Quote from: Hi-T...so by increasing the compression, we increase the number of potential booms (or molecules) that can fit in the cylinder...

Not really no. The compression is defined by the shape and dimentions of the combustion chamber (stroke, bore, crown and head essentialy). That volume doesn't change. You can change the density of the mixture going in with a turbo, super charger or other things, but this is not related to compression in this sense. Higher compression simply means that the pre-ignition temp is higher and thus easier to ignite and that all of the fuel molecules are as close together and ready to ignite each other (flame front and flame propagation).

Hi-T, it sounds like you got it for the most part, but that one point seemed to need a bit of clarification.

Wrencher - that makes sense to me- But...

A turbo/super charger is a forced induction system.  It's purpose is to provide (ie, force) more air into the engine.  If more air is added to the equation, then more gas is added too (espescially if we are refering to an 8 to 15 psi boost).  That would increase the volume of gas in the cylinder and immediately increase the pressure felt within the cylinder.

So it seemed to me that with the added gas in the cylinder we are increasing the compression ratio (more gas in the same amount of space = higher pressure).  So I think I just used the wrong wording....  let's try:

"So by using a turbo we are increasing the number of molecules (potential booms) in the cylinder.  As a result the compression ratio increases.  As compression increases, pressure increases.  As pressure increases temperature increases.  As temp increases the risk of preignition increase requiring the use of a higher octane fuel..."

or something.

Seriously, thanks for the input,

Dathan

Engines are mass flow machines. The more mass we can flow in a given time, the more power we can get out of them.  More fuel and air at one time gives us more horsepower.  There are two ways we can do this: increase displacement or increase the mass flow.  Turbos increase the mass flow by compressing a large volume of air into a smaller area.  Thus our 250cc turbocharged cylinder now has more mass of fuel and air that it has any right to and delivers more power.

Wrencher wrote:

QuoteHigher compression simply means that the pre-ignition temp is higher and thus easier to ignite and that all of the fuel molecules are as close together and ready to ignite each other

Wrencher is right that pre-ignition temps are higher.  BUT, a denser fuel charge actually slows the flame front.  While turbo engines have a higher effective pressure in the cylinder, they also have a MUCH longer burn impulse.  This is another reason why Toulene in the fuel is so important (see prior postings).  

Wrencher wrote:  

QuoteThe compression is defined by the shape and dimentions of the combustion chamber (stroke, bore, crown and head essentialy). That volume doesn't change.

Wrencher....see my earlier post: Compression is Compression.  Whether it happens in the turbo or the engine, the pre-ignition temperature and pressure are the same.

Hi-t wrote:  

Quote"So by using a turbo we are increasing the number of molecules (potential booms) in the cylinder. As a result the compression ratio increases. As compression increases, pressure increases. As pressure increases temperature increases. As temp increases the risk of preignition increase requiring the use of a higher octane fuel..."

Correct.  This is an accurate but very simplified expression of what is going on.

Bling!

Quote from: Bling!Wrencher....see my earlier post: Compression is Compression.  Whether it happens in the turbo or the engine, the pre-ignition temperature and pressure are the same.

I did read the earlier post, and we seem to be saying the same thing. I was trying to point out the difference between the intake density (variable) and the combustion chamber's volume (fixed).  

Sweet!!! (I decided this year to go for MEEN- I might have a chance at making it after all) thanks Bling.

So that takes care of the "why" it works... so how about a little more on the how you got it to work.  I'd like to see your turbo set up a little closer- some the part that were fabricated for the manifold and intake.

Later and thanks again,

Dathan

Intercoolers.

Intercoolers make a huge difference in the temperature of the intake charge.  Because air from the turbo is heated from compression to 300 to 350 Deg F,  unless we want to run extremely high octane, we try to cool it before the cylinder sees it.  We do this with intercoolers.

An intercooler can drop the intake temperature from 350 deg to 160 or lower with the given conditions.  They are dependant on the outside environmental air to soak away all that excess heat.

Here's the catch: as the temperature drops, so does the pressure.  Then you have to increase boost pressure to make up for what you lost...and the temperature rises...etc...

What happens in reality, is that the temp and pressure increase simultaneously together.  The turbo and the intercooler find an equilibrium which is determined by the amount of boost you have proscribed for the turbo.  This simultaneous solution of the equations is known as a Gauss-Seidel iteration process.  With it we approximate a solution for 3 equations and 2 unkowns.  However, we just keep re-iterating until our values have more decimal places than we require or use.

Isn't it great that mother nature does this so easily?  

Bling!

Dang- I had no idea that the intercooler could drop the temp that dramatically.  

Do you use one on the bike?

Good Point Wrencher.

The great thing about turbos is that we CAN vary the amount of boost.  We don't always want to run 15 psi, when 5 will do.  

Hi-T: the cylinder is always moving, but the basics of science is that if you take a snapshot of one period, and another of a second period, you could draw a line between the two that describes the behavior pretty well.  

So, more snapshots mean more lines, until you have a perfect replica of the behavior.  This is what we do for engineering.  take lots of snapshots.  

Bling!

PS.  Hi-T, how was that for your first Calculus class?  
PPS. What's a MEEN?

