OK Ill put it out here at the expense of looking stupid as this goes against everything I have read learned and absorbed from people highly respected in tuning, racing, R&D. Ive thought about this a bit in the past couple weeks and think I have come to my own conclusion based on my current setup and turbo system. I have an Xede, cams 264I/272E and a 3" DB exhaust. This is current before this I had the Xede, 264I/272E, a 2.5" testpipe and a 2.5" axleback (the rest was stock exhaust components). So what Ive noticed is more boost with the 2.5" combo going back over my notes. Not just at the low end but throughout the range as well as peak boost but not as much near or past 7K. I have been thinking that this was due to disturbances and backpressure in the 2.5" pipe when the wastegate opens and actually the gases prolly prefer to turn the wheel and escape adding to the boost differences I have seen. I had to use the RPM dependant boost controller on the Xede to make some of this up and to an extent It did a great job- but some thoughts-

1. Tuners - ALL of them seem to fancy flatening out that initial boost spike (Thats what it is) and what goes with it is that initial torque hit (something made sure was tuned in). Dont get me wrong my car is FAST it zings through the RPMs its dynamic and has good flat torque everywere, But It doesnt have that enjoyable barely dip into the throttle satisfying torque slam
( From my observations the small spike it totallly safe and I never heard knock from it) This might not be the tuners thought to a perfect tune with a ruler flat torque curve and straight line HP increase curve but it sure feels great and whose to say its a wrong way to tune if its safe?? Its like a ruler flat stereo Its absolutely accurate but there is something totally enjoyable about a small little hump at 80 hz

2. From the many articles Ive read of turbo applications and system dynamics the perfect exhaust would be one with the littlest backpressure and the most pressure differential across the exhaust wheel. In a perfect world I agree that works out mathwise if taking into account MAXIMUM FLOW. Well My 3" certainly has more flow near and past 7K and revs like a beast.
I have to an extent dialed back in a significant amout of boost spike using the Xedes many settings but It makes me wonder a bit if the streetgoer ultimate torque setup wouldnt use a 2.5" tube to induce a slightly better throttle/torque response. I can do everything with my3" and more up top but the throttle feel and torque was pretty bad *** with the 2.5 setup.


I know its long and ranty and somewhat simplistic as to convey the thought but If any of you want to talk in more tech terms about this right here is the perfect place. Also I know Im going against the grain and prolly could be straightened out on a few points- hey we all need to be set straight sometimes. I could be overlooking the obvious.

BTW all boost differences are a max of <1.5 psi And we are at the end of the FBC unless we go bleedvalve or bigger hose

 

Tooners?

 

Lets see if I get this right, you are wondering if the a 2.5" exhaust will offer increased torque down low over the full 3" system. I would say no. What you are noticing is probably how switching to larger plumbing quickened and smoothed out boost response and spool up. Now how you are running less boost is beyond me unless it has something to do with how the exede controls boost. That king of thing usualyl happens when you increase the flow so much that the compressor wheel is unable to mantain a boost level. This is not a bad thing but I didn't think you would be able to dial the lost boost back in.
Everything with these cars is a trade off, which I am sure you are awarw of. To get more power up top, you will generally have to give it up somewhere.

 

I felt the same thing in my TT rx-7. I did one pipe at a time and the last pipe KILLED the low end Tq, I could not even make it up the driveway but the top end rocked. I dono what to say. Maybe it costs some down low to get the top end.

 

Thanks for your reply. Id like to meet up and check out your TSi sometime The quasi-empiracal data I have unfortunately didnt include a dyno just noted boost charts from the best I could eyeball and remember. The same road with the same entry speeds. With the 2.5" setup I could break all four loose quite easily ath the same line and entry speed. The first 25% of the throttle was nasty. I am able to change WG opening with the independant control of the Xede so I can control boost to an extent down low. The map Im using was always for a 3" exhaust which I used for my 2.5" and the initial throttle response vas great though the 3" outpowers it up top

 

With any car you always sacrifice a little low end when changing your exhaust or even your intake but up top it makes it worth it. Once you up to 6 in first gear you wont be low enough in the rpm band for it to matter. I dont think even a dyno will tell the whole stock. youll see the higher power at the top end and the lower power low end but the only way to know if your car is "faster" instead of "more powerful" (which is what the dyno will tell you) is to run it at the track with the different setup. But I can pretty safely say(especially with a turbo car running this much boost) that the 3 inch is def goign to be the best choice.

 

I've stubled onto this site cause of a buddy of mine so don't crusify a vw guy for his thoughts on the matter . I have a 1.8t and changed out the stock piping for a full 3" turboback exhaust. I noticed that the low end doesn't seem as punchy but the mid and upper rpm is rediculous compared to the stock piping as well. What the other guy said. Your just feeling a smoother boost and power delivery. I'm going to try to dig up a dyno of a 2.5" system compared to a 3" so you can see the power increase along the entire power band with the 3" system.

 

I dont doubt that I have said it in this post the thing I am getting at is through the inherent characteristics of a 2.5" system induces a nice boost spike and pleasurable torque hump that is actually as nice a comprimize as the gain of top end power. A 2.5" exhaust is not so bad though might not get you absolute Top end you wont have absolute bottom end either. The real question is Tuners have razor flat power and TQ curves, I noticed with the extent of my tuning knowlegd and tools available that I can keep that top end and get a little low end back. So the question can tuners start using this or not? Did and it makes the car "feel" faster

 

What about mating a 3" dp to a 2.5" cat-back. Still give you the benifits of the larger dp but allows you to keep some of your back-pressure. Alot of the vw guys do that too. I'm probally just not getting the idea behind this though. You're just trying to get the feeling of low end punch back, but keep the top end screeming right?

 

Are you saying that by going to the 3" ex, the throttle input feels a little numb down low in city driving or general all around driving.

 

Yes but in context of a cammed car (Higher VE) and a seeming "anomoly" of the "Dumb Luck" right 2.5" system I was running. It was an 1/8" from a powerslide going around any corner now it doenst have that 10-15Ft# hit. In essence its smoother more civil more Power.

 

MP5, is this the downside to basic Xede and Dynoflash? People point out the gains up top but are they sacrificing the great low-end punch? Is this true for both Xede and Dynoflash?

 

No it has nothing to do with the ECM it has to do with 3" exhausts (Any of them). At least that is what I am concluding myself based on my experiences and on my car. I know many more knowledgeable people will disagree but I just cant ignore it

 

Here is what you need pimp.

https://www.evolutionm.net/forums/sh...ward+and+scott

Send that shinny POS back to the motherland

 

hahaha funny you mention that!