Polished intake manifolds are VERY BAD!
06-29-06, 06:33 AM
#26
Rotary Freak
Originally Posted by adam c
A smooth surface will reduce friction, and reduce turbulence. Reducing friction and turbulence will result in increased flow. I don't believe your "expert" 
True... but low to no turbulence will ahve a negative impact on fuel mixing with air in the intake and in extreme cases let fuel condensate on the intakes walls, causing a lean spots in the mixture.
Don't see how polishing would affect outside temperature. To have metal disapate heat to air you need a lot more than the graining on the manifold.
06-29-06, 06:43 AM
#27
I have never heard of applying term surface tension to enclosed air flow. Surface tension applies to liquids, not gases. In fact, it is the one major difference between them.
Cheesey makes an interesting point - the more turbulent the flow, the better that it will turn corners. By the time the air flows from the turbos to the LIM, a little extra stirring can't be all bad.
The rest of these intake examples don't appear to be related to turbocharged engines, although it could be said that increasing the turbulence as the air approaches the fuel mix zone is a good thing. But I'd have to guess that since this is a turbocharged engine with injection taking place almost inside the combustion chamber, the improvement will be much smaller than with piston engine or NA rotary engines.
Dave
Cheesey makes an interesting point - the more turbulent the flow, the better that it will turn corners. By the time the air flows from the turbos to the LIM, a little extra stirring can't be all bad.
The rest of these intake examples don't appear to be related to turbocharged engines, although it could be said that increasing the turbulence as the air approaches the fuel mix zone is a good thing. But I'd have to guess that since this is a turbocharged engine with injection taking place almost inside the combustion chamber, the improvement will be much smaller than with piston engine or NA rotary engines.
Dave
06-29-06, 11:03 AM
#28
Originally Posted by Cheesy
if you could build a manifold that was straight or had very gentle bends a polished surface will give better flow. The rough surface is not a vortex generator but it does trip a laminar BOUNDARY LAYER into a turbulent boundary layer (you are not going to get laminar flow in an inlet manifold). Now, a turbulent boundary layer is benificial in most inlet manifolds because the boundary layer will stay attatched to the surface over larger pressure gradients (such as bends in the runners) than a laminar boundary layer. This is the reason that carbon mans roughing up of the at area changes and bends works
06-29-06, 01:23 PM
#29
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Originally Posted by Speedworks
True... but low to no turbulence will ahve a negative impact on fuel mixing with air in the intake and in extreme cases let fuel condensate on the intakes walls, causing a lean spots in the mixture.
Don't see how polishing would affect outside temperature. To have metal disapate heat to air you need a lot more than the graining on the manifold.
Don't see how polishing would affect outside temperature. To have metal disapate heat to air you need a lot more than the graining on the manifold.
What I'm not seeing is how all this effects the rotary since the fuel injectors are damn near in the intake chamber and the only thing were moving is the air itself. I can see all this being an issue with fuel as well as air moving through the runners but it's not the case with our motors. We do everything in our power to increase air flow, larger exhaust, freeier intakes, larger TB ports, gasket matching ports, larger intake and exhaust port timming, it seems air acts very much like a fluid when moved through tubing so there would infact be less friction/drag with polished intake runners and therefore more flow. Someone explain how that would effect our cars with our fuel and air setup. ?
06-29-06, 02:19 PM
#31
Super Snuggles
A rough finish helps keep atomized fuel in suspension, which is especially important with the intake reversion common to naturally aspirated engines with higher duration cams. In other words, air with fuel suspended in it coming back out of an intake runner into the common plenum, then entering another intake runner. This keeps the fuel from pooling in the runners or the plenum, promoting better combustion no matter which intake runner it eventually goes down.
As Alex mentioned, the interior of my Hogan's intake had a "220 grit" finish. Relatively smooth to the touch, but not perfectly smooth or anywhere near polished, obviously. Hogan's builds intakes for many of the most powerful naturally aspirated racing engines on the planet, so it's safe to say they know their business.
As Alex mentioned, the interior of my Hogan's intake had a "220 grit" finish. Relatively smooth to the touch, but not perfectly smooth or anywhere near polished, obviously. Hogan's builds intakes for many of the most powerful naturally aspirated racing engines on the planet, so it's safe to say they know their business.
