I just got a used 2008 MCS with JCW exhaust. I plan to upgrade the exhaust from the turbo back and like what I've read about the Alta exhaust. I plan on getting a FMIC as well as the Alta AP but was wondering if the turbo back exhaust (specifically the Alta) is a worthwhile improvement? When I go on the Alta website and look at their claims of 10WHP, is this in comparison to a standard MCS exhaust? Is the JCW exhaust any better (free flowing) than the standard exhaust? Would the added benefit be due mainly to the replacement of the downtube connecting the turbo to the exhaust? Thanks for any answers or opinions.

 

I would just get a downpipe and delete the cats.

 

Aren't the cats required for the car to meet emissions? The Alta downpipe still has two cats, only they are free flowing, at least that is what is advertised on their site.

 

The Alta cats will give you a CEL (as with most aftermarket cats for our car... the ecu/o2 sensors are VERY sensitive).
If you're looking for something more free flowing than your JCW exhaust, I have a custom 2.5" resonated magnaflow setup (sounds very similar to alta's exhaust). Look at my videos on youtube-- you can search "akakong" and you should be able to find my videos, theres quite a few of the exhaust on there.
Granted I have a stock DP, but compared to a stock car, I saw about 7wtq higher on the dyno with my exhaust. Vendor's claims are usually (almost always) dramatically inflated. You'll never see 10 whp from an intake and 10whp from an exhaust alone without a tune, etc.

I'd be willing to work out some deal on trading if you'd be interested...! PM me if so.

 

Exhaust Depot makes a down pipe that doesn't throw a CEL.

http://www.exhaustdepot.net/exder56do.html

It depends on where you live, whether or not you could get away with a cat less down pipe. Some local governments require equipment and emissions testing, others don't.

Dave

 

Yes and no... its more a hit or miss. If his '08 has been in for any service at a dealership, and gotten a new firmware update (which is usually required by dealerships upon visits that include any repair/maintainence) then it will have the new o2 sensor reading parameters, which are a lot tighter due to ULEV (ultra low emissions vehicle) requirements. There have only been a handful of people who have gotten away with the non-cel's, even with ED's downpipe. Its also unknown if hes still in business, as he hasn't posted on here in a while and his phone number is disconnected.

And yes getting away with the catless as some states don't check emissions, but then you'll be throwing codes, which I believe all(I could be wrong) states check if any lights are on the dash (that light being a CEL from codes thrown). The only way around the CEL is the cobb access port + tune ($900).

I wish this car wasn't so damn complicated.

 

Yes. For inspection in NY, all they do is check for emissions related CELs, which the ALTA AP clears. I'm not sure how it works in other states, but if you're getting the AP anyways, catless is the way to go IMO.

 

I renew my tags online and they send them to me in the mail, no inspection, no emissions test.

I have a Volvo that has had the CEL on for years. It's for a blower that feeds air to the catalytic converter in the first five minutes of operation to get it to temperature faster, then it shuts off. The fan costs $600, I can live with the CEL. So, no, my state doesn't look at the CEL.

Dave

 

Yes, I was planning on going with the AP which I understand will clear any CELs. I plan to replace the downpipe for certain. I guess my question is will replacing the rest of the exhaust add any benefit? Would the exhaust be any better (or worse) than the currently installed JCW kit? I like the sound of the current JCW be I've heard the Alta and Invida and like those as well, so for me at least, I am looking to get more performance, not a different sound, out of the exhaust. If I can do that with a replacement of just the downpipe, then that would be the way I would go.

The other question I have is are all downpipes the same length as the factory piece? Can I just buy a downpipe from manufacturer X and expect it to fit in the space of the original JCW?

With the exhaust replacement (either complete turbo back or just downpipe) and tune from the AP, could I reasonably expect to see another 10-20WHP? I also plan to replace the FMIC but so far in my quest, all of the major sellers are out of stock for the next 3-4 weeks (or longer), so I haven't made a decision on which one to go with just yet.

Thanks!

 

Just think about it all like a water hose... If you have a fire engine, with a fire truck water hose, then at the end of that hose you hook up a garden hose, what will happen? Pressure will increase (backpressure from a bottleneck) and velocity will decrease as smaller area = lower velocity (slower turbo spool). So putting a larger diameter downpipe will do nothing if a smaller diameter exhaust is hooked up after it as a bottleneck.

And no, any generic downpipe wont work as you need to have mating surfaces and curvatures be correct at the inlet and outlet

 

No offense but your analogy is a little over the top for me. We are talking about a 3" DP to 2.5" JCW exhaust. Fire hose to garden hose, really?

