[David1]

I have looked at the act more and been through the courts with it. And lost and one once. Modify the vehicle from OEM specification and you loose especially on emission parts. That is what we are talking about here, MODIFICATION and ILLEGAL ones at that. My brother manages a Chevy store and GM denies coverage all the time once the ECU is downloaded to HQ. Tuned ECU....no coverage anymore on the entire drivetrain. All manufactures do it and its legal.

[PrematureApex]

Originally Posted by David1

I have looked at the act more and been through the courts with it. And lost and one once. Modify the vehicle from OEM specification and you loose especially on emission parts. That is what we are talking about here, MODIFICATION and ILLEGAL ones at that. My brother manages a Chevy store and GM denies coverage all the time once the ECU is downloaded to HQ. Tuned ECU....no coverage anymore on the entire drivetrain. All manufactures do it and its legal.

Once again, no one is stating they can't deny coverage, as you just stated. There's a difference between that, and a stating generically that your warranty is voided, which it is not.

The law is the law. You can call it semantics, but again, the warranty is not legally voided, it still has to be denied on a claim by claim basis. A dealer can have a policy that all drivetrain components will not be covered if you've added x and y mods. While potentially semantics, your drivetrain warranty is not voided, but claims will be denied.

You could easily have a case where a defective drivetrain part, which has failed on many other stock cars, fails on a modified car, and that part would likely still be covered if you fought about it.

The links explaining the law posted about are quite clear. Legally speaking, the warranty is 100% not voided. But claims have the right to be denied in view of some showing of causation.

[3tekcorps]

Originally Posted by PrematureApex

Once again, no one is stating they can't deny coverage, as you just stated. There's a difference between that, and a stating generically that your warranty is voided, which it is not.

The law is the law. You can call it semantics, but again, the warranty is not legally voided, it still has to be denied on a claim by claim basis. A dealer can have a policy that all drivetrain components will not be covered if you've added x and y mods. While potentially semantics, your drivetrain warranty is not voided, but claims will be denied.

You could easily have a case where a defective drivetrain part, which has failed on many other stock cars, fails on a modified car, and that part would likely still be covered if you fought about it.

The links explaining the law posted about are quite clear. Legally speaking, the warranty is 100% not voided. But claims have the right to be denied in view of some showing of causation.

I think you're just confusing people with your convoluted legal interpretations and semantics.

Q If Consumer Bob does a tune and down-pipe does this jeopardize the drive train warranty offered by BMW? Lets assume we don't have a buddy in the service department or can expect any favors from the dealer.

YES / NO

[David1]

Originally Posted by 3tekcorps

I think you're just confusing people with your convoluted legal interpretations and semantics.

Q If Consumer Bob does a tune and down-pipe does this jeopardize the drive train warranty offered by BMW? Lets assume we don't have a buddy in the service department or can expect any favors from the dealer.

YES / NO

Yes

[Adem1534]

Originally Posted by David1

Yes

What if I just do the downpipe?

[Adem1534]

Originally Posted by PrematureApex

That's good news.



Doesn't make sense, nor do you see that on the dyno.

He may be hanging onto the complete myth that engines need some backpressure to make low-end power.

That's exactly what he said, and I immediately discredited it in my head. The turbo should spool up faster, if anything there should be a positive bump.

[3tekcorps]

Originally Posted by Adem1534

What if I just do the downpipe?

I would assume the same thing. Why don't you just run it stock for a while and see how things unfold with the reliability of a different engine. If people start having early engine/turbo failures I wouldn't do anything that messes with the warranty. If it's a bullet proof engine you can mod away in 18 months and not worry so much.

Sign up for some track days and work on your driving skills while you've got a full warranty. It's not like the car is down on power or anything.

[PrematureApex]

Originally Posted by 3tekcorps

I think you're just confusing people with your convoluted legal interpretations and semantics.

Q If Consumer Bob does a tune and down-pipe does this jeopardize the drive train warranty offered by BMW? Lets assume we don't have a buddy in the service department or can expect any favors from the dealer.

YES / NO

Originally Posted by David1

Yes

Yes.

But his drivetrain warranty IS NOT VOIDED. Which is the only thing I said.

He's is 100% at risk of having claims denied if the dealer can put forth a reasonable position that the modification caused (or could have caused) the failure.

