SurfnSun

if you keep the resonator on the Corsa, you can run with LTH's and still have zero drone. Its a masterfully engineered system.

FYI, I can already tell you that plugging one side of the borla will work. Several ZR-1 guys did that with their B&B systems for road trips. I would guess plugging one reflects the sound wave like Corsa cutting the resonance.

Tom400CFI

Dyno charts, please. I think the opposite is true. "Seen it a million times".


You DO realize that is b/c the intake pressure is going up too...right?

Tom400CFI

Are you making this up as you go? It seems like you are.


Speaking of "folly"...did you watch the video that I posted?? It's exhaust 101...but it seems like it might be helpful if you checked it out.

Kingtal0n

A random article I googled up in 10 seconds that has an interesting thing to say,

http://www.superchevy.com/how-to/exhaust/0505phr-exh/


If you install too large of a pipe, whether the system is turbo or NA, the cylinder can suffer dramatically, VE can drop. I've seen it, I've felt it. It is real.


You DO realize that the exhaust gas pressure is rising 2:1 on some systems... right?
30psi on the exhaust and 15psi on the intake... that would be the same as 0psi on the intake and 15psi in the exhaust (like having a N/A engine at WOT with 15psi of exhaust pressure, thats like 3 mufflers or something). And yet, power continues to climb even with all that backpressure.

You also realize if you lift your foot from the gas pedal, backpressure drops and engine output diminishes. If a decrease in exhaust gas pressure always met with an increase in power, you might be able to find a relationship that worked there. But it doesn't. They are completely independent. It is useless to try and say one has anything to do with the other without a proper model.

Kingtal0n

Oh I think I you misunderstood my passage, allow clarification please,


In general the size downpipe is provided for the turbine by the manufacturer. The owner should select a turbine based on matchbot, for example here was mine
http://www.turbos.borgwarner.com/go/H4KASH


This a model of compressor and turbine behavior provided by the manufacturer.
This model will help us select for best performance. It will show us a snapshot of the engine running so we can ensure the compressor is properly sized.


And this is where everyone gets confused with turbo mapping their engines. They see the little middle island and say "oh, its most efficient there, so that is where I want to be". They find that the larger the turbo, the more likely they are to land in the middle.

This is a trend you find all over, LS people do it, 2JZ people do it, everyone is looking at the center and thinking that is where they wanted to be because that is where the adiabatic efficiency is best.

Im trying to find a way to explain this without using so many words next. Basically, if we size a turbo 'perfectly' so that it runs into the center of the map, and stays there most of the time, the turbo is actually "too large" because we never used the right side of the map. Since the right side of the map represents a portion of compressor flow available, it means the compressor is physically able to provide that airflow, which means its size and mass will represent this feature even if we are not using that flow. In other words, it will be more difficult to turn, because it is heaver, so it will "spool slower". Also, because the turbine is sized for max output, it will be far too large. It will have too large of a downpipe on it. part throttle recovery efficiency will be reduced and overall it will perform poorly at any situation besides max or near max output.

For example, I took my map from above and changed the compressor
http://www.turbos.borgwarner.com/go/7NFPYR

Now the map is showing me "running into the center" and stays in the center. It never runs to the right of the center on that engine config.

This is perfect if I am going to use a 2-step, transbrake, and nitrous to spool the turbo from a dead stop. This setup is ideal for drag racing, because we don't need to depend on the engine to spool the turbo, we have all these goodies. Furthermore, it will never need to get good fuel economy or recovery any exhaust gas energy while cruising. The downpipe provided with the turbine (based on it's manufacturer's size) Is perfect for this application.


However, if I was going to put that turbo onto a street car, without nitrous, t-brake, everything that is good about it is now bad.
It is too large overall. The downpipe is too large. The compressor is too large. The shaft and wheels are too large and heavy. It will react poorly and transient response will suck. Sure, it will put out 4-6% cooler air at 15psi of boost (When it finally gets there) than the properly sized turbo; but that will be the only good thing about it.

Again, basically, what happens is the downpipe you "get" with a turbo is the downpipe size required to feed it's max output. The downpipe you are essentially forced to run is what is provided. You can neck it down all you want; the main losses are occuring in the turbine housing which itself is simply too large for what we want to do with it. It is therefore essential to understand the compressor map, at least, and determine if the application suits the turbo. A daily driver will want a compressor which is just about to run off the map at max output. That is why you see the little red dots on my original map going near the edge with all the variables I've setup to simulate my install/swap (notice I have a high exhaust gas pressure simulated for multiple mufflers. Also notice that if boost pressure is raised, the map "widens" slightly and I have more headroom to make more power if I need to.)

