400 rpm

[Trials]

For a particular application I need to run a 4 cylinder petrol injection engine at speeds as low as 400 rpm controlled by an S60.

Can it me done?

Is it possible to measure engine speed accurately enough at such low rpm?

[stevieturbo]

With a 36-1 crank trigger wheel, an ecu will measure speed etc every 10 degrees of crank rotation.

So 400rpm is not a problem. Although it must be a very unusual engine to operate at such low rpm ?

[Trials]

The engine is a Suzuki m15a, it’s in a sporting trials car. There are many driving techniques in sporting trials depending on the conditions. One technique called trickling involves running the engine as slowly (375 rpm) and as gently as possible to maintain traction in very slippery conditions.
Cars on carbs can do this. Fuel injected cars seem to struggle at such low speeds, this may be because of variations in speed even within one revolution of the engine.
How can this be overcome?

[stevieturbo]

The engine is a Suzuki m15a, it’s in a sporting trials car. There are many driving techniques in sporting trials depending on the conditions. One technique called trickling involves running the engine as slowly (375 rpm) and as gently as possible to maintain traction in very slippery conditions.
Cars on carbs can do this. Fuel injected cars seem to struggle at such low speeds, this may be because of variations in speed even within one revolution of the engine.
How can this be overcome?

I would struggle to believe what you are saying is correct...especially given it is a regular modern 16v engine ?

https://en.wikipedia.org/wiki/Suzuki_M_engine

But I see no reason why a fuel injected engine would struggle if tuned correctly. It should be better than a carb equipped engine as air velocities through any carb would be much lower which will negatively affect it's operation.
Which is where an OEM ecu may fail here too, as at such low rpm it may just consider it a stall.

If you're expecting an OEM ecu to do it however...I would never expect it to as that would be far outside how it is designed to operate, and the OEM ecu would likely be less flexible in that regard even for those who can reflash them.

And with full control over fuel and timing...EFI should be better all round.

Only thing not 100% sure about is how low DTA allows so it can distinguish between cranking and running. As cranking on the starter is usually around 200rpm.

[Trials]

I can assure you that’s how slowly the top cars run.
Don’t want to use the OEM ECU want to use the S60.

Would really like to solve this as so many advantages to fuel injection.

[Rob Stevens]

There is an rpm setting called transition from cranking, below this the ecu has a simple timing strategy, i.e. it fires one tooth before tdc, but once running is detected this strategy is not used again. To help with this unusual requirement I would recommend sequential injection with a hall cam sensor. Also TPS with MAP corrections or even MAP as load. Also have loads of rpm set points at this low rpm.

[stevieturbo]

If gearing was correct...

I'd think running the engine at a higher rpm, but with reduced timing for example to reduce torque would be a better option. And this would have the advantage of being able to ramp torque back in very quickly too if needed, which would not be possible with very low rpm

[Trials]

I was thinking TPS with MAP corrections so will think through MAP as load pros and cons and read up on it.
700 rpm with retarded ignition is an interesting prospect could be the solution. Gearing is not a problem.
Thank you both, you have given me a lot to think through.

[katana]

But I see no reason why a fuel injected engine would struggle if tuned correctly. It should be better than a carb equipped engine as air velocities through any carb would be much lower which will negatively affect it's operation.

Whilst I generally agree, a carb equipped engine can be considerably 'choked down' to improve air velocity and carb function. It wouldn't produce much HP as such but in this sport (from what I've seen) its low rpm torque and traction that is key. Whilst the TB could also be choked down to improve airflow - this is maybe why FI engines are not favoured? Bigger throats hurt cylinder filling efficiencies at low revs although long inlet tracts are of a benefit. The engine spec is also square ( B x S) so better than its smaller siblings for torque production.

[stevieturbo]

But I see no reason why a fuel injected engine would struggle if tuned correctly. It should be better than a carb equipped engine as air velocities through any carb would be much lower which will negatively affect it's operation.

Whilst I generally agree, a carb equipped engine can be considerably 'choked down' to improve air velocity and carb function. It wouldn't produce much HP as such but in this sport (from what I've seen) its low rpm torque and traction that is key. Whilst the TB could also be choked down to improve airflow - this is maybe why FI engines are not favoured? Bigger throats hurt cylinder filling efficiencies at low revs although long inlet tracts are of a benefit. The engine spec is also square ( B x S) so better than its smaller siblings for torque production.

FI maybe not favoured because people don't know how to make them work ?

Bit like many years ago when people said motorbike engines couldn't work fuel injected. Pretty sure they got that wrong.

Although I have heard a lot of these trials vehicles are LPG ? I'd say the main caveat with fuel injection is maintaining the fuel supply to the engine at silly angles. Not difficult though.