starter is engaged. After letting go of the starter, while the engine was still spinning down the voltage recovered enough for some pulses to be injected, enough so that so on the 2nd attempt it started.

Starting with LPi involves operating the fuel pump for < 1 minute prior to cranking in order to purge/condense any vapour and pressurise the fuel rail to 5 bar above the 25 bar tank pressure. Then, because I am triggering by a 36-1 wheel on the cam (distributor), I will have to crank up to 2 revs before the ecu knows enough to squirt sequentially. For minimum cranking I could initially batch fire, although injectors are nominally (@ 12 V) 4 A peak, I A hold, i.e. ~ 48 A injector current draw which would further drag down the starting voltage at a critical time.

So maybe, for me, a geared starter is essential, despite they are noisy and only engage 2/3 of the tooth width …?

[MarekH]

It sounds like you are making an argument for having a good battery, rather than "needing" a high torque starter motor.

The v12 engine you are starting is still the same engine, irrespective of fuel type, so the same amount of work has to be done in starting it. By comparison with the carburettored engine, you are injecting the propane into the air runners, where it vapourises and becomes perfectly mixed, so from that point onwards, your engine ought to be easier to start than the carburettored engine, especially as you will work from a fuel map which meters out exactly the correct amount of propane rather than an unatomised random quantity of petrol, not all of which reaches the cylinders in a timely manner. Against that, you have more electrical devices to run prior to startup than the carburettored car does.

Your ECU may well batch fire at cranking speed anyway. It doesn't necessarily have to turn the engine fully twice over just to find a cam sensor to start up. If it does, it'll know not to inject needlessly. It also ought to adjust injector opening time for dropping voltage.

A high torque starter uses the same energy as the old Lucas to fire up the engine because the same net work is being done - all that changes is one will use more current and less voltage than the other and on a different time profile. The critical thing to get right is the fuel quantity versus temperature.

I hadn't considered the number of teeth on the flywheel, but that was always a constant in the before (carburettor) versus after (fuel injection) argument. There is nothing wrong with having a high torque starter; it's just my experience that this is wrongly attributed to helping starting when it is actually just masking the wrong amount of poorly atomised fuel delivery.

Your car should start faster at all temperatures than the carburettored equivalent as you have done away with float bowl fuel level, the randomness of the choke lever setting, the poor atomisation of fuel and condensation of fuel all around the inlet manifolds, all of which has to be paid for with cranking.

On a more worrying note, my v12 spins over at 120rpm with plugs in and at 160rpm with the plugs out. On that basis, it sounds like you may have a tight engine. I'd try to prelube it with an inseticide sprayer into the oil sender port until the oil light goes off and then look at a start attempt. FWIW, I had the same trouble as you when I started my "new" injected v12 on petrol for the first time. Both the heads had to come off, piston rings derusted and the crank loosened and retorqued before it freed up - it had been standing far too long without ever having been started.

To test whether you have a physical problem, pull all of the unnecessary fuses and see what speed you turn over with just an ECU (for logging purposes) and a starter motor connected. If it is lower than 120rpm, you have an engine problem and the whole injection talk is a red herring.

kind regards
Marek

[Fspp369]

Marek
Noting your observations in this case but thinking about the HE Efi engine, (mine) because the injectors stuff fuel in, on a slightly OTT basis, do you have any recommendations about the type of injector used and if the voltage drops during the start cycle, expectedly, then are there more efficient injectors that work/draw less current and hence drop the voltage less?
Or am I plunging up the wrong throttle body without a filter?
Peter

[MarekH]

Your injectors have to match the hardware and the software that act as drivers to open them and keep them open for the right amount of time, so you can't just swap things around and expect it to correctly fuel the engine.

The earlier v12 HE ran low impedance injectors which flowed ~180cc/min. The 1995/6 used high impedance injectors. It's the pre-HE fuel injected engine that ran the higher flowing injectors.

Unless you run an ECU that allows you change the settings, you can't do anything other than swap out the same part number equivalent components. (Best start a separate thread for a totally different topic. This thread is, it turns out, about an engine that turns over slowly at cranking.)

kind regards
Marek

[Fspp369]

[MarekH]

Colin,
do you have any "lost volts"?

With the battery disconnected, is there any significant resistance between the battery terminal and the starter motor connection? By the same token, is your grounding strap from the block back to the battery earth terminal similarly spec'd?

Any resistance depletes your starter's ability to run.

