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  #46 (permalink)  
Old 01-15-2009, 07:47 PM
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Quote:
Originally Posted by RustoRod
Maybe I misunderstood. I thought the momentum of the air that was already started in the intake tract was strong enough to keep filling the cylinder while the piston was starting the compression stoke just after BDC and before the intake valve closes. Where do you need to achieve .6 mach ? In the cylinder or in the port ? And how much is that in feet per second ?
Compressed air in engineering terms means it actually changes density. Not compressed like a compressor. Remember, air is a fluid in this terms. Picture if you will a full glass of water and being able to move the water level down 1/4 way in the glass, without taking any out, then topping it off. That's density changing.

What you refer to is compression stroke. The goal is to fill the cyl up 100% before the intake valve closes, as that is how you define compression stroke is. So wherever the piston is, the cylinder should be filled.

There is no simple question about how to get to .6 mach. That takes calculations and time and is way over my head. The engineers I worked with in my education on this stuff say that it is statistically negligable and weeks and weeks and weeks of math to figure it out, they just disregard it. Air RARELY gets to that speed in very high performance NA motors, and NEVER gets to that speed in the motors we are discussing here.

Forced induction is the easy way to get to over 100%VE, and you see how much power a blower/turbo can add. If you can't get to .6 mach, you can't jam the cyl more than 100%, and speeds never reach that. Make sense?

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  #47 (permalink)  
Old 01-16-2009, 01:01 AM
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Forced induction is the easy way to get to over 100%VE, and you see how much power a blower/turbo can add. If you can't get to .6 mach, you can't jam the cyl more than 100%, and speeds never reach that. Make sense?[/QUOTE]


NO. I think we have two different definitions of volumetric efficiency. The way I understand it it is a simple ratio of actual air mass consumed by the engine divided by theoretical air mass. In other words if your engine uses 100 pounds of air and it calculates out to needing 100 pounds of air it has 100% VE.

I looked over at Speedtalk and they seem to think a well setup single 4 barrel engine can make 105 % VE.

Last edited by RustoRod; 01-16-2009 at 12:50 PM.
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  #48 (permalink)  
Old 01-16-2009, 01:05 AM
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[QUOTE=Jsup]Compressed air in engineering terms means it actually changes density. Not compressed like a compressor. Remember, air is a fluid in this terms. Picture if you will a full glass of water and being able to move the water level down 1/4 way in the glass, without taking any out, then topping it off. That's density changing.

Doesn't anything compressed change density ? How would you compress water ?

So where does the .6 mach occur in the cylinder or in the port ?
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  #49 (permalink)  
Old 01-16-2009, 08:03 AM
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Quote:
Originally Posted by RustoRod

So where does the .6 mach occur in the cylinder or in the port ?
It typically doesn't. In very high end very expensive applications, yes it can. Those who say they are getting over 100% VE are either VERY optimistic or spending lots of money.

I believe what they are saying is on paper the intake tract will allow for VE, but to actually get it we need to see the dyno chart. Until or unless you can get .6 mach, you aren't compressing air or increasing VE past 100% without forced air.

http://en.wikipedia.org/wiki/Volumetric_efficiency

I'm not saying VE over 100% is not possible, I am saying there's a lot of conditions that make it happen, and port velocity isn't one of them as a single factor. Way too much has to happen in all areas.
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Old 01-16-2009, 12:21 PM
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I suspect I am not really nailing it down in my explainations.

A friend of mine put this together pretty well:

http://forum.grumpysperformance.com/...php?f=52&t=796
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Old 01-16-2009, 05:58 PM
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I believe what they are saying is on paper the intake tract will allow for VE, but to actually get it we need to see the dyno chart. Until or unless you can get .6 mach, you aren't compressing air or increasing VE past 100% without forced air.

http://en.wikipedia.org/wiki/Volumetric_efficiency

The link here supports what I say about the definition of VE except they say volume rather than pound or mass of air and shows a range up to 120 % for NA engines. Why do you insist it must be done with forced induction ? Your link to Grumpy's garage is not taking me to anything. I would really like to see how you can get air moving at .6 mach in the cylinder to compress the air. If it is at .6 mach in the cylinder it must be really moving through the port.
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  #52 (permalink)  
Old 01-17-2009, 08:56 AM
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I don't think we're discussing this correctly. .6mach has little to do with compressing air. Its not like some magic switch or anything. From my understanding the .6 mach is more about a/f seperation, also its a general guideleine even for that, its not an absolute.
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Old 02-03-2011, 11:22 PM
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327 w/ 220cc heads

Has anyone actually tried this yet? (327 w/ 220cc heads).

There is plenty of discussion about the volume of the head port sizes, but I can't find the volume of the RPM air gap's runner. Shouldn't the total runner volume be considered, not just the head if you are talking about port volume.

I don't understand how the velocity of air would be slower in the intakes runner simply by changing heads. The engine will still be using the same volume of air. The same amount of air will be pulled through the carb.

If the "too much head" argument is true, is it also true that engines with gigantic tunnel ram intakes have no bottom end torque?

Can using a small intake compensate/offset using large heads?
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  #54 (permalink)  
Old 02-04-2011, 12:49 AM
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Somebody might`ve did so by now, this thread is 2 years old.
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  #55 (permalink)  
Old 02-04-2011, 07:22 AM
How fast is fast enough?
 
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Quote:
Originally Posted by ssparko
Has anyone actually tried this yet? (327 w/ 220cc heads).

There is plenty of discussion about the volume of the head port sizes, but I can't find the volume of the RPM air gap's runner. Shouldn't the total runner volume be considered, not just the head if you are talking about port volume.

I don't understand how the velocity of air would be slower in the intakes runner simply by changing heads. The engine will still be using the same volume of air. The same amount of air will be pulled through the carb.

If the "too much head" argument is true, is it also true that engines with gigantic tunnel ram intakes have no bottom end torque?

Can using a small intake compensate/offset using large heads?
These are good questions, but they should go in their own thread, or you can do some research to get a satisfactory answer, its been discussed several times.

To give a simple and brief answer though, the engine does not use the same volume of air, tunnel rams can be tuned to give great low end torque- but not many are cast that way, a small intake and large head is used in restricted class racing (restricted to a stock intake but open head rules) but it is far from optimal, having an intake and head combo that compliment each other is what is optimal (that does not mean they flow the same, the intake should always flow more).
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