If sequential firing of the injectors means only squirting fuel one cylinder at a time as opposed to batch firing squirting fuel down all cylinders each time,why is it the fuel consumption isnt four times as good on a 4 cylinder engine or at least alot better? just curious as I have been looking at the differences between Megasquirt and VEMS....Decisions decisions!

Sequential injection will allow a degree of fine tuning to fuel consumption at the lower rev bands, it will also be more econimical, but it will never equate to a four-fold increase in fuel efficiency.

Also, as revs go up, the differences between sequential and batch firing tends to nought. At high revs those injectors are closing and opening so rapidly that you might aswell be batch firing them.


02GF74 ... it all depends if it is single point or multi point injection. Most modern fuel injection engines are multi-point, ie the injector sprays onto it's respective cylinder's intake valve.

I am running Vems on the v8 batch fire at the moment ( split left and right ) but my loom allows me to 'upgrade to seqential' later.

a major plus on the vems side is the ability to run Lambda on board.

have you had a dig arround www.vems.co.uk ?

regards

Agriv8

To answer your original question, each injector squirts exactly the same amount of fuel per engine cycle but with sequential it is timed to coincide with a particular point in the cycle for each cylinder. The difference is probably marginal but I believe it can have good advantages for pickup from low rpm when you need to fire acceleration enrichments.

Hmm, The Vauxhall XE engine has Sequential injection as standard and makes good power even for a modern engine.

But if you catch it in the wrong gear it will not pull! like if you come out of a tight corner in 3rd and put your foot to the floor it coughs and bangs and carries on really violently, wheras normal injection just won't pull and bogs down.

But as said at higher RPM's it makes little or no difference as its all happening so fast.
Also if a normal injector fires when a valve is closed the atomised fuel just sits there waiting until it opens as per a carb'd car.

Out of interest has it come back into use? do most modern cars have it now or is it deemed un-nessacery?

quote:

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Originally posted by matt_claydon
To answer your original question, each injector squirts exactly the same amount of fuel per engine cycle but with sequential it is timed to coincide with a particular point in the cycle for each cylinder.

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It is one of these things that go in and out of favour. It used to be thought there was no clear advantage but thinking these days is it gives small gains in economy and power.

Most injection systems fire the injectors in groups -- 2 groups for a 4 pot.

Back in the old days of mechanical injection the injectors pointed actually backwards towards the throttlebody. as this gave the best atomisation for this type of set up.

[Edited on 23/11/07 by britishtrident]

There is really no gains in power to be had with sequential, mainly because by the time you hit peak power RPM the amount of overlap on the injector periods means it's pretty much batch fired anyway.

If you read PPC, Dave Walker (of Emerald fame) has tried both batch and sequential modes back to back on the same engine and never found any significant gains in power.

The main reason for it's existence is for emissions, and to a lesser extent economy. With batch fired systems at low RPM the fuel being fired at closed inlet valves can have time drop out and puddle, leading to less complete combustion and higher emissions.

Cheers all,
I was'nt really looking for more power,just wondered how much it would help with economy and about town driving being as I will be driving on the road 99% of the time

Further to this - If you are running the injectors in pairs, which ones do you pair together?....Do go for the 1 & 4, and 2 & 3?....

Cheers.
PAul.

Yup