what are the advantages or disadvantages to the sequential efi system verses the other firing styles of efi? Is one better than the other for a high rpm ( 8500) application? Driveability of each?

 

https://www.theturboforums.com/smf/index.php?topic=118421.0
Little searching homeslice.

 

Gary, rule of thumb is that sequential is the best configuration but that only applies at low injector pulse times. Like cruising or idleing around.
As you load it down and the injector pulse time increases then the injector is not just firing during the intake stroke but is open through almost the entire 720 degrees of crank rotation for all 4 cycles. The end result under WOT is that there is no advantage of either programming. There is no WOT HP advantage of sequential over batch fire or multipoint.

With my setup the 160# injectors go static at 28# boost.

 

How is this even possible with a crank sensor? The crank sensor will cut the injector duty cycle off at the specified duration so you arent sraying fuel on closed cyliners. The crank sensor translates a specific angle/position of the crank and describes the orientation of the cylinders and valves being open or closed. The angle is translated by the injector driving system and the ECU as to the when to open and close the injectors. Unless bypassed it is virtually impossible to spray fuel in a closed cylinder (especially for a full engine cycle). Your IDC may tell your ECU you have a 120% injector duty cycle but the fact of the matter is it really stopped at 100% and now you have a lean condition.

IMO the advantages to sequential firing are fuel economy and faster engine ramp rates.

Jeremy

 

Sequential can have one other advantage, allowing tuning the cylinders separately. But this is only an advantage if (1) your ECU has this feature, preferably with tables instead of a fixed percentage, and (2) you have a big enough dyno budget to actually get it dialed in. Without it, the power at high RPM is going to be the same and the only difference you'll see is at idle and light throttle.

I believe what Mark was talking about was hitting 100% duty cycle - the injectors are on all the time, and spraying on closed valves. With that much boost, you've got to do what you've got to do.

 

The 100% IDC means the injectors are spraying for the entire open angle event not the entire engine cycle. A quick illustration... 0-30 degrees cyl 1 (open duration 10ms) ECU feedback injector pulse width = 12ms... 30-60 cyl 2, 60-90 cyl 3 etc... In reality, the ecu thought you sprayed for 12ms and had a 120% IDC but in reality the crank sensor cut the fuel off at 10ms so you didnt blow up your car . One of the crank sensors functions is to cut off the injector pulse width at an angle in which it knows the cylinder is closed and over ride the ECU.

Another advantage to batch vs sequential is reduced injector driver temps.

 

Per megasquirt....

"The benefits of sequential injection are that:

you may get slightly better mileage and lower emissions at low engine speeds,
you can tune each cylinder's fuel amount and spark timing independently (if you know how).
The effect on maximum horsepower is general small.

However, sequential injection does not necessarily mean you are injecting into an open intake valve all the time. The intake valve is only open less than 30% of the time in a typical 4 stroke engine. Once you are trying to produce more than about 25% of maximum HP your injectors are firing for longer than the intake valves are open. If your maximum HP corresponds to a safe 80% duty cycle, your injectors are injecting well over 50% of the time on closed valves. With MegaSquirt® EFI Controller, fuel is injected on ignition events only, and while these are loosely related to cam events, it is a complex relationship, Try to 'squirt' through an open valve under all conditions is generally a bit hopeless, because:

fuel that is injected when the valve is closed doesn't go anywhere, it just sits near the valve vaporizing until the next time the valve opens (some OEMs deliberately squirt against a closed valve to improve vaporization). So squirting against a closed valve does not generally affect the AFR for that cylinder (though there may be a small effect on the combustion quality, good or bad, depending on the port wall temperatures, etc.)
the valve is generally effectively open (0.050") less 300° of a 720° 4-stroke cycle (and closer to 200 for 'stock' engines). So hitting the open valve requires precise cam related timing,
to inject the full fuel charge at high loads/RPMs through an open valve requires very, very larger injectors, about 2.5 to 4 times larger than is usually recommended,
as the duty cycle for the injectors rises, the injectors come closer and closer to squirting all the time, and injection timing becomes irrelevant. "

There is further detail with RPM thrown into the equation here... http://www.megamanual.com/v22manual/mfuel.htm#batch

 

Normally, injector duty cycle is real duty cycle, at least with the sequential systems we've worked with. A system that only sprayed during an open intake valve would need much larger injectors than anything outside of a direct injected system. Most sequential systems can and will extend the duration for an entire engine cycle, or at least all but a small percentage of the cycle. The only exceptions I've seen have been some Formula One engines and GDI systems, and those need obscene amounts of fuel pressure because they have such a limited time to inject fuel compared to normal engines.