06-29-06, 04:35 PM
#32
He speaks! 
https://www.rx7club.com/3rd-generation-specific-1993-2002-16/polishing-uim-bad-heat-dissipation-398617/
Originally Posted by Speedworks
Don't see how polishing would affect outside temperature. To have metal disapate heat to air you need a lot more than the graining on the manifold.
06-29-06, 04:38 PM
#33
Rotary Freak
Originally Posted by CantGoStraight
What I'm not seeing is how all this effects the rotary since the fuel injectors are damn near in the intake chamber and the only thing were moving is the air itself. I can see all this being an issue with fuel as well as air moving through the runners but it's not the case with our motors. We do everything in our power to increase air flow, larger exhaust, freeier intakes, larger TB ports, gasket matching ports, larger intake and exhaust port timming, it seems air acts very much like a fluid when moved through tubing so there would infact be less friction/drag with polished intake runners and therefore more flow. Someone explain how that would effect our cars with our fuel and air setup. ?
The runners will casue a swirl throughout the intake runner and into the combustion chamber. Hence why intake ports have a certain shape. The shape should improve the intake flow and spread the mixture as optimal as possible in the combustion chamber, partially enhancing the flame front/movement art combustion.
Look at piston engines where different manufacturers have different shape inlet ports and piston shapes. Both to optimalize the combustion and to spread the mixture.
You need to see the bigger picture and look at it from intake manifold to runner with injector to intake port to combustion chamber.
FDNewbie ;-) twisted minds think alike :-):-)
Last edited by Speedworks; 06-29-06 at 04:46 PM.
06-29-06, 07:51 PM
#34
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Originally Posted by Speedworks
The runners will casue a swirl throughout the intake runner and into the combustion chamber. Hence why intake ports have a certain shape. The shape should improve the intake flow and spread the mixture as optimal as possible in the combustion chamber, partially enhancing the flame front/movement art combustion.
Look at piston engines where different manufacturers have different shape inlet ports and piston shapes. Both to optimalize the combustion and to spread the mixture.
You need to see the bigger picture and look at it from intake manifold to runner with injector to intake port to combustion chamber.
FDNewbie ;-) twisted minds think alike :-):-)
Look at piston engines where different manufacturers have different shape inlet ports and piston shapes. Both to optimalize the combustion and to spread the mixture.
You need to see the bigger picture and look at it from intake manifold to runner with injector to intake port to combustion chamber.
FDNewbie ;-) twisted minds think alike :-):-)
Again I agree to a point (where fuel is mixed with the incomming air before it hits the combustion chamber) our motors are not very good at burning all the fuel as it is, I just don't see how increasing the flow is a bad thing or we wouldn't spend all the money we do to do exactly that.
06-29-06, 07:59 PM
#35
Originally Posted by CantGoStraight
I just don't see how increasing the flow is a bad thing or we wouldn't spend all the money we do to do exactly that.
Dave
06-29-06, 09:07 PM
#37
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I believe in collecting DATA!
Having enough information before a modification and then after tells a big story.
I had a customer 2 weeks ago that had run 2 different engines in his RX7 from 2 different engine builders and both engines had similar peak power outputs on the dyno and he thought that one engine felt faster on the track than the other, but from the data we could see that the engine that he felt was slower actually made more touque lower in the rev range with a flatter torque curve and was actually faster on the track. The engine that he felt was faster actually came on harder and felt like it had more power.
Becarefull doing modifications and just feeling like it is faster, collect data.
Fixing only one part of your air intake may not have any effect if that part is not the bigest restriction on your intake.
Ian.
Having enough information before a modification and then after tells a big story.
I had a customer 2 weeks ago that had run 2 different engines in his RX7 from 2 different engine builders and both engines had similar peak power outputs on the dyno and he thought that one engine felt faster on the track than the other, but from the data we could see that the engine that he felt was slower actually made more touque lower in the rev range with a flatter torque curve and was actually faster on the track. The engine that he felt was faster actually came on harder and felt like it had more power.
Becarefull doing modifications and just feeling like it is faster, collect data.
Fixing only one part of your air intake may not have any effect if that part is not the bigest restriction on your intake.
Ian.
06-29-06, 10:05 PM
#38
Originally Posted by carbon man
Fixing only one part of your air intake may not have any effect if that part is not the bigest restriction on your intake.
Ian.
Ian.
