Back to the ECU Debate - Batch v. Sequential

[JeffYoung]

Hate to drag up a rather bitter topic that seems to have died, but have done some reading this weekend (scary) and now have some limited knowledge about this stuff.

In particular, I have read a fair amount from Motec and Megasquirt about the advantages (perceived or real) of batch v. sequential firing of the injectors, which seems to be one of the big issues the anti-rule crew had with this change.

As I read the Motec and Megasquirt literature, sequential injection of course gives you the ability to control the firing of individual injectors with the goal being to ensure that they fire only when the intake valve is open. Further reading suggests (and I'm not saying this is 100% accurate, just looking for viewpoints on this) stock injectors will for the most part be unable to deliver the full injection charge in the short period of time the intake valve is open (usually less than 300 degrees of the camshaft rotation). Thus, even with sequential FI, on MOST cars, you are going to end up with the injector firing against a closed valve.

Motec still claims that despite the above sequential firing will smooth idle (ok, but don't care), reduce emissions (don't care), increase fuel economy (don't care) and may improve mid range torque (ok, like that, but it is qualified -- MAY).

Megasquirt is pretty adamant that batch firing is fine for stock injectors. They contend that firing against a closed valve doesn't really cost you anything -- the intake sits there for a split second until the valve opens and draws the charge in. Really the only negative effects could come from the port wall temperature increasing the intake charge temperature, but even that Megasquirt claims is minor.

Last, you have to have a cam position sensor to make sequential work. I'm new to FI world -- do most cars have this? The FI setup for my car, a dinosaur, does not. I know SMs do. In any event, it seems that sequential would only be availble to cars that had this stock, since you can't add sensors that aren't there in the first place.

In any event, this new rule has made up my mind for me. FI motor, probably with Megasquirt, being built over the winter. We'll see how this goes.

[Joe Harlan]

Hate to drag up a rather bitter topic that seems to have died, but have done some reading this weekend (scary) and now have some limited knowledge about this stuff.

In particular, I have read a fair amount from Motec and Megasquirt about the advantages (perceived or real) of batch v. sequential firing of the injectors, which seems to be one of the big issues the anti-rule crew had with this change.

As I read the Motec and Megasquirt literature, sequential injection of course gives you the ability to control the firing of individual injectors with the goal being to ensure that they fire only when the intake valve is open. Further reading suggests (and I'm not saying this is 100% accurate, just looking for viewpoints on this) stock injectors will for the most part be unable to deliver the full injection charge in the short period of time the intake valve is open (usually less than 300 degrees of the camshaft rotation). Thus, even with sequential FI, on MOST cars, you are going to end up with the injector firing against a closed valve.

Motec still claims that despite the above sequential firing will smooth idle (ok, but don't care), reduce emissions (don't care), increase fuel economy (don't care) and may improve mid range torque (ok, like that, but it is qualified -- MAY).

Megasquirt is pretty adamant that batch firing is fine for stock injectors. They contend that firing against a closed valve doesn't really cost you anything -- the intake sits there for a split second until the valve opens and draws the charge in. Really the only negative effects could come from the port wall temperature increasing the intake charge temperature, but even that Megasquirt claims is minor.

Last, you have to have a cam position sensor to make sequential work. I'm new to FI world -- do most cars have this? The FI setup for my car, a dinosaur, does not. I know SMs do. In any event, it seems that sequential would only be availble to cars that had this stock, since you can't add sensors that aren't there in the first place.

In any event, this new rule has made up my mind for me. FI motor, probably with Megasquirt, being built over the winter. We'll see how this goes.
[/b]

Well Jeff I am not going to get into a big deal here as I hope the BOD will shoot this rule down in flames. You can trigger the sync-signal from a bolt head. Since any ignition that fits the stock distributer is legal it woul not be an issue to have 2 mag pickups a sync signal in that unit. Completely legal as the ignition system is part of the ecu.

