c20get

[C20GET]

definitly recognize the name Slowej.....

Chris, I don't care if you piss me off. I just might learn something, too. As long as we don't end up lobbing hand grenades across the border I don't think there's anything to worry about. I've signed up to a couple of forums with some good technical content using an alias, mainly to see how people respond to the ideas I present.

I don't really have the means to measure cylinder pressures in my engine. There are some really kewl pressure sensors being developed by Kistler / DaimlerChrysler which may become standard equipment on production vehicles. As you'd guess, Daimler is proposing to move away from the current engine management strategy based on EGO content. Instead they plan to use measured cylinder pressure as a primary input. If this is put into production we could see some real gains in efficiency and and reliability, especially as power output is increased over stock. And we, the general public, could get our hands on some very interesting tools. For the graphs I'm only planning to sit down and look through different research papers to determine some general trends as a starting point. Concerning graphing exhaust pressures at the manifold, it's just something I'd like to do. It's much easier and less expensive to evaluate exhaust system changes by pressure at the head of the system than by the dynomometer or my not so well calibrated seat of the pants meter.

The stock springs seem fine with the boost turned up. I know Tony has run past 25psi with new stockers. It's the combo of raised rev limit and increased boost I don't like.

This seems like a valid concern to me. I think my argument is against the argument, which sends people out to buy springs simply because they've installed or upgraded a turbocharger.

[exist3nce]

Just wanted to say I enjoyed reading thru these long tech posts.......... we need more of this and yes, its own section

[PrecisionBoost]

Just so you know.... I'm the kind of guy that can agree with what your saying but push a different point to see what response I get.... so... I guess we are alike somewhat.

I'm one of those "there is no right answer.... just a bunch of good approximations" kind of guy.... lots of times I say stuff that isn't technically correct.... but it's so that non-technical guys can actually understand what I'm talking about.

I'm more concerned with getting a general point across than giving some hugely technical discussion that nobody wants to read.

Don't worry about hand grenades.... I have no plans to raid the USA any time in the near future


Cylinder pressure measurement tools would be very cool.... I wonder if you could somehow integrate a pressure sensor into the newer direct injection systems.


I've been doing lots of research on Laminar and turbulant flow.... but I am having real troubles figuring out Reynolds Numbers for intake paths to see if they are creating "turbulant" flow.

I did however come to a realization that the reason you want to keep your flow velocity well under 330m/s is so that you don't approach the "speed of sound" and create a shock wave... for some reason I never thought of it that way before.

Did some calculations on the factory C20GET 2" tubing and throttle body..... based upon quick calculations it looks like 19psi on the stock throttle body, turbo, piping is about as high as you want to go.... after that... your velocities start to get close to the speed of sound. (of course there are a whole pile of issues with calculating the actual "speed of sound" in the intake due to the fact that your compressing the air and changing density... which changes velocity)

I sure wish I could get the Reynolds numbers worked out.... I'm expecting numbers in the 2000 to 3000 range and instead I'm getting numbers in the hundreds of thousands.

It was a huge pain figuring out air viscosity in units that matched what I was calculating with respect to mass airflow..... perhaps I screwed up somewhere with a conversion..... all the units canceled out (leaving a unitless number) but I can't imagine I did it correctly.

Is there anyone else out there ( Stefan??? ) that has fooled with air dynamics equations??

[Audacity Racing]

You think of me for fabrication but not engineering, so sad...

[Audacity Racing]

I'm curious why you expect to see Re's there. That's a totally unpredicatble range of numbers seeing as that's midway between turbulant and laminar.... I don't know that you'd get an accurate prediction though I suspect you're trying to get close.

[PrecisionBoost]

I did think of you.... but you haven't been in on the conversation.... where as Stefan has here and there.

I can't remember... you took Mechanical engineering right???

Basicly.... I know the target velocities I want to look at.... but the transition from Laminar to Turbulant flow is dependant on the length of the tube as well as diameter.... and there are also issues with curves..... which I'm sure are going to give me a hell of a time.

I want to mathmatically model the entire engine from scratch.... taking into account everything... working out temperature, density, velocity, pressure throughout the entire system.

The reason for this is because I want to design a new type of engine management...... come spring time I think I'm going to hire on a full time electronics tech to work on my electronics designes under Precision Boost Systems (my company )

The more I understand the engine.... the better I can understand management.

I really want to move into a whole new area.... I want to use drive by wire throttle bodies to control the exact flow and pressure from the turbo to make it the most efficent.

for example.... sometimes you have the boost but not the mass air flow to get into the "sweet spot" on the compressor map (because your turbo is a little big )

Well.... I want to use a secondary throttle body to increase the mass airflow of the comprssor by allowing some of the air flow to move from compressor outlet back into the intake side.

Thus.... I am flowing more air and moving the compressor points into a more efficent area..... plus... by routing the "extra" air back to the compressor inlet it further increases efficency.