~Ramy
06-29-06, 11:09 PM
#39
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I have been useing a MoTeC ADL Dash logger to do most of my development work for about 10 years,
for example using pressure and temperature sensors before and after a lot of the intake components, like measuring the air box before and after the air cleaner element, before and after the IC and after the throttle body when coupled to the rest of the engine and car data tells the true story especialy when you can collect the data in the conditions the vehicle has to be used in. With this data I can see clearly when it works and why.
When Mazda Australia developed the RX7-SP we used Pi Research data logging, we had to produce a competative race car out of road going RX7 with a minimum amount of modifications, like the modifications for the air intake, the main restrictions we found were in the air inlet to the box, air box to turbo plumbing and the intercooler. We were able to test the modifications at the race track that we were going to race the car at.
Ian.
for example using pressure and temperature sensors before and after a lot of the intake components, like measuring the air box before and after the air cleaner element, before and after the IC and after the throttle body when coupled to the rest of the engine and car data tells the true story especialy when you can collect the data in the conditions the vehicle has to be used in. With this data I can see clearly when it works and why.
When Mazda Australia developed the RX7-SP we used Pi Research data logging, we had to produce a competative race car out of road going RX7 with a minimum amount of modifications, like the modifications for the air intake, the main restrictions we found were in the air inlet to the box, air box to turbo plumbing and the intercooler. We were able to test the modifications at the race track that we were going to race the car at.
Ian.
06-30-06, 02:20 AM
#40
Rotary Freak
Originally Posted by CantGoStraight
Again I agree to a point (where fuel is mixed with the incomming air before it hits the combustion chamber) our motors are not very good at burning all the fuel as it is, I just don't see how increasing the flow is a bad thing or we wouldn't spend all the money we do to do exactly that.
I see your point, but increasing flow and the behaviour of the flow are 2 different aspects.
Opening up an intake port will increase flow. The shape of the port and the finish on it's walls will determine the swirl of the incoming air.
They have little to do with eachother when it comes down to the volume of air being transferred.
I would prefer smooth polished exhaust ports and rougher intake ports than the other way around.
06-30-06, 02:22 PM
#41
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Originally Posted by Speedworks
I see your point, but increasing flow and the behaviour of the flow are 2 different aspects.
Opening up an intake port will increase flow. The shape of the port and the finish on it's walls will determine the swirl of the incoming air.
They have little to do with eachother when it comes down to the volume of air being transferred.
I would prefer smooth polished exhaust ports and rougher intake ports than the other way around.
Opening up an intake port will increase flow. The shape of the port and the finish on it's walls will determine the swirl of the incoming air.
They have little to do with eachother when it comes down to the volume of air being transferred.
I would prefer smooth polished exhaust ports and rougher intake ports than the other way around.
06-30-06, 02:32 PM
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Originally Posted by jimlab
A rough finish helps keep atomized fuel in suspension, which is especially important with the intake reversion common to naturally aspirated engines with higher duration cams. In other words, air with fuel suspended in it coming back out of an intake runner into the common plenum, then entering another intake runner. This keeps the fuel from pooling in the runners or the plenum, promoting better combustion no matter which intake runner it eventually goes down.
As Alex mentioned, the interior of my Hogan's intake had a "220 grit" finish. Relatively smooth to the touch, but not perfectly smooth or anywhere near polished, obviously. Hogan's builds intakes for many of the most powerful naturally aspirated racing engines on the planet, so it's safe to say they know their business.
As Alex mentioned, the interior of my Hogan's intake had a "220 grit" finish. Relatively smooth to the touch, but not perfectly smooth or anywhere near polished, obviously. Hogan's builds intakes for many of the most powerful naturally aspirated racing engines on the planet, so it's safe to say they know their business.
This pretty much covers my point, it's more important/more crittical with N/A where the fuel is mixed/flowing with the air than with direct port injection (which our engines appear to be)
06-30-06, 02:53 PM
#43
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i dont think intake manifold texture has anything to do with mixing fuel and air. the air that "sticks" to the rough metal helps the air touching only air move smoother, and quicker
06-30-06, 03:37 PM
#44
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Originally Posted by dgeesaman
It's entirely possible that this person is describing the difference between laminar flow (flow without any mixing - think about the molecules marching in order) and turbulent flow (flow is mixing as it travels). As a fluid flows further thru a system, it becomes more turbulent, and if the system has rough surfaces, it become turbulent faster.
In some situations, turbulent flow actually flows better and more consistently than laminar flow. So if you want turbulent flow at the engine, then if the piping surfaces are too smooth it will still be laminar. The dimples on a golf ball change the airflow over the ball in this manner. Certain aerodynamic features on cars do also. I suspect this person was referring to this kind of concept.