[JeffYoung]

Ok, so you can get around the cam position sensor fairly easy? Meaning you can read cam position off the distributor? That makes sense, they are mechanically connected (on my car anyway).

But what about the idea that sequential doesn't really get you anything at race RPMs?

[C. Ludwig]

Most OEM sequential systems revert to batch or multipoint above about 3500 rpm. The large gains, as you've read, are at low RPM. It's very noticeable at idle. The gains up top are usually going to be minimal though there are gains to be had.

If your stock injector is large enough you should be able to over come latency issues and not have an issue running sequential. The response time of the injector is more a function of the driver than the injector. There are faster and slower injectors but a lazy driver is the biggest contributor.

If you want to run sequential all you need is a 720* signal. The cam and distributor are the obvious sources. Anything that spins at half crank speed that can tell the ECU when you've started a new 720* cycle.

Even though most OEM cars in the last 10 or so years have some sort of cam sensor since they're running sequential doesn't mean that cam sensor will be a plug-n-play part. There are OEM cam sensors that use 2 trigger events per cam revolution with a long phase and short phase event. The OEM ECU can interpret which phase corresponds to which part of the cycle but the aftermarket ECU may not. It's usually easy enough to modify these sensors to produce the 720* signal you need. Just an FYI.

[Joe Harlan]

Ok, so you can get around the cam position sensor fairly easy? Meaning you can read cam position off the distributor? That makes sense, they are mechanically connected (on my car anyway).

But what about the idea that sequential doesn't really get you anything at race RPMs?
[/b]

Well Jeff, What is your RPM Split on a short too mid course? Don't discount it just because you have read about it. What if you were able to improve torque enough to save 1 or more shifts a lap? Has to be some value in that?

[JeffYoung]

At say CMP, I am shifting at around 5500, with an RPM drop back to about 3800 or so. I can vary that more with tire size than anything else.

But that is beside my point I guess. ANY mid range torque gain is a good thing, obviously. The question is one of degrees. It seemed there was a concern that sequential injection was going to result in serious gains across the RPM band and at leas the literature I read suggests that with stock injectors, there is not a lot of advantage to it except at idle and for emissions.


I do understand you would prefer that ECUs go back to stock - and that is a valid position to take. Would that include a flash of the existing ECU code? Is it free code you are concerned about, or just the functionality of Motec/Megasquirt et. al.

[Joe Harlan]

At say CMP, I am shifting at around 5500, with an RPM drop back to about 3800 or so. I can vary that more with tire size than anything else.

But that is beside my point I guess. ANY mid range torque gain is a good thing, obviously. The question is one of degrees. It seemed there was a concern that sequential injection was going to result in serious gains across the RPM band and at leas the literature I read suggests that with stock injectors, there is not a lot of advantage to it except at idle and for emissions.
I do understand you would prefer that ECUs go back to stock - and that is a valid position to take. Would that include a flash of the existing ECU code? Is it free code you are concerned about, or just the functionality of Motec/Megasquirt et. al.

[/b]
Jeff, The fact that the hardware is not in most ECU's to perform most of the stuff we are talking about I am al for open code on factory boards. From here I am done, I am not interested in covering ground that has been covered way too many times here. At this point should this rule pass I will be following the new rules and collecting money for following those rules.

[GKR_17]

Well Jeff I am not going to get into a big deal here as I hope the BOD will shoot this rule down in flames. You can trigger the sync-signal from a bolt head. Since any ignition that fits the stock distributer is legal it woul not be an issue to have 2 mag pickups a sync signal in that unit. Completely legal as the ignition system is part of the ecu.
[/b]

Ignition is basically free, but that doesn't mean you can add sensors to the ECU package. You need to install a completely separate ignition computer that can't communicate with any other system to legally add sensors; even then the timing signal has to come from the stock source.

Every EFI car has a cam, crank, or distributor position sensor, that's all you need, the computer can do the math. If that sensor doesn't speak the right language, then replace it with one that does (in the stock location only).

Grafton