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LandSpeed-DSM said:

It's not a theory, it's not an opinion, it's not about "drag only"

It's a fundamental principle of how turbomachinery works. Pressure differential

The biggest you can get your delta P, the faster you can accelerate that wheel and the more shaft torque you can produce. Period

End of discussion.

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Thank you for actually applying scientific principles in an argument. Very refreshing indeed.

Human beings default to their "senses" when they do not have a better explanation (lack of knowledge). Unfortunately, it has been proven time and time again that human senses are very misleading and cannot be relied upon to establish facts. This is why in science, we test time and time again with equipment and processes that do as they're told, completely objective. This is done to keep the human being out of the loop when collecting data.

It becomes scary when one human spreads misinformation based on their senses, gets buy in from other humans and somehow this is good enough to be perceived as fact.

+ 1 on the biggest/ shortest pipe you can find.

I still think if OP is only getting 10 lb/min out of a 16g there is a serious problem with his setup or a massive boost leak.

LandSpeed-DSM said:

Just for fun, because I know net to none of you measure drive pressureck.

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I've been monitoring driver ratios on a modified 1st gen zt-2 since 2003. In that time I've compared every exhaust side configuration you could think of with 16 and 20g compressors. 06 and 05 variants in the differeng housings. I had a few different exhaust system setups as well just in the natural progression of mods. Like moving from a ported 02 housing to tubular, going to external waste gate, etc. I have seen the whole range of fuc-ed up drive pressures that the mhi wheels and housings produced. Ie also sseen some very good ratios on Mazda race cars I've built. Knowing what I know from first hand experience, you can't see the forest for the trees. You listed quite few benefits of having good ratios. And a few readers may think your the smartest guy on the forums because you spend more time with engineering articles than the fairer sex. But at the end of the day your 16g powered cars are all going to make the similar power at the same manifold pressure. And that is what the owner of a car with a 16g tryinv to decidd on an exhaust syztem cares about. Its just not that important on that car and to the owners. so all the data in the world is useless when no one gives a shit. Now to people likd you,who are building a car so signifi ant and speciL that it must be referenced in everg thread, the length and material of the exhaust hanger matters. Ohh wait you don't have exhaust hangers. You have a for real race car!

If you say so bud

I've never had reason to take you serious in the past and looks like I won't have to start now.

Its fine I have trouble taking you serious too. Let's see a 10,000 rpm log. 67mm turbo,31psi, 10 grand.... I bet your making more than the 380 you used to have. Have you eclipsed 200 wheel torque yet?

OTE="LandSpeed-DSM, post: 153441157, member: 133780"]If you say so bud

I've never had reason to take you serious in the past and looks like I won't have to start now.[/QUOTE]

I

This thread really turned into a cluster f*k of sorts. I respect the amount of information that has been posted here. I learned a lot about drive pressures and things that I've never taken into consideration before. I know for a fact that less back pressure is better and it was from a butt dyno experience. When I had my stock exhaust I wanted to remove the catalytic converter because I thought it would sound better. I ended up hacking my exhaust off at the down pipe. For one reason or another I didn't finish the job that night and was forced to drive the car the following day, and the difference in turbo response is staggering. The 14b was hitting full boost in the low 2000 rpm range. Instead of 2800 or so. The less effort it takes to get the exhaust out, the more efficient you'll be. That's just my experience, and keep in mind that I had less than 12 inches of exhaust pipe on the car.. But I think it reiterates landspeed and others stance that less restriction is always better.
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I think one person in the thread claims that smaller exhaust will outperform larger exbaust. Butback when running a garret on a DSM was a bug deal and everyone had 550cc injectors and a 16g or 20g, cars were still consistently making 350hp on those turbos through 2.5 inch exhausts. Some press bent even. And doing this with abacas for engine management. So I don't understand why land speed has to come in here like every other thread he posts to with a novel about his car and why its the best way. His car has a big frame, divided turbo setup and a fart cannon sticking out of his hood. It has nothing to do with a guy who was to have fun hitting g his torque peak between stop lights with his 16g and 2.5 inch exhaust. His car is irrelevant. And sure his advice would be welcome if it were any good. But this guy has an aftermarket exhaust in place and has a million other things he can i improve to get big gains for the money. So why make it sound like his exhaust us choking his car when its not. Who in their right mind advises someone to run no exhaust on their 300hp street car? The same guy who argued how front drive is superior of course! Haha

