450cc Injectors -- What size RRFPR

[m90daytona]

Quote:

Originally Posted by Ondonti You are missing something A good fuel injection setup can run 1000 cc injectors at NORMAL fuel pressures and not have a problem. The things you keep mentioning are bandaids when something else is not up to par. Running low fuel pressure when you dont even have very big injectors just indicates that your fuel injection system is not adequately adjustable. 1600cc..now that might not be able to get the injector pulse width low enough but no one here is trying to make 1800hp.

can you run your 500cc's at normal fuel pressure?

[87turbodance]

You'll quickly run into injector pw resolution / minimum opening time problems if you go much over 40 lb/hr. Injectors cant run less than a 2ms pw on a high impedence injector due to how fast the injector can open and close. Low impedence injector are a little quicker but not by much. I remeber I had my turbo 2 Sundance pass an emission test I had to set the idle pw right around 2 ms. This was with 4 33 lb injector with a 2.2 litre motor.

[Ondonti]

Sorry you guys are soooooo wrong.

Evo comes stock with 550 CC injectors and those almost always upgraded.



I cant run huge injectors because Im using mechanical means to increase fueling with my turbo.


Buy an AEM and 1000 cc injectors are cake.
im sure MS can do the same.

[Ondonti]

Quote:

Originally Posted by 87turbodance You'll quickly run into injector pw resolution / minimum opening time problems if you go much over 40 lb/hr. Injectors cant run less than a 2ms pw on a high impedence injector due to how fast the injector can open and close. Low impedence injector are a little quicker but not by much. I remeber I had my turbo 2 Sundance pass an emission test I had to set the idle pw right around 2 ms. This was with 4 33 lb injector with a 2.2 litre motor.

Well the evo has 50lb injectors and has a smaller displacement engine so it needs less fuel to idle etc and they love bigger injectors..........

[Ondonti]

Quote:

Originally Posted by m90daytona can you run your 500cc's at normal fuel pressure?

Im running a bandaid fuel system just like your friend must have been so no I cant run big injectors adequately.

[Moparbishi]

Quote:

Originally Posted by Ondonti There are 2 people who had turbo acclaims and 1 of them was NOT the person you were talking about.....he decided to see what a 14b would do when you rev up the engine and dont have any intercooler hosing hooked up....hello overspin. His car never ran correctly. The guy who built the turbo sohc and then tried the dohc project is a different person. He actually had a turbo 3.0 that ran.

hey i resent that my acclaim ran for a little bit. i over spun acouple of the turbos but it did run for at least a couple WOT runs

[87turbodance]

Idle Pulse Width

You have to select your injectors based on the maximum horsepower your engine can produce to prevent the engine from running lean at wide open throttle. But why not just pick the biggest ones you can find?

The answer has to do with idle and cruise pulse widths. If you use very large injectors, your idle pulse widths get very short. This can drastically reduce the mixture ratio control that you have during idle and cruise situations, and lead to very poor driveability and seemingly strange tuning behavior.

To illustrate, suppose you have established that your engine produces the lowest MAP reading at an idle pulse widths of 1.2 milliseconds, and your opening time is 1.0 milliseconds (considered the 'standard opening time'). Recall that MegaSquirt can only change fuel by 0.1 milliseconds at a time.

And also recall that MegaSquirt assumes NO fuel is injected during opening (which is close to true, since the injectors remain closed until the coils charge, then they snap open at the end of the opening time). Now if the net effect of the enrichments change by 2%, the pulse widths don't change at all. Even if they change by 49%, nothing changes. But once they change by 50%, the pulse widths suddenly changes to 1.3 seconds.

So the next leaner possibility is 1.1 seconds, and the next richer is 1.3 seconds. However 1.3 milliseconds is not 1.3/1.2x100% = 8.3% richer, instead it is (1.3-1.0)/(1.2-1.0) = 50% richer! The mixture becomes very, very rich, and the engine runs poorly.

To confuse your tuning efforts further, it may be that you are already near a threshold, so that a small change in one parameter makes a very big change in the air/fuel ratio in one direction, but no difference at all in the other direction!

