MASSIVE TYPE IV wrote: We have already proven that the engine definately loves split duration, with more suration on the exhaust side of things so perhaps the manifolds are enhancing that effect further????
Some tuning observations of "BIG" engines
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Santas Brother
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HAM Inc
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It's well established that higher ex. flow % makes more peak power on the dyno. No debating this. This is one of quircks and shortcomings of relying soley on dyno and flow data to set-up an engine. Since we know that higher ex. flow % makes more peak power why stop at 80%? or 85%? Why not just make the ex. flow the same as the intake?
The answer lies in the performance characteristics desired. Race engine designers figured out by the early 60's that the magic # for good all around performance (acceleration and throttle responce) is right at 75% for normally aspirated engines.
And I have gotten positve feed back from street customers about the amazing throttle response and acceleration of engines with heads I've prepped at 70%.
Remember on a well balance head the ex.port won't limit peak torque. but rather peak H.P. This is because peak torque falls at a much lower RPM than peak H.P. Assuming the cam matches the combo, at the lower speeds there is enough time (measured chronologically, not in crank degrees) to evacuate the cylinder. (Remember we are still talking about a 75% head) As RPM's increase and real cycle time decreases the ports ability to evacuate also decrease. But an interesting side effect of this is a steady increase in port velocity. This is where it gets complicated.
Sound waves that move up and down the ex. tract come in postive and negative waves. A sound wave will move through the tract at around 1700ft./second. The gas speed may only be 300ft/second. It doesn't take a rocket scientist to figure out that a sound wave moving through a gas at around 6 times the gas speed will have a profound effect on the scavenge cycle. Here's the nice thing about ex. velocity. The positve waves moving up the ex. (toward the valve) have a less negative impact if the gas speed is up. And the negative pulse moves more freeely up the tract (toward the valve) in a lower pressure conduit. And since the higher the velocity through a pipe, the lower the pressure, we can see that velocity is very important.
Now as for Jakes findings, another posibility that hasn't been explored is the ex. system itself. A system that is just right for a 175 HP will be wonderful at lower RPM's on a more powerful engine, but it will clip peak performance. Once again we are dealing with a compromise.
The compromise on H.P. street engines is actually more of a trick than on a race engine. I always know what a race customer wants. But street customers come with a variety of desires. And some THINK they want a 7,000 rpm screamer, but they still want that baby to pull off the red light at 2,000 RPM's. Something has to give. 99% of the time if we take away some peak power and move it down low the customer is going to love it. 99% of the time if we take away the bottom end power and move it up high the customer will be frustrated with the lack of drivability.
Start prepping your combos solely by the flowbench and dyno and you'll wind up with 85-90% heads with long cams and big venturies and you'll have a pig to drive that only performs well for about 300RPM's at the high end of the scale.
The answer lies in the performance characteristics desired. Race engine designers figured out by the early 60's that the magic # for good all around performance (acceleration and throttle responce) is right at 75% for normally aspirated engines.
And I have gotten positve feed back from street customers about the amazing throttle response and acceleration of engines with heads I've prepped at 70%.
Remember on a well balance head the ex.port won't limit peak torque. but rather peak H.P. This is because peak torque falls at a much lower RPM than peak H.P. Assuming the cam matches the combo, at the lower speeds there is enough time (measured chronologically, not in crank degrees) to evacuate the cylinder. (Remember we are still talking about a 75% head) As RPM's increase and real cycle time decreases the ports ability to evacuate also decrease. But an interesting side effect of this is a steady increase in port velocity. This is where it gets complicated.
Sound waves that move up and down the ex. tract come in postive and negative waves. A sound wave will move through the tract at around 1700ft./second. The gas speed may only be 300ft/second. It doesn't take a rocket scientist to figure out that a sound wave moving through a gas at around 6 times the gas speed will have a profound effect on the scavenge cycle. Here's the nice thing about ex. velocity. The positve waves moving up the ex. (toward the valve) have a less negative impact if the gas speed is up. And the negative pulse moves more freeely up the tract (toward the valve) in a lower pressure conduit. And since the higher the velocity through a pipe, the lower the pressure, we can see that velocity is very important.