Although the temperature of the airflow is hotter than ambient.... it will be cooled prior to moving back to the inlet.... and by reverting flow the compressor does less "work" and temperatures will drop.

I don't know if you understand what I'm getting at..... I allready crunched some numbers.... but I need to crunch more complex numbers which include flow restriction calculations.

I've allready accounted for losses in the filter.... losses in the compressor.... losses in the intercooler.... losses due to temp changes... and a bunch of other things.

Right now the only problem I'm having is with the forces lost from moving the air through the intake tubing and tubing from the compressor outlet to the throttle body... then into the intake plenum.

I have about 10 pages of calculations and math information... and I have graphs for things like air viscosity at various temperatures and densities... but I just can't figure out at what point flow goes turbulant inside a tube of a given length and diameter.

Hell for all I know it's allways turbulant at all velocities or it's completely laminar all the way up to the velocity at which you hit the sound barrier.

I wonder if the compressor would be able to push enough energy to cause a sonic boom...... I would think that would be impossible but who knows.

[Audacity Racing]

The sonic boom thing is possible, very possible. In small displacement, high revving engines, you can easily hit supersonic intake velocity, both at throttle and at valve surface. Now whether or not you could do it with an 8k redline motor... I don't know (I do kinda doubt that actually).

As for curvature through the manifold, a simplified calculation (i.e. not pages and pages) would lend itself to just the centerline length of the tubing (assuming a semi-large bend radius). I guess the funky thing is that in order to get accurate results you'll have to change your calculation based on the different areas (geometries) of the intake system. It really gets to be a pain in the butt when you're getting from manifold to head pathway.

I'm not sure how sharp of a bend radius you're dealing with on the manifold though... post pics or an approximate measurement

http://www.mysharefile.com/v/8646563/Th ... s.zip.html <= A compilation of DOE and a couple other thermodynamics books and supersonic/ultrasonic wave information.


I'm a mechanical / materials science (that's chemical engineering in disguise).


I gotta wrap my head around this for a bit more, I'm not sure I fully understand what you're after in my 3 or 4 minutes of reading here...

[exist3nce]

I really want to move into a whole new area.... I want to use drive by wire throttle bodies to control the exact flow and pressure from the turbo to make it the most efficent.

for example.... sometimes you have the boost but not the mass air flow to get into the "sweet spot" on the compressor map (because your turbo is a little big )

Well.... I want to use a secondary throttle body to increase the mass airflow of the comprssor by allowing some of the air flow to move from compressor outlet back into the intake side.

Thus.... I am flowing more air and moving the compressor points into a more efficent area..... plus... by routing the "extra" air back to the compressor inlet it further increases efficency.

Now that sounds like a cool idea. I'd really like to see something like that.

[PrecisionBoost]

I gotta wrap my head around this for a bit more, I'm not sure I fully understand what you're after in my 3 or 4 minutes of reading here...

Basicly imagine if you plot your Pressure ratio vs Mass Air flow point on the compressor map and it's just left of the highest efficency point.

If you were to open up a throttle body (taking the place of a dump valve) it would allow flow to the engine as well as out of the throttle body.

Thus.... the mass airflow would go up.

Now of course your probably thinking.... when he opens up the variable dump valve (drive by wire throttle body ) you will loose all the pressure in the system.

This would be corrected by the wastegate.... which would shut and add energy to the compressor wheel to drive up the pressure and flow rate.

However.... since your not just venting the extra flow to the atmosphere.... your redirecting it back to the intake side (as all dump valves should be to create better efficency)

That redirection of energy back into the intake path reduces the amount of energy required to create more pressure and flow.

So the wastegate would partially close again.

It's a feed back loop.... kinda hard to explain.... hopefully you understand where I'm coming from.

By moving the compressor point into a more efficent area you end up decreasing the temperature of the air coming out of the compressor

As well.... by rerouting excess flow back into the intake the direct result is that the compressor is not adding as much energy... thus... the air temperature should also decrease to offset the fact that the feedback flow into the intake is a higher temperature than the intake air.

In theory a dual row intercooler would be best..... the air goes through the front portion of the intercooler... splits off between the engine and dump valve (throttle body) and then the throttle body flow is redirected through a second row (behind the first intercooler) and then back into the intake path.

My thought is that it might be a good thing to increase the resistance going back towards the intake path so that there is a better "dampened" response to the throttle body opening up (since the air will want to move towards the path of least resistance)

Imagine that the electric dump valve (throttle body) is the exact opposite twin of the engine throttle body...... when the engine is gulping air and making major power.... almost all the flow goes into the engine because the electric throttle body is nearly closed.

Then as the engine throttle body closes the electric throttle body opens (just like a regular dump valve) and the flow goes back into the intake

This way you can keep the turbo spooled while maintaining a very balanced and efficent flow from the compressor.