 

And as suspected the requirement is a cam sensor (crank sensor min req for other standalone units) to relay the cam position for ignition trigger and injector timing. If you properly size your injectors you shouldn't have to worry about submerging your valves with fuel. Unburnt fuel is wasteful, dangerous, and damaging the VSS. If you properly size your injectors and dial in the injector timing you dont run into problems like floating valves. stay in the 80% injector duty cycle safety net with properly sized injectors and adequate fuel pressure.

 

I think we can agree the appropriate way to approach this is to properly size the injector to spray the required fuel in the time allowed for optimum performance. In a controlled environment such as a preset ecu the sequential real injector time is normally never exceed.

 

J. Fast, are you saying it is possible to only spray fuel when the intake valve is open under any condition?

 

I find it almost impossible to believe you can spray enough fuel while the intake valve is open to feed a 1000hp 7000rpm engine.

 

Yes, but you need something like 2.5 times the required injector size to shoot the same fuel in the small period of time. One of the reasons I have had a hard on for 16 injectors. Less injector, same idle quality. A guys locally I have talked to has seen 50 hp difference in the seq tuning at higher RPM.

 

That is interesting. I wonder why there are so many heads up guys only using 8 until they are forced by the fact 8 can no longer get it done.

 

Adding onto what 10secgoal said you must have the driver extensions to fire that many injectors. On my AEM I only have 10 AEM version2 has 12 . The tuner is responsible for programming the injection safety parameters. IMO when you can't squeeze all the fuel in on one IDC with an elevated fuel pressure it's time to add more injectors. This is why when you start making big power you move to an aeromotive fuel controller.

http://aeromotiveinc.com/products-p...nics/16306-billet-fuel-pump-speed-controller/

 

The only thing I could really think was the time to tune and cost. BS3 does 16 drivers but at an added option of 1k. My buddy does run 8 160's, and seq at high RPM , but he makes about 1800hp with High ports and a 345cid. I asked him about it and the elbow on a carb intake he runs, which is only a super victor, all he said was "it works." Is the juice worth the squeeze as far as I can tell.

 

Ok I think I understand what some were referring to about exceeding IDC. As rpm increases the amount of time for injection decreases. This is 100% the case wether you're batch firing or sequential firing. Batch firing systems have what some consider to be an advantage over sequential (not me but that's my opinion) wherin they can inject fuel for the entire crank rotation. A sequential will be limited to cam timing (or crank timing). On a typical cam profile of 200 degrees or so (with .05 valve liift) a sequential system has just over half the time to inject fuel versus a batch fire setup (this is why you need bigger injectors and more fuel pressure on sequential injection setups).

As rpm increases with sequential setups the valve opening and closing durations are miniscule (like a few microseconds) so you need not worry as much if you are driving at WOT everywhere all the time. With batch fire the fuel is already sitting in the port from spraying for the full crank angle and as rpm increases the time unexpended fuel hangs around decreases.

Batch fire sytems are much more forgiving and require only a tach freqency signal. Sequential EFI is a pure science of timed events.

 

Sorry. You don't understand. With sequential injection, at WOT you still open the injector when the intake valve is closed. That is why there is no advantage to sequential injection when it comes to WOT power. The only difference is that the injector is closer to the valve.

Duty cycle means amount of time on vs time off. Duty cycle is not influenced by anything except time. 100% duty cycle means the injector is open non-stop and never closes. It's impossible to exceed 100% duty cycle.

 

It's easy to figure out with a calculator.
At 7000 rpm the intake stroke takes just 4.2ms
That's not enough time to get all the fuel in.
At 100% DC the injectors are open for all 4 strokes.

That points out the reason why direct cylinder injection is always going to be limited for performance use.
They only have at best the intake and part of the compression stroke to get all the fuel in.