Max Exhaust Port Width
04-30-2004, 07:31 AM
#21
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Originally Posted by mazdaspeed7' date='Apr 28 2004, 06:32 PM
Well, Ill have to disagree on the blanket statement that some is always good. For instance, F1 engines run zero overlap, and the redlines are creeping past 19K rpm. Many new production cars, most notably the newer hondas, including the S2000, run zero overlap, as well as the Renesis engine. Yes, I know those two examples are polar opposites, but its to make a point. In both cases, the advantages of overlap did not outweigh the disadvantages.
Now, take old school pushrod V8's. They need a lot of overlap to make power at higher rpms. But they lose a lot of low end from the overlap, and drivability as well.
I pretty much only port down. I take the top edge up to the top of the stock bevel, and then bevel that. I get enough extra overlap from the early open SP. Then I just port down and out.
Now, take old school pushrod V8's. They need a lot of overlap to make power at higher rpms. But they lose a lot of low end from the overlap, and drivability as well.
I pretty much only port down. I take the top edge up to the top of the stock bevel, and then bevel that. I get enough extra overlap from the early open SP. Then I just port down and out.
Here is an article from honda about the s200 mentioning the overlaphttp://www.hondauk-media.co.uk/hondauk/press_packs/s2000_pack.htm
here is an article talking about exhaust systems on formula one engines talking about overlap:
"The moment the outlet valves open, all hell is let loose. One of the 10 cylinders in an f1 engine has just inhaled 300cc of air, laced it with a jet of fuel, compressed the mixture to 10x atmospheric pressure and flung in a spark. At 900 degrees Celsius the gasses produced when the mixture explodes whip past the titanium outlet valves and into the exhaust system at the speed of sound. But far from being a simple means of evacuating hot, high-speed gases, modern exhaust systems have a crucial part to play in determining the power and performance of a racing engine.
Compared with the exhaust of a road-going car, the short but serpentine system in a formula racer looks pretty simple. Each bank of cylinders features a number of artistically twisted steel tubes, with no catalytic converter and no silencer to hinder the flow of the exhaust gases and prevent the engine breathing freely. And yet designing a F1 exhaust system is an extremely complex business that calls for an intimate knowledge of the laws of acoustics if the engineers are to tease the last reserves of power out of the engine. That’s because, like in a trumpet, the exhaust gases vibrate at a specific frequency depending on the speed of the engine. As the valves open and close, they generate a pulsating column of exhaust, with regular peaks and troughs of pressure. To ensure that the 5 cylinders per bank don’t interfere with one another in this respect, all the exhaust pipes must be the same length. And at the end of the collector, the exhaust gasses from each bank exit the car from a single tailpipe.
Racing engines bred for maximum power work with a high degree of valve overlap. That is to say, the inlet valves are opened before the piston reaches top dead center (TDC) while the outlet valves are still open. At this instant, a perfectly tuned exhaust system will ensure that there is already under pressure in the combustion chamber, drawing in the mixture for the next charge. So the induction stroke which is generally triggered by the downward motion of the piston is in this case initiated by the exhaust system . Thus the intake and exhaust system together form an integrated and highly sensitive gas vibration system which influences both maximum power and torque.
At peak revs, a formula engine will blast out exhaust gases 95,000 times a minute. To scavenge maximum power the exhaust pipes need to be as short as possible. Unfortunately , to help generate maximum torque and responsiveness at lower revs, longer splender pipes are called for. As F1 regulations don’t permit variable-geometry exhausts, the answer lies in the best possible compromise.
The current preference for tailpipes that emerge upwards through the rear trim at either side of the car has made life easier for exhaust designers.
Nevertheless, F1 exhausts rarely completes more than 1200km since the need to save weight means they have to be designed close to the limit. The thickness of the heat-resistant steel adopted from the aerospace industry varies but is never more than 1 millimeter. But when eventually kills these waste-gas works of art is not vibration or temperatures of 1000 degrees and more, but stress, The different radii of the various pipes ultimately produce fatigue which leads to cracks where the stress is greatest. Not surprisingly, at this high level of performance even the best exhaust are soon exhausted !!"
heres an article talking about i-vtec and how it is able to dial out overlap, twards the end it talks about the f20c and how using i-vtec on it to dial out alot of the mid range overlap would improve the engine: http://asia.vtec.net/article/ivtec/
Heres another article talking about F1 engines and overlap:
http://www.f1technical.net/article6.html
bottom line is F1 engines wouldnt work at all without overlap, the acceleration of the intake charge would be to great if it had no overlap, at 19k you need a steady flow into the motor and out the exhaust.
04-30-2004, 07:38 AM
#22
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Infact i cant think of a single high specific output NA piston engine with zero overlap....
