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 Post subject: Re: Webers on a......
 Post Posted: Sat Jun 02, 2012 7:36 pm 
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hysteric wrote:
Man i just wrote a whole page then submitted it and was asked to re-login...

Hysteric


When this happens if you hit the "Back" button on your browser most of the time it will carry you back to your document intact. An even better choice is to type up the post in a word processor so that if the board software throws you a curve you will still have the original document.

I don't know what type of internet connection you have, but my USB data card will "disconnect" after XX amount of time and has to do a re-login to make the connection again.

But again, the safest way is to use a word processor to create the document then copy and paste it to the board when you're ready to post it. ;-)


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 Post subject: Re: Webers on a......
 Post Posted: Sat Jun 02, 2012 8:09 pm 
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hysteric wrote:
Is time AND ENOUGH COMPRESSION critical?
Is this not RPM dependant as rpm rises so fill time diminishes and does not carb function become critical in this process as the carb transits from 1 circuit to the next?

Yes time and enough compression is critical, thats what I said. Whats the question?
As RPM rises fill time reduces but porting efficiency etc increases. The dynamic compression constantly changes. All the different dynamics of the air motion change constantly up the rev range. The carby transitions happen very early in the rev range. A correctly sized carby will perform AFR transitions in line with the engines load and requirements for NOx suppression. Every engine is different in that regard.


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 Post subject: Re: Webers on a......
 Post Posted: Sun Jun 03, 2012 5:24 pm 
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Thanks Ken ill try that next time.

Hey Shrinker,

Can you please explain the "TIME" aspect

Quote:
Yes time and enough compression is critical, thats what I said. Whats the question?


Was wondering if the compression component is where most go wrong? Could you please expound on "Compression". I understand that enough compression is required to vapourise the fuel but is this also a moving target in regards to manifold and carb choices? Where does cranking compression come into this as i have read many times over where notable engine builders state not to exceed 185 psi on pump gas builds yet others they have acheived 215+ and made power.

Quote:
The dynamic compression constantly changes


Please explain? =;

Hysteric


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 Post subject: Re: Webers on a......
 Post Posted: Sun Jun 03, 2012 9:37 pm 
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Why don’t you ask a simple question.
In an engine we need to consider compression of a gas with liquids present.
Compression of a gas increases the collision events of the molecules. It’s the speed and the number of collision of a gas molecule into a liquid molecule that transfers energy to the lower state liquid molecule, thus heating it and vaporizing the liquids. Its called convection.
As the gas molecule transfers energy to the lower state liquid the gas molecule is cooled. Every time a gas molecule collides with a liquid it bounces off and re-collides with other gas and or liquid molecules. Each time less and less energy is transferred. If the cylinder has all the fuel concentrated into one droplet there is a minimum possible surface area for collisions. If the fuel is in bezillions of droplets there is maximum surface area for collision and also maximum chance of the first rebound being into a droplet. That’s what homogenization is all about.
When you listen to a hotrod engine builder who restricts the compression to 185 for pump fuel you are listening to a builder who has poor homogenization. If the Homogenization is poor it means that there are larger distances between droplets which correlates into more heating of the air and less heating of the fuel. It’s the temperature of Oxygen that matters. Oxygen is the starter of combustion NOT the fuel. So when you have poor homogenization you have to reduce the compression pressure to avoid overheating the oxygen and causing it to react too fast and build a detonating pressure.

There are 2 forms of compression, Isothermal (slow rate of compression) and Adiabatic (fast enough rate of compression). Isothermal is when the compression is slow enough that heat can be measured or lost to the surroundings. Engines only operate in isothermal mode at low revs generally below 2500 rpm. Adiabatic is when there is no heat lost to the surroundings. Engines don’t operate in perfect adiabatic, they just get close for part of the time. The point of the rev range where the compression changes to adiabatic is a defined point in molecular physics but actually calculating it is nearly impossible due to the effects of the cooling from the fuel and the chemicals of the fuels different adiabatic index’s. Seeing as they don’t know everything that’s in gasoline its not possible to accurately calculate it. However it can be observed. The piston speed is the controller of adiabatic. Now when the cam shuts the intake valve at around 90 degrees ABDC the compression starts at the fastest piston speed. This places the compression instantly into adiabatic but once the piston slows down it drops back to Isothermal. Its only the isothermal phase that increases the molecular kinetic energy and thus the collisions. How this relates to the tuning is as the revs increase the adiabatic phase occurs over a greater distance of the compression stroke. During the adiabatic phase the vaporization rate is constant. During the isothermal phase the vaporization rate follows the temperature increase. Because an engine doesn’t obtain perfect adiabatic the vaporization is indeterminable.

