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Spark table doesn't make sense. 30 degrees at 90KPA and 40 degrees at 100KPA is backwards for starters....
1. Timing needs to drop as pressure increases
2. Max timing for Small block Chevrolet combustion chambers is around 32 to 36 degrees for moderate compression gasoline engines, usually
3. Cylinder VE follows torque and inversely with timing, e.g. as VE drops timing may increase to some maximum but not further at WOT
4. TPI torque should peak near 4400rpm iirc and fall from that point, meaning cylinder VE is falling as well
5. Generally 37+ degrees of timing is reserved for cruise ONLY where KPA is near 40 to 50KPA. Cruise timing may be as high as 45 degrees.
my question would be
A. where did you get that timing map, it lacks cruise timing and has wrong timing vs KPA
B. Did you verify the timing at the crank matches what the computer assumes
C. what is the A/F ratio during WOT
D. Did you (you need to do this) compression test the engine, if so write it down, each cylinder RECORDED no plugs in any cylinders during
Heres an example of what I would expect to see in the 90 95 100KPA vertical line
3000rpm 35*
4000rpm 33
4500rpm 32
5000rpm 35
6000rpm 36
Then you wiggle that on the dyno + and - a couple degrees, if the difference in torque is less than 5% when adding timing you don't add,
Please take this with a grain of salt, and correct me if I am wrong, I am absolutely not an expert. Watching the datalog, the things that stand out to me are: the relatively low SA past 3900 rpm and the fairly lean AFR. Correcting that might be worth some horsepower, but nothing massive.
I would want to richen up the WOT AFR for the sake of safety, and there were no knock counts or knock retard during the pull so a few more degrees of timing would be helpful. Most SBCs are happy around 34-36 degrees. Looking at the pull, you were at 35 at 3900rpm, right as you went WOT, but then timing dropped off.
Your SA table doesn't seem to match up with the data log during the pull. In fact, there seems to be quite a bit of Spark Advance from 95kpa and above in the 3000-6000rpm range. There is a large jump in SA in the transition between 90-95kpa as well. Maybe timing was being pulled and it wasn't shown in the datalog? I'm not super familiar with how that is configured or if your setup even uses a knock sensor.
I'd think with those changes you might gain some horsepower and see the peak shift up a couple hundred rpm, but again, I don't have much hands on experience with this so I may be totally wrong or missing something.
The red flag to me is not the HP number, it is that it peaked at such a low rpm. Even a stock TPI intake should make peak power closer to 4500rpm. Larger runners and a ported base won't change that curve much, it will just increase power proportional to that curve.
I think consideration should also be given to the dip in the power and torque curves at 3100 RPMs. This is a very mild engine which should show a nice steady rise in power. That dip followed by a sharp increase in power looks more like a nitrous shot.
That graph is not typical of a healthy running small block V8.
A stock L98 has its torque peak at 3000rpm or thereabouts. Where are you getting this?
Okay, peak power then. Around 4200-4400rpm depending on the air temp, water hammer is causing a drop in VE as sound waves created by opposing valves are bouncing from the opening valve just prior to the open event. I suppose the peak VE would be near 3000-3500 then, peak torque region
Okay, peak power then. Around 4200-4400rpm depending on the air temp, water hammer is causing a drop in VE as sound waves created by opposing valves are bouncing from the opening valve just prior to the open event. I suppose the peak VE would be near 3000-3500 then, peak torque region
Not sound waves from opposing valves. The drop in VE is caused by the opposite-phase Helmholtz resonance in each individual runner. It is in phase around 2800 or so and gives positive pressure when the valve is open to help push more air into the chamber at that RPM. At 50% more RPM, it's out of phase and causing a loss of pressure in the runner, thereby blocking flow. This is why TPI intakes suck.
Not sound waves from opposing valves. The drop in VE is caused by the opposite-phase Helmholtz resonance in each individual runner. It is in phase around 2800 or so and gives positive pressure when the valve is open to help push more air into the chamber at that RPM. At 50% more RPM, it's out of phase and causing a loss of pressure in the runner, thereby blocking flow. This is why TPI intakes suck.
