c20get

[PrecisionBoost]

Basicly...... R1 is fairly small... and causes a drop in voltage/pressure of 0.7...... although the resistance changes with current flow..... we will keep it a static 0.7 for this example to simplify things.

Now R2.... that's the engine.... which is a linear resistor..... as pressure/voltage rises so does the flow/current throught the engine..... yes.... it's resistance is based upon engine RPM but we can take "snapshots" at various RPM to calculate feedback.

R3 is the resitance created by the electric flapper valve.... if it's wide open.... then the flow goes allmost entirely back throught the feedback loop.


Ok...... I don't have this modeled.... but lets just use some quick guessing to show you what I'm talking about.

Now..... I'm just going to throw out some numbers here.... and I'm going to go back to using voltage and current.... but the conservation of mass is identical to the conservation of energy theories.... so they can be switched into each other without any real problems.

Ok.....so we have a voltage of 14.7V on top of R1.... then the input to the current amplifier must be 14V

Now.... the current amp increases flow and thus voltage..... so lets just say that the output of the current amplifier is 28V ( sort of like 14psi of boost )

Lets just now say that R2 = 1 ohm....... so the current flowing through it is 28 Amps

However.... at 28 Amps the current amp is very inefficent..... it is 20% more efficent running at 35 Amps.

So let's just pretend that the Current amp is putting out 35 amps..... and since 28 Amps are going to the engine 7 amps must go through R3

Given the voltage differencial between the output and input of the current amp is 28V -14V = 14V and we know that 7 amps must go throught R3 then we can calculate R3 by the following formula....

R1 = 28V / 7 amps = 4 ohms.

Now for conservation Vin * Iin = Vout * I out .......... so.... ( 14V )( I in ) = (28V )(35 Amps)...... I in = 70 A

We allready know that 7 amps is flowing through R3.... so that means 63A must have flowed in through R1

In this case you can see that only 1/4 of the output from the amplifier "feeds back" and 3/4 of it goes into the engine.

It would be very hard to regulate the electric throttle to open exactly enough to flow just 1/4 of the compressors output..... but if there were other "resistances" in the path such as a secondary intercooler or some other thing that sucks some energy out of the flow (such as a turbine used to compress a fluid used to cool the intake charge) it wouldn't be too hard.


Now.... what significance does the fact that 7A is flowing back into the intake???

Well.... it means that the amplifier doesn't have to work as hard.... some of the input current is provided from the feedback path.

Had the feedback path not been there.... well.... all the current would have been sourced through R1..... now lets go back and visit this.

Because there was no feedback path and the engine can gulp only so much flow.... the amplifier would run at the less efficent 28A output.

So.... 28V X 28A / 14V gives you 56A of input flow

Now you might say ....... 56A is less than 63A.... but don't forget that the "current amplifier" is running off free energy (thanks to the turbine) so it doesn't matter if it does slightly more work.

The big question is whether the extra work to use the feedback path is offset by the increase in efficency of the compressor.

My thinking is that it the efficency change is the most important factor.

Sure there is roughly 12.5% more energy transfer to get the higher flow..... but if the turbine energy is virtually free then that shouldn't matter too much.

you would be creating slightly more backpressure on the turbine.... but I have to think that would help it rather than hurt it if it's not a large difference.... not sure about that one

Technically the exit temperature of both should be the same if the pressure is the same..... as it's only flow that is increasing ( I could be wrong about that )

But if this is true then the more efficent setup should allways produce a lower exit temperature.

I suppose if I wasn't too lazy to go upstairs and get my books I could guess at the difference in temperatures you would get if you increase the compressor efficency by 5% to 10%


Anyways..... my theory might be flawed..... and perhaps I did a few things wrong.... I don't know.... I think the only way to know is to test it out.

My brain isn't firing on all cylinders..... and I even question myself while writing this.... but I have to think it's worth checking out.

If one had lots of time on his hands..... I'm sure you could throw this stuff into software and get some real world modeling of the situation.

Chris

[superbee]

Sorry to bump an old thread, I dont even know if this forum is used anymore but anyways ive ran across this post. there is some good debate in here and about ignition timing.

Ive made my own tune for my turbo sunbird, I had no table to go from so i just ran max timing under boost at 4800 rpms high teen's as that sounds normal...well, after looking at a stock tune finally i looks like at around 20 psi they run around 25 degrees of advance roughly... ive never ran it that high as i figured it was a bogus tune and well, ive always had knock retard, not a ton but some. it was very frustraiting.

Well now I finally went and bumped the timing way up.....27 degrees at 4800 and now i Finally have no more knock. car runs better than ever, makes enough power to slip the clutch at times. This is on 91 octane. My car is E85 compatable im going to see what it does over 30 degrees timing. That just sounds obsurd so idk if there is something in the tune file that takes away, but ive looked at every table, mat, coolant temp, etc and it appears thats what total advance is.

Am i missing something? If no id say these engines definatly like timing and using more than stock makes them run even better.


So anyways, any knowledge of ignition timing on these would be appriciated. i mean, that car likes what it likes, but it would be nice to hear what some people have done as the upper 20's just doesnt sound right to me.

[PrecisionBoost]

I have seen guys on each end of the spectrum, honestly I don't exactly know what to make of it either and I have been playing with C20GET's for over 15 years.

I haven't played much with timing, for the most part I was happy with the stock engine with stock management at around 12psi in a lighter car ( Passport Optima = Pontiac Lemans = Opel Kadett = Astra MK2 )

Found that the car was very fun and manageable at that boost, very quick but not totally scary.