The time spent in isothermal compression is critical to the vaporization level of the chamber. When you close the intake valve earlier you increase the time of isothermal compression, thus the engine gains low down power, however the trade off is as you rev it faster the valve closing goes straight into adiabatic and the vaporization suffers and the engine looses power. What ever the temperature of the air in the chamber at the point where it crosses to adiabatic will be the temperature until it drops back out of adiabatic somewhere as the piston slows in the top half of the stroke.
So now can anyone see why I say what I keep saying?

Hint, if you decrease droplet size you will increase vaporization at all points especially in the zones where its inhibited by the type of compression
That’s what carby sizing does too. The whole intake system is a vital part of the vaporization.

Dynamic compression is the term for how much air you actually have in the cylinder being compressed. It’s a lower ratio than the advertised because we don’t shut the valve at BDC.


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 Post subject: Re: Webers on a......
 Post Posted: Sun Jun 03, 2012 9:52 pm 
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I should add this, While compression is adiabatic energy is still being input to the molecules and when the compression drops back into isothermal the energy that was input during adiabatic is instantly transformed into temperature. The temperature jumps instantly to the value it would have been if it was isothermal all the way (Plus the losses) So compressing in adiabatic is a good thing as it conserves losses and then bashes the temp up real quick. Its how this interacts with the vaporization and the ignition point that determines the engine tuning needs.


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 Post subject: Re: Webers on a......
 Post Posted: Mon Jun 04, 2012 3:03 am 
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Quote:
Why don’t you ask a simple question.


Because i dont want to be just another parts changer........... I prefer to leave mediocrity to the masses ;-)

Now we're getting somewhere Shrinker! =;

Quote:
If the fuel is in bezillions of droplets there is maximum surface area for collision and also maximum chance of the first rebound being into a droplet.

And
Quote:
Hint, if you decrease droplet size you will increase vaporization at all points especially in the zones where its inhibited by the type of compression
That’s what carby sizing does too. The whole intake system is a vital part of the vaporization.


SO from a basic carb perspective(Holley) how far would improving emulsion and using annular boosters go towards acheiving this goal?

Quote:
When you close the intake valve earlier you increase the time of isothermal compression, thus the engine gains low down power,


How does reversion affect isothermal compression when using cams with low lca's?

Hysteric


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 Post subject: Re: Webers on a......
 Post Posted: Mon Jun 04, 2012 8:25 pm 
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theres not much you can do with a holley, there are things but its not a big change. You have to go to different design forms to change droplets sizes. Double booster work well, see the stuff webermaniac is doing.
reversion doesnt affect. the types of compression are from the speed or rate of compression not the actual starting temperature or the amount of compression. Having a high compression ratio has nothing to do with it, its just piston speed.


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 Post subject: Re: Webers on a......
 Post Posted: Tue Jun 05, 2012 8:28 pm 
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Quote:
theres not much you can do with a holley, there are things but its not a big change. You have to go to different design forms to change droplets sizes


I understand what your saying in regards to this style of carb not that i really understand the whys....i'll get to that later no doubt ;-)

I have to start some where from a practical stand point and the Holley and Carters seem like a good point.

Can you explain what can be done to the holleys that can improve them?

Ive been reading "Scientific design of exhaust & Intake systems" and have more questions but i may PM you with stuff that other may not be interested in.

Hysteric


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 Post subject: Re: Webers on a......
 Post Posted: Tue Jun 05, 2012 10:20 pm 
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Holleys need a tubular main well emulsion system, double stage boosters, proper air horn design (the HP's are wrong) Fix a Holley and it will work like a Carter.

I'm really sick at the moment and it will take me a couple of weeks to get over this so dont expect much.


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 Post subject: Re: Webers on a......
 Post Posted: Tue Jun 05, 2012 10:50 pm 
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Quote:
I'm really sick at the moment and it will take me a couple of weeks to get over this so dont expect much


Get Well Soon!

Quote:
Fix a Holley and it will work like a Carter.


Interesting..........

Hysteric


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 Post subject: Re: Webers on a......
 Post Posted: Fri Aug 17, 2012 6:43 pm 
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In reference to the emulsion on Carter and Edelbrock carbs i think Shrinker may be refering to these tubes on the boosters

Image

Hysteric


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