Aside from having to prime a high pressure pump, you ought not be a significantly worse position than the rest of the v12 fuel injected community. With a view to that, appended is a screenshot of a table of the car starting at different temperatures on both propane and on petrol. Your data will be different but the trends ought to be the same. It's a v12 HE with skimmed heads ~13.5:1. Cranking time is generally ~0.5seconds and the slowest was a heatsoaked 1.6 seconds.

kind regards
Marek

cranking pulsewidth start comparisons.jpg (252.78 KiB) Viewed 1783 times

[lowact]

On a more worrying note ... If it is lower than 120rpm, you have an engine problem

That's were I'm at. Engine is still out, sitting on blocks of wood. Very reluctant to reinstall it before I have a handle on this issue. I.e. I'm testing a bare engine, no alternator, fuel pump, steering pump or water pump. Starter motor directly connected to 1800 A jump starter.

The torque values I posted were measured with a torque wrench on the crankshaft. I am hoping someone will have done the same, can confirm that my 50 lb.ft without plugs is about right? Before fitting the starter I was thinking it was turning over by hand relatively easily ...

If it is just a tight motor then I'll push on, as long as it will start, it will loosen up eventually. However, to have any chance of starting, clearly, I will need the hi torque starter motor, which is the subject of this thread ...

[jagwit]

This thread is, it turns out, about an engine that turns over slowly at cranking.)

IMHO:
This thread is, it turns out, about an engine that IS BELIEVEDTO BE turning over slowly/too slow at cranking. Its not like the problem engine's cranking rpm was actually measured was it?? Or did I miss that bit?

[lowact]

Yep u missed it. Technique wasn't very scientific, or difficult. Count the revs during 10 seconds of cranking.

[MarekH]

For minimum cranking I could initially batch fire, although injectors are nominally (@ 12 V) 4 A peak, I A hold, i.e. ~ 48 A injector current draw which would further drag down the starting voltage at a critical time.

It isn't going to draw 48amps AND drag your voltage down.

Let's do some maths.

The way a peak and hold injector driver works is that it'll draw 4amps for about 1mSec (the time it takes to open the injector), then it'll draw on average, 1amp (in a staccato way) to keep the injector open for the rest of the commanded time. At 120rpm, that's 2revs per second, that's one engine cycle per second, so even a mammoth 25mSec pulse of fuel represents a duty cycle of 0.025:- 2.5%, so the average current drawn is SMALL because it isn't drawing any current at all for 97.5% of the time. Now add to that that you are injecting liquid, not gaseous propane - it'll ought to ~250 times lower than that.

If these figures don't inspire, then consider that the next best comparison will be a common rail diesel - these run at very high pressure but diesel cars still turn over and start.

My p&h setup runs gaseous lpg injectors at 6amps/1.5amps and it's never blown a fuse. The voltage doesn't drop past 9.8v even at near zero temperatures and that's because of the starter motor running, not because of the rest of the kit. It's never blown a fuse (yet).

Your problem appears to be that you have an engine you can't turn over, irrespective of what its ancillaries are. I base that on your reported cranking speed and even lower voltage. And ten seconds is a long long time. Your wiring will be more than "warm".



kind regards
Marek

[lowact]

Yep, more than warm. Didn’t test the OEM starter with the plugs in for the full 10 seconds, stopped at the first whiff of lacquer being cooked. So, from that test the reported cranking speed (30 rpm) is half guess.

Staying on topic just for the moment. What I’ve demonstrated conclusively is that, compared to OEM starters, a little geared “high-torque” starter will: spin your engine faster, draw less than half the current, not drag down yr voltage nearly as much. I.e. significantly better performance together with massively reduced stress on the car’s electrical system. Game. Set, Match, little high-torque starters are hands-down better.

You say: “A high torque starter uses the same energy as the old Lucas to fire up the engine because the same net work is being done.” Imo not true. A high torque starter uses LESS energy to do the same or more work. Because it is more efficient.
Voltage, RPM and torque were measured.
Output kW = Torque x 2 x π x RPM / 60.
Input kW = starter motor rating.
Efficiency = output kW/ input kW.
Amps = input kW /voltage.

The main point you make is that, with properly sorted low-pressure EFI, the engine can start so quickly that a high torque stater motor would be of little benefit. Imo this would mean the converse should also be true, anyone with a carb’d car should find a high torque starter beneficial.

I will be high-pressure EFI, 6 to 10 times higher than your relatively low pressure EFI, so your point may not be applicable to me either. All your explanations assume that the injectors open, what if they don’t? What if, due to very low cranking voltage together with the very high fuel rail pressure, the injectors stay firmly shut, not enough energy (voltage) available to open them against the monstrous fuel pressure that is holding them closed? Clearly (to me) this will be less likely to be an issue with a high torque starter.