SurfnSun

Kingtal0n

Actually I made one small post after an argument between other members in order to provoke thought. They in turn asked me questions to which I politely responded, including you. I don't make more than one small post without being asked any questions because then you would be right, but luckily that wasn't the case.

The question in the above statement was regarding downpipe size, "why don't they use a 3" or smaller". It is necessary to examine the compressor when dealing with the exhaust turbine, the two must "make sense" together. And there are many options to choose from, all manner of exhaust turbine is available, twin scroll tech exist now for OEM style manufacturers.

SurfnSun

Kingtal0n

This is the small post
https://www.corvetteforum.com/forums...post1596347138

I've been defending it ever since, and I stand behind it still. You cant just lop a piece of the exhaust system off wherever you want, and happen to measure less backpressure and have more engine Volumetric efficiency throughout the rev range.

MatthewMiller

That is simply not true. You are 100% wrong about this. So in every road race series in existence and every circle-track series in existence, if the rules don't mandate mufflers and other restrictions, they run an open exhaust (or as close as they can get while still keeping gases out of the cockpit). Every. Single. Time. That includes the tightest road courses where low-rpm and midrange power is vital ("area under the curve," as you put it). Ditto for circle-track racing on ovals with long straights and tight curves, where "area under the [power] curve" is king. I guess they're all idiots, including all the pre-hybrid years of Formula One engineers.

Earlier, I requested that you present data to support this. Bring it or be quiet. You are making things out to be way more complicated than they are. Are you related to this guy on here with the username Penix? Asking for a friend...

Yes, and that word is "bullshit."

Holy confusion, Batman! I don't have enough time to unravel all of this silliness. It's another example of you trying to make things more complicated than they are. There is no pressure differential between the air inlet and exhaust outlet of an n/a engine. You said so yourself. The exhaust flow on an n/a engine is caused a little bit by the positive displacement push of the piston, but mostly because the expansion of combustion creates localized pressure differentials across the valves, and the exhaust flows past the exhaust valves once they open. That combustion pressure then continues to create exhaust flow until it reaches the outlet, at which point it is back to atmospheric. The greater the pressure differential from the exhaust valve to the atmosphere, the better the VE.

But guess what? After all of that over-complication, the problem with your restriction myth is that restrictions actually create localized backpressure. IOW, by adding a needless restriction in the exhaust system, you've reduced the pressure differential from the exhaust valve to downstream. And you have thereby reduced the VE of the engine! And there is never a time when that is a good thing. Ever. None. Not for peak power at WOT, not for midrange power at WOT, not for partial-power cruising, not for idle. Never.

If you substitute the word "exhaust" for "turbine," and "valve" for "turbine outlet," he'd still be correct and it would be exactly the same thing I just wrote above! Your own expert just proved you wrong.

You can't be this dumb. When you measure exhaust gas pressure, you are implicitly comparing it to atmospheric pressure. You ARE comparing pressures! Here's a fun and relevant quiz: what's the difference between PSIG and PSIA?

I'm about to go Red Foreman on you. I wrote about exactly this in Post #130, dumbass. "Primary pipe diameter" != "restrictions in the post-collector exhaust." This entire thread is about the post-collector exhaust system, not about header primaries! And notice the part I kindly highlighted in red for you? In the header primaries, what enhances the scavenging effect? Is it backpressure? No. Of course not. That would defy a basic law of physics: you cannot increase gas flow by reducing the pressure differential from beginning to end (e.g., by reducing the pressure differential across the exhaust valve). No, the characteristic that enhances scavenging is velocity (see, at this point I'm just giving you the answers)!

And how does gas velocity in a resonant system like a header primary tube enhance scavenging? It does so by creating a phase of lower (or even negative) pressure at the exhaust valve. IOW, it increases the pressure differential by lowering backpressure for half the valve cycle (one of the two phases of the pressure cycle). The goal for sizing the primary tube is to find the diameter that optimizes that negative-pressure phase against the opposite, high-pressure phase; for best power within your desired operating rpm range.

