Boost Switching & PCM Calibration

[SpookSVT]

I bought a Turbosmart e-boost 2 for my turbo build and one of its features is that you can set-up remote switches to increase or decrease the boost pressure from the turbocharger during a run. I've been contemplating exactly how the PCM is going to know to switch to a different program so I don't run lean and fry the pistons.

This means I can't run the Xcal2 now since it is a flash device and requires the car be turned off and won't work in the middle of a run. That's fine since I have Alex Pepper's OBD-II setup and I'm probably going to go with the LM-1 wideband so I can still datalog that parameter and will have to get the XD-16 gauge as well unless I can datalog from the gauge onto a laptop. Is that possible?

So I'm thinking I need to get the SCT 4-bank chip but how do I set it up electronicly so that when I hit the + button, the switch for the chip will change to the necessary program for that boost level?

[RodneyBur]

you will have to have several different tunes on your chip that are tuned for a specific boost level. You can turn up the boost to your predetermined level and then switch to the tune on your chip. It would be a two step process: 1. turn up boost 2. flip the chip. There is no way to switch tunes automatically using the chip. For example: get a tune for 5lbs, 10lbs, 15lbs, 20lbs.


I think you would be fine turning up the boost a little from your tune. If you tune at 5lb then you should be able to turn it up a little. How much you can turn it up would depend on how you have the MAF flow tables setup and the injector settings. Turning up the boost to a point where your timing would need adjusted would also be another factor.

For example if you have your MAF signal on your stock tune set where the max airflow at that tune is set to the highest possible MAF signal volts then when you turn up the boost more air would be going through at the MAF signal is reading incorrect. You could set the tune where you have an adjustment buffer.

Hope that helps but I'm no expert so maybe someone else can chime in.

[SpookSVT]

So what you're saying is have a single tune where the MAF is set as high as it would be and as I hit the switch it would adjust fuel accordingly? I would just go off the tune for the higher boost level then, correct? Would the fuel tables for the lower pressure be correct too? Spark would have to be set according to the higher boost level to keep anything from getting hurt. If this would work I could keep the Xcal2 which is more practical for me.

I was originally wondering if you maybe have the EBC and PCM joined into one switch where I would press a given switch for a given boost level and it's respective tune. But again I'd like to keep the Xcal2. I would just have to work it out with the tuner then.

[warmonger]

Originally Posted by SpookSVT

I bought a Turbosmart e-boost 2 for my turbo build and one of its features is that you can set-up remote switches to increase or decrease the boost pressure from the turbocharger during a run. I've been contemplating exactly how the PCM is going to know to switch to a different program so I don't run lean and fry the pistons.

This means I can't run the Xcal2 now since it is a flash device and requires the car be turned off and won't work in the middle of a run. That's fine since I have Alex Pepper's OBD-II setup and I'm probably going to go with the LM-1 wideband so I can still datalog that parameter and will have to get the XD-16 gauge as well unless I can datalog from the gauge onto a laptop. Is that possible?

So I'm thinking I need to get the SCT 4-bank chip but how do I set it up electronicly so that when I hit the + button, the switch for the chip will change to the necessary program for that boost level?

This is going about it all wrong.

With a proper tune on your turbo the same tune will work fine for low and high boost. The computer takes into account the extra boost based upon load, which comes from the mass airflow sensor. The higher the airflow, the higher the load and consequently the pcm will adjust timing and fuel delivery accordingly.
That is the way the car is SUPPOSED to work. Hack tuning might not though...

Just for example, my car was able to run from 0psi up to 14psi with no modifications to the tune, no flip-chips, etc.

[SpookSVT]

Alright that makes sense. So the computer basically calculates everything based on incoming air and the throttle position. I should have realized that because the turbo isn't always at full boost anyway.

So basically all I would need is one tune for 93 octane and I would be all set, right?

[warmonger]

Originally Posted by SpookSVT

Alright that makes sense. So the computer basically calculates everything based on incoming air and the throttle position. I should have realized that because the turbo isn't always at full boost anyway.

So basically all I would need is one tune for 93 octane and I would be all set, right?

Well I don't know. With a turbo for the street I find that just using the regularly obtained gas is what you should use for tuning. Then tune to the max on that. The highest perfromance 91-93 octane or whatever is available in your area is the only smart choice anyway with a boosted car, but again use whatever brand/grade you can obtain readily anyplace that you go.