Its sound waves. The correct term is water hammer. Its in the fluid mechanics book. "resonance" implies some matching frequency - in this case the frequency of the engine with the frequency of the sound arrival to the valve. When the sound arrives just as the valve opens the cylinder fill is increased. When the sound bounces from the valve just as it opens the cylinder fill is decreased.
This is the book of fluid mechanics physical description for the acoustic pressure wave (sound wave).
There is a whole chapter where it will discuss the difference between the speed of air, and the speed of sound in the air, the topic of "Mach".
When we shut a valve off, like a water faucet or air faucet (water and air are both fluids) a pressure wave is created termed 'water hammer' that travels up the pipe at the speed of sound.
You're conflating two different things. "Water hammer" refers to a pressure wave from a single closing of a valve. That pressure wave occurs upstream of the valve. "Resonance" refers to a repeated oscillation, in this case the oscillation of a column of air. Resonance in air, a sound wave, and an acoustic wave are all the same thing. Resonance in the intake runner is created by a cyclical water hammer effect; but it functions no differently than the resonance inside an organ pipe or a tuned exhaust pipe on a two-stroke engine, neither of which are created by a water hammer. The frequency is determined by the speed of the engine (it's half the frequency of the RPM). The frequency where the resonance reinforces or obstructs cylinder packing is determined by the length of the pipe: the longer the pipe, the lower the frequency. Just like with the tuned pipe and scavenging, there's a frequency where the resonance reinforces cylinder filling and a frequency where it obstructs it. The problem with the TPI intake is that the runners are too long, which places the obstructive frequency too low in the RPM range, thereby kneecapping the RPM range of the engine and seriously impinging its potential to make power with other modifications.
Also:
Originally Posted by Kingtal0n
as sound waves created by opposing valves are bouncing from the opening valve...
this is just wrong. It has nothing to do with "opposing valves." This same thing will happen in single-cylinder engine or an engine with individual throttle bodies where there is no other valve opposing the intake valve. The phenomenon takes place within a single valve and air column and is controlled solely by the RPM of the engine and the length of the air column, not any other valves.
You're conflating two different things. "Water hammer" refers to a pressure wave from a single closing of a valve. That pressure wave occurs upstream of the valve. "Resonance" refers to a repeated oscillation, in this case the oscillation of a column of air. Resonance in air, a sound wave, and an acoustic wave are all the same thing. Resonance in the intake runner is created by a cyclical water hammer effect; but it functions no differently than the resonance inside an organ pipe or a tuned exhaust pipe on a two-stroke engine, neither of which are created by a water hammer. The frequency is determined by the speed of the engine (it's half the frequency of the RPM). The frequency where the resonance reinforces or obstructs cylinder packing is determined by the length of the pipe: the longer the pipe, the lower the frequency. Just like with the tuned pipe and scavenging, there's a frequency where the resonance reinforces cylinder filling and a frequency where it obstructs it. The problem with the TPI intake is that the runners are too long, which places the obstructive frequency too low in the RPM range, thereby kneecapping the RPM range of the engine and seriously impinging its potential to make power with other modifications.
To resonate
Physics
the reinforcement or prolongation of sound by reflection from a surface or by the synchronous vibration of a neighboring object.
The engine can't reinforce or prolong sound energy by reflecting it up a tube, it will disperse. It 'resonates' because it is in sync with something else. A radio antenna and it's associated radio frequency does not 'resonate' unless the two are in sync, then we pick up the station. A mechanical device with an operating frequency does not 'resonate' unless mechanical motion or electrical/magnetic fields aligned harmonically with an supplied energy source. The engine does not 'resonate' unless the intake valve (or some other part) is in sync with a sound in question.
Notice the book says "will repeat itself in a periodic manner" says nothing about resonation. It is not a resonating wave, it is a periodic wave. The fact it has some frequency is akin to all sound waves: all sound waves have a frequency vibration. But we do not say that all sound waves resonate.
