Why Ram-Air is BS, according to this guy...
06-10-2003, 12:41 PM
#61
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</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">Originally posted by Geo:
<strong>[QUOTE]No such thing. It's Internet BS. CR is a static measure. The rest is volumetric efficiency.</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">Interesting. I first heard of dynamic CR from someone who doesn't use the internet. His reference related to two stroke engine and port heights. The port heights in a two stroke are similar to valve timing in a 4 stroke engine. Perhaps the vernacular was incorrect, but as an engine builder, he was more concerned with the combination of port height and static compression than either of these individually.
Here is a link that mentions dynamic compression. I didn't mention anything about turbocharging, and neither did this article:
<a href="http://www.rehermorrison.com/techTalk/08b.htm" target="_blank">http://www.rehermorrison.com/techTalk/08b.htm</a>
Still, engines which are relatively efficient and make similar power will require similar amounts of air over time, even if one has four times the displacement.
A car has much more frontal surface area than a motorcycle, so you could have a larger scoop, narrowing to speed the airflow up. The trick is turn the high speed 'ram-air' into pressure in the airbox.
<strong>[QUOTE]No such thing. It's Internet BS. CR is a static measure. The rest is volumetric efficiency.</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">Interesting. I first heard of dynamic CR from someone who doesn't use the internet. His reference related to two stroke engine and port heights. The port heights in a two stroke are similar to valve timing in a 4 stroke engine. Perhaps the vernacular was incorrect, but as an engine builder, he was more concerned with the combination of port height and static compression than either of these individually.
Here is a link that mentions dynamic compression. I didn't mention anything about turbocharging, and neither did this article:
<a href="http://www.rehermorrison.com/techTalk/08b.htm" target="_blank">http://www.rehermorrison.com/techTalk/08b.htm</a>
Still, engines which are relatively efficient and make similar power will require similar amounts of air over time, even if one has four times the displacement.
A car has much more frontal surface area than a motorcycle, so you could have a larger scoop, narrowing to speed the airflow up. The trick is turn the high speed 'ram-air' into pressure in the airbox.
06-10-2003, 12:54 PM
#62
</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">Originally posted by Brian Wilson:
<strong>I don't think that you can compare a scoop on a trans am to a F1 car or a race bike. Like someone else said, look at the location of the scoops and how they feed the engine.</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">You have to consider the location of the engine. With the T/A, it's a front engine so the intakes are at the front the hood where it takes air in at the highest pressure (the leading edge of the bodywork). F1 cars have a mid-engine configuration require intakes in a different position. Indy cars have their intakes above the drivers head.
Motorcycles have their airboxes under the fuel tanks so Honda and Kawasaki have put the intakes at the center of the front fairing (RC-51, ZX-6, etc).
<strong>I don't think that you can compare a scoop on a trans am to a F1 car or a race bike. Like someone else said, look at the location of the scoops and how they feed the engine.</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">You have to consider the location of the engine. With the T/A, it's a front engine so the intakes are at the front the hood where it takes air in at the highest pressure (the leading edge of the bodywork). F1 cars have a mid-engine configuration require intakes in a different position. Indy cars have their intakes above the drivers head.
Motorcycles have their airboxes under the fuel tanks so Honda and Kawasaki have put the intakes at the center of the front fairing (RC-51, ZX-6, etc).
06-27-2003, 03:38 AM
#63
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</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">Originally posted by streckfu's951:
<strong>Sport Rider made the determination tha positive pressure wasn't achieved with most of the motorcycles until after 80 mph because of what you stated.</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">Sorry for bringing this back up, but here is a link to (I think) the first sport rider article, from the bikes in the test, and the URL title it looks like it is from August of '95.
<a href="http://www.sportrider.com/tech/146_9508_ram/" target="_blank">http://www.sportrider.com/tech/146_9508_ram/</a>
I am sure the systems are much more effective now. They do work but not as much as some may expect. The ZX-9 in the test was generating 1/2 PSI of pressure in the intake (boost) at an indicated 150MPH.
<strong>Sport Rider made the determination tha positive pressure wasn't achieved with most of the motorcycles until after 80 mph because of what you stated.</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">Sorry for bringing this back up, but here is a link to (I think) the first sport rider article, from the bikes in the test, and the URL title it looks like it is from August of '95.
<a href="http://www.sportrider.com/tech/146_9508_ram/" target="_blank">http://www.sportrider.com/tech/146_9508_ram/</a>
I am sure the systems are much more effective now. They do work but not as much as some may expect. The ZX-9 in the test was generating 1/2 PSI of pressure in the intake (boost) at an indicated 150MPH.
