Sequential Vrs. Batch

[petert 550]

At the track on Wednesday, I had interesting chat with a professional tuner. He's also an Autronic dealer, so naturally the debate started about what makes a good ECU. My 205 has an Autronic SMC. His main focus is how well an ECU can handle a large capacity injector at low RPM (idle). eg. a 1000cc/min injector on a 500cc cylinder. I couldn't see the point in that until he started talking about sequential injection.

 

I've always gone along with the debate that batch firing is simple stupid and there's no hp benefit from sequential eg http://www.sdsefi.com/techseq.htm. However, a typical track car has an RPM range from 4000-7500. An what makes a car accelerate out of a corner? Torque. He also pointed out that ECU companies who focus on racing markets (eg Motec and Autronic) are sequential only. Whereas Haltech for example, who also target the street brigade, offer user selectable batch or sequential.

 

So his theory is, that to maximise the benefits of sequential you need a very large injector, so that the opening time (and duty cycle) is small enough to fit in the valve open period, hoping to match up with the maximum velocity of the incoming air. It might be also possible to delay the injection period to avoid the overlap period at lower revs. Thus the importance of the his first point.

 

I had a good look around the Autronic website and found a very useful tool, which calculates the duty cycle and allows you to match the injector period into the valve open period;

Injector Range Tool

 

With an injector double the size of a std. Mi16, so the injection time stays the same for sequential (2.8 to 7.5ms), it's possible to get some interesting figures with this tool.

 

The Autronic software allows the end injection point to be moved, to allow for different load and RPM points. The injection end angle is a point in degrees of the cycle, 360 deg. being TDC intake.

 

 

 

 

 

Any other thoughts

Edited December 8, 2005 by petert

[DrSeuss 0]

Out of interest I presume its the better charge mixing that results in the greater torque. And shouldn't it be the injection start point to avoid the overlap period?

 

Oh, if the xu10j4 uses 196cc injectors, is it sequential? to generate the 160hp surely they'd be nearer 380cc? Only reason i ask is a friend claims to have hit about 200hp with his s16 on standard injectors (with tb's and a 9k rev limit)

[petert 550]

I agree, the XU10J4 must be batch if it only has a 196cc injector. Or it fires one 15ms pulse, rather than two 7.5ms pulses at full noise.

 

Mechanically, the Autronic uses the cam trigger to determine the injector end point. It's logical to put this at TDC intake, so the ECU can calculate a delay from there. So you need to use the tool described, entering valve events, injection time, RPM etc., to see when the injection point will start.

 

200hp from four 196cc injectors is physically impossible!

Edited December 9, 2005 by petert

[Martin@PRD 0]

That site is very bias, doesnt quote many sequential advantages at all. Do they sell non-sequential hardware?

 

From what I have found out the only advantage with Sequential is low down torque, which Im still contemplating whether to spend the extra quid on, as am using the v6 that isnt as high revving as a MI16, though I doubt Ill be using the lower rev band anyway (just messing). The injectors Im sure will play an important role has the 406 management could be sequential with ever tightening emission laws, so I need to find out a little more before I can put my money down on the table.

 

If I can find huge capacity injectors, then Im sure I could gain the extra torque with improved burn/mix from sequential at higher rpm though seems extremely time consuming and having to be painstaking accurate with all the variables to take in to account (not sure v6 has cam Tdc sensor, which Im thinking the xfx has)

 

Im sure having a lambda sensor in each of the exhaust branches (four branch) would improve smoother power delivery, release stress on the crank and also increase torque and bhp with sequential

 

Though it still all heavy depends on who maps the engine, and how well they do it (human error is more likely) and also what hardware they have to offer, as they try and sell mud to a pig farmer, (you go for chips and gravy and you come out with chips and curry). I hate the uk market!!!

 

Oh.. Thanks for the injector tool that will be handy in the next couple of months, when I get my head around the v6 and it injectors, not that I dare to ask anyone in here about!!

[M3Evo 0]

If the V6 doesn't have cam positions sensors then it's pretty unlikely to be capable of running sequential

 

Just a thought on a sequential benefit: Would it give better fuel economy? If so, it could perhaps explain why the companies making race ECUs exploit it.