And I'd hardly call repeating what the law says with "convoluted legal interpretations".

The law is abundantly clear: Your warranty cannot be VOIDED for installing aftermarket parts. However, warranty claims can be denied due to the installation of aftermarket parts. Just read the links I posted.

Not exactly convoluted or hard to understand.

Just trying to keep the information correct. As this is a common misconception across the internet. A few forums have gone so far as to create stickies explaining how your warranty cannot be voided in an effort to correct the common misunderstanding

[Adem1534]

Originally Posted by PrematureApex

Yes.

But his drivetrain warranty IS NOT VOIDED. Which is the only thing I said.

He's is 100% at risk of having claims denied if the dealer can put forth a reasonable position that the modification caused (or could have caused) the failure.

And I'd hardly call repeating what the law says with "convoluted legal interpretations".

The law is abundantly clear: Your warranty cannot be VOIDED for installing aftermarket parts. However, warranty claims can be denied due to the installation of aftermarket parts. Just read the links I posted.

Not exactly convoluted or hard to understand.

Just trying to keep the information correct. As this is a common misconception across the internet. A few forums have gone so far as to create stickies explaining how your warranty cannot be voided in an effort to correct the common misunderstanding

Originally Posted by 3tekcorps

I would assume the same thing. Why don't you just run it stock for a while and see how things unfold with the reliability of a different engine. If people start having early engine/turbo failures I wouldn't do anything that messes with the warranty. If it's a bullet proof engine you can mod away in 18 months and not worry so much.

Sign up for some track days and work on your driving skills while you've got a full warranty. It's not like the car is down on power or anything.

Originally Posted by David1

Yes

Well guys, just ordered 90 mm Polished Stainless Steel tips and the catless Downpipe.

I also bought he o2 sim.

All in all, 520 dollars for what I think is a lot for that money.

[Bigcatkian]

Originally Posted by Adem1534

Well guys, just ordered 90 mm Polished Stainless Steel tips and the catless Downpipe.

I also bought he o2 sim.

All in all, 520 dollars for what I think is a lot for that money.

Agreed, I ordered a downpipe the other day but please post some pics of the new tips I was strongly considering it but ill wait to hear your impressions

[Adem1534]

Originally Posted by Bigcatkian

Agreed, I ordered a downpipe the other day but please post some pics of the new tips I was strongly considering it but ill wait to hear your impressions

Will do man, look for the thread in the photos/videos, I might forget to tag you.

[caminator]

Im not looking forward to stripping wires to put the catsim in so I'm going to live with the CEL for a while until someone with an M2 posts pictures

[DKX4///M]

Originally Posted by 3tekcorps

Really wish they put the CAT somewhere else. Turbo and Cat right there seems like a terrible idea. I don't know about BMW CATs, but other cars I've had can end up with fried CATs after a few hard track days. It almost seems mandatory for extensive track use.

It is abnormal. However, It's smart considering the hotter the cat the more effective. and the faster it gets hot the faster it works...also allowed them to pretty much utilize a 3" straight pipe with minimal bends and muffler thats not too restrictive...

To the person that stated "Back pressure to make power low end is a myth" its not...Unless the engine is completely designed to ONLY make power low end, for an engine to make power mid/higher rpms which is obviously how most ICE make power it needs back pressure to idle properly and make smooth driveable power at low RPM's...

In turbo cars however, the turbo itself supplies the needed back pressure...

Run open exhaust on a N/A engine its a blatant loss of power...Its not tuning or other variables....When there is no exhaust restriction, and the Throttle body or Carb is closed or only partially open the engine "chokes" and will usually stall...The idle would need to be brought up to 2-3k rpm (by allowing more air in (Through a more open static idle position of the TB, or a much less restrictive idle air control valve) just to run. Just wanted to clarify that...

Very common misconception.

[PrematureApex]

Originally Posted by DKM3Power

It is abnormal.

It is not at all abnormal in modern cars. In fact, it's very common.

Originally Posted by DKM3Power

To the person that stated "Back pressure to make power low end is a myth" its not...Unless the engine is completely designed to ONLY make power low end, for an engine to make power mid/higher rpms which is obviously how most ICE make power it needs back pressure to idle properly and make smooth driveable power at low RPM's...