But doesn't the EGO correct? Actually, it can't. Even if you set the step size to 1%, nothing happens until the 50% (i.e. 1.3 milliseconds) threshold is reached. That is, the step size only takes effect once the 0.1 threshold of PW is reached. And if the number of ignition events between steps is large, the engine may stumble and die before it recovers and leans out. So in fact you may be better to set the O2 step high (50%), and the number of ignition events low (say 2) so that the average over just a few injections is correct. It is a band-aid approach, however, and likely to induce ignition related problems.

Obviously the converse is true if the engine goes lean. It has to go at least (1.1-1.0/(1.2-1.0)=50% lean before anything happens. If does go lean, it may back fire and die before it gets a chance to become richer.

You might think you can get around this by decreasing the injector opening time (to get a larger "adjustable time") and increasing the VE (or req_fuel), but that doesn't work because the 'ideal' injection time is still 1.2 seconds, and the permissible step is still 0.1msec, regardless of the way you add the components of the pulse width up.

And making matters worse is the fact that many high-performance engines will want even lower pulse widths at cruise than at idle, compounding the tuning problems and introducing more driveability issues. A system with a very short pulse widths like this will be difficult to tune. It will appear not to respond at all to enrichments over a certain range of a parameter (say IAT), then suddenly it will seem to change so drastically that you seem to require an entire new set tuning values.

Now even if your engines idles perfectly at a very low pulse widths, changing load, speed, and other variable (EGO, IAT, etc.) will demand slightly different air/fuel ratios. However, none of them are likely to need exactly the +50% you have to choose from!

This is why several aftermarket ECU manufacturers recommend an idle pulse widths of not lower than 1.7 milliseconds. If yours is lower than this, you need to address it before you will be able to tune your engine for all operating conditions. The high-resolution code, or lowered fuel pressure may help. Ultimately the best solutions are appropriately sized injectors or staged injectors.

http://www.megasquirt.info/

[m90daytona]

+1...good info

[Ondonti]

What does that have to do with the question at hand?
Generalized copy and paste with no calculations regarding the application we are dealing with.

What does that have to do with thousands of people running bigger injectors then m90 thinks are possible and they idle like butter?

Point is if you cant get 50lb injectors to idle then its cause you dont have a decent system. Cars come with 50lb injectors from the factory and can get away with more than doubling that.

[Ondonti]

Quote:

Originally Posted by Moparbishi hey i resent that my acclaim ran for a little bit. i over spun acouple of the turbos but it did run for at least a couple WOT runs

Failure to run correctly does not mean the car did not "run"

[87turbodance]

My point is that the car may run but it would run like ass the throttle would be an on/off switch unless you had a way to pull fuel pressure down at idle. I believe DSM cars do something like this. They kick in higher fuel pressure when in boost because they run a low fuel pressure at idle and cruise for good driveability / economy. There's no way a car could get away with doubling the size of it's fuel injectors without some adverse effects using normal FI methods like we have on our cars. You can only open and close an injector so quickly. These are mechanical devices. They have mass. They DON'T move at the speed of light.

[m90daytona]

Quote:

Originally Posted by Ondonti What does that have to do with the question at hand? Generalized copy and paste with no calculations regarding the application we are dealing with. What does that have to do with thousands of people running bigger injectors then m90 thinks are possible and they idle like butter? Point is if you cant get 50lb injectors to idle then its cause you dont have a decent system. Cars come with 50lb injectors from the factory and can get away with more than doubling that.

first of all, point to where i said its "impossible" for a car to idle w/ 50lb injectors. you misquote me and make yourself look like a fool. i saw a supra idle fine w/ 1600cc injectors before, my point is its easier to use an fmu. you obviously dont like the fmu, and your entitled to your opinion, but that doesnt mean that everyone has to agree w/ you so stop trying to start an argument.

secondly, 87sundance made some good points that will be valuable for me to use when i tune my ms so thank you. if you would actaully read and understand it, you may find it helpfull and finally get your ms up and running too.

[Ondonti]

Quote:

Originally Posted by m90daytona first of all, point to where i said its "impossible" for a car to idle w/ 50lb injectors. you misquote me and make yourself look like a fool. i saw a supra idle fine w/ 1600cc injectors before, my point is its easier to use an fmu. you obviously dont like the fmu, and your entitled to your opinion, but that doesnt mean that everyone has to agree w/ you so stop trying to start an argument. secondly, 87sundance made some good points that will be valuable for me to use when i tune my ms so thank you. if you would actaully read and understand it, you may find it helpfull and finally get your ms up and running too.

I have and use one, its a bandaid.