 

Guess the less time spent refueling the better if you're racing someone

[Rob_the_Sparky 9]

I suspect that if you get a bunch of experienced tuners together then you will get conflicting answers! Sequentail is clearly more ideal from an engineering point of view but if the difference is not significant then why bother? The problem is measuring the difference and I bet the amount of difference will vary from engine to engine.

 

Also how does a twin injector set-up fit in with this? Could you not have the outer injector have a larger flow rate for the high revs and the inner have a lower flow rate?

 

Also surely it makes a difference whether you injector is injecting onto the back of the (hot) valve or into a TB...

 

Rob

[DrSeuss 0]

Injector end point tells you when the valve will be closed? Start point will be determined by a fuel calculation based on load points. Lord, this is all confusing.

 

I prefer to think in terms of interrupts

[Martin@PRD 0]

If the V6 doesn't have cam positions sensors then it's pretty unlikely to be capable of running sequential

 

Just a thought on a sequential benefit: Would it give better fuel economy? If so, it could perhaps explain why the companies making race ECUs exploit it.

 

Guess the less time spent refueling the better if you're racing someone

 

Doesnt need to have cam Tdc sensors to run sequential injection, though requires painstaking cam calculations of Duration and overlap set by the operator, though the sensor takes the guess work out so the Ecu can calculate it and from what peter was explaining sequential requires the sensor to take the full benefits of sequential at high rpm, that requires lager injectors as they only trigger once per engine cycle, meaning the duty is raised and reached a lot sooner, were batch or multi point injectors trigger all together on every cycle so that the injector triggers a few times (depending on stroke) for each cylinder.

 

I hope I explained that correctly,

[M3Evo 0]

Think I read somewhere that the NSX uses sequential for low revs and switches to batch up on high so it gets the best of both worlds

[Martin@PRD 0]

Think I read somewhere that the NSX uses sequential for low revs and switches to batch up on high so it gets the best of both worlds

 

Thats more than likely as the Japanese they are bloody wizards with a soldering iron!

 

Im interested to see a four-cylinder engine running full sequential with 8 injectors that would be simply awesome! Though calculating the outer injectors through out the entire rev band under different loads would be one hell of and joggling act if you were to use sequential so I reckon it would be fare to say to use these as a batch at higher rpm to add fuel where the sequential injectors positioned cylinder head port could be the left small to do the more important low down rev range.

[DrSeuss 0]

With modern large capacity injectors the need for 8 injectors is minimal and only ever failure prone.

[Martin@PRD 0]

True , though 8 injectors offer better atomisation for fuel mixture

[petert 550]

The point I was making however ( or more correctly the guru tuner), is if you can control a very large injector at idle, than sequential is going to out perform batch, or even staging, under all RPM's.

[DrSeuss 0]

Presumably you'll end up with a better charge. This is the principle all the direct injection lean burn engines work on. Unfortunately for emissions not performance.

 

But the shift to FSi in the golfs gained about 20hp in engine performance (admittedly with other fairly major design changes)

[M3Evo 0]

Doesnt need to have cam Tdc sensors to run sequential injection, though requires painstaking cam calculations of Duration and overlap set by the operator,

 

Pretty sure it does. You can't tell the engine management which cylinder's about to compress, fire, induct or whatever from the crank position alone. Think if you tried to, you'd end up with an engine that would sometimes start and run fine because it was lucky enough to guess correctly, and that would sometimes not.

 

Then you'd run into problems with the ECU getting it wrong even if it did run and from what I gather in the literature in with my OMEX 700, it only looks at the cam position sensor every once in a while (every x miliseconds) to make sure it's got it right.

[Martin@PRD 0]

Yes, I see were your coming from, though I was only going off what I told/filled with, when I was taking to the guy at Omex there was no mention of needing a cam Tdc when using sequential with the v6, if this does turn out to be true I can safely say I wont be using them again. Can any one enlighten me on this further; do I need cam Tdc for fully sequential ignition and fuel?

[DrSeuss 0]

They key piece of information is in what way the flywheel tdc sensor provides a position reference. If you 'hard code' everything relating to the cam timing into the ecu it should be possible to create a mathematical position reference from this.

 

As the fly wheel will always be at a certain position with regards to the top end. Its a right ballache, but it must be possible. Motec doesn't necessarily require a cam position sensor if it simply doesn't support batch firing.