Now as for Jakes findings, another posibility that hasn't been explored is the ex. system itself. A system that is just right for a 175 HP will be wonderful at lower RPM's on a more powerful engine, but it will clip peak performance. Once again we are dealing with a compromise.
The compromise on H.P. street engines is actually more of a trick than on a race engine. I always know what a race customer wants. But street customers come with a variety of desires. And some THINK they want a 7,000 rpm screamer, but they still want that baby to pull off the red light at 2,000 RPM's. Something has to give. 99% of the time if we take away some peak power and move it down low the customer is going to love it. 99% of the time if we take away the bottom end power and move it up high the customer will be frustrated with the lack of drivability.
Start prepping your combos solely by the flowbench and dyno and you'll wind up with 85-90% heads with long cams and big venturies and you'll have a pig to drive that only performs well for about 300RPM's at the high end of the scale.
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HAM Inc
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The notion that one system (the intake) can be given short thrift while the other system (the exhaust) is focused on is not sound theory. For an engine to have optimum performance it must have the proper combo. Jake has been saying this for years and he is absolutely correct.
The proper combo will address the intake and ex. systems, the chamber shape, the rod:stroke ratio, bore:stroke ratio, the cam, and the valve train compnents. The tranny gearing figures in as well.
Since all T4 heads are wonderfully designed as 75% heads, modifications must address both sides (intake and Exhaust) of the engine.
All engines benefit from sonic tuning of the ex. system. It has been my contention for years that nearly all street headers and most racing headers have oversized pipes and especially collectors. Performance will be somewhat forgiving to oversized pipes, but not to oversized collectors, especially if the collector is short with an aggressive taper and an oversized outlet.
Moving away from a focus on peak #'s is the first step toward achieving peak overall performance.
The proper combo will address the intake and ex. systems, the chamber shape, the rod:stroke ratio, bore:stroke ratio, the cam, and the valve train compnents. The tranny gearing figures in as well.
Since all T4 heads are wonderfully designed as 75% heads, modifications must address both sides (intake and Exhaust) of the engine.
All engines benefit from sonic tuning of the ex. system. It has been my contention for years that nearly all street headers and most racing headers have oversized pipes and especially collectors. Performance will be somewhat forgiving to oversized pipes, but not to oversized collectors, especially if the collector is short with an aggressive taper and an oversized outlet.
Moving away from a focus on peak #'s is the first step toward achieving peak overall performance.
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arlo
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It just struck me that I think I may have had the same experiance Jake described on a V8 I built up through years of trial and error many years ago. Jakes description of its behavior couldn't be any closer to what I saw including the intake port matching experiance!
Forget the fact it was a V8 and look at one bank of 4. Tuning was touchy with jetting, cam grind, ignition, induction etc making very real differances in performance until the last time I bored it over square to 3.25" stroke X 4.0" bore (82mmx102mm, look familiar?) with a 10:1 CR. The only big differance was it had a Paxton blower which you could use at this CR since pump premium was 102 octane at that time. After the big bore it was not very responsive to all the changes that it used to be sensitive to. It was quite fast though and I just decided that the combo must be as good as I could get it. It was no fun to tinker with anymore since it didn't respond to any more of my efforts so I just drove it since it had nice drivability and was reliable.
Then an aquaintance with a lot of exhaust system design experiance talked me into a total custom exhaust system from ports to tail pipes. The effect was unbelievable! This was the part of the combo that was once in ballance with the smaller engine but now holding everything back on the much larger one.