Seamus said:

I think one person in the thread claims that smaller exhaust will outperform larger exbaust. Butback when running a garret on a DSM was a bug deal and everyone had 550cc injectors and a 16g or 20g, cars were still consistently making 350hp on those turbos through 2.5 inch exhausts. Some press bent even. And doing this with abacas for engine management. So I don't understand why land speed has to come in here like every other thread he posts to with a novel about his car and why its the best way. His car has a big frame, divided turbo setup and a fart cannon sticking out of his hood. It has nothing to do with a guy who was to have fun hitting g his torque peak between stop lights with his 16g and 2.5 inch exhaust. His car is irrelevant. And sure his advice would be welcome if it were any good. But this guy has an aftermarket exhaust in place and has a million other things he can i improve to get big gains for the money. So why make it sound like his exhaust us choking his car when its not. Who in their right mind advises someone to run no exhaust on their 300hp street car? The same guy who argued how front drive is superior of course! Haha

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I think you really misunderstand the points landspeed, myself, and others have made in this thread. The whole issue was the notion that a turbo will make more power with backpressure than without backpressure, which is 100% incorrect, regardless of setup. This was proven by basic laws of thermodynamics, turbo design practices, and even experience from individuals from some of the most reputable companies. If you really still disagree after all of this, then there is no hope for you. Go ahead and keep thinking backpressure is good for turbos, but please dont spread the misinformation on this forum.

I touched on that the loss of low end power was probably related to the exhaust velocity at 0 boost conditions. So yes, a smaller exhaust may help this turbo in the low end, but that doesnt come without a price. The price of running a small exhaust for low end power is you lose mid/high end power. How much can only be shown on a dyno.

Landspeed uses math to prove his points. I understand math, so I dont have any issues. For the most part, he has been extremely helpful for some of the questions I have had where no one else could answer them. People who dont understand math will always have issues. The fact that you have to attack him to debate just means you lose.

For the record, I didn't bring up my cars.. go back to page 1, post 16.

But since youkeep bringing it up, he's some food for thought next time you think you're being clever it made ~410whp at 15psi on short pulls just to stretch her legs for the first time on the new drivetrain, cams and turbo.

In December, installed the MBC and she made 597whp/384wtq @ 25.x psi at 8500rpm redline on a Mustang dyno with the base tune. Ran into ECU issues and put the car away for the winter.

I've gradually pushed the tune since we got full E85 again here. 11.8-12.0:1 AFR, 9250rpm and 30-31psi.

At 25psi this turbo was making ~24.5whp/psi boost, and now I'm sitting in a more efficient part of the map. I've also logged a few 0.63x-0.65x sec 70-90mph pulls.. you get the picture.

As far as FWD vs AWD comments of mine, I have owned AWD, RWD and FWD. I currently own an AWD and two FWDs. The closest you'll find me touting "FWD superiority" is going to be directly related to my motorsport of choice and specifically my class within it.

It's really bizarre how you tend to bring up my car, making statements and asking me questions about it ... then complain about how it keeps coming into the discussion.

My original involvement in this thread was solely because of the same tired "common sense knowledge" on exhaust systems being thrown out. Then, as athlete3344 pointed out, the whole conversation had changed to address this misconception now being applied to turbos.

Where there's some (incidental) half-truth to what you hear waiting in line at autozone about "NA exhaust needing backpressure" it's completely ass-backwards to how turbomachinery operates.

There's no exceptions there either.

Haha gone a few days and whew! I never said my car made more power by adding the exhaust restriction, just that it was MUCH funner to drive, but I guess that's just flat out impossible, I just "had other things wrong with my setup", and somehow tossing a muffler on fixed them .

