| Author | Message | ||
     Greg_e |
Does anyone know if this theory is sound: I put in injectors that are roughly double the flow rate from the stock injectors. In order to make this engine fire up does it sound right to just go in and edit the fuel table and cut each value in half? Any side effects like poor low throttle and poor idle performance? | ||
| Syonyk |
That should work enough to get it running, but I'm guessing you will have very poor idle and low throttle running. Note: Knowledge here is from the RX-7 world. Injectors are injectors, but take this with a grain of salt. There were constant questions of "Why can't I just put huge injectors in the primary spots?" RX-7s have two sets of injectors - primary and secondary. They also have, when turboed, HUGE fuel flow requirements under boost. The primary injectors were there for low speed running, and the secondaries opened up at higher flow requirements. Putting huge injectors in the primaries was a mistake... The issue with injectors is that there are, functionally, 3 different "stages" of flow: - Injector opening. From totally closed, the injector opens. This takes a non-zero amount of time, and flow during this period is VERY difficult to model, and rather non-linear. - Injector open. This is the injector flowing at the rated flow (however many pounds per hour). - Injector closing. From open, it snaps shut. Again, fuel flow during this period is complex, and difficult to model. The problem with larger injectors is that the opening and closing takes, proportionally, more of the time. And, as this is difficult to model and rather non-linear in behavior, it's hard to figure out how much fuel flows during this time except by experimentation. If you double the injector size, you need roughly half the pulse width - but at low flow rates, that opening and closing time is more significant. It's possible, with large enough injectors, to run into a situation where you *can't* flow little enough fuel - if you just pop the injector open and snap it shut immediately, it squirts out too much fuel for the demand. Also, metering fuel at low flow rates is tricky - you end up with an injector flow that looks like R(t) + C - rated flow times time open, plus a constant value from the opening and closing times - except this may not be terribly constant, depending on the injector. As the injector size goes up, C increases, and adds to the complexity of fueling. ... so, TL;DR version, good luck. It should work, it will probably work fine at higher fuel flow rates, and it may work OK at low RPM and idle, but if you have funky fueling down low, good luck fixing it cleanly. | ||
| Greg_e |
I've also thought about the directed flow of the later stock injector where they squirt towards the valve and thought about fixing atomization issues with a screen like in the RX-7 (had an 86 many years ago). The guy at the injector place seems to think doubling the flow rate should still be OK and looking at the numbers it appears there should still be plenty of open time. That said I'm still thinking about it. I'm also going with the estimate that the stock injectors flow about 28 to 32 pounds per hour. But your concerns are the same ones that I have knowing that flow during the on and off transition can be tricky and that running the injectors at really low duty cycles is bad for performance. I need to pull up a fuel table and look at the number of 85ms blocks the low RPM stuff is programmed for and see what I think. I have no doubt that full throttle performance will be fine because the higher rate injectors will be working to at least 50 percent duty and should be pretty linear up there. It's the 10 percent duty and possibly lower that bothers me. The other option is I might be able to find a lower pressure regulator which will allow me to add a little bit more on time to the injectors. (Message edited by Greg_E on June 26, 2011) | ||
| Syonyk |
I had an 88 N/A '7 - great car  A bit fuel hungry, though, and I got rid of it because it was *terrible* in the winter - I lived somewhere with a gravel parking lot, and literally couldn't get it out of its spot 3-4 months of the year when stuff was piled up behind it. Nothing like putting it in reverse, letting the clutch out... getting out and watching the wheels spin on the ice going nowhere... I got into Subarus after that. Much better suited to the weather... It sounds like you're well aware of the issues, so have fun Why did you want to double the flow? | ||
| Greg_e |
Because it is easy to buy injectors that fit at about 60lb/h, not so much for the stockish 30lb/h Think I am going to send the stock injectors out for service and see what happens. One of them is full of crud on the inlet side so I'll let a specialist handle the cleaning. Not sure what happened to these before I bought them to be filled with this crud. | ||
| Glitch |
Got a sonic jewelry cleaner? | ||
| Greg_e |
They claim to take the filter out of the inlet and the nose cone off and back flush the things as well as ultra sonic cleaning. Looks like $15 per injector so probably a decent deal and then we'll know what the stock flow rate really is and they will be able to build more for replacements. I'm going to ask them to get video of the spray pattern and to see if they can change the angle of the spray to better match the TB. There are spots on the side of my TB where the fuel was hitting the wall instead of spraying down the intake. I've offered to send the entire TB down if they are willing to think about changing the angle. | ||
| Syonyk |
Oh, yeah. The "pro" injector cleaning services that take the injectors when they're off the vehicle and reverse flow ultrasonic clean them in awesome solvents are well worth it if you've got dirty injectors. Really, if that's the only problem you've got, send the injector (s?) in for cleaning, and figure out what's wrong with your fuel system filter. I thought you were asking because you were going to do something silly-awesome that needed twice the fuel, like forced induction.  | ||
| Greg_e |
Nope, just looking for easy to buy injectors. The ones that need cleaning are something I bought with a spare TB. The ones that came off the bike look pretty decent but I have an 03 XB9 which uses the older style TB and switching to the newer larger style TB which is the one I bought and has the cruddy injectors. | ||
| Xoptimizedrsx |
do a search on here from EricZ he posted the link to direct replacement injectors he uses on his turbo bike. they have OEM rate flow and higher. please note going larger will require twice the flow to get the spray pattern to atomize well. this is what you look for. sometimes less is more. I run a smaller 5 hole injector on mine since I was not getting my fuel values to 255. this increased power by making the spray pattern even finer for more burn. the finer the mist the better the burn. I used the less is more trick... works great for me. 90 plus hp on the xb9 that way. | ||
| Greg_e |
That's exactly why I keep thinking about the screen in the RX-7, the injectors spray onto this screen to help atomization, it supposedly worked pretty well for them, but I think they were also kind of a single stream injector. I should add that the drop in Eric found was a 60lb/h injector which is somewhere around twice the flow rate, cheap too at around $54 but I think the on time would be so short in an NA engine that you will loose some quality at idle. The link above has a Harley injector that they can build anywhere from 28lb/h to 60lb/h and I might still end up with a set of those but I want them to look at the stock XB12 injectors and see how we can change them. (Message edited by Greg_E on June 28, 2011) | ||
| Slaughter |
It is NOT just pounds per hour but atomization. Kind of why it seems to work better with the higher pressure ("race") regulator and stock injectors (the later Throttle Bodies) | ||
| Greg_e |
Typically with the really short times you get really poor atomization too. It would be nice to use a different computer that would handle 4 injectors and then you could do the same thing Mazda did with the rotaries and use two intake runners with two butterflies and have a low speed runner and a second runner to handle full throttle. Put something like an 14 to 18 lb/h in the smaller runner and whatever you needed to fill in the rest in the second runner. That would let you keep the times nice and long so the injector is working well and still get really good low RPM response. | ||
| Slaughter |
I dont' think the flow through the funky split throttle body could really deal with multiple injectors. Flow would be extremely complex. HIGHER pressure (race regulator is almost double fuel pressure) means short fuel calls and good atomization | ||
| Xoptimizedrsx |
on the Xb Just put a ddfI3 ecm on it and activate the empty fuel tables for the shower heads. then you can get 4 injectors... you can retro fit a ddfi3 ecm to a ddfi2 bike. best way to do it is to get a used ddfi3 harness and 1125 ecm ddfi3 Helicon... This will get you what you are after. you will need to modify the xdf to get the turn on feature for those maps and the adx to read the data in a history table... Its all doable... xopti |