Now I'm gonna blow your mind: if there were no exhaust valve opening and closing, and therefore no resonance or high/low pressure phases in the primary tube (like measuring flow on a flow bench), would there be any benefit to choosing a smaller primary tube diameter? In fact, would there be any benefit (to power) for having a primary tube at all? No, there would not. If the flow rate were constant and steady (no pulses), then the biggest possible opening would always allow the highest pressure differential, and therefore it would always allow the fastest flow and most scavenging (i.e., the best VE). What you have to get through your head is that after the collectors, the exhaust system stops operating on resonant principals and starts working as constant-opening system. There are still pulses in the gas flow, of course. But once the gases have merged in the collector of any multi-cylinder engine, you can no longer tune those pulses to affect the pressure differential across the exhaust valve. The only thing you can do to increase flow after the collectors is to reduce backpressure, thereby increasing the pressure differential from collector to exhaust outlet, thereby improving VE.

This is super-easy to test empirically. Get two identical balloons. Zip tie one balloon's outlet to a tube that is 1mm in diameter. Zip tie the other balloon's outlet to a tube that is 10mm in diameter. It doesn't matter how long the tubes are, as long as they are identical in length. Inflate the balloons to equal pressures/volumes, and then onblock the ends of each outlet tube at the same time. Which balloon will empty (scavenge) the quickest (i.e., which exhaust tube allows the best VE)? Now experiment with any number of different tube diameters as you care to try. You will never, ever, find that a smaller-diameter tube allows the balloon to empty faster than a larger-diameter tube. After the collects, any exhaust system is exactly the same as this.

Please stop babbling about turbos. You are confusing yourself. As Tom said, even turbocharged engines respond positively to decreases in exhaust backpressure.

Instead, provide the test data that shows a more restrictive muffler or a variable valve placed in the exhaust improves power or "area under the curve" or VE anything else. Also, answer my questions about PSIG vs PSIA. Do those things before you post anything else. Otherwise, just don't post.

Tom400CFI

If you install too large a pipe where? Did you read the whole article? On a stock car, you could put dual 6" pipes after the cat and it ain't going to make one wit of difference. I.e. you ain't gonna lose any VE.




Oh! I get it! Power is going up b/c of the BACK PRESSURE! Yeah...right. Now I need to go stuff a banana in my tail pipe so I can increase my VE.



More

IDK WTF you're talking about here. I don't think you do, either.

MatthewMiller

Oh man, I forgot about this.
Quoted for awesomeness. From this we get the following points:

• Backpressure and power are completely independent from one another - there is no relationship between them at all. Nevermind that his whole argument is that there is an inverse relationship between them, such that increasing backpressure increases VE/power at certain loads/rpms.
• If you close the throttle on an engine, backpressure drops and power is reduced; thereby proving that reducing backpressure doesn't improve VE or power.
• There is no model to empirically demonstrate any relationship between backpressure and VE/power.

Well, gee. Backpressure and VE/power are very much related, as his own quoted experts wrote.
Of course if you close the throttle the backpressure drops. You've changed the load and (most likely) the rpm. But that's not a test of exhaust restriction - it's a test of variable intake restriction (namely, the throttle blade)! Seriously, do you read what you write before you post it?
Finally, of course there's a simple and proper model for testing the effects of exhaust backpressure. Put an engine with headers, collectors, and a downstream exhaust system with variable restriction (could be a valve/blade, could be a Supertrapp muffler with different numbers of disks, whatever) on a dyno. Run said engine at a constant rpm and load - you can pick any rpm and load you want, as long as you keep it constant. Vary the exhaust restriction and measure the power with each level of restriction. If you want, you can re-run the test at a number of different loads and speeds, so you can get a complete picture of how restriction changes the power output.

I can save you all the trouble of running this test, though. You'll find that at any load or rpm, there will never be a result where increased backpressure causes an increase in power. Never. And you'll find that the higher in load and/or rpm you run the test, the bigger the decreases in power will be as restriction/backpressure increases.

ddahlgren

Ah the unspoken speed secret a potato in the tail pipe.. LOL Some of the posts need to start with 'Once upon a time in a land far far away where physics as we know it ceases to work'...

Kingtal0n

Those are not my words. If you gonna pretend to quote someone at least use real quotes.

1. I never said there was no relationship. I said the relationship does not work the way its being presented, i.e. a lack of backpressure does not indicate a properly filling cylinder.

2. I never said backpressure increases anything. Please re-read what I have written for it is entirely correct and does not mention that backpressure is desirable nor wanted, anywhere.

