nevermind

 

oh, I should add to keep it on topic here....please show us the data about exhaust diameter on an R56 and how it needs a 3".

 

So i am home now, and i grabbed my copy of Maximum boost.
Throughout this book, Corky has these little "RULES" which are quick little note to keep in mind. On the first page of Chapter 11(which is all about exhaust systems on turbo cars), the RULE is:
Backpressure in an exhaust system is EVIL!

The last sentence is:............. lowest possible back pressure.

Where its gets confusing is when he does say that the larger the better is not always the best case. This is only said because he explains how you shouldn't exceed 250ft/sec of exhaust speed, and it can make the exhaust too loud. If that number is the magic number, then lets go with that for a second.

If we look at the chart (which is all about "approximate" piping size base on HP) we shoud be keeping the stock exhaust. According to the chart, a 2.5" system is good to 500HP and the stock-ish sized 2.25" is good to about 300HP. They also mention that the exhaust only needs to be 10% larger than the turbine oulet. If you have ever seen the Mini's outlet you know you would be running about a 1.75" exhaust!

Next thing we are going to see is guys quoting the graph explaining, in order to run 14psi of boost with 92 octane, you need a 7 to 1 compression motor. If i use that chart at 10.5-1 CR, the most boost i can run is 3psi of boost. Now we all know thats not true

On good note there is lots of good info about turbo sizing, exhaust manifolds, and how wastegates work, intercoolers, and types of intercooler (funny how they say a bar and plate is the best choice, and funny how he started Bell intercoolers)

With this book, there is alot of good info, but you have to take it for what its worth. Meaning there is lots of good info if it was 11 years ago. This book has the word carburator in it (many times and a chapter about them) and that goes to show what was still on the mind of tuners.

This is still a great book to buy, i would recommend it to everyone. What is best is for everyone to read as much as possible, talk to as many people as possible and make your own decision. For instance, i looked to the V8 world when i was looking at buying a Vette. They were the experts in their own world. I wouldn't look there for info about big HP turbo cars (but they might look here when the new Camero comes out with a turbo!).

Sorry if my last post seemed cranky, i kind of was. It was time to go home and Mr.Poopy-Pants ruined it for me.

 

I wrote that not seeing PGT's post. BUt i mean it, we will just build one and show people where it looses power. Simple (although will take some time) and effective. We will build one using 2.5" piping, 2 cats, and the same straight through mufflers. Then show you.

 

I just put on my 2.5" Invidia and although it feels I have some added power, especially up top, slight loss of low end torque is apparent. I'd hate to see how this is magnified with a 3" exhaust. Just the ever trusty butt dyno talking so whatever, but it just reconfirmed my belief that 2.5" is big enough.

Maybe if Jan comes out with a 2.0L stroker for the R56, THEN i'll run a 3" .

But then again maybe the loss of torque feeling is because it was 108 here today....LOL. Damn heat.

 

Why use 2 cats....maybe thats half the problem right there.

 

I am sure your 2.5" system made power everywhere. A bigger exhaust on a turbo car doens't loose low end power. If it did how do we explain our results. Even if some don't believe us, the car launches with more boost, the car makes more TQ. EVEN the catback graph shows the same thing, just not as big of a difference.


Graph shows TURBOBACK installed between runs.

 

But like you said its all marketing fluff, so maybe we don't. I mentioned that if our 3" system, is as light or lighter, quite enough no one has ever complained, is going to make at least as much power, and cost the same or less than a 2.5" system, then we don't even need to build one..... If this logic still makes people say you don't need a 3" system, then i am lost.

The stock turbo back exhaust contains 2 cats. To be as legal as possible, we make our system with 2 cats just like the stock system. To be as legal as possible the cats even need to be in the same places as they are in stock form. "Half the problem" with replacing cats in general are that its not legal to replace them unless they are damaged or out of warranty. Keep that in mind when buying an exhaust and understand why we have 2 cats.

I should be clear here, we are going to build a turbo back in 2.5" not just a catback exhaust. So on our build it will use the same cats same everything, but 2.5".

 

I would like to help out openeyes a little here since he started the thread, and is the one looking for answersI did some research and found that the Borla Exhaust is only 2.25". This is smaller than stock. I am surprised our DP fit to it though! But with that said if you free up the exhaust right after the turbo, you generally only benifit from quicker spool, not much upper end power.

Is this what you felt?

What if you were interested in an ALTA exhaust and we made you a deal you couldn't refuse?

 

.

 

Your right, i can make an educated guess as to what might happen. I feel confident, based on past things we have done, that the 3" will outperform it. Just like you feel confident that the 2.5" will provide the same results.

Your right, if we make the 2.5" and its the same HP as our 3" system then damn us for not trying it first! Just like we would have to eat crow, i woud expect the same from onlookers.

For that matter i could say that the onlookers already have their opinon set in stone. And even if the results are in our favor, they will make excuses for it not being necssary stil. But i won't say that because the community is a rather smart community and geneally learns fairly quickly with things like this.