94awdcoupe has a long history on this forum, testing and sharing results long before I showed up, and I've been here and have tried lots of different setups long before Dr. Land-Speed and his google phd got here. Of course we know about exhaust velocity vs backpressure etc. We're not saying a smaller exhaust makes more power, only trying to give GOOD advice as to what upgrade path to take. I guess I made the mistake in forgetting that if you want a fun streetcar it's supposed to be built exactly like a salt flats car. I'll leave now and won't bother you guys anymore since I know nothing.

If you understood those relationships, this thread would have like 3 posts in it.

Further you would likely have developed the reading comprehension to grab the parts where it would decrease boost threshold (spool) and transient response (lag)

Jerry's "testing" is thoroughly flawed, primarily because he doesn't know or care for the scientific method.. which is a set procedure by the way. Here and on the Link forums he has a nasty habit of jumping the gun on opinions.

Always get a laugh out of folks who try to trivialize education when they can't cop the content. I also operate in the field for the largest and oldest hard infrastructure company on the planet.. They pay me for these types of considerations.

Day in and day out, applying these and other physical principles. On paper, then get my hands dirty.

How do you reconcile your argument against thermodynamics, especially when it's been broken down in crayon for you and demonstrated with s much larger turbo? Cognitive Dissonance.. it's a motherf*cker.

There's no opinions, controversy or participation trophies on this. Like arguing with a calculator.

It's not you vs. me, or Jay @ Garrett Turbo.. it's you vs. established fields of post-doctorate level research on heat transfer and turbomachinery that powers everything from the grid feeding the technology your posting on to the dinky compressor in your DSM.

This isn't my two cents or personal hypothesis (what you probably mistake for a "theory").. it's derived from official Theories. Meaning repeatedly tested and survived scrutiny and the real world.

If you're genuinely convinced by your BS go find an MS or PhD candidate in need of a dissertation. They need something new and unique for their field in order to be awarded.. and you'd be recognized too.

But we both know you're full of BS and arguing for the sake of argument.

So, max HP, thermodynamics, and dong whipping aside, I searched for the word "creep" being mentioned in line with the OP's original intent "assumed". I didn't turn anything up.

So, we're ignoring the possible introduction of a problem (assuming, again, no upgraded flapper or external dump) for the sake of confirming testicular diameter.

Tell me why?

FWIW, in the digression, I do agree with LandSpeed.

LandoAWD said:

So, max HP, thermodynamics, and dong whipping aside, I searched for the word "creep" being mentioned in line with the OP's original intent "assumed". I didn't turn anything up.

So, we're ignoring the possible introduction of a problem (assuming, again, no upgraded flapper or external dump) for the sake of confirming testicular diameter.

Tell me why?

FWIW, in the digression, I do agree with LandSpeed.

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That would be avoided by that O2 dump I mentioned.. as well as porting the internal gate like you should have learned in researching new exhaust systems in the first place.

Further, if you have the appropriate supporting mods to begin with that potential for "creep" goes from a bug to a feature.

Threads like this are a god send when you are waiting in-line somewhere or just plain bored.

Also, i don't understand why it's so important to try and change someone's mind. Just share your experiences and/or opinions and leave it at that.

With that said, i'm all for math and science but about 99% of scientific "theories" don't hold up in the real world because of other factors. Just because it's in the science article you read on Google doesn't mean that's how it's going to be in real life.

To the OP, 2.5" exhaust is plenty for 350-400 hp on a max effort 16g. You might benefit some with a bigger exhaust but it will certainly not prevent you from making power.

All engineers I know use google, after all, its an extremely useful tool. For whatever reason, my points just arent being understood. Maybe video would be more useful?

https://www.khanacademy.org/science/physics/thermodynamics

If youre bored, educate yourself. These lessons can be found in any decent engineering department in the nation, along with the required books to boot.

Wow, so much misinformation in here. In a na car, the exhaust can't be to large or you lose velocity, which helps scavenging. Back pressure is never good. In a turbo car, the larger the exhaust, the better. The best way to make low rpm torque in a turbo car is not exhaust gas scavenging, but quicker turbo spool. The less restriction after the turbo, the quicker it spools, and the less exhaust manifold pressure you need per psi of intake boost.
Any non believers, just look at what an exhaust cutout on a full exhaust does for a turbo car dyno.