Also:
this is just wrong. It has nothing to do with "opposing valves." This same thing will happen in single-cylinder engine or an engine with individual throttle bodies where there is no other valve opposing the intake valve. The phenomenon takes place within a single valve and air column and is controlled solely by the RPM of the engine and the length of the air column, not any other valves.
Maybe I was too general. It comes from 20 years of thinking about this situation. In my conceptualization, the wave travels up the runner into the plenum. Then, I can clearly see the wave is spreading out into the plenum and interfering with other waves. Therefore the coincidence will be constructive or destructive regarding nearby or recently closed cylinders. The wave which reflects back into the tube is then a combination of influences from other runners who's waves have recently arrived into the plenum. Some engines rely on neighbors to reinforce their waves and engine firing order may reflect that.
When a light or a sound wave strikes an object that is already vibrating at some particular frequency, and if that frequency happens to match the resonant frequency of the object it's hitting; then you'll get what's called resonance.
me: "What is sound?"
In physics, sound is a vibration that propagates as an acoustic wave, through a transmission medium such as a gas, liquid or solid.
'As was mentioned in Lesson 4, musical instruments are set into vibrational motion at their natural frequency when a person hits, strikes, strums, plucks or somehow disturbs the object. Each natural frequency of the object is associated with one of the many standing wave patterns by which that object could vibrate. The natural frequencies of a musical instrument are sometimes referred to as the harmonics of the instrument. An instrument can be forced into vibrating at one of its harmonics (with one of its standing wave patterns) if another interconnected object pushes it with one of those frequencies. This is known as resonance - when one object vibrating at the same natural frequency of a second object forces that second object into vibrational motion.'
= "When one object vibrating at the same natural frequency of a second object"
Resonance for intake systems like TPI is a misnomer, because valves aren't forced to vibrate at the frequency of sound like in an instrument. The valve is isolated mechanically and damped by mass and physical attachment to the engine. So it isn't really resonance at all, we just use that term to imply there is some matching of frequency. Its more like the timing of the sound wave and the intake valves lines up at specific operational frequency with respect to fluid properties (air temp mostly, and some lesser extent density).
I'm not going to keep arguing about terminology with you. If you don't want to believe this is a matter of resonance in a tuned pipe, then call it a water hammer or a dingleball umbrella or a douche canoe or whatever the hell you want. You're the epitome of "a little knowledge is a dangerous thing." The point is that the problem with the TPI is that the runners are too long and therefore interfere with cylinder filling after about 3000rpm.
Originally Posted by Kingtal0n
Maybe I was too general. It comes from 20 years of thinking about this situation. In my conceptualization, the wave travels up the runner into the plenum. Then, I can clearly see the wave is spreading out into the plenum and interfering with other waves. Therefore the coincidence will be constructive or destructive regarding nearby or recently closed cylinders. The wave which reflects back into the tube is then a combination of influences from other runners who's waves have recently arrived into the plenum. Some engines rely on neighbors to reinforce their waves and engine firing order may reflect that.
Your conceptualization is wrong. What you're describing sort of does take place in the collector of an exhaust header. However, what is happening in the intake is contained within each individual runner. You could cut the plenum off the intake and use individual throttle bodies and it would still happen. It would happen if this were a single-cylinder engine with only a single intake valve. It would happen in a pipe with no TB or valve at all. It happens in a bottle when you blow across the top of it.
"The fact it has some frequency is akin to all sound waves: all sound waves have a frequency vibration. But we do not say that all sound waves resonate."
This is roughly the type of language I would use.
While single resonant frequencies are an intrinsic fundamental characteristic of all simple or approximately simple harmonic oscillating systems, the notion of "resonance" generally requires two frequencies, the resonant frequency of the oscillator and then the frequency (or lack thereof in the case of noisy drives) of some drive.
In the case of our favorite TPI question, my take is that the runner length combined with the density of the medium (air) which by extension determines a sort of characteristic stiffness of the medium, dictating the speed at which modulations of the medium density travel through the medium itself, determine the resonant frequency of our idealized system, in this case a pipe full of air. So we have our first frequency, the resonant frequency of our oscillating system. Note that this frequency exists, at least in a sort of metaphysical sense, even in the absence of any actual energy or oscillation in our system.