 

extremes help us understand difficult concepts, which can later be scaled down to real-life situations. He wasn't being condescending

 

FYI on HP from a catback, Not going to gain. I did a ton of testing and the most HP ever gained from any catback alone was 3whp. So save your money and put it in the intercooler first, there is real power there and no check engine lights.

 

Thanks for the validation. This is exactly what I thought. I figured the biggest gain would come from the downpipe and a small amount from the JCW exhaust versus the base exhaust. As far as FMIC goes, I would buy one tomorrow if someone had one for sale that I could get in a reasonable amount of time. So far, I am looking at anywhere from 3 to 4 weeks and by then I will be back at my job in the ME. The downpipe I can get no problem and I will install along with the AP.

 

it's the old Pi * r^2. Yes, modest changes in radius change the cross sectional area and thus theoretical flow a lot. Basics of any piping system. See further below on the relevant diameters (albeit O.D. not I.D.) to do some calcs on.

On the other hand, various commentary I have seen is beyond 2 1/2"--or perhaps even less--the motor (1.6 liter after all, even allowing a lot of extra credit for a turbo) really doesn't have that kind of exhaust flow requirement at the available RPM's and boost.

By the way, I changed my MCS exhaust to a factory JCW; I don't recall it is 2 1/2" or even close. Flared dual rear final outlets aside, both MCS and JCW basic plumbing is 55mm O.D., or about 2.175". Surprised me a little when I changed it that the O.D. is the same from S to JCW. Factory (not kit) JCW exhaust does have the second cat deleted and the larger (longer) resonator can up in the mid section area. Boston R56S (...who I think I remember from his Audi (C5?) board posting days) did mention a 2.5", but that was a customized set up.

 

Just trying to draw it out for you. Figure someone asking if a larger dp to a smaller exhaust will be worse than a larger dp with a larger exhaust wouldn't understand if I started talking about bernoulli's equation relating pressure and velocity of fluids. I'm not trying to be an ***, but simply helping you visualize.

Basically, a DP will only be helpful if you have a larger diameter exhaust to go with it. a JCW is not 2.5" its more like ~2 1/5" diameter. So .8 inches in diameter change is pretty significant. In addition, an aftermarket exhaust that you get custom piping on can be made more "straight" through with less bends, thus disrupting flow less. General rule of thumb... the easier the gases flow out, the better the car will be able to perform.

But just like an exhaust won't give you gains without a tune, a dp won't give you gains without a larger exhaust. Everything works as a system, can't change one thing and have it improve the whole system.


@MP1.6T, it was a C4, haha i miss quattro. That was a 2.8 V6 with a 2" diameter piping I believe, and i brought it up to a 2 1/4" with a magnaflow muffler haha. Good times, still a way underpowered wagon though. And as to Cross Section, thats what I meant by "area" haha, but we don't have ME's in this thread anyways, so I should have specified.

 

New cars don't require inspections for the first few years, so running an aftermarket downpipe won't be a problem at first, but you'd better hold onto the oem one as they're worth a small fortune when testing is required.
That being said it looks like both the Alta accessport and RMW's tunes can now loosen up the parameters enough to let aftermarket downpipes function without any codes like modding a playstation or xbox, firmware/software updates from the dealer could close the door to this work around and/or tuning at any time.

 

Buh?

Dave

 

While I agree with most of what you said, you definitely don't need to be an ME to understand Bernoulli's principles. I understand you are trying to help so don't interpret this as a shot. I deal with ME's all day long in the jet engine business and sometimes I wonder about these guys.

Anyhow...if you are, in fact, looking at Bernoulli for an example of flow characteristics then you know that the velocity is interpreted in different ways and that "less bends" or "Flow disruption in terms of straightness" doesn't neccessarily equal more or better. As simple as the theory is, the math is very, very complicated on a systems level and quite frankly the only way to really know that the performance is there is to do real life back to back testing. In a nutshell, Way is correct in that an exhaust system might gain you small benefits. Placed in a system with other components...yes, the game is again different. At the end of the day for a regular modder, an intercooler is a better investement than an exhaust system.

 

LOL...
Where do you work? I'm a ME in the jet engine business, IN CONNECTICUT.

 

Pratt & Whitney...

 

Hahaha That was going to be my guess... What do you do there?
P&W is our Customer.. we do outsource work for GSE

 

Keep engineers in line! F135 Systems Design/Component integration Configuration mgmt.