I guess in the big picture of things the engine combo was now back in ballance but the rest of the system was now out of ballance because I proceded to one by one break every shaft and gear between the flywheel and the rear wheels, explode the pressure plate with no scatter shield sending parts of the clutch and bell housing through the floor into the passenger compartment at 6000 rpm and got numerous tickets for drag racing on public streets, once at 145mph. Bummer! Now with a more seriously "out of ballance combo" tinkering with it was again no more fun so I sold it with the exploded clutch and bought my first air cooled VW bug to break the street racing habbit.
So, if that experiance relates at all, I would say leave it be as a reliable very good performing combo that is easy to tune or else do a lot more work on things that occur after the point of ignition, especially looking at exhaust system components. Just my quick opinion Jake. I'm sure your way ahead of us already in figuring this out though!
Forget the fact it was a V8 and look at one bank of 4. Tuning was touchy with jetting, cam grind, ignition, induction etc making very real differances in performance until the last time I bored it over square to 3.25" stroke X 4.0" bore (82mmx102mm, look familiar?) with a 10:1 CR. The only big differance was it had a Paxton blower which you could use at this CR since pump premium was 102 octane at that time. After the big bore it was not very responsive to all the changes that it used to be sensitive to. It was quite fast though and I just decided that the combo must be as good as I could get it. It was no fun to tinker with anymore since it didn't respond to any more of my efforts so I just drove it since it had nice drivability and was reliable.
Then an aquaintance with a lot of exhaust system design experiance talked me into a total custom exhaust system from ports to tail pipes. The effect was unbelievable! This was the part of the combo that was once in ballance with the smaller engine but now holding everything back on the much larger one.
I guess in the big picture of things the engine combo was now back in ballance but the rest of the system was now out of ballance because I proceded to one by one break every shaft and gear between the flywheel and the rear wheels, explode the pressure plate with no scatter shield sending parts of the clutch and bell housing through the floor into the passenger compartment at 6000 rpm and got numerous tickets for drag racing on public streets, once at 145mph. Bummer! Now with a more seriously "out of ballance combo" tinkering with it was again no more fun so I sold it with the exploded clutch and bought my first air cooled VW bug to break the street racing habbit.
So, if that experiance relates at all, I would say leave it be as a reliable very good performing combo that is easy to tune or else do a lot more work on things that occur after the point of ignition, especially looking at exhaust system components. Just my quick opinion Jake. I'm sure your way ahead of us already in figuring this out though!
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HAM Inc
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Arlo I believe you hit the nail on the head. Jake has spent a lot of time developing his combos to the point that they are very well refined. I have spent countless hours developing port and chamber combos. The engine packages that Jake has made his most recent observations on have the latest developments fresh off my bench and there is a sizeable jump in intake flow. Plus we've been working closely on chamber shapes for these big boys as well and have developed a shape that is giving a really good burn. The only thing missing out on massive R&D (I believe) is the ex. system.
BTW was the friend that helped you sort out your header issues Ed from Headers By Ed? That man is a character and knows his $hit when it comes to exhaust.
Most people miss the boat when it comes to headers. They will swap all sorts of parts. Change gear ratios and after it all bolt the same header on the car. If it happens to be just right for one of their combos great. Otherwise they just wonder why all of their changes didn't work as expected.
BTW was the friend that helped you sort out your header issues Ed from Headers By Ed? That man is a character and knows his $hit when it comes to exhaust.
Most people miss the boat when it comes to headers. They will swap all sorts of parts. Change gear ratios and after it all bolt the same header on the car. If it happens to be just right for one of their combos great. Otherwise they just wonder why all of their changes didn't work as expected.
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Plastermaster
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Santas Brother
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arlo
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I think so too. Also temperature may be a variable and I think the speed of the gas is added to the speed of the sound travelling through it.
Len, Ed is a local guy who has been building race proven headers for something like 30 years. I know him and have spent quite a bit of time discussing the design of custom headers for my type 4 and also FI intake runners and plenum. He is a charactor with a lot of opinions but he has proven what he believes and is very helpfull and generous with his time.