In turbo cars however, the turbo itself supplies the needed back pressure...

Run open exhaust on a N/A engine its a blatant loss of power...Its not tuning or other variables....When there is no exhaust restriction, and the Throttle body or Carb is closed or only partially open the engine "chokes" and will usually stall...The idle would need to be brought up to 2-3k rpm (by allowing more air in (Through a more open static idle position of the TB, or a much less restrictive idle air control valve) just to run. Just wanted to clarify that...

Very common misconception.

No, you are completely mistaken and perpetuating one of the biggest myths in the automotive community.

What you need for low-end power production is exhaust gas velocity to promote scavenging. Somewhere along the line, someone confused running relatively narrow headers to increase gas velocity with needing backpressure.

Backpressure is NEVER a good thing.

Take a read...(or google the subject, plenty of technical articles explaining the misunderstanding)

Backpressure: The myth and why it's wrong.

I. Introduction
One of the most misunderstood concepts in exhaust theory is backpressure. People love to talk about backpressure on message boards with no real understanding of what it is and what it's consequences are. I'm sure many of you have heard or read the phrase "Engines need backpressure" when discussing exhaust upgrades. That phrase is in fact completely inaccurate and a wholly misguided notion.

II. Some basic exhaust theory
Your exhaust system is designed to evacuate gases from the combustion chamber quickly and efficently. Exhaust gases are not produced in a smooth stream; exhaust gases originate in pulses. A 4 cylinder motor will have 4 distinct pulses per complete engine cycle, a 6 cylinder has 6 pules and so on. The more pulses that are produced, the more continuous the exhaust flow. Backpressure can be loosely defined as the resistance to positive flow - in this case, the resistance to positive flow of the exhaust stream.

III. Backpressure and velocity
Some people operate under the misguided notion that wider pipes are more effective at clearing the combustion chamber than narrower pipes. It's not hard to see how this misconception is appealing - wider pipes have the capability to flow more than narrower pipes. So if they have the ability to flow more, why isn't "wider is better" a good rule of thumb for exhaust upgrading? In a word - VELOCITY. I'm sure that all of you have at one time used a garden hose w/o a spray nozzle on it. If you let the water just run unrestricted out of the house it flows at a rather slow rate. However, if you take your finger and cover part of the opening, the water will flow out at a much much faster rate.

The astute exhaust designer knows that you must balance flow capacity with velocity. You want the exhaust gases to exit the chamber and speed along at the highest velocity possible - you want a FAST exhaust stream. If you have two exhaust pulses of equal volume, one in a 2" pipe and one in a 3" pipe, the pulse in the 2" pipe will be traveling considerably FASTER than the pulse in the 3" pipe. While it is true that the narrower the pipe, the higher the velocity of the exiting gases, you want make sure the pipe is wide enough so that there is as little backpressure as possible while maintaining suitable exhaust gas velocity. Backpressure in it's most extreme form can lead to reversion of the exhaust stream - that is to say the exhaust flows backwards, which is not good. The trick is to have a pipe that that is as narrow as possible while having as close to zero backpressure as possible at the RPM range you want your power band to be located at. Exhaust pipe diameters are best suited to a particular RPM range. A smaller pipe diameter will produce higher exhaust velocities at a lower RPM but create unacceptably high amounts of backpressure at high rpm. Thus if your powerband is located 2-3000 RPM you'd want a narrower pipe than if your powerband is located at 8-9000RPM.

Many engineers try to work around the RPM specific nature of pipe diameters by using setups that are capable of creating a similar effect as a change in pipe diameter on the fly. The most advanced is Ferrari's which consists of two exhaust paths after the header - at low RPM only one path is open to maintain exhaust velocity, but as RPM climbs and exhaust volume increases, the second path is opened to curb backpressure - since there is greater exhaust volume there is no loss in flow velocity. BMW and Nissan use a simpler and less effective method - there is a single exhaust path to the muffler; the muffler has two paths; one path is closed at low RPM but both are open at high RPM.