06-27-2003, 07:14 AM
#64
"I am sure the systems are much more effective now. They do work but not as much as some may expect. The ZX-9 in the test was generating 1/2 PSI of pressure in the intake (boost) at an indicated 150MPH"
They are more effective now. Honda and Kawasaki have designed straight tubes running through the steering head to reduce turbulance and Suzuki has redesigned their intakes as well.
.5 psi of positive pressure is far better than 14in hg of vacuum. It's quite an accomplishment to get any positve pressure on a N/A motor.
And don't forget, these systems were designed to work on the track where they are doing 150-180mph. There is no advantage on the street. To use these advantages on the street would be stupid (there's no ay to exceed 150 safetely).
They are more effective now. Honda and Kawasaki have designed straight tubes running through the steering head to reduce turbulance and Suzuki has redesigned their intakes as well.
.5 psi of positive pressure is far better than 14in hg of vacuum. It's quite an accomplishment to get any positve pressure on a N/A motor.
And don't forget, these systems were designed to work on the track where they are doing 150-180mph. There is no advantage on the street. To use these advantages on the street would be stupid (there's no ay to exceed 150 safetely).
06-27-2003, 08:50 AM
#65
Race Director
</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">Originally posted by Steve Lavigne:
[QB]Interesting. I first heard of dynamic CR from someone who doesn't use the internet. His reference related to two stroke engine and port heights. The port heights in a two stroke are similar to valve timing in a 4 stroke engine. Perhaps the vernacular was incorrect, but as an engine builder, he was more concerned with the combination of port height and static compression than either of these individually.
Here is a link that mentions dynamic compression. I didn't mention anything about turbocharging, and neither did this article:
<a href="http://www.rehermorrison.com/techTalk/08b.htm" target="_blank">http://www.rehermorrison.com/techTalk/08b.htm</a>
Still, engines which are relatively efficient and make similar power will require similar amounts of air over time, even if one has four times the displacement.
[QB]</font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">Steve, sorry I missed your reply when this thread was originally active.
I'm quite familiar with piston port 2 cycle engines. I used to race a Yamaha powered racing kart and the Yamaha KT100 engine is a piston port engine.
Anyway, there are people who talk about "dynamic compression ratio" and what they are really talking about it volumetric efficiency, even if they don't know it. Let's step back for a second. What affects "dynamic compression?" Cylinder filling. What affects volumetric efficiency? Cylinder filling.
So, CR is a static measure. Cylinder filling is purely volumetric efficiency, or how effectively the engine is able to ingest and expell air.
[QB]Interesting. I first heard of dynamic CR from someone who doesn't use the internet. His reference related to two stroke engine and port heights. The port heights in a two stroke are similar to valve timing in a 4 stroke engine. Perhaps the vernacular was incorrect, but as an engine builder, he was more concerned with the combination of port height and static compression than either of these individually.
Here is a link that mentions dynamic compression. I didn't mention anything about turbocharging, and neither did this article:
<a href="http://www.rehermorrison.com/techTalk/08b.htm" target="_blank">http://www.rehermorrison.com/techTalk/08b.htm</a>
Still, engines which are relatively efficient and make similar power will require similar amounts of air over time, even if one has four times the displacement.
[QB]</font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">Steve, sorry I missed your reply when this thread was originally active.
I'm quite familiar with piston port 2 cycle engines. I used to race a Yamaha powered racing kart and the Yamaha KT100 engine is a piston port engine.
Anyway, there are people who talk about "dynamic compression ratio" and what they are really talking about it volumetric efficiency, even if they don't know it. Let's step back for a second. What affects "dynamic compression?" Cylinder filling. What affects volumetric efficiency? Cylinder filling.
So, CR is a static measure. Cylinder filling is purely volumetric efficiency, or how effectively the engine is able to ingest and expell air.
06-27-2003, 09:02 AM
#66
Race Director
OMG, this guy is a monkey......
From the website:
"Dynamic compression is much more difficult to measure because it depends on how efficiently the cylinders are filled when the engine is running."
As I said, this is pure volumetric efficiency.
His discussion about cams is rather misleading too.
Furthermore, if one takes the discussion to pressures inside the cylinder, then what we are discussing is Mean Effective Pressure.
From the website:
"Dynamic compression is much more difficult to measure because it depends on how efficiently the cylinders are filled when the engine is running."
As I said, this is pure volumetric efficiency.
His discussion about cams is rather misleading too.
Furthermore, if one takes the discussion to pressures inside the cylinder, then what we are discussing is Mean Effective Pressure.