The guy who helped with the exhaust system on the engine that reminded me so much of Jakes obsevations was in Seattle 40 years ago. The underlying science for this stuff never changes but many times people either don't want to pass it on, don't know how to explain it correctly or find things that seem to work and don't really know why so people have to keep rediscovering it for themselves.
Len, Ed is a local guy who has been building race proven headers for something like 30 years. I know him and have spent quite a bit of time discussing the design of custom headers for my type 4 and also FI intake runners and plenum. He is a charactor with a lot of opinions but he has proven what he believes and is very helpfull and generous with his time.
The guy who helped with the exhaust system on the engine that reminded me so much of Jakes obsevations was in Seattle 40 years ago. The underlying science for this stuff never changes but many times people either don't want to pass it on, don't know how to explain it correctly or find things that seem to work and don't really know why so people have to keep rediscovering it for themselves.
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Bobtail
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So following on from that idea, Turbo's dont rely as much on the header design to produce power as they use mostly heat to spin the turbine.
So you make up for the losses with the forced induction and also using the waste heat from the combustion process.
Who knows what the best header design is? looking at an F1 car they have a header which is similar in length to a most rear engined layouts so are most aftermarket systems too short? (short headers for high rpm 18k rpm in an F1 car)My bet is F1 systems are the right length and most aftermarket systems are way short for a lowly 6 to 7k rpm bug motor.
So you make up for the losses with the forced induction and also using the waste heat from the combustion process.
Who knows what the best header design is? looking at an F1 car they have a header which is similar in length to a most rear engined layouts so are most aftermarket systems too short? (short headers for high rpm 18k rpm in an F1 car)My bet is F1 systems are the right length and most aftermarket systems are way short for a lowly 6 to 7k rpm bug motor.
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HAM Inc
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Yes, Ed Henneman is a character. Over the years I have spent hours on the phone with him. He is very forth-coming with his vast knowledge of ex systems. Very early on I was drawn to Ed because his "preaching" about ex. design matched up precisely with my fathers observations in his extensive dyno testing of store bought and eventually a plethora of homemade designs for our T1 race engines. My fathers systems (which won over 150 races) were dramatically smaller than the competitions.
Santos you are correct, sound wave velocity is tied to pressure and temp. The lower the pressure the faster the wave moves. Hence the importance of velocity in an ex. system.
Most rear engine systems are WAY to short in my opinion (and the dynos) because of space limitations. But all is not lost. One of the peculiarities of header design is that if the optimum length for a given application is 6' a system 3' in length will have somewhat similar characteristics.
For more mind blowing (and often confusing) info about ex. systems pick up the Scientific Design of Ex. and Intake Sytems by Philip Smith. Barnes & Noble can order it. Or call 612-729-2802 and order the Headers By Ed catalog. It contains damn near everything you need to build your own system and comes with a ream of tech advise regarding the design of systems.
I would never design a street system with a pipe diameter more than a 1.5mm larger than the ex. valve head diameter. For my own system I would make the pipes as small as I could with out having a lip where it meets the head.
I have built, used and recently won circle track races with a header for a 12.25:1, 8300RPM 2.3l Ford (gasp! don't hate me, I used to race aircooled roundy- round but they banned them around here) that had 1.5 O.D. primaries and a 2.25" collector.
99.99% of my competitors use a Schoenfeld system with 1.75 O.D. pipe and 3" collector. I blister them off the corners and have no overheating problems.
(BTW the system I built the system using the bends from old 2.0 914 F.I. intake manifolds!)
The point I'm trying to make is that while I know the guys with the bigger systems make more peak H.P than I do, they don't make more peak torque, and torque is what accelerates you out of a corner (or away from a stop light) What good is gobs of peak power if it takes a lifetime (or a straight away) to get the revs to that elevated point?
Santos you are correct, sound wave velocity is tied to pressure and temp. The lower the pressure the faster the wave moves. Hence the importance of velocity in an ex. system.
