How does Hotwire know Where it is?

Ian Anderson · Post by **Ian Anderson** » Mon Oct 27, 2008 9:54 pm

I've been reading up on the alternative ECU's and most / all of them want a trigger wheel on the crank so the Ecu can get an exact point of reference for where it is in the cycle.

But on the Hotwire I cannot find where / how it picks up that No1 is TDC so it knows to fire bank 1

Or is it just really "gash" and it picks up the number of pulses from the dizzy and then fires the injectors based on these - the injectors could then actually be "squirting" when the inlet valve is closed causing the fuel to come out of the mist onto the sides of the intake n one cylinder and be firing at the correct time for another.

If this is the case thenin laymans terms for how much of the revolution of the engine (1 cycle of 720 degrees at the crank) is the injector actually open for?

How many people run independenly fired injectors that only "swuirt" when the Inlet valve is open and ir rushing in?

Oh so many questions

I'm trying to learn but he simplicity of a carb makes a lot more sense at the moment.

Ian

Eliot · Post by **Eliot** » Mon Oct 27, 2008 10:09 pm

It doesn't know where it is. Its batch fire - just fires the injectors at any time, regardless of valve opening. (per cycle)
All megasquirts are exactly the same, regardless of having the wheel. Only sequential systems know there they are and that is done with a 2nd trigger, typically a cam sensor.

Post by **Coops** » Mon Oct 27, 2008 10:09 pm

it fires in banks mate,
its not seqeuncial,
it has no set firing pattern for the injectors

ChrisJC · Post by **ChrisJC** » Tue Oct 28, 2008 8:32 am

Flapper (& I imagine Hotwire to be the same) pulses the injectors once per engine revolution, so you get two pulses per combustion cycle. It generates a cloud of petrol vapour behind the valve, ready to be sucked in when the valve opens.

And all four injectors on the bank are fired at the same time.

Chris.

Ian Anderson · Post by **Ian Anderson** » Tue Oct 28, 2008 8:59 am

Well that does not sound a very efficient method of getting fuel into the engine

Yes it works but surely injecting when the valve is open would be better

So who does sequential injection that is proven on a V8 Rover set up?

Ian

ChrisJC · Post by **ChrisJC** » Tue Oct 28, 2008 10:05 am

GEMS & Thor are both sequential.......

Chris.

spend · Post by **spend** » Tue Oct 28, 2008 12:10 pm

You need more than crank signal for sequential, not many have cam phase hence the popularity of wasted spark ignition.

Many seem to run batched injection, the argument being at high duty cycles the injectors are open nearly all the time anyway.

VEMS is one of the few alt ecus capable of doing what you asked.

Ian Anderson · Post by **Ian Anderson** » Tue Oct 28, 2008 2:08 pm

Quote
Many seem to run batched injection, the argument being at high duty cycles the injectors are open nearly all the time anyway.

So from that I read that at say 4000rpm the injector is squirting almost all the time? Say open gor 80% of the time.

If that is the case why then do they consider EFI better than a carb?

So on sequential presumably the injectors flow a lot more and only "inject" at the time the valve is open - or are they still flowing when the valve is shut?

Surely something like a 4 barrel carb with a fairly constant flow of air through the throat can be made to do the same job and is, to an electronics challenged person (me) umpteen times easier to work!on

After all the engine will do Idle and then 1500 - 3500 most of the time - sure on a track it may see 6000 but that is far from the norm. (1500 is 30mph in 4th and 3000 is about 80 in 5th)

I must say I am leaning towards a nice 4 barrel and get rid of all the wires!

Ian

ChrisJC · Post by **ChrisJC** » Tue Oct 28, 2008 2:40 pm

Ian Anderson wrote:
If that is the case why then do they consider EFI better than a carb?

One main reason - emissions, but over and above that, the fuelling on an EFi engine is spot on under all conditions (temp, load, atmospheric pressure, etc etc.). A carb is sort of close most of the time.

Fuel Injection is superior to carbs in every respect apart from complexity, nothing is for free!

How long is it since cars started starting on cold mornings?, about the same amount of time that fuel injection became widespread?

Chris.

bill shurvinton · Post by **bill shurvinton** » Tue Oct 28, 2008 10:24 pm

Ian:

You have a few confusions over what is more 'efficient' in terms of injection. It is a tricky thing to work out. For indirect injection engines (i.e. everything except the latest petrol engines), you get best fuel efficiency when you inject against a closed valve, as the heat evaporates the fuel and the air/vapour mix then gets sucked into the engine as a nice homogenous mixture. Having this means less fuel is wasted to avoid stratification and misfires. Yup, sequential injection is primarily for emissions and meeting economy targets. Tests I have read would indicate up to 10% reduction in fuel consumption for same power output with properly tuned sequential. sadly no additional power

For max power you want atomised fuel as you are not worried about a bit of waste but would prefer not to reduce the amount of oxygen you can get in with fuel vapour. This becomes measurable at F1 levels but not with yer common or garden V8.

batch EFI is better than a carb for most applications because it can be adjusted for every part of the torque curve. You have more inputs to play with (a carb just has airflow and accel). Or to put it another way you have to balance power, drivability and economy. With a carb you can have any 2 of them, but not all 3. With EFI you get your cake and eat it.

Now if you understand a 4bbl, know how to tune it and can live with the limitations, then no probs. But keep the ignition mapped. Mechanical dizzy based ignition really is horribly compromised.