IV. So how did this myth come to be?
I often wonder how the myth "Engines need backpressure" came to be. Mostly I believe it is a misunderstanding of what is going on with the exhaust stream as pipe diameters change. For instance, someone with a civic decides he's going to uprade his exhaust with a 3" diameter piping. Once it's installed the owner notices that he seems to have lost a good bit of power throughout the powerband. He makes the connections in the following manner: "My wider exhaust eliminated all backpressure but I lost power, therefore the motor must need some backpressure in order to make power." What he did not realize is that he killed off all his flow velocity by using such a ridiculously wide pipe. It would have been possible for him to achieve close to zero backpressure with a much narrower pipe - in that way he would not have lost all his flow velocity.

V. So why is exhaust velocity so important?
The faster an exhaust pulse moves, the better it can scavenge out all of the spent gasses during valve overlap. The guiding principles of exhaust pulse scavenging are a bit beyond the scope of this doc but the general idea is a fast moving pulse creates a low pressure area behind it. This low pressure area acts as a vacuum and draws along the air behind it. A similar example would be a vehicle traveling at a high rate of speed on a dusty road. There is a low pressure area immediately behind the moving vehicle - dust particles get sucked into this low pressure area causing it to collect on the back of the vehicle. This effect is most noticeable on vans and hatchbacks which tend to create large trailing low pressure areas - giving rise to the numerous "wash me please" messages written in the thickly collected dust on the rear door.

C/N: You want narrower pipes just off the exhaust ports to increase exhaust gas velocity, NOT to create back pressure. Ideally, you want sufficient velocity with NO backpressure at all.

http://www.gomog.com/allmorgan/exhaustbackpressure.html

I had a past ME professor of mine do a lesson on it on our first day of classes...opened a lot of eyes.

Three biggest pet peeves...

1. people don't know the relationship between power and torque
2. people thinking engines need backpressure
3. people not realizing that the torque split on an open differential is ALWAYS 50/50.


Please, please stop the spreading of bad information!

[DKX4///M]

Originally Posted by PrematureApex

It is not at all abnormal in modern cars. In fact, it's very common.




No, you are completely mistaken and perpetuating one of the biggest myths in the automotive community.

What you need for low-end power production is exhaust gas velocity to promote scavenging. Somewhere along the line, someone confused running relatively narrow headers to increase gas velocity with needing backpressure.

Backpressure is NEVER a good thing.

Take a read...(or google the subject, plenty of technical articles explaining the misunderstanding)



C/N: You want narrower pipes just off the exhaust ports to increase exhaust gas velocity, NOT to create back pressure. Ideally, you want sufficient velocity with NO backpressure at all.

http://www.gomog.com/allmorgan/exhaustbackpressure.html

I had a past ME professor of mine do a lesson on it on our first day of classes...opened a lot of eyes.

Three biggest pet peeves...

1. people don't know the relationship between power and torque
2. people thinking engines need backpressure
3. people not realizing that the torque split on an open differential is ALWAYS 50/50.


Please, please stop the spreading of bad information!

My pet peeves are 1 and 3 as well...

But you pull up articled to back up anything. Im not bashing, Intelligent ME and engineers in general have differing opinions......

My Auto tech (Opinion is meaniless) and one of my engineering profs told me the opposite...Another said it was a myth.

Im not saying it needs backpressure for anything else than a smooth low idle...Urestricted, ehaust velocity is very high, vacuum in cylinders thus manifold very high...TB or Carb closed...at 600 RPMS engine stalls...

I ran hundreds of n/a cars open exhaust some with ported exhaust ports and NO HEADERS and they coudln't idle.

I value your opinion but Ive been taught and just believe differently from experience.

Google "why engines need back pressure to idle" a million articles would come up...If your not busy pull up an accredited study on it, as if Im wrong, I'd like to know it...Seriously.

Just internet, you can find anything.

[PrematureApex]

Originally Posted by DKM3Power

I ran hundreds of n/a cars open exhaust some with ported exhaust ports and NO HEADERS and they coudln't idle.

Of course they couldn't idle...they had no exhaust gas scavenging, because exhaust gas velocity was so low (big pressure drop) right at the port exit. To get it to idle, you need a header at cylinder exit. But not to generate backpressure as most people think, but rather, to keep velocity up. Two different things accomplished by the same thing in an N/A car...relatively narrow headers.

