Few Questions about DSMchips

[nickrule99]

Alright-

Ive got a few quick questions about these chips.

Im planning on running a FP Red with 770's (so the chip would for for 770's.)

What I plan to do is run daily at around 20psi and then turn it up for racing, but also have the ability to run stock boost for emissions and such.

With this chip, can I run around at 20psi daily, then up the boost to say 25psi without having to worry about the fuel curve?

What if I were to throw the T25 back on there, would I end up running extremely rich, or will the ECU know that its running stock boost again and give me the correct fuel for it?


Looking at what I wrote, it seems kind of confusing, but thats really the best I can do. If I can figure out a more clear way to ask, I'll be on here.

Thanks guys.

 

[slickster]

The chip simply allows the ecu to control the new injectors like they came on the car to begin with. You will need to tune it for the boost, but it should idle and off throttle well.

 

[slickster]

What I plan to do is run daily at around 20psi and then turn it up for racing, but also have the ability to run stock boost for emissions and such.

With this chip, can I run around at 20psi daily, then up the boost to say 25psi without having to worry about the fuel curve?

What if I were to throw the T25 back on there, would I end up running extremely rich, or will the ECU know that its running stock boost again and give me the correct fuel for it?

This part scares me. You tune your car for one boost level. You change the boost...you change the fuel curve. You change the turbo...you change the fuel curve. You change anything...you change the fuel curve.

 

[98spydert]

The fuel maps will match the injector size unless he's making other adjustments for you. My car ran fine with DSMchip, 650s, and a T-25. It ran the same with DSMchip, 650s, and a evo III 16G. I haven't had to change anything yet according to my logger.

If you're tuning by air flow (i.e. MAFT, DSMlink) you shouldn't have to make much of an adjustment, if any.

If you're fine tuning with something like an SAFC, you'll probably have to change your adjustments slightly.

 

[slickster]

The fuel maps will match the injector size unless he's making other adjustments for you. My car ran fine with DSMchip, 650s, and a T-25. It ran the same with DSMchip, 650s, and a evo III 16G. I haven't had to change anything yet according to my logger.

If you're tuning by air flow (i.e. MAFT, DSMlink) you shouldn't have to make much of an adjustment, if any.

If you're fine tuning with something like an SAFC, you'll probably have to change your adjustments slightly.

Are you trying to say that you swapped turbo's from a t25 to an evo and you didnt have to adjust your fuel controller?????? I admit idle will probably be ok and you might not notice part throttle, but wot is ok???? Maybe i am misunderstanding.

 

[98spydert]

Yep, everything was fine. At the top of 3rd gear, timing to around 20, good o2v, knock gauge reads no knock what so ever. I suspect I can thank the MAFT for my good fortune, if I had been using an SAFC I would most likely had to change the settings.

 

[nickrule99]

Thats what I was thinking.

Since the computer now knows it can give twice as much fuel as stock, I would think that it would be able to compensate for twice as much airflow as well?

I doubt at WOT the ECU is going to be throwing all the injectors have into the engine if its reading normal airflows, but if the airflow goes up, say to 20psi, it is able to compensate with the extra feul it now knows it has.

 

[kpt4321]

Since the computer now knows it can give twice as much fuel as stock, I would think that it would be able to compensate for twice as much airflow as well?

I doubt at WOT the ECU is going to be throwing all the injectors have into the engine if its reading normal airflows, but if the airflow goes up, say to 20psi, it is able to compensate with the extra feul it now knows it has.

I am not sure what you mean by this question. I think that you don't quite understand how the ECU works.

It has an airflow signal, and it uses that to calculate the amount of fuel that is required (it's a simple mass ratio). From there, it gets an injector pulsewidth. The injector size changes basically just change a multiplier for the IPW; if you run twice the injector size, it cuts the pulsewidth in half.

The ECU doesn't know "how much" fuel it can supply stock, nor does it know when you install larger injectors. It just comes up with a pulsewidth, and sends it to the injectors. Then whatever happens, happens.

 

[nickrule99]

Sorry I wasnt to clear with the question- I dont really know the correct terms.

Heres my attempt to explain whats going on in my head. Ill leave this up for a bit, but delete it soon after (if im wrong) so others dont see this information and think its anything to take stock in.


Alright, here I go, good luck understanding this.