The renesis runs no overlap because rotarys are dirty little motors by design, it has nothing to do with performance. Rotarys tend to not burn part of the intake charge in the "squish" zone, compiled with the fact we burn oil and youll see why the only way mazda could bring out a rotary in 2004 with tightening emmisions is using the zero overlap internal egr scheme, that or going to preheated metal honeycomb cats, which is expencive, unproven (the s2k runs metalic core cats but there not preheated, i am unaware of any production care that have them yet) and i doubt metal cats would hold up to rotary exhaust for long.
now, as to weather or not we have to much overlap stock i have no clue.. a little goes a long way...
The renesis runs no overlap because rotarys are dirty little motors by design, it has nothing to do with performance. Rotarys tend to not burn part of the intake charge in the "squish" zone, compiled with the fact we burn oil and youll see why the only way mazda could bring out a rotary in 2004 with tightening emmisions is using the zero overlap internal egr scheme, that or going to preheated metal honeycomb cats, which is expencive, unproven (the s2k runs metalic core cats but there not preheated, i am unaware of any production care that have them yet) and i doubt metal cats would hold up to rotary exhaust for long.
now, as to weather or not we have to much overlap stock i have no clue.. a little goes a long way...
04-30-2004, 10:40 AM
#24
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Posts: 480
Originally Posted by Drago86' date='Apr 30 2004, 04:38 AM
Infact i cant think of a single high specific output NA piston engine with zero overlap....
The renesis runs no overlap because rotarys are dirty little motors by design, it has nothing to do with performance. Rotarys tend to not burn part of the intake charge in the "squish" zone, compiled with the fact we burn oil and youll see why the only way mazda could bring out a rotary in 2004 with tightening emmisions is using the zero overlap internal egr scheme, that or going to preheated metal honeycomb cats, which is expencive, unproven (the s2k runs metalic core cats but there not preheated, i am unaware of any production care that have them yet) and i doubt metal cats would hold up to rotary exhaust for long.
now, as to weather or not we have to much overlap stock i have no clue.. a little goes a long way...
The renesis runs no overlap because rotarys are dirty little motors by design, it has nothing to do with performance. Rotarys tend to not burn part of the intake charge in the "squish" zone, compiled with the fact we burn oil and youll see why the only way mazda could bring out a rotary in 2004 with tightening emmisions is using the zero overlap internal egr scheme, that or going to preheated metal honeycomb cats, which is expencive, unproven (the s2k runs metalic core cats but there not preheated, i am unaware of any production care that have them yet) and i doubt metal cats would hold up to rotary exhaust for long.
now, as to weather or not we have to much overlap stock i have no clue.. a little goes a long way...
The side exhaust port stops the trailing wedge of HC's from getting tossed out vs. the peripheral exhaust port. Additionally, the lower internal EGR at light throttle allows a leaner mixture. (see the "Renesis paper" for better info)
I don't think the oil injection increases emissions very much - plenty of boingers use more oil than a rotary. I think the "oil injection=dirty exhaust" idea comes from two stroke engines, which have oil injection and are very dirty. However, the emissions from a 2 stroke are really more from the extreme misfire rate at anything under full throttle and less from the 1% or so (?) oil in the fuel.
04-30-2004, 02:21 PM
#25
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Originally Posted by Drago86' date='Apr 30 2004, 08:31 AM
I dont know where you got your info that F1 engines and the s2000 run zero overlap, but its dead wrong. an F1 engine wouldnt work at all at high rpm without crazy overlap. Ive read articles on the F1 engines and at 19 grand the air fuel mixture doesnt have time to run zero overlap, the next chamber fill must be initiated by the exhaust stroke of the preceding charge, if it didnt the air could never accelerate enough to fill the chamber at that many revs.The s2000 definatly has overlap, thats what the whole Vtec thing does, besides higher lift. If the motors ran zero overlap they wouldnt need vtec because the motors would idle fine and make decent torque without it.
Here is an article from honda about the s200 mentioning the overlaphttp://www.hondauk-media.co.uk/hondauk/press_packs/s2000_pack.htm
here is an article talking about exhaust systems on formula one engines talking about overlap:
"The moment the outlet valves open, all hell is let loose. One of the 10 cylinders in an f1 engine has just inhaled 300cc of air, laced it with a jet of fuel, compressed the mixture to 10x atmospheric pressure and flung in a spark. At 900 degrees Celsius the gasses produced when the mixture explodes whip past the titanium outlet valves and into the exhaust system at the speed of sound. But far from being a simple means of evacuating hot, high-speed gases, modern exhaust systems have a crucial part to play in determining the power and performance of a racing engine.