The dump valves are usually ON/OFF... the transition is fairly quick and I would bet that pressure waves are created throughout the intake path.

With a variable electric throttle body it should be a very smooth setup with next to zero pressure waves because it's not ON/OFF... it varies the flow to keep everything in a steady flow state.

Honestly........ I have to do some testing to see how well the system would work.

Another thought I had was to make the excess flow do work..... it might be possible to convert this "work" into a device which would cool the flow before it get's back into the intake stream.

Basicly.... you would be taking some of the free energy of the exhaust/turbine and using it to help cool the intake charge.

My thought is that the flow could go through a small turbine and compress a fluid ( such as refrigerant ) and then the refrigerant could used to cool the intake charge.

The end result is that the waste gate could allways stay shut...... so the turbine is extracting the maximum free energy from the exhaust.

That excess energy would be redirected into making the compressor side more efficent and also to decreasing charge temperature.

Who knows... it might even be possible to get a efficency above 100% at full boost (as the intake air would be significantly cooler than ambient air )

You could even use the excess turbine energy to help cool off other systems.... oil.... coolant.... the options are endless.

I don't really know how things would end up working out..... experimentation would be required to see how the system reacts.

Hopefully you get an idea of what I'm proposing..... I spent many hours thinking about it and drawing flow charts.... and I think it has some merit.

[PrecisionBoost]

Ok..... lets say we want 18psi... which is a pressure ratio of 2.2.... I'm going to approximate what I think the points would be on a fairly large T3/T04E turbo using the 2.0L

The Red line is what you might get with a stock setup.

The green line is what you might expect with the setup I'm talking about..... with the electric throttle body open during spool up..... the turbo will spool up quicker... because there is less resistance on the compressor side.

You can keep the pressure low while increasing flow.... then push up very quickly once you get into a more efficient spot.

You might think that it would create more lag... but if you think about it.... your spooling up the turbo quicker.... so although your delaying pressure.... the quicker spool up (with flow going back into the intake.... the compressor will spool even quicker) should offset the lag.

The blue line is another scenario... where you keep the electric throttle body open even longer... and then as you close it.... the flow levels move backwards towards what the engine is pulling through it's cylinders.

There are endless options with this kind of system.... here is a sample diagram. (don't take it litterally.... I did some very rough calculations to grab a few points )




Think about it.... even with the blue line..... you might be able to push 30lb/min at 1500RPM if the compressor is free flowing (not creating boost) and then as you start to close the electric throttle body that flow level moves backwards towards the natural engine flow levels and pressure rises very quickly.

I don't think the "blue" line would be ideal...... but who knows.... the only way to know is to do some experimentation.

[PrecisionBoost]

In the case of this rather large compressor.... at redline it is just barely approaching the most efficent part of the compressor map.

If you set up the electric throttle plate such that 20lb/hr goes into the engine and 5lb/hr goes throught the dump valve and back into the intake path.... you end up in a more efficent area of the compressor map.

So................. please......... poke holes where you can..... I'm still not 100% convinced it will work the way I think it will..... I just figure there must be a way to use some of that waste exhaust going out the wategate to increase the overall efficency of the system.

[Audacity Racing]

Wow... I'm grappling with this one.


I'm wondering if you would gain any efficiency at all by diverting some of the air... that doesn't seem to make sense mathematically. You'd be gaining energy somewhere (i.e. not gonna happen). I'm thinking the loss would be in that diverting some of the energy through the intake tract you'd be developing a syphon effect towards your exit, thus pulling total flow from the engine's breathing. It just doesn't seem right that you'd get flow to divert like that and magically end up with a greater flow.

I gotta really sit and think about this...

[Stefan]

If you set up the electric throttle plate such that 20lb/hr goes into the engine and 5lb/hr goes throught the dump valve and back into the intake path.... you end up in a more efficent area of the compressor map.

This is already done on large turbochargers... It's called a ported shroud housing! Simple and effective. There are some papers I can post up later (when I'm at my laptop) for you.

[PrecisionBoost]

Wow... I'm grappling with this one.


I'm wondering if you would gain any efficiency at all by diverting some of the air... that doesn't seem to make sense mathematically. You'd be gaining energy somewhere (i.e. not gonna happen). I'm thinking the loss would be in that diverting some of the energy through the intake tract you'd be developing a syphon effect towards your exit, thus pulling total flow from the engine's breathing. It just doesn't seem right that you'd get flow to divert like that and magically end up with a greater flow.

I gotta really sit and think about this...

I have no idea where your path of thinking is leading here..... I'm a little confused about what you've said here.

I allways model things into electronics (as virtually anything can be modeled via a combination of resistors, inductors, capacitors, power supplies )

here is the general diagram for the air...... I did not include the flapper valves.... it's just a very simple diagram showing the flow

[PrecisionBoost]

Here is the general diagram for the Electrical circuit....