Timing is important but it isn't like you can just go cranking the ignition advance up just because you have 93+ octane fuel. Timing has to do with the burn rate of the fuel in the cylinder, airflow characteristics/cam profiles, compression, charge temperature, RPM, etc.
You don't really make more power increasing the timing, you make it because there is more Air/fuel in the cylinder...period.

By this I mean if you put in 105 octane it doesn't mean you could give the engine another 10* of timing and expect a bunch of power.
If that theory worked, you could run 200 octane fuel and then run your timing 150* of advance or something!
But wait, this timing is based on the rotation of the crankshaft so that means you'd be sparking the fuel back on the exhaust stroke or something.

I know this sounds extreme but bear in mind that timing the spark only partly has to do with the fuel and partly has to do with the dang position of the piston. You wouldn't want to start sparking the fuel without hardly any of it in the cylinder now would you?

In order to determine this you would use the research tested timing curves that the factory uses for your engine. Then you can make some educated assumptions about how much to modify it based upon the grade of fuel.

Also, boosting the cylinder full of more air/fuel doesn't really change the octane rating of the fuel but it does raise the charge temperature more. This is your main concern with engine knock.
You would be better off running reduced timing with a turbo to prevent knock and keeping air/fuel optimum and putting big$ into a better intercooler system to keep the charge temps down.


Okay, so RANT OFF. If all you want is a tune for a turbo then it is a simple matter of setting up all your tables in your tune to support higher loads, that the air fuel is the correct level, and that you take some steps to alter the timing as load increases, usually less timing.

Think about it, the normal engine load range is .1-.9 or 10-90%. With a turbo you will see loads upwards of 1.2-1.5. With really big boost over 15psi you will be close to 1.6-1.8 loads.
The timing you had at a load of 0.8 is still valid but you need to figure out how to reduce that timing at loads of 1.2 and such. That is where trial and error breed experience.
If you do this correctly then you will generate a tune that behaves perfectly at normal speeds and cruising getting great fuel economy, then allowing you to raise your boost levels all the way up to whatever the engine internals can take. Simple as that. One tune is all you really need.

Now when you introduce nitrous, all of this changes....so don't confuse it. Turbo/supercharger are essentially the same though each has slightly different flavors with the timing curves.

[SpookSVT]

I'll be running 93 all the time. I don't like the idea of mixing fuel grades because of inconsistancy.

Real good write up on everything else, I got a better idea on what you go through to tune the car. A couple questions though, how is it that load can exceed 100% on a forced induced car? Wouldn't the max airflow coming through the throttle be considered 100%? Why less timing as load increases? Is this because of increased cylinder pressure that causes knock?

I've read where you can pull too much timing down low on a turbo car where it will increase lag time, how does this work? Also, you advance the spark timing because the piston is moving faster and the fuel can only burn at a certain rate. So if you didn't start the burn sooner, the piston would be on it's down stroke before the air/fuel mixture had completely burnt and you would loose that potential energy to drive the piston down faster? When and how really, does too much timing advance cause knock?

[warmonger]

Too many questions. It's good you are curious though.

I want to help but you can read many answers just searching around for what is already written.

Load is calculated from the amount of air measured coming through the MAF divided by the volume of the cylinders at that rpm. For the sake of argument,
3cyl x (81mm/2)^2 xPi *79.5mm *3000rpm = 3.7 m^3/min or about 130 cfm

So lets say your are pushing 180 cfm through the maf due to your turbo.
you have 180/130= 1.38

OH, and just FYI you are ALWAYS mixing fuel grades when you buy from different gas stations, manufacturers, time of the year. You are still getting gasoline but the exact composition varies. It is no big deal but if your tune can handle the premium fuel in your area during the heat of summer then you can pretty much call it good.

Correct: The burn speed of the fuel must also be taken into account but piston position and valve opening point is even bigger.

Increasing pressure increases the burn rate therefore less timing is required for maximum power. It is like burning gunpowder in the open on the ground versus putting it in a sealed pipe. In the pipe it burns so fast it causes the pipe to blow up. Gas/air is the same way.

Knock is a complicated subject. Lets just say simply that if you ignite the fuel too soon and it develops too much pressure before the cylinder goes through TDC then you will Knock. If the air charge is too hot, it burns quicker and causes the same thing, therefore temperature is a factor.
If you don't ignite fast enough the fuel burns up as the piston is already down and goes out the exhaust port. You can figure out the rest.

[cpapashley]