Considering that an FD is turbocharged and intercooled, I guarantee the air is pretty well stirred up (turbulent) before reaching the engine. So this line of thinking probably doesn't apply to an FD very well.
Dave
In some situations, turbulent flow actually flows better and more consistently than laminar flow. So if you want turbulent flow at the engine, then if the piping surfaces are too smooth it will still be laminar. The dimples on a golf ball change the airflow over the ball in this manner. Certain aerodynamic features on cars do also. I suspect this person was referring to this kind of concept.
Considering that an FD is turbocharged and intercooled, I guarantee the air is pretty well stirred up (turbulent) before reaching the engine. So this line of thinking probably doesn't apply to an FD very well.
Dave
just my .02
06-30-06, 04:52 PM
#46
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Originally Posted by kwman
Intake manifolds themsevles are fine when polished. He meant polishing the ports of the intake themselves I'm sure. THAT is detrimental.
06-30-06, 05:39 PM
#47
2/4 wheel cornering fiend
Originally Posted by CantGoStraight
I understand he was referring to the "inside" of the manifold, and i understand the consept of needing the turbulence for mixing the fuel in the intake runners (N/A) but i fail to see the rough texture promoting a higher flowing condition than a smooth one. Rough causes turbulence, eddies, or whatever you want to call them and I believe the air will flow smoother and faster if all the air is indeed going in the same direction not all over the place, were talking strickly air flow not air fuel mixture. I can garuntee you a pipe with smooth walls will flow water faster than a tube with rough walls and air acts very much like water when it comes to flow. Less restriction, friction, or turbulence will give you higher flow, you can even prove this theory with a mass air flow meter.
The next stage of boundary layer airflow before it separates from the surface completely and tumbles into a wake (which slows down airflow drastically and creates pressure drag) is called a turbulent boundary layer. The advantages of this stage of boundary layer is that it has more energy, which gives the airflow momentum (and speed) to follow gentle curves and bends that the laminar boundary layer cannot.
The rough internal surface basically "trips" the airflow into the turbulent boundary layer stage more quickly, so that the airflow can follow the bends of an intake with more speed. It's the same concept as the dimples in a golf ball; the dimples create an earlier formation of turbulent boundary layer that allow the airflow to maintain speed and cling to the trailing surface of the ball longer, reducing drag and allowing the ball to travel farther.
Originally Posted by jimlab
A rough finish helps keep atomized fuel in suspension...This keeps the fuel from pooling in the runners or the plenum, promoting better combustion no matter which intake runner it eventually goes down.
I'm probably a little off technically on this (any aerodynamicists out there can correct me), but I'm pretty sure the basic premise is correct.
Last edited by Kento; 06-30-06 at 05:42 PM.
06-30-06, 10:44 PM
#50
Reynolds number
http://en.wikipedia.org/wiki/Reynolds_number
Turbulent flow in a fluid occurs when the inertial forces of the fluid overcome the viscous forces. It is easiest to visualize with a lit cigarette in a still room. The smoke will ascend smoothly, and then start tumbling over itself. That is the speed at which the fluid viscous forces become smaller than the inertial forces. The fluid kind of trips on itself and rolls into eddies.
Kento is exactly right. Turbulent flow over a concave surface will separate later than a laminar flow, causing a smaller low pressure zone (which is why golf ***** have dimples - the smaller low pressure zone behind the ball means less drag). I am guessing it is these low pressure zones that condense out the gasoline (like the contrails behind a jet airplane formed by condensed water), so keeping them smaller would be good, hence the rough surfaces helping on the curves. But that's just an educated guess.
Turbulent flow in a fluid occurs when the inertial forces of the fluid overcome the viscous forces. It is easiest to visualize with a lit cigarette in a still room. The smoke will ascend smoothly, and then start tumbling over itself. That is the speed at which the fluid viscous forces become smaller than the inertial forces. The fluid kind of trips on itself and rolls into eddies.
Kento is exactly right. Turbulent flow over a concave surface will separate later than a laminar flow, causing a smaller low pressure zone (which is why golf ***** have dimples - the smaller low pressure zone behind the ball means less drag). I am guessing it is these low pressure zones that condense out the gasoline (like the contrails behind a jet airplane formed by condensed water), so keeping them smaller would be good, hence the rough surfaces helping on the curves. But that's just an educated guess.