We are not one to falsify records, or dyno graphs. I am not sure why NAMers have this automatic Bias toward vendors making things up. Yes we have a dyno, but that doesn't mean we spend $100K just to make up graphs and things. If that was the case, i could just use excel and make some really nice graphs! I can assure you that when this test completes there will be lots and lots of data backing up what happens. Weather its in our favor or not.

No its not demeaning to the engineers in the least. They have to design around tons of parameters that don't justify making the most power from an engine. Emissions, costs, space,.............. You can make more power on the stock exhaust(we have seen this with stock R56 Unichip tunig we have done) But you can make more with an exhaust. But they don't need to. They just need an engine to make X power and they did it! Your argument is basically saying all these cars are making the most power they can?? Or 2.5" pieces are common??

What you are saying sounds like work in the turbo world, or you read something somewhere about recent turbocharging that was somewhat generic. New turbos can make more power more efficiently, but that doesn't change that a turbo works best with ZERO exhaust back pressure. The whole thing about less engery in the exhaust is not really correct. A given engine making 200 HP on a new turbo vs old turbo just means that the newer turbos compressor is more efficient (cooler charge temps)makes more power, or the turbine has less back pressure. But the turbo is still seeing the same airflow as is the exhaust. Airflow is HP. I am not arguing that its running less stressed, but the turbo is still dealing with the same airflow.

Backpressure in a turbo exhaust is a restrictor to letting the turbo spin up. Its as simple as that. WHat is in question is "how much does it matter", not even the question "does it matter".

I am not trying to argue please don't take it that way. Just trying to educate a little more as there are many on lookers reading NAM.

It just seems as though many people here are stuck on Normally aspirated engine mentality. Which is fine, that is why we are here explaining things. What we are preaching itsn't anything new to the turbo world. Which is why turbo companies like Garrett, Turbonetics and others will all say the same thing.

This is something we expected with the new Mini turbo. We knew we would have a sligth uphill battle with Mini switching gears on us. It will just take time to get passed this.

 

Wow, amazing how you just give up, I was trying to have a converstaion with you about your thougths. In many cases people think a certain way because it was a conclustion they came to on their own. And in many cases they can be further educated on something by someone who deals with it everyday. Just like when we talk to Garrett about applications, we learn new things all the time. I am just trying to pass along our learned knowledge.

 

I can definitely attest to the fact that that the numbers I saw on my dyno at ALTA were what ALTA posted. I supplied their test vehicle for the PnP ECU on an automatic R56.

I have found ALTA to be reasonably priced and they have outstanding customer service.

 

I have been following this 2.5" vs 3" vs 4" battle for several weeks. As intense and heated as some of these thead got, I'm surprised that no one did a real world comparison/shoot out of all the systems that are available. A test like this would be difficult about a year ago because there weren't that many choices available for the new R56, but I think there are enough systems out there now to perform such a test. Is this really a difficult thing to do?

 

No, I think it's just timing, and tests will eventually come. These exhausts haven't been around that long, and the 3" was one of, if not the first to come out.

Most of the aftermarket guys were still focusing on the R53, and were willing for someone else to test the waters, or dawdled. The first exhaust to come out would would grab the market right off the bat, but would be the most scrutinized. No one knew (or knows) how much power potential these engines have, so how do you know how big to make the exhaust? I am guessing that it was better to err on the big side, and still use standard size tubing to minimixe manufacturing cost. Other manufacturers decided to bet on the 2 1/2", 'cause it would not be as loud, and probably ( guessing again) sound tuned more easily.

The 2 1/2" exhaust may be enough for the present state of engine development, but there is still years to go, I expect 300+ whp engines to be common with bolt-ons within the next few years, after someone comes out with a better head, cams, and figures how to control & tune the intake cam timing with the ECU, along with turbo development. With turbo replacement development, it would be silly not to enlarge the exhaust. The 3" exhaust size was probably the result of forward thinking.

The 3" exhaust will already be here, to take advantage of upcoming development. The 2.5" may become more common in the near term, but in a few years, the 2.5" guys will be playing catch-up with their own 3" exhaust. Ideally, the mfgr that has both will have the advantage in the market, especially if they are high-quality. Exhausts are expensive, I would rather go "big" in the near term to avoid replacement in a few years.

 

+1 to that

 

Li'l Red's Rider is correct, or pretty close. When we released our R56 (3"), the Miltek was either out just before or just after. This was a 2.5" system. The only real issues they had was they posted results, with no base runs done.

I am all for an exhaust shootout. ALTA will supply an exhaust, or for that matter, if people shipped us their exhausts we will do the work. Our test mule R56 is going back to the stock turbo (in favor of a new JCW) and has EGT probes installed, and i would be willing to install a pressure sensor into the exhaust for Backpressure testing. If this is the direction we are going, we should start another thread.