YZFR1 said:

Threads like this are a god send when you are waiting in-line somewhere or just plain bored.

Also, i don't understand why it's so important to try and change someone's mind. Just share your experiences and/or opinions and leave it at that.

With that said, i'm all for math and science but about 99% of scientific "theories" don't hold up in the real world because of other factors. Just because it's in the science article you read on Google doesn't mean that's how it's going to be in real life.

To the OP, 2.5" exhaust is plenty for 350-400 hp on a max effort 16g. You might benefit some with a bigger exhaust but it will certainly not prevent you from making power.

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Oh look, someone else has managed to confuse hypothesis with a scientific Theory. Theories tell us shy and how through Laws that describe specific mechanisms.

This is a Theory in the same way that Gravity and Evolution are Theories. The nice thing about science is that it doesn't care about your beliefs and biases.

donniekak said:

The best way to make low rpm torque in a turbo car is not exhaust gas scavenging, but quicker turbo spool. The less restriction after the turbo, the quicker it spools, and the less exhaust manifold pressure you need per psi of intake boost.
Any non believers, just look at what an exhaust cutout on a full exhaust does for a turbo car dyno.

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I 100% agree with this. That's essentially what I was alluding to in my post earlier on. Unfortunately I think this thread has degraded into an argument over what *can* be done versus what is optimal. If the dude wants 2.5" exhaust on his car then let him put it on there.

Athlete,

I get their point and not being afool I agree with them. But I don't see the point in going nuts with physics over a guy who just wants to burn up trannys around town with a 16g and have fun. I'm not an engineer. I'm a salesman. I see the big picture and have a practical way of thinking. And it bugs me how land speed has to bring up his car in every thread and show his one log that really shows nothing but his timing and boost pressure and sometimes air flow.

Any ways some food for thought. For a long time they have been thought of as sort of inferior and definatly old scbool, but the most optimal back pressure ratio I personally have ever logged was a tuebonetics stage 5 wheel hooked up to a t66 compressor which was one of the silliest wheels I've ever seen. I've only used mhi turbos for the most part ob my dsm's. And in my opinion the 16 and 20g turbos defy all logic in what they can do. But I've used a ton off different turbochargers on other cars.rotary engines are fragile and a long time ago I decided to look beyond the tuning into things like back pressure and studying everything Mazda ever thought, knew, or wrote about trailing ignition. So I have been hooking up my emap on everything ever since.

Again, you injected my car into this discussion. It's on page one.

Then you brought it up again, and asked how much torque I was making now in that same post about how I 'won't stop bringing it up" ...

Do you have Alzheimers?

Also to recap: the discussion went from the OPs 16G to exhaust systems in general when folks kept banging the "backpressure is gud!I hurr durr" drum and making statements like "X inch pipe is good for 'Y' horsepower"

You guys are really twisting around what I am saying. And I am being touted the idiot by wasting my time trying to convince you. and its a shame because I AM really just trying to teach you something. I am 100% certain what I am saying is true.

On my own personal car which was an 89 mirage turbo it was not easy making exhausts for the car. the car has a solid rear cross bar so the rear pipe has to be snaked up and around and through this frame work. getting the 3 inch on that car took about 12 hours. no one makes exhausts for those cars. After the swap to the 3.0 inch exhaust. I was stinking disappointed in the loss of torque I actually made a third exhaust for the car with 2.75 inch tubing. I was hoping to get half the torque loss back but it didnt happen. It was closer to the 3.0 performance than it was a 50/50 split between the 2.5 vs 3.0.

To anyone who needs a resume for respect I have been playing with turbocharged cars for over 30 years. I have zero notoriety on forums because i absolutely hate going to the track. I do not build record setting fast cars which is what gets the attention and respect. I do get local respect because my cars are well known to be stupid fast, very effective daily driven street racers. I was in the 97 percentile in nation wide tests for math while going to school. my major was mechanical engineering at the university of florida. I am the farthest thing from stupid when it comes to building cars.