Yes, its on the left side,



Its the long silve rectangle near the cylinders.

i think this is the deepest most informational topic gstwin has ever seen.   At lest from my experience :dunno:

Ok, now,  im not that savvy on CV carbs, Does not vacume raise the slides in thecarbs in relation to throtle plate position? if so, how do you keep the +boost pressure from compressing the diaphrams to into the the caps? i understood you haveing to reinforce them with tie downs do to the pressure. is the waste gate manualy controled by throttle or just spring pressure?  would not Standard Av Gas have sufficed for your needs? it is a fuel designed for high compression engines.(namely Aircraft) How much over stock did you have to Richen the jetting?



so a simple home made kit say like a 1Liter Mitsu turbo from local junkyard, home made plumbing and oil feeder for bearing on turbo. running some Cam2 purple in theory would yeild some interesting results, makeing it reliable and predictable would require alot more homework and refining of the numbers.  sound about right?

Blueknyt,

I don't have a lot of time today, but here goes...

Yes, Av Gas would work fine, It's just higher octane with more refining.  The waste gate is controlled by boost feedback from the plenum.  I have put a controlled leak into the feedback loop.  This controlled leak makes the turbo think there is less pressure than there actually is in the plenum.  This controlled leak is called a Dial-a-boost.  

The carbs are sealed from outside air, so as far as they are concerned, the carbs are seeing regular pressure, and work normally.  Under boost, though, the Density of air passing through is higher, and thus my need for jets that are 4 times larger than stock.  I have needles from Factory and larger jets, and am still running leaner than I should...As a result I am considering converting to FI.  FI would solve all this.  

Quoteso a simple home made kit say like a 1Liter Mitsu turbo from local junkyard, home made plumbing and oil feeder for bearing on turbo. running some Cam2 purple in theory would yeild some interesting results, makeing it reliable and predictable would require alot more homework and refining of the numbers. sound about right?

Correct.  That is basically what I did. A little more detailed though....

Bling!

Gotta go to work....  

Even without the turbo, we would all like to see an F.I. conversion. Figure an SV650 Based rig would be nice.  Just outa curiousity, if a split plenum manifold was made for the GS wouldnt ONE 34mm carb not feed both just fine? Truth be told, only one cyl is drawing from the carb at a time anyway. i know the Rebel 250 works this way. but if talking FI or turbo, this would simplify a few things yes? instead of draw pulse being every other 720*    it would be every 360* but still only feeding each cyl every 720*     which would work better, piping and syncing 2 carbs/TBI's or 1?

(instead of draw pulse being every  720* it would be every 360* but still only feeding each cyl every 720*)

Do it yourself EFI info:


software - http://megasquirt.sourceforge.net/
computer - http://www.bgsoflex.com/megasquirt.html

Dana Goulston is in the process of adapting the Megasquirt system to his GS450 land speed racer. Unfortunately, he sent the system to someone for some tuning help and it has disappeared.

Anyway, if you want to learn EFI retrofit, join the yahoo group:

http://autos.groups.yahoo.com/group/megasquirt/

Lol.  Dana Goulston and I have talked quite a bit... I have sent him everything I have on the turbo system....I think that is one of the reasons he was looking at EFI.   He's a really nice guy...

There's a bit of an technical arguement about running 1 or 2 carbs.  In theory, yes, 1 carb would serve both cylinders. However, when the 1st cylinders draws intake, the plenum pressure drops before the boost can recover, and the 2nd cylinder doesn't see quite as much mass flow into it.  Therefore, the since the jets would be the same for both cylinders, the second cylinder is running slightly rich.  

There's arguements both ways, and successful turboengines have been built both ways.  The preference in the industry today is to have a separate carb for each cylinder to make tuning easier.  

In truth though, ALL big engine builders prefer EFI with separate throttle bodies...It is much easier to tune with.    EFI has it's own demons, though, that's why some manufacturers still use carbs.  

Bling!

i'm not sure i follow your argument on the 2nd cylinder business.  what happens when the first cylinder fires again?  suddenly, it's firing after the second cylinder, and now it's got the same A/F mixture.  unless i'm missing something about the phase between the two cylinders.

on a side note, a lot of turbo cars just use bigger plenums, so the pressure doesn't drop as much, and you allegedly get better throttle response.

Since most twins fire in an asymetrical order "1,2, wait, wait, 1,2...", the plenum can suffer a slight pressure drop for the second cylinder and the 1st cylinder gets a chance to recharge.....Remember that air has some inertia and takes that split milli-second to get moving and fill the plenum.  

To answer the question about the plenum, simply take the idea to extremes...if the plenum was the size of a soda can, even filling of one cylinder will drop the pressure substantially, but turbo lag vanishes.  Conversly, if the plenum was the size of a living room, filling a small cylinder would not dramatically drop the pressure, and turbo lag is monumental. For road racing, smaller plenums are preferred, while drag racers prefer larger plenums.  The industry trend right now is for the plenum to be 3 to 5 times the displacment of the turbo.  

Remember that throttle response is NOT, repeat, NOT the same as turbolag.  The throttle response how long the engine takes to respond to the pressure already inside the plenum, while turbo lag is the time it takes for the turbo to bring the plenum up to pressure again.  NOTE: there is a critical engine RPM required before the turbo will be able to pressurize the plenum AT ALL.  This is the "critical boost RPM" or the "Boost Threshhold" when plenum pressure is more than atmospheric pressure.  

This also leads me into the little known fact that on a standard turbo system running at less than the critical boost RPM, the plenum can actually be at a lower pressure than atmospheric, because the turbo is acting as a restiction of the intake (much like a closed throttle).  Advanced turbo systems have a 1-way opening to allow atmopheric air into the plenum at low idles.

Are you talking about this bike, from the WOF?

yes.  thats my bike.[/url]