Most rear engine systems are WAY to short in my opinion (and the dynos) because of space limitations. But all is not lost. One of the peculiarities of header design is that if the optimum length for a given application is 6' a system 3' in length will have somewhat similar characteristics.
For more mind blowing (and often confusing) info about ex. systems pick up the Scientific Design of Ex. and Intake Sytems by Philip Smith. Barnes & Noble can order it. Or call 612-729-2802 and order the Headers By Ed catalog. It contains damn near everything you need to build your own system and comes with a ream of tech advise regarding the design of systems.
I would never design a street system with a pipe diameter more than a 1.5mm larger than the ex. valve head diameter. For my own system I would make the pipes as small as I could with out having a lip where it meets the head.
I have built, used and recently won circle track races with a header for a 12.25:1, 8300RPM 2.3l Ford (gasp! don't hate me, I used to race aircooled roundy- round but they banned them around here) that had 1.5 O.D. primaries and a 2.25" collector.
99.99% of my competitors use a Schoenfeld system with 1.75 O.D. pipe and 3" collector. I blister them off the corners and have no overheating problems.
(BTW the system I built the system using the bends from old 2.0 914 F.I. intake manifolds!)
The point I'm trying to make is that while I know the guys with the bigger systems make more peak H.P than I do, they don't make more peak torque, and torque is what accelerates you out of a corner (or away from a stop light) What good is gobs of peak power if it takes a lifetime (or a straight away) to get the revs to that elevated point?
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Santas Brother
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raygreenwood
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The speed of sound does vary by air density. Since one way air density is changed is by addding pressure...yes the speed of sound changes. The higher the air density, the higher the speed a sound wave must achieve to break the sound barrier. Off the top of my head...speed pf sound at one atmosphere at seas level is something like 722 mph. Thats like 1058 feet per second. At 30,000 feet where the air is thinner....its like 670 mph...or somewhere around 997 feet per second.
There are some issues people will run into when just tuning by sonic speed alone. You have gas pressure and velocity coming out of the valve. The "pop" sound of exhaust...is generally the combustion mixture breaking the speed of sound. That "expansion"....that causes that pop....will create a shock wave. The amount of force/expansion (which creates velocity) that shockwave creates....will depend upon how much higher than the gas temp is.....from what was needed to cause expansion to sonic speeds. The longer it can keep that elevated temperature....the faster the velocity before it disipates.
Gas temp is important to exhaust tuning.
On the other hand...there is also sound created...that does not break the sound barrier. Probably more of that than sonic sound. That does not generally create pressure waves. On the intake tract...many times when you have sound oscillation created in the intake, people mistake that for sound created by sonic speeds. They sometimes try to tune based upon sonic speeds...and get incorrect intake tract tuning. Ray
There are some issues people will run into when just tuning by sonic speed alone. You have gas pressure and velocity coming out of the valve. The "pop" sound of exhaust...is generally the combustion mixture breaking the speed of sound. That "expansion"....that causes that pop....will create a shock wave. The amount of force/expansion (which creates velocity) that shockwave creates....will depend upon how much higher than the gas temp is.....from what was needed to cause expansion to sonic speeds. The longer it can keep that elevated temperature....the faster the velocity before it disipates.
Gas temp is important to exhaust tuning.
On the other hand...there is also sound created...that does not break the sound barrier. Probably more of that than sonic sound. That does not generally create pressure waves. On the intake tract...many times when you have sound oscillation created in the intake, people mistake that for sound created by sonic speeds. They sometimes try to tune based upon sonic speeds...and get incorrect intake tract tuning. Ray
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Tony Z
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????? not when I look ?????Bobtail wrote:
Who knows what the best header design is? looking at an F1 car they have a header which is similar in length to a most rear engined layouts so are most aftermarket systems too short? (short headers for high rpm 18k rpm in an F1 car)My bet is F1 systems are the right length and most aftermarket systems are way short for a lowly 6 to 7k rpm bug motor.