When I built the yellow car which is an awd platform shoe horned into an 94 mirage coupe. The car was built 99% by me. only the roll bar and original aem tune was not done by me. The car went through a development stage to make it what it is. Four different turbos, three different cams, four different intake manifolds, four different driveshafts, four different twin plate clutches. ETC Etc etc. I know I have about 60k into the car from all the part swapping that went on. in the end the car has the most incredible power band you cant imagine. its just ridiculous how sweet the end result is. I will not go into great length but cams that were supposed to work did not, intake manifolds that were supposed to work did not, turbos that were supposed to work did not. some people call me eccentric but those who know me will flat tell you if there is a part on my car its because the part was tested by me and works. not because there was an accepted internet norm that the part should work.

If go on the internet and search for 2.5 vs 3.0 downpipe you will find every forum discussing this. and every forum has members who are aware that a 2.5 pipe produces more drivability torque. here is a good quote from vw forums:

"AWE Tuning 2.0T Exhaust Dyno Tests
Below are comparision dyno tests as performed on our Mustang MD-500-SE AWD dyno.

All tests were performed on the same car (an 06 GTI 6speed), with controlled ambient conditions. Each test is average of 3 runs performed.

Cat Back Exhaust Testing

(Below) Our first prototype for the A3/GTI/GLI was a 3" diameter cat back system. Careful before and after dyno testing showed that for this car, bigger was definitely not better. The air mass found inside the 3" tubing proved to be a restriction to the engine until the higher rpm region, and even at that point gains were minimal. Our reputation is to bring only proven products to market, and a 3" system is definitely not the wise choice for power on this car. Design was rejected.

After further dyno testing, we found that a 2.50" diameter gave the best overall balance of torque and horsepower gains. Peak gain were 3.1whp and 0.1wtq.

In the graphed gains sheet below you'll find the measured differences between baseline and test in dyno sheet of AWE Tuning 2.50" Cat Back Dyno Test vs stock exhaust. The AWE Tuning 2.50" exhaust produces a maximum increase of 4 wheel hp at 5300 rpms and 28 wheel torque at 2400 rpms vs. the stock exhaust. Overall, gains are seen over practically the entire powerband.


3 inch Cat Back Dyno Sheet 2.5 inch Cat Back Dyno Sheet 2.5 inch Graphed Gains

Turbo Back Exhaust Testing

(Below) In the interest of accurate data, we conducted careful tests with our downpipe design. As we saw with our cat back testing, a 3" inch design is absolutely too large for this vehicle. We even tested with an aggressive GIAC X-Chip installed in the vehicle, to simulate the kind of power levels that most people will choose for their vehicle. Even with the extra power of the performance chip, 3" diameter tubing was too much air mass for the engine to move, resulting in a clear disadvantage compared to the 2.50" turbo back design.

Intake temps were closely monitored for the test. It is extremely difficult to obtain exactly the same test conditions run after run, and we found that the 3" tests were done with a slightly cooler intake air temp. Even with this advantage, the 3" design could not make as much power at the 2.50". Identical cell count cats were used for both tests, and the same chip file was in the vehicle for both tests. The tests were done on the same day and on the same car, just as they were with the cat back tests above.

2.50" diameter gives the best overall balance of torque and horsepower gains. Peak gains for the 2.50" system were ~20 crank hp and 14 ftlbs crank torque over the stock turbo back exhaust, while the 3" system could only muster ~9 crank hp and 1.5 ftlbs crank torque over the stock turbo back exhaust. There was no debate on what diameter worked better at this power level.



2.5 vs 3 inch Turbo Back Dyno Sheet 2.5 vs 3 inch Turbo Back Graphed Differences


2.5 vs stock Turbo Back Dyno Sheet 2.5 vs stock Turbo Back Graphed Differences "

Full exhaust vs a cutout right at the down pipe. More power everywhere. In a turbo car, sometimes a smaller exhaust makes the car feel torquier, because it smoothes out boost onset, and spool. A large exhaust makes more torque, but can feel softer down low because the boost onset is much more violent, and you get a huge change in torque, very fast.

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"I am 100% certain what I am saying is true."

Which is precisely the problem.

LS: you have fought the good fight bro. There's no schooling Luddites.
2+2=5, god damnit!!!!! and i wont hear anything to the contrary!