Small motor, BIG injector and idling

I am at the next phase of the Fiat project and that involves boost.

Current setup is MS2 on a Ver3 board, one 425cc injector and throttle body from a 2008 Raptor 700R fed by a Suzuki GSXR fuel pump. On the dyno the needle on the injector pulsewidth gauge was pegged at peak power and a staggeringly low 47hp. Not that it was starving for fuel or anything. The AFR's looked good I am just at the limit of that injector it seems.

I am looking into an injector of about 850cc when I put some positive manifold pressure into action but this line from the megamanual haunts me

Megamanual said: However, do not install injectors with a much larger flow capacity than you need. Very large injectors will create idle pulse width issues that will make tuning very difficult

Are there any tricks to tune around idle pulsewidth issues?

Also every calculator says that I should be able to hit more than 80hp with 425cc, yet I am at its limit under 50whp. I need to double check my fuel pressure but I am pretty sure it is good. Even the Raptor that this came off of made 70hp. Not sure I understand what is going on there.

Use a smallish primary injector for idle and low loads, then bring a secondary injector (as big as you need) online under heavy load/high rpm.

I know you can run big injectors on small motors, each of our 4 cylinders in our 2.3L (.575L/cyl) has a 75#/hr or a 787.5cc/min injector on it and it idles arguably better than stock 35#/hr injectors. I've heard of people running bigger than that with no ill effects, the only complaint is at 120#/hr on a 2.3L but you're running so much boost (drag car) you don't care about idle. You can alter pulsewidth and I'm only running MS-I v3.0 w/MSnSExtra...

If you're running 1 injector for that tiny motor, I think you're going to be just fine, yes you might have to play with settings, but you will get it...

I think you have other issues.

Wait what is the impedance of the injector?

If it is low what is the duty cycle percentage you are running? Do you know the peak & hold Amps? What is the Ohms for the injector you are using as it will determine the peak and hold as well as the duty cycle and the duty cycle percentage OR are you using a resistor? If so what is its rating.

I am just going through ll of this with my 924s . Injector selection / tuning is a bit of a black art in the MS world. IT kind of reminds me of the old "if then" statement when programing as there are alot of options and each ash both good and bad aspects After spending a couple nights researching and reading I think I have got it.

You may be on to it with the FPR as well. I was surprised to find that the fuel pressure does not increase the amount of fuel as much as you may think. There is a calculator in the mega-manual that addresses this. However if you are only running say 25-30 PSI and you should be up in the 40-50 range that may be the difference between a duty cycle of 100 percent versus 80 percent.

Anyway post up more info I like a good mystery!!!!

Here is a link to my bit of fun. My injector dilemma / discussion is towards the end of the 2nd page.

http://clarks-garage.com/phpBB2/viewtopic.php?t=8338

Dumb question but I asume that you dont have "multi port" selected in the MS

The injector is high impedance 13.5 ohms. Injector port type set to throttle body. Thanks for making me double check. For some reason the PWM Current limit was set to 75% and that aint right. Changing that back to 100% now. I will try and datalog a hard 3rd gear pull and see if that helps.

I am shooting for at least 100hp and if I can manage as much as 130. I want enough injector to comfortably support that. 75 to 80 lb/hr sounds about right for that.

I am asuning the 700R = 700cc motor?

Next question.

What would the pitfalls of running a standard port injector in a TBI setup?

The raptor injector has a grid on the end instead of a normal injector pintle. I am assuming that this is for better atomization, Cool beans right? Well the folks that offer upgrade injectors appear to just use a standard top feeder from RC engineering and claim better atomization.

So... Do you learned people think I could make one of those super cheap Siemens 835cc injectors work without issue?

These guys are $55 all day long and looking very attractive right now.

The manifold in question

dean1484 wrote: I am asuning the 700R = 700cc motor?

700cc twin

how is the injector normally oriented in the stock location? Most port injectors have a narrow angle spray pattern to target the back of the two intake valves on a 4 valve head. With your manifold the two pencil streams would peg the back of the bend pretty fast creating a real bad wall wetting effect (pooled gas does not burn) A larger cone spray pattern should help keep things atomized. What about using a rising rate fuel pressure regulator? That should allow for longer pulse-widths at lower rpm. This can be helpful because at low pulse-widths the injector flow is not linear. There is a dead time in there as the coil energizes which varies with battery voltage and there is the momentary state that the injector is in the process of opening but is still developing a good flow/spray. If you end up with such short pulse-widths that a good portion is in this sketchy not-so-predictable state tuning gets ugly.

edit: the hole grid determines the spray pattern. I think you just want a single cone. There are all kinds of different patterns out there. I had good results spraying the injector into open air with a push-button and a battery to activate the injector to observe the spray pattern. I do NOT recommend this without someone handy with an extinguisher. some varieties: http://farm4.static.flickr.com/3044/2296071319_0dd1a8d570_o.jpg

Out of curiosity, what is the bore on that throttle body?

