staged injection questions

[Electroman]

for those of you that don't frequent they type 4um or haven't seen my post, I'm currently building a 1911 type 4 motor to go into my 67' beetle. I plan on an ITB setup with motorcycle throttle bodies and a staged fuel injection using megasquirt 1 extra.

anyway while I'm waiting for some engine parts from the machine shop I hooked up my megasquirt to my computer and started playing around with the settings. the main thing I haven't decided on yet is how I'm going to do the staged injection. this might get a little wordy so bare with me. the obvious choice would be to use the staged injection code. I could set it up to stage over RPM and MAP tell it how many injection cycles to transition over and I'm done. from that point I can tune the car just like it had only 4 injectors. but this method on megasquirt 1 can only transition partially, meaning i can only inject from just the primaries or the primaries and secondaries combined.

the other way I could do it would be what I was leaning towards up until yesterday. that would be to use the dual table code and do all of the staging and transitioning through the two fuel tables. obviously this would be much harder to tune the engine, but it would allow me to stage completely to the secondaries alone.

my main question which after 8 hours of reading yesterday I still cant answer is, is there a performance benefit to switching completely to the secondaries over running both primaries and secondaries together?

after thinking this through I cant quite decide. obviously both would get the same advantage of staged injection but would one either run better or provide more power than the other?

[gearheadgreg]

At higher RPMs, the further out the injector, the more time it has to vaporize, which also cools the intake charge, which has obvious benefits. I know there are street motorcycles that have this. How much benefit to be gained by going 100% through the outer injectors vs 50/50 through the inner and outer injectors? On a fairly striaightforward ACVW build, I'd be willing to guess not enough to go through the trouble, but I am just guessing.

[Electroman]

thats kinda what I'm thinking, but I cant find any empirical data that anyone has ever actually tested that.

[gearheadgreg]

Can you find any empirical data on switching injectors from 100%/0% to0%/100%?

If that is a 5% power increase, you can bet you will be somewhere in the middle, and how hard do you want ttwork for 1 or 2% ?

[Electroman]

the only testing I have found so far has been injector placement. and I have seen dyno sheets that show anywhere from a 10% to a 25% increase in top end HP by placing the injectors around 12" or so away from the intake valves. so assuming i get the low end of that 10% is worth it to me. but those engine also only had one set of injectors, so 100% of the fuel was coming from the upper placement. hence why I'm questioning it.

[gearheadgreg]

Also, I suspect they were much more highly tuned with a better VE than an ACVW, so consider that as well.

[Electroman]

ya they were I only expect maybe 5% difference. but I still see that as free HP

[Jadewombat]

my main question which after 8 hours of reading yesterday I still cant answer is, is there a performance benefit to switching completely to the secondaries over running both primaries and secondaries together?

after thinking this through I cant quite decide. obviously both would get the same advantage of staged injection but would one either run better or provide more power than the other?

Years ago it was said by one of the Cosworth engineers that no one injector could do it all, especially turbo engines. One set fed the needs of the motor, while the secondary fed the needs of the turbo. This makes the most sense to me considering the boost is variable and the engine needs are--as well as if you run just one set of injectors you have to size them to the engine. It seems plausable two sets of smaller injectors are more susceptible to fine tuning that one set of larger injectors. Mind you, all of this was all before direct-injection gasoline technology came about.

I think there still is potential for more power with a "regular" indirect injector setup with secondaries though. Would be worth trying it and see what happens, even if the you are running a N/A motor. Just the others suggested, you could experiment with varying the supply between the two sets. Have the primary (closer) set at low RPMs and the secondaries take over at higher RPMs or something like that. I really doubt this experiment would be a performance inhibitor though, at least once you get past the learning curve.

[gearheadgreg]

I'm sure you've seen these, but

http://imageshack.us/a/img682/9749/mg2973resize.jpg


http://www.ducatiglasgow.co.uk/document ... 8-main.jpg



In the water-methanol world, where injection was predominantly varied through a single fixed (continuous) spray nozzle, and varying the pressure behind it, the flow range was limited. Using stepped and/or staged injectors was a simple way to get increased flow range, but I don't think that's your dilemma here. Most applications have fuel injectors that can cover an engine from idle to max hp on normal applications, with headroom to spare. Most. I think the drive here would be to see what additional charge cooling can be gained by injecting gasoline a little further upstream.

If you compare the latent heat of vaporization for gasoline, and for methanol, and then water, I think it would be eye opening. However, being that you have an ECU capable of doing this, and throttle bodies with them already there, why not give it a go?

[Electroman]

ya thats where I'm at, just gonna do it and see what happens. I think to start just to make it easier on myself I'm going to set it up with the standard MS staged injection setup. then once I get it tuned ill give the more complex setup a shot. thanks guys!

[shag55]

Anyone interested. I'm selling my Aquamist HFS3 system. $450 shipped. It's for EFI piggybacking.

[Piledriver]

The MS staging code works well on the bench, it does a bit more than just hard switch between 2 sets of injectors.

I don't have a staged injection "worthy" motor running yet, but staged/sequential capability is why I upgraded to MS3.
There was some work awhile back doing similar for MS2-extra.(or at least adding a staged toggle output and fuel calculations allowing it/other support)

[Paul H]

I recently did some tests on the dyno with SP1's and found no change in HP switching from high mount to low mount positions.
Personally I wouldn't run 8 injectors unless I really needed the flow for a meth engine it's just more pain for no gain

[gearheadgreg]

Can you give more data on your dyno testing for the staged injection? The motorcycle engines that showed benefit were really only at high rpms, IIRC, and very high VE.

[Paul H]

I guess there may be an advantage on engines that rev over 10k but the most I deal with is 7800rpm and I was switching between 2 stroke mode and sequential-crank trigger to distributor trigger. I even changed injector type Pico/GM. Head temps make more change to HP of 0.5 to 1hp within the safe window