2 squirts vs 4 squirts
Discussion
For those with aftermarket ECUs, what's you preference for injector 'squirts' per engine cycle?
On my megasquirt I was originally running 4 Squirts per engine cycle alternating, but was advised that switching to 2 squirts per cycle may improve idle. I believe the theory is that it reduces the impact of injector opening time (dead time) errors and battery voltage fluctuations.
To be honest I haven't really noticed a lot of difference between the two settings, so was wondering what other folks are using. Would also be interested to know how MBE, Canems etc. are set up.
On my megasquirt I was originally running 4 Squirts per engine cycle alternating, but was advised that switching to 2 squirts per cycle may improve idle. I believe the theory is that it reduces the impact of injector opening time (dead time) errors and battery voltage fluctuations.
To be honest I haven't really noticed a lot of difference between the two settings, so was wondering what other folks are using. Would also be interested to know how MBE, Canems etc. are set up.
Im on Emerald and use the standard batch fire of 4 squirts.
If you go down to 2 per cycle, you are going to have to make sure your injectors are big enough to cope at high rpm because they will be having to flow twice as much fuel than what they originally were.
To be honest ive not heard this theory before. I think id stick to what is tried and tested with the rv8 or go fully sequential which apparently has some benefits.
What differences did you see ?
If you go down to 2 per cycle, you are going to have to make sure your injectors are big enough to cope at high rpm because they will be having to flow twice as much fuel than what they originally were.
To be honest ive not heard this theory before. I think id stick to what is tried and tested with the rv8 or go fully sequential which apparently has some benefits.
What differences did you see ?
I thought that 4 squirts needed larger injectors, since you are effectively doubling the dead time.
I suspect 4 squirts should be better in general provided the ECU has the correct dead time for the injectors and the duty cycle at full load isn't too high.
I'm going to try and check the dead time on my injectors later, by switching from 2 squirts to 4 squirts and checking the AFR. If it stays the same, the dead time would be correct. If the AFR goes up the dead time setting is too high and vice versa. That's the theory anyway.
BTW I'm running Bosch red 30Ib injectors.
I suspect 4 squirts should be better in general provided the ECU has the correct dead time for the injectors and the duty cycle at full load isn't too high.
I'm going to try and check the dead time on my injectors later, by switching from 2 squirts to 4 squirts and checking the AFR. If it stays the same, the dead time would be correct. If the AFR goes up the dead time setting is too high and vice versa. That's the theory anyway.
BTW I'm running Bosch red 30Ib injectors.
angus337 said:
I thought that 4 squirts needed larger injectors, since you are effectively doubling the dead time.
I never thought about the dead time. I just presumed only opening twice they have to flow twice the fuel than if they opened 4 times. In fact the more i think about it you could well be right. carsy said:
If you go down to 2 per cycle, you are going to have to make sure your injectors are big enough to cope at high rpm because they will be having to flow twice as much fuel than what they originally were.
That's not quite true, when using 2 squirts the injectors will be open for 2 longer duration's rather then 4 little ones. The fuel flow with the same, or very close depending on how bad your dead times are. Its not twice and you wouldn't need bigger injectors. Dead times add more complications when calculating fuel so the fewer of them the better. Ideally you're looking for fully sequential and only opening the injector once per cycle. By using 4 squirts you're effectively keeping the injector in its opening state more often which injects a guessed amount of fuel. Which is going to lead to more inconsistency. I use 2 myself, it works nicely and its easier to work out the dead times. If you're using 4 squirts on bigger injectors at idle the injectors will probably be opening and closing almost immediately and most likely result in a very rich idle that can't be weakened regardless of the value on the fuel table.
Another advantage to fully seq is with only one injector open at any one time the pressure in the fuel rail is more consistent. As standard our cars open 4 injectors at a time so the only advantage I can see for 4 squirts is maybe you're giving the fuel rail more time to recover but its marginal.
I'm looking to swap to a fully seq setup at some point mainly for the timing the injectors relative to the inlet valve benefit. But with what effectively is a straight 8 fuel rail I think its a terrible idea opening 4 injectors at the start and then opening the other 4 at the end and expecting the fuel delivery of each to be the same. One of each set of 4 injectors maybe timed some what right to the inlet valve but the others wont be so some will end up puddling and you'll need to injector more then to get your desired AFR.
QBee said:
My brain hurts.....
I just had a read before reaching for the aspirins!sequential fuel injection is a type of multi-port fuel injection system in which each injection valve will open just before the cylinder intake valve opens. So in essence, the individual injectors work by themselves because they are fired individually. Other multi-port systems will fire all the injectors in groups no matter if the cylinder is ready or not. While sequential variable fuel injection has many benefits, direct injection is quickly becoming the system of choice and is replacing the SEFI systems.
Advantages
The main advantage of a sequential system is that the entire system has a fast response time when the driver makes a quick change. More or less fuel can be released when the next intake valve opens. For systems that do not use sequential fuel injection it will be necessary for the entire engine to complete a revolution before the fuel to air ratio can be altered. This type of injection also produces much lower emissions and provides even better fuel economy. Because the fuel is altered for each cylinder, you can potentially get the best performance out of the engine that is possible. The throttle response is immediate, which allows for very rapid changes in the fuel to air mixture. Because fuel is used more economically, the emissions released are lower. This is very important where vehicles are being produced to meet stricter emissions.
Disadvantages
Because there is a single injector for each cylinder, the larger the engine the more expensive the system. A V6 engine will need 6 injectors and a V8 would need 8 injectors. Sequential systems are also more expensive because they require an additional wiring harness that is used to ensure that the injectors pulse sequentially. The electronic control is more complicated and requires additional equipment to run properly. Because the system is more complicated it is very difficult to install and most drivers will require professional installation. This in turn also increases the cost of the system.
When to Use SEFI
Fuel injection systems are very common today. However, a sequential system is not the most common. For those that are looking for very fast handling response and the ultimate in performance, a sequential system is the best option. Almost all cars are sold with fuel injection, but to increase performance there are aftermarket systems available. While carburetors really are best for adding more horsepower, the SEFI systems require much less maintenance, are very reliable, make driving easy, and reduce noise and emissions.
Aftermarket System
Many drivers look to upgrade to aftermarket sequential systems because the stock systems are quite limited and the tuning software used is very inexpensive. An aftermarket system can supply real time tuning, particularly if the manufacturer has yet to make a tuning software program for your engine (not all engines have their own programs). Expect to find a computer, tuning software, wiring harness, sensors and cable for computer interface in an aftermarket kit. If you are planning to replace the entire multi-port system, then expect to pay about $4,000 depending on the make and model of the vehicle.
full seq inj will be present over this winter's must do's 
the new loom config is something else 
carsy said:
I`ve been reading up on this MS lark and i`m impressed, it looks like an extremely capable ecu. And that Tuner studio for diy tuning looks awesome. I`m going to be looking further.
Phil Tobins Tunerstudio is a fantastic bit of software I use the paid for one which is an absolute bargain Message Board | Chimaera | Top of Page | What's New | My Stuff