Compared with the exhaust of a road-going car, the short but serpentine system in a formula racer looks pretty simple. Each bank of cylinders features a number of artistically twisted steel tubes, with no catalytic converter and no silencer to hinder the flow of the exhaust gases and prevent the engine breathing freely. And yet designing a F1 exhaust system is an extremely complex business that calls for an intimate knowledge of the laws of acoustics if the engineers are to tease the last reserves of power out of the engine. That’s because, like in a trumpet, the exhaust gases vibrate at a specific frequency depending on the speed of the engine. As the valves open and close, they generate a pulsating column of exhaust, with regular peaks and troughs of pressure. To ensure that the 5 cylinders per bank don’t interfere with one another in this respect, all the exhaust pipes must be the same length. And at the end of the collector, the exhaust gasses from each bank exit the car from a single tailpipe.
Racing engines bred for maximum power work with a high degree of valve overlap. That is to say, the inlet valves are opened before the piston reaches top dead center (TDC) while the outlet valves are still open. At this instant, a perfectly tuned exhaust system will ensure that there is already under pressure in the combustion chamber, drawing in the mixture for the next charge. So the induction stroke which is generally triggered by the downward motion of the piston is in this case initiated by the exhaust system . Thus the intake and exhaust system together form an integrated and highly sensitive gas vibration system which influences both maximum power and torque.
At peak revs, a formula engine will blast out exhaust gases 95,000 times a minute. To scavenge maximum power the exhaust pipes need to be as short as possible. Unfortunately , to help generate maximum torque and responsiveness at lower revs, longer splender pipes are called for. As F1 regulations don’t permit variable-geometry exhausts, the answer lies in the best possible compromise.
The current preference for tailpipes that emerge upwards through the rear trim at either side of the car has made life easier for exhaust designers.
Nevertheless, F1 exhausts rarely completes more than 1200km since the need to save weight means they have to be designed close to the limit. The thickness of the heat-resistant steel adopted from the aerospace industry varies but is never more than 1 millimeter. But when eventually kills these waste-gas works of art is not vibration or temperatures of 1000 degrees and more, but stress, The different radii of the various pipes ultimately produce fatigue which leads to cracks where the stress is greatest. Not surprisingly, at this high level of performance even the best exhaust are soon exhausted !!"
heres an article talking about i-vtec and how it is able to dial out overlap, twards the end it talks about the f20c and how using i-vtec on it to dial out alot of the mid range overlap would improve the engine: http://asia.vtec.net/article/ivtec/
Heres another article talking about F1 engines and overlap:
http://www.f1technical.net/article6.html
bottom line is F1 engines wouldnt work at all without overlap, the acceleration of the intake charge would be to great if it had no overlap, at 19k you need a steady flow into the motor and out the exhaust.
Here is an article from honda about the s200 mentioning the overlaphttp://www.hondauk-media.co.uk/hondauk/press_packs/s2000_pack.htm
here is an article talking about exhaust systems on formula one engines talking about overlap:
"The moment the outlet valves open, all hell is let loose. One of the 10 cylinders in an f1 engine has just inhaled 300cc of air, laced it with a jet of fuel, compressed the mixture to 10x atmospheric pressure and flung in a spark. At 900 degrees Celsius the gasses produced when the mixture explodes whip past the titanium outlet valves and into the exhaust system at the speed of sound. But far from being a simple means of evacuating hot, high-speed gases, modern exhaust systems have a crucial part to play in determining the power and performance of a racing engine.
Compared with the exhaust of a road-going car, the short but serpentine system in a formula racer looks pretty simple. Each bank of cylinders features a number of artistically twisted steel tubes, with no catalytic converter and no silencer to hinder the flow of the exhaust gases and prevent the engine breathing freely. And yet designing a F1 exhaust system is an extremely complex business that calls for an intimate knowledge of the laws of acoustics if the engineers are to tease the last reserves of power out of the engine. That’s because, like in a trumpet, the exhaust gases vibrate at a specific frequency depending on the speed of the engine. As the valves open and close, they generate a pulsating column of exhaust, with regular peaks and troughs of pressure. To ensure that the 5 cylinders per bank don’t interfere with one another in this respect, all the exhaust pipes must be the same length. And at the end of the collector, the exhaust gasses from each bank exit the car from a single tailpipe.
Racing engines bred for maximum power work with a high degree of valve overlap. That is to say, the inlet valves are opened before the piston reaches top dead center (TDC) while the outlet valves are still open. At this instant, a perfectly tuned exhaust system will ensure that there is already under pressure in the combustion chamber, drawing in the mixture for the next charge. So the induction stroke which is generally triggered by the downward motion of the piston is in this case initiated by the exhaust system . Thus the intake and exhaust system together form an integrated and highly sensitive gas vibration system which influences both maximum power and torque.