I dont know what numbers to use, so Im just going to make them up- so you can see what Im trying to get at. Also, Im going to assume the IPW is actaully a percentage of much fuel the injector is flowing (so .90 is 90%)

Airflow at 10psi = 500 molecules of air
Airlow at 20psi = 1000 molecules of air

Air:Fuel is 5:1

So the IPW = .20*(molecules air)

Max stock injectors can supply is 125 molecules fuel
Max 770's injectors can supply is 214 molecules fuel

So....

When the boost is 10psi, the airflow sensor reads 500molecules air.
The ECU then calculates the IPW needs to be .8 because .20*(500)/125 = .8

When the boost is 20psi, the airflow sensor reads 1000molecules air.
The ECU then calcualtes the IPW needs to be 1.6 because .20(1000)/125 = 1.6

We all know that the injector cant flow at 160%, and bad things happen in the engine

When the give the ECU a chip for 770's, the IPW is multiplied by .584 (the difference in flows... the 770 can flow 58.4% more than stock).

so with the chip, at 10psi the Airflow sensor reads 500 molecules air.
The new IPW is going to be .4672 by using IPW)= .584*((.20*(500))/125) = .4672

also, at 20psi the new IPW is going to be .9344 by using IPW = .584((.20*(1000))/125) = .9344

Since the injectors can flow 93% of their max, the engine runs fine.

At 10psi, without the chip but with 770's, the ICU would set the IPW to .8
With the IPW set to .8, the 770's would flow 171.2 molecules feul which is far to much, givin that at 10psi the engine only needs 100 molecules fuel.

At 20psi, without the chip but with 770's, the ICU would set the IPW to 1.6
With the IPW at over 100%, the 770's would be wide open, flowing 214 molecules feul into the engine. This again is too much, since the engine only needs 200 molecules fuel.


What Im basicially trying to get at is this:

The chip changes the IPW to a factor of what the difference of flows between the two injectors is. So if your chip was for 770 injectors, the computer would safely be able to provide as much feul as needed up until the IPW reaches 100%.

Regardless of boost pressure or turbo, the ECU is now able to supply the correct amount of fuel, up until the injectors are at 100% duty. If I choose to change the boost form 10psi to 20psi on the fly, the ECU will see the increase in air flow and adjust the fuel accordingly.

Alright, Im done. Somehow all I just said makes sense to me, which worries me, and probably means Im completely wrong.

Eh......

 

[kpt4321]

You're basically right, in general. However, there are a couple things that I have singled out and commented on below.

Also, Im going to assume the IPW is actaully a percentage of much fuel the injector is flowing (so .90 is 90%)

IPW is "injector pulsewidth," which is the time the injector is open, generally in milliseconds. This is directly related to AFR (air to fuel ratio) and airflow per rev. IPW will generally range from 1-20 ms.

If you want to talk about the percentage of the avaliable on-time that the injector is open, that's injector duty cycle, or IDC. IDC is represented as a percentage. This is related to total mass airflow, rather than airflow per rev.

Airflow at 10psi = 500 molecules of air
Airlow at 20psi = 1000 molecules of ai

Pressure is not, generally, diretly related to airflow. Due to the fact that you can change airflow without changing pressure, and there are other factors that effect airflow (VE, temp, etc), if you want to double the flow you can't assume that doubling the pressure will do it.

Read this: http://users.wpi.edu/~ktarry/dsmtech/flowpress.html

Air:Fuel is 5:1

Desirable AFR's will range form about 10:1 to 15:1.


Otherwise, you seem to have the general idea.

 

[nickrule99]

Awsome, thanks for the site.

So.... bascially, i can switch my boost settings on the fly, provided their flows will not excede what the injectors can compensate for?

 

[kpt4321]

Welcome.

Yes, that is correct. However, due to changes in knock propensity as boost level changes, you can usually grab a little more power by a slight retune when you make a decent boost level change.

 

[kpt4321]

Brads, good catch. I was totally back-asswards on that, I don't know why I slipped.

I'm going to edit it so some toolbag who doesn't read the whole thread doesn't get all mixed up.

Thank you!

 

[98spydert]

Brads, I just deleted mine. I'm just gonna confuse myself and someone else too if I keep going.

 

[brads]

Brads, good catch. I was totally back-asswards on that, I don't know why I slipped.

I'm going to edit it so some toolbag who doesn't read the whole thread doesn't get all mixed up.

Thank you!

No problem. It's good to have someone with the patience and organization to not only write posts like this, but put it onto webpages for other people to reference. If I can help out with a little correction here or there, I'm more than happy to do so.