[Martin@PRD 0]

The crank rotates twice and the cams once per cycle, so how can the ecu tell if cylinder one for example is firing or on the induction stroke?

 

Easier to think about it if your trying to start the engine.

[Rob_the_Sparky 9]

Well the problem is that on a 4 stroke you don't know whether it is an exhaust or an inlet stroke for each cylinder without some information from the cam. I can't see how you could do sequential without this knowledge as the point is that you fire the injector on the inlet stroke.

 

Rob

 

P.S. Thought that having an injector far away from the inlet was better for top end power and close to inlet better for torque. Hence figured you would also make the closer one a lower flow rate closer and a large one further away from the head. However, will freely admit to having bugger all experience, just interested to learn!

[DrSeuss 0]

Very good point.

[CJ_2_0_5 0]

Well the problem is that on a 4 stroke you don't know whether it is an exhaust or an inlet stroke for each cylinder without some information from the cam. I can't see how you could do sequential without this knowledge as the point is that you fire the injector on the inlet stroke.

 

Rob

 

P.S. Thought that having an injector far away from the inlet was better for top end power and close to inlet better for torque. Hence figured you would also make the closer one a lower flow rate closer and a large one further away from the head. However, will freely admit to having bugger all experience, just interested to learn!

 

One way that I know of negating the need for a cam sensor is to try and start the engine assuming the engine is on one cycle, if it doesn't start in a certain amount of time switch to the other cycle. Sounds crude but works just fine for race applications.

 

CJ

Edited December 15, 2005 by CJ_2_0_5

[Owain1602 0]

if you are going to use sequencial injection then you must tell the ECU exactly which cylinder is going to fire next, it no good saying its going to be either 1 or 4 like you would get from a crank sensor. if you tell the ECU that 1 and 4 are approaching TDC and want sequencial injection what is stopping the ECU from injecting on cylinder 1 when actually cylinder 4 is going to be firing, nothing! so some means of identifying exactly what is happening is needed, either through a cam sensor or you can use a distributor with a hall senor with an optical pick-up on a certain cylinder so then it knows when cylinder 1 or whatever is going to be firing. as the dizzy is rotating and the beam gets broken by the rotor and its been set up so its broken when 1 is firing next, the it will know when cylinder 1 is firing, it will constantly be recieving the crank sensor pulses too for injector duration and so on.

i believe it would be possible to write a piece of software to simplify this. Say you had specific perameters the system obeyd to: when crank sensor pulses a signal to the ECU saying 1 & 4 coming up it would then check if it had recieved a signal from the optical pick-up (the device which tells the ECU when its cylinder 1's time to be injected), if it had recieve a pulse then inject cylinder 1, if not then inject cylinder 4. it only needs to know 1 exact position for a whole engine cycle, so it can easily work out if has just injected cylinder 1 when the next pulse comes from the crank sensor, fire cylinder 3 or 2 or whatever.

its complicated stuff and im beggining to muddle my-self up by now. very complicated but also very interesting. its the way things are now with modern cars and things are only getting more complex so i recon people should get on the band-wagon as soon as possible, money permitting!

let me know what you think guys,.

[veloce200 3]

I think sequential more useful when dealing with cat equipped cars and stringent emissions. We're lucky enough in the UK for most of our pugs to not have cats so I think sequential in the £Spent vs HP/Economy/Driveability is not that compelling. I'd sooner spend the extra cash on another component. My Pugs just running Emerald ECU on batched pair and the economy and power increase over the original injection was marked.

[DrSeuss 0]

I agree in principle veloce200, but think of it this way, in a race series where modifications are limited. Or where every few lbft counts, you would go sequential. Surely the extra cost of mapping pales in comparison to most race spec modifications?

[veloce200 3]

I agree in principle veloce200, but think of it this way, in a race series where modifications are limited. Or where every few lbft counts, you would go sequential. Surely the extra cost of mapping pales in comparison to most race spec modifications?

 

Well you'd need cam sensor, bigger injectors (possibly), and mapping (assuming you already have batch or grouped). Not sure on cam sensor cost or set up but this could be £500 all in.... Driver training vs 3Lb torque... well I intend to prove this year how much 50 hp gives and how much driver training gives and my hunch is driver skill can negate even large chunks of power, yet most don't bother...!