I think a problem with a rising rate FPR would be getting the MS to play nice. Not impossible if you are a bit twiddler, just something else to fiddle with. As for injector spray pattern testing, don't use gasoline. Mineral spirit or similar low volatile, into a large glass jar or a plastic tube is easy to observe, with suitable background. Consider video of your testing..

Adding a different fuel pressure regulator would require a complete reworking of my fuel system. I welded a flange to the bottom of my fuel tank to accept the gsxr sport bike fuel pump which is internally regulated and filtered. I really like how it worked out and dont want to change it.

The throttle body is 46mm.

On that set up- two questions: 1) being a V twin, using the orientation as shown in the picture- is the one cyl on the left, and the other on the right? Or does it split differently? 2) is the throttle heated?

I would suggest that one of your main problems is maldistribution- the first firing cylinder is getting most of the fuel, the second, not so much. Can you check a/f on each bank?

Second, your injector aiming is basically putting all of the fuel into the wall- it's spraying right into the middle of the corner- which will force the fuel down the side. Can you change the orientation so that it's center on the air flow?

In terms of idle, typical min pulse widths are sub 2 msec, so if you are higher than that, the injector isn't too big.

One other thing- the pattern of the multi hole injector is typically customized for a particular engine- so that it feeds both ports on a 4v engine. It should work alright for your application, assuming you are not just spraying it on the walls.

While it is not optimal for the injector to be pointing right at the wall, every TBI setup I have seen does something similar. Most shoot the injector straight down into a bowl and then let the fuel find its way to whatever runner it can.

Having never seen a raptor in real life I am unsure how the injector orients but I do know that one injector feeds both cylinders

Here is a pic of a yamaha motor with a rag where the TB should be

Right now the car runs great. A good power increase over the carb. The idle could be better but with the lumpy cam I don't expect too much there. Going back to the stock cam for boost should really help that. Horsepower is lower than I had hoped but not totally out of line. My innovate shows great AFR's and the Dyno confirmed it was correct. I cannot afford to toss another LC1 into each runner to compare them right now.

Would it spary on the walls or would the air felocity through the intake "bend" the spray down into the cylinder?

dean1484 wrote: Would it spary on the walls or would the air felocity through the intake "bend" the spray down into the cylinder?

probably would bend at WOT, but at idle, its splashin the wall for sure.

edit:
without seeing your setup installed in the car its hard to tell, but how out of the question is mounting the whole assembly using a tube with less bend?

You could put a screen in there (flow straightener honeycomb style, northstar would be a cheap one ot get one off in a J/Y) to help more properly dispurse the fuel...

OK so here are some more descriptive pics. Behold! The staggering awfulness of the intake port on an 850 cylinder head. That diamond shaped hole splits right and left to each pair of siamesed intake ports.

On the motor

In the car. The motor is hanging about 3 inches low here. In everyday use there is very little space above the throttle body.

So anyway. You can see that even if I pointed that injector straight down the intake port it would still be spraying onto a wall. As non-optimal as it is, it is working pretty well.

to Raze. You mean like one of those grids in a MAF?

In reply to ditchdigger:

Yup, that's the one, could be from any car, just remember nice 'depth' in the N* intake honeycomb...

ditchdigger wrote: In the car.

Mr. Digger of Ditches: Beautiful!

Im gonna keep pushing...since you have some lateral room, how about lengthening the distance between the injector and the bend -3 or 4 more inches of straight tubing run between the bend and the TB might give the spray enough time to move to the center of the air flow before it has a chance to impinge on the tube wall.

FYI, that looks like it would be a hella fun project for me to try to cast you a real manifold rather than a hunk of tube...lemme know if you want to work on something - Id do it free just for the fun of it and the casting practice. All I would need would be a dimensional drawing of the flange and a few dimensions of the space...maybe could cast ports for multiple injectors. If you wanted to make the intake port bigger, I could accommodate that as well!

I think the "manifold" is the cylinder head too. I'm just guessing, but backyard casting a cylinder head might be a bit much.

Love the project ditchdigger.

4cylinder, I've got a G10 head (3 cyl metro) collecting dust if you want to try making an intake manifold for fun. They're throttle body injected in stock form, but I think going to individual runners for ITBs would be awesome and relatively easy to cast.

-guy who works in aluminum foundry

You should be able to hit ~70whp per 42lb/hr injector @ 3bar fuel pressure. You sure you were maxing it out at 44hp?

I will try and get some time to datalog it tonite. A hard 3rd gear pull at 6200RPM should let me know. At the dyno the tuner mentioned that the pulse width needle was pegged at peak. Of course PW current limiting was set to 75% at that time.

Totally interested in a cast manifold.

One neat thing I forgot to brag about on this TB. All of the idle air, either cold idle boost or the screw idle adjustment that bypasses the butterfly is routed to a port that surrounds the injector tip. I am assuming that will help guide the squirt as it is enveloped in the moving air stream.