3. There are models that exist; this is how engine manifolds are designed. They compare myriad details, however, not just backpressure by itself, the way it is being suggested in this thread. You can't get useful data just with backpressure alone. Just because it goes does doesn't mean the engine is gaining or losing power.



next time try actually quoting me instead of trying to paraphrase what you imagined in ur head

So this would have been a great question to ask instead of the way you wrote it. The idea of a "throttle body" is negligible. In other words, it may or may not exist on an engine at WOT. If it does 'exist' that means it is represented as a restriction. To put it a third way, the throttle body is only 'present' when it is 'not fully open' because pressure behind it drops. For our purposes, we have to examine both the closing positions, and fully open 'not present' position of the throttle body, because the engine does not always operate at WOT in our vehicles. First key point here is to realize that there is little difference between a restrictive throttle body on an engine at WOT, and a restrictive air filter. They both look "the same" to the intake manifold, i.e. a lower pressure than atmospheric is present just after the throttle body, less air density per unit volume is available in the intake manifold. When the intake valve opens, however, the change in density is not reflected in the actual VE of the engine. It only changed our "theoretical VE", i.e. if the pressure was double we could say 200% theoretical VE. But because an engine cylinder can only become 100% Full and not a single 0.00001% fuller, in reality our cap is still 100%. So we have to distinguish between theoretical VE and actual VE when we discuss pressure/density relationships in the air pathways to avoid confusion. Another possibly confusing thing is combustion gasses left in the cylinder from previous events. Those portions will count towards actual VE because they physically fill the cylinder, and yet they would subtract from theorectical VE the same way reduced pressure would because now less actual unburnt air is available in the cylinder.

So to be clear, if I Put an engine in a container and accurately measure both intake and exhaust manifold pressures and find them to be equal, or unequal, I could still have a theorectical VE ranging from 0% to 100%. There is no way that backpressure alone is going to give me that information, I would need to look at engine output to confirm any changes to output. A maf sensor which measures mass/time could give me an idea; but not all of the air passing the maf sensor is burnt in the combustion chamber, and not all chambers react optimally to adjusting conditions. In other words, I could be filling the cylinder with more theoretical VE and STILL have a loss in power because of something to do with the fuel or compression ratio at those theoretical VE %'s.

The point of all of this is to realize that backpressure doesn't really mean anything by itself. You can't measure it to determine cylinder performance (theoretical VE) or engine performance directly. And also that intake pressure needs to be examined when measuring backpressure (whether turbo or NA) to form even just an idea of what the engine is really doing.



Many years ago it was found that increased exhaust gas velocity even in untuned tubes induced scavenging gains in the cylinder, clearing the cylinder more effectivelly than the piston alone, especially in non-acoustically tuned exhaust systems such as those found on most OEM utility/truck type vehicles, whether 4 or 8 cylinders. The auto manufacturer sizes the exhaust according to this exact theory; that the "right" exhaust tube is one which maximizes the "free cylinder scavenging available" even with tight, terrible exhaust manifolds they are still able to achieve a high theorectical VE through proper camshaft timing in RPM ranges where the vehicle is most frequently operated (named, idle to 4500rpm for trucks). It is these configurations which stand to lose the most area under the curve when those exhaust systems are removed. There are several books available on the subject. Several tests concluded that a properly sized exhaust tube could pull something like 10 times harder on the intake valve than the descending piston.



You just need to expand your terminology some, or word use. I never said increasing backpressure increases power. I wouldn't say it because it isn't true, so I think you need to re-read and ask or quote me exactly where you are getting confused. I will happily clarify.

GREGGPENN

Quote:

Originally Posted by Kingtal0n

I never said increasing backpressure increases power. I wouldn't say it because it isn't true, so I think you need to re-read and ask or quote me exactly where you are getting confused. I will happily clarify.

ANYONE reading what you initially wrote....as you stumbled into this thread with Kramer-like finesse....

Quote:

Originally Posted by Kingtal0n

If yall are tryna measure what portion of exhaust system pressure differentials needs adjustment in real time you can't do that by looking at backpressure data. Instead, you measure rwhp on a dyno, then make changes, then another pass. If you have a cutout you can open it 1/8" at a time, make a pass each increment, and find the peak performance. The ideal curve would be one where the cutout is mostly shut at the start, then opens gradually to compensate for exhaust gas volume of higher output while maintaining a similar exhaust gas velocity throughout.

sheesh

would conclude that you were trying to make some correlation between backpressure and power....at partial throttle opening. Your obvious guidance (above) is to increase "backpressure" (partially close a cut-out) to increase gas velocity and therefore power....in the course of [electronically] tuning a cutout.