There is then the frequency of the drive, which in our case I believe is the opening and closing of the valve at the end of our tube. The opening and closing of the valve at the end of the tube drives oscillations in the air density along the length of our tube. The frequency of this drive depends on the frequency of the valve opening and closings, which depends on the cam and engine RPM.
We would say we are driving on resonance or that our system is on resonance when the frequency of the drive is close or matching the resonant frequency of the oscillator. This fundamentally is why I think the notion of resonance requires at least two frequencies or perhaps more generally it requires at least one, and then some drive which has some Fourier transform describing the distribution of power (in our case acoustic energy per unit time or perhaps amplitude of sound pressure) in frequency space.
Where I start to get really confused with TPI is when I try to contend with the fact that in our tube there isn't just some idealized standing wave of time and space periodic air compression and rarerification, but rather I imagine a traveling wave with a group velocity related to the cross section of the runner (I think this is where runner cross section might start to interact with the resonant RPM) as well as the runner length, as well as the cylinder displacement, in effect a function of our required or desired flow rate set at some level by engine RPM.
Just my $0.02 (when will we inflation adjust this phrase lol)
Back to the OP
I do think Yariv that your power peak is occurring a bit low in RPM, and I still think that the peak power number itself of roughly 250 rwhp is a bit low considering the mods done. Which I want to repeat again for those that might be interested and also for you to perhaps confirm that I got the mod list right:
195 CC Blueprint heads
LT1 Cam
Ported GM TPI base and plenum
Ported Arizona Speed Marine long tube TPI runners
52mm throttle body
1 5/8" OBX Long tube headers, and presumably an exhaust system after that
Injectors
Tune
30 thou bored over
Those should be all the main mods contributing to power rights?
This is of interest to me because I had a similar build planned for my L98, with perhaps a different cam and heads, and a TPIS Big Mouth Base, and I was hoping for 300rwhp on the lower side of things with that sort of mod list. Optimistic perhaps lol
I wouldn't say the numbers are low based on what is done, the cam is small. The factory base can't be ported out enough to flow like an Accel or Bigmouth base.
There may be some power left in the tune, of course that is almost always the case.
I wouldn't say the numbers are low based on what is done, the cam is small. The factory base can't be ported out enough to flow like an Accel or Bigmouth base.
There may be some power left in the tune, of course that is almost always the case.
Fair, and perhaps a good example of the importance of a "systems" approach to engine builds.
In the case of our favorite TPI question, my take is that the runner length combined with the density of the medium (air) which by extension determines a sort of characteristic stiffness of the medium, dictating the speed at which modulations of the medium density travel through the medium itself, determine the resonant frequency of our idealized system, in this case a pipe full of air. So we have our first frequency, the resonant frequency of our oscillating system. Note that this frequency exists, at least in a sort of metaphysical sense, even in the absence of any actual energy or oscillation in our system.
There is then the frequency of the drive, which in our case I believe is the opening and closing of the valve at the end of our tube. The opening and closing of the valve at the end of the tube drives oscillations in the air density along the length of our tube. The frequency of this drive depends on the frequency of the valve opening and closings, which depends on the cam and engine RPM.
Yes, I'd just add that the drive is the combination of the valve opening/closing along with the lower pressure inside the chamber that causes the air in the runner to move into the chamber. If there were no pressure differential across the valve, I don't think it would drive any oscillations.
Where I start to get really confused with TPI is when I try to contend with the fact that in our tube there isn't just some idealized standing wave of time and space periodic air compression and rarerification, but rather I imagine a traveling wave with a group velocity related to the cross section of the runner (I think this is where runner cross section might start to interact with the resonant RPM) as well as the runner length...
The runner cross section does affect the resonant RPM. Somewhere a million years ago I found a Helmholtz formula showing that. It's just that the cross section can't be massively increased on a TPI intake because the intake port is part of it, so there's not a lot of change that can really be made. Changing length is way more effective and practical.