Anyway, it's not my opinion. It's fact. If you have some explanation for why you actually need backpressure and not just high exhaust velocities, we're all ears. You want no backpressure, with high velocities. The reality is, you typical introduce some backpressure in order to keep velocity up...and hence the confusion.

You could run huge headers (or no headers) that would otherwise work badly in the low end, and pull vacuum on them (anti-backpressure) to restore the low end performance.

If you don't like the explanation I posted above, there are countless articles written on the subject trying to correct this myth.

Just google "backpressure myth". It is not an opinion.

But anyway, back to DP talk...

[David@ActiveAutowerke]

PrematureApex is 100% correct. Exhaust velocity is commonly mistaken for backpressure and is the main reason people believe that engines need backpressure.

We've noticed decreased spool times by removing the cat which is amplified even more when you open up the exhaust system. Our F8X M3/M4 mid pipe on an otherwise stock car made 80lb/ft of torque more at the wheels under between 2700rpm and 3400rpm compared to a bone stock, simply by promoting exhaust velocity and reducing back pressure.

We currently have our prototype downpipe for the M2 complete and are working on the full exhaust right now. I'm pretty excited to release details once it's complete because I believe the design that we're working with is going to be a winner.

[DKX4///M]

Originally Posted by PrematureApex

Of course they couldn't idle...they had no exhaust gas scavenging, because exhaust gas velocity was so low (big pressure drop) right at the port exit. To get it to idle, you need a header at cylinder exit. But not to generate backpressure as most people think, but rather, to keep velocity up. Two different things accomplished by the same thing in an N/A car...relatively narrow headers.

Anyway, it's not my opinion. It's fact. If you have some explanation for why you actually need backpressure and not just high exhaust velocities, we're all ears. You want no backpressure, with high velocities. The reality is, you typical introduce some backpressure in order to keep velocity up...and hence the confusion.

You could run huge headers (or no headers) that would otherwise work badly in the low end, and pull vacuum on them (anti-backpressure) to restore the low end performance.

If you don't like the explanation I posted above, there are countless articles written on the subject trying to correct this myth.

Just google "backpressure myth". It is not an opinion.

But anyway, back to DP talk...

Agreed, But how do you increase exhaust velocity without introducing a bottle neck or restriction to the system?

And regarding a ctalytic converter being directly conected to or exremely close to the engine is abnormal. I was an ASE Certified Tech most of my life...General mechanic from 15 to 25. Worked on thousands of cars and MOST primary cats were at least 2-3 feet away from the engine. Except for on modern BMW's...Dont know about other cars for the last 4-5 years I Gojo's my hands for the last time in 2012 (except for my cars)

[David1]

Originally Posted by DKM3Power

Agreed, But how do you increase exhaust velocity without introducing a bottle neck or restriction to the system?

And regarding a ctalytic converter being directly conected to or exremely close to the engine is abnormal. I was an ASE Certified Tech most of my life...General mechanic from 15 to 25. Worked on thousands of cars and MOST primary cats were at least 2-3 feet away from the engine. Except for on modern BMW's...Dont know about other cars for the last 4-5 years I Gojo's my hands for the last time in 2012 (except for my cars)

The cats mounted closer to the engine is the norm now. The closer they are the quicker they function and the o2 readings are more precise. The new honda motors have no exhaust manifold and the cat is bolted right to the head.

[PrematureApex]

Originally Posted by DKM3Power

And regarding a ctalytic converter being directly conected to or exremely close to the engine is abnormal. I was an ASE Certified Tech most of my life...General mechanic from 15 to 25. Worked on thousands of cars and MOST primary cats were at least 2-3 feet away from the engine. Except for on modern BMW's...Dont know about other cars for the last 4-5 years I Gojo's my hands for the last time in 2012 (except for my cars)

Well, I don't know what to tell you...obviously it's increasing in prevalence given modern emissions standards...

But that being said, turbo Subarus for the past, oh, 20 years, for example, have had a cat in the DP just after turbo exit, as have many others...particularly turbos...although plenty of others have had cats in the headers too (FA20, BMW I6s, N/A Mazdas, etc.). Obviously, packaging constraints play a roll, but they often try to get them as high up as possible...especially in recent years.

Just google "catted downpipe" or "catted headers" and you'll find many applications having cats right after the turbocharger/integrated into the headers.