At peak revs, a formula engine will blast out exhaust gases 95,000 times a minute. To scavenge maximum power the exhaust pipes need to be as short as possible. Unfortunately , to help generate maximum torque and responsiveness at lower revs, longer splender pipes are called for. As F1 regulations don’t permit variable-geometry exhausts, the answer lies in the best possible compromise.
The current preference for tailpipes that emerge upwards through the rear trim at either side of the car has made life easier for exhaust designers.
Nevertheless, F1 exhausts rarely completes more than 1200km since the need to save weight means they have to be designed close to the limit. The thickness of the heat-resistant steel adopted from the aerospace industry varies but is never more than 1 millimeter. But when eventually kills these waste-gas works of art is not vibration or temperatures of 1000 degrees and more, but stress, The different radii of the various pipes ultimately produce fatigue which leads to cracks where the stress is greatest. Not surprisingly, at this high level of performance even the best exhaust are soon exhausted !!"
heres an article talking about i-vtec and how it is able to dial out overlap, twards the end it talks about the f20c and how using i-vtec on it to dial out alot of the mid range overlap would improve the engine: http://asia.vtec.net/article/ivtec/
Heres another article talking about F1 engines and overlap:
http://www.f1technical.net/article6.html
bottom line is F1 engines wouldnt work at all without overlap, the acceleration of the intake charge would be to great if it had no overlap, at 19k you need a steady flow into the motor and out the exhaust.
04-30-2004, 02:25 PM
#26
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Location: Honolulu, Hawaii USA
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Yeah, I was confused about the zero-overlap F1 engines myself...
The advantages of overlap on cross-flow heads has been thoroughly documented, and if F1 doesn't take advantage of it, I'd be seriously surprised.
On my exhaust ports, the Stage I porting can easily surpass 300hp up to 400hp. I try to keep the earlier exhaust porting opening to a minumum, as this kills (low end) torque. I run the Stage II porting on my car, and it only put down 253hp but only 207lb-ft of torque; milder porting jobs will easily gain 20 to 30 more lb-ft of torque on the same type of motor.
On the Stage II ports, this is for engines running 400hp or higher. Engine pumping out this kinda power will not feel the drop in (low end) torque and top-end power is significantly increased.
Like everything in life, it's all a compromise.
-Ted
The advantages of overlap on cross-flow heads has been thoroughly documented, and if F1 doesn't take advantage of it, I'd be seriously surprised.
On my exhaust ports, the Stage I porting can easily surpass 300hp up to 400hp. I try to keep the earlier exhaust porting opening to a minumum, as this kills (low end) torque. I run the Stage II porting on my car, and it only put down 253hp but only 207lb-ft of torque; milder porting jobs will easily gain 20 to 30 more lb-ft of torque on the same type of motor.
On the Stage II ports, this is for engines running 400hp or higher. Engine pumping out this kinda power will not feel the drop in (low end) torque and top-end power is significantly increased.
Like everything in life, it's all a compromise.
-Ted
01-13-2005, 09:17 PM
#27
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Join Date: Oct 2004
Posts: 110
I like to revive this threat. Mainly because lots of things have been touched on but very little resolve here.
Porting down will open the exhaust port earlier allowing for faster gas exchange. Porting up will close the xport later and will allow for longer gas exchange but dilutes intake charge. Porting sideways will compromise apex seals.
Clearly for high powered rotaries you need a large exhaust port to vent all the xhaust gases. So, I like to see a little more discussions on the pro and cons for porting up or down.
With piston engines there is no problen opening the xport earlier since most of the power transfer happens in the beginning of the stroke. Is this true for our engines as well. The significant loss of torque people report from earlier opening lends me to believe that there is a significant late stroke power transfer. The angle eshaft / rotor being favorable at the end of the power stroke might give us more power transfer than what we know from piston engines late in the stroke?
As for porting up, it is just plain overlap, or is it not? The engine really coming alive a high rpms and struggling down low since gases mix and mess up combustion?
Thanks for listening and hoping for more insight
CW
Porting down will open the exhaust port earlier allowing for faster gas exchange. Porting up will close the xport later and will allow for longer gas exchange but dilutes intake charge. Porting sideways will compromise apex seals.
Clearly for high powered rotaries you need a large exhaust port to vent all the xhaust gases. So, I like to see a little more discussions on the pro and cons for porting up or down.
With piston engines there is no problen opening the xport earlier since most of the power transfer happens in the beginning of the stroke. Is this true for our engines as well. The significant loss of torque people report from earlier opening lends me to believe that there is a significant late stroke power transfer. The angle eshaft / rotor being favorable at the end of the power stroke might give us more power transfer than what we know from piston engines late in the stroke?
As for porting up, it is just plain overlap, or is it not? The engine really coming alive a high rpms and struggling down low since gases mix and mess up combustion?
Thanks for listening and hoping for more insight
CW
01-14-2005, 09:06 AM
#28
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