Because we ALL know people with cutouts synch/open them in conjunction with throttle blades! So you're rolling down the road opening your cutouts in a new version of olympic synchronized gas-pedal/cutout-****? That's a new sport!

I'll anxiously await you to engage us about what you really meant and how it apparenty related to my suggestion to use a cutout/muffler combo?

Don't feel afraid to explain why "sheesh" was cleverly leveraged in a captivating salutation in order to convey your superior intellect?

MatthewMiller

Ahem:
"If a decrease in exhaust gas pressure always met with an increase in power, you might be able to find a relationship that worked there. But it doesn't. They are completely independent."

You're joking, right? Because you most certainly did say that certain modes of operation, too little backpressure decreases VE and power. Ergo, there are modes wherein backpressure increases VE and power as compared to less or no backpressure. Except, of course, that you're wrong about that.
No, you're completely ignorant of how the scientific process works To test a hypothesis, you only test one variable at a time. You don't test "a myriad" of variables. The model that exists is exactly what I wrote. If you don't understand that, then you're too dumb to participate in this discussion.

Speaking of which, I told you not to post here again until you can bring us the data to prove your assertion that backpressure is required for best VE. I also told you to demonstrate the ability to explain the difference between PSIG and PSIA. Don't type here again until you've done those things.

Tom400CFI

Matt....I appreciate you fighting the good fight. You're saying, what I'm thinking...but with better articulation. IDK if it will help Tal0n or not...but you're certainly providing good info...as usual.





^Totally.

Kingtal0n

Nay, I never said power. When you say power, you mean that one single peak at the top end of the graph. It has no context for us at any other RPM (which is what we care about, every other rpm leading up to the peak if we can't hold the peak like a race car does) and especially "at part throttle opening" because as I have previously delivered... there is no such thing. I.e. there is no such thing as a perfect throttle body or perfect air filter or perfect intake tube... all of them will act as a "part throttle opening" thus the engine is always at part throttle.

Somehow you guys started thinking that just because the throttle blade was closed 1% or 0.01% suddenly magic happens and exhaust gas pressure rules no longer apply and we should ignore those situations. lol


Its called an electric cut-out. And yes I adjust it based on performance needs. With a half-open cutout there is certainly an improvement to torque from idle to around 4000rpm on my previous vehicle, which was turbo. It would remove around half of the turbo lag when stabbing the pedal from a highway cruise as well when partially closed.


Ah the sheesh. I could see that this was "one of those threads". If you want to argue, its different than learning.

Kingtal0n

No, you're completely ignorant of how the scientific process works To test a hypothesis, you only test one variable at a time. You don't test "a myriad" of variables. The model that exists is exactly what I wrote. If you don't understand that, then you're too dumb to participate in this discussion.

Speaking of which, I told you not to post here again until you can bring us the data to prove your assertion that backpressure is required for best VE. I also told you to demonstrate the ability to explain the difference between PSIG and PSIA. Don't type here again until you've done those things.[/QUOTE]


we aren't testing anything. Nobody here has the equipment the manufacturer has nor the number of employees.
Exhaust gas pressure by itself is meaningless; It can be 0psi or 15psi or 30psi and the engine could run absolutely fine or like total trash. You can't tell by the pressure alone, just like the pressure in the intake manifold by itself is useless. 15psi on one setup is 200% VE where on another setup it is 130%. It depends on too many other factors to be useful that way.

Another way to see it is, if you can prove to yourself that occasionally a decrease in backpressure is met with a decrease in engine output (torque), then how can you possible correlate a decrease in exhaust gas pressure with an increase in output (torque)? Just because you feel like it? It doesn't work that way.

Kingtal0n

Nowhere in any of my posting does it say backpressure is desirable or wanted;
I completely agree with this:


Next the same post on this very forum also contains these details which is what I was presenting here, more or less,

https://www.corvetteforum.com/forums...ml#post1703136

For: "This is the primary paradox of exhaust flow dynamics and the solution is usually a design compromise that produces an acceptable amount of throttle response, torque and horsepower across the entire powerband. "

I suggest using a cut-out to this end.