# Large Exhaust Pipe After Turbo?



## Spaceme (Jan 20, 2011)

Hello. Let me first introduce my self. I just purchased a 2011 Chevy Cruze LTZ and I am really enjoying it. I am very impressed with the quality of this car. Gas mileage is great. I drove a 130 mile trip today doing about 55-60 MPH for 60% of the distance and 65 MPH for the other 40% with some stop and go driving while in two small towns. I averaged about 36 - 38 MPG. It rides great, and handles like a high end sports car. Great car. Love the turbo and will more than likely be getting the Trifecta Tune for it soon.

So on to my question. Does anyone know what the large canister-like pipe that is directly after the turbo on the exhaust pipe is? It does not look like a catalytic converter as it seem to be seemlessly integrated into the exhaust pipe and not welded in like a cat would be but I could be wrong. Is it an expansion chamber? Could someone shed some light on this?


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## ChevyPower (Nov 9, 2010)

Welcome. I'm not a Cruze owner, but i had the chance to drive one for a few days. I have driven and owned a few sports cars and went behind the wheel of one high end sports car and I can tell you from my experience the Cruze handles good, but doesn't handle anything like a high end sports car. 

That pipe after the turbo your talking about might serve the purpose of releasing some of the built up pressure from the turbo, i could be wrong.


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## 70AARCUDA (Nov 14, 2010)

...as exhaust gas cools down, it shrinks in both density and velocity.

...the turbine converts the high-velocity of the exhaust gas coming_ from_ the cylinders into a high-pressure intake air going_ into_ the cylinders via the turbine blades...and in the process the exhaust gas in transformed from a AC-like pulses into an almost DC-like constant exhaust flow...hence the 'purr' heard from the tail pipe rather than snappy individual cylinder pulses even at max. throttle.

...so, unless the original OEM exhaust pipes & muffler system is _undersized_, adding a larger "bore" cat-back won't gain much (except extra money in the Muffler Shop's pocket).

...gotta remember this is a small capacity engine--envision two 1-liter bottles of soda, one "full" and the other just under "half-full" (ie: 4/10's of liter)--that's what the 1.4L engine capacity is.


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## montgom626 (Jan 16, 2011)

70AARCUDA said:


> ...gotta remember this is a small capacity engine--envision two 1-liter bottles of soda, one "full" and the other just under "half-full" (ie: 4/10's of liter)--that's what the 1.4L engine capacity is.



Very very small. I think I am going to have some soda, maybe a "big gulp" 

PS I like the idea of driving a 1400 cc motor. My last small motor was 1600 cc VW Beetle from 1970.


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## 70AARCUDA (Nov 14, 2010)

...both my '56 Simca and '65 MG Midget had 1.3L engines

...and, my '84 Honda Civix DX was just slightly bigger at 1.5L.


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## montgom626 (Jan 16, 2011)

70AARCUDA said:


> ...both my '56 Simca and '65 MG Midget had 1.3L engines
> 
> ...and, my '84 Honda Civix DX was just slightly bigger at 1.5L.


What is old is new.
And to think, 1400 cc with better mileage, quiet and smooth ride. Superb crash protection, Stabilitrack, sweet stereo, heated seats, ABS, TC.

Cars just keep getting better.


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## 70AARCUDA (Nov 14, 2010)

...almost, but not quite (ha,ha)!

...my '84 Honda Civic DX _consistently_ got 42 mpg, using A/C, and 45 mpg often on the higway, but I must admit it had a 5-speed manual, not an automatic, and weighed much less than 3,000 lbs...probably closer to 2,200 lbs.


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## shawn672 (Oct 31, 2010)

70AARCUDA said:


> ...almost, but not quite (ha,ha)!
> 
> ...my '84 Honda Civic DX _consistently_ got 42 mpg, using A/C, and 45 mpg often on the higway, but I must admit it had a 5-speed manual, not an automatic, and weighed much less than 3,000 lbs...probably closer to 2,200 lbs.


and would crush like a sardine can if you ever got hit lol


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## 70AARCUDA (Nov 14, 2010)

shawn672 said:


> and would crush like a sardine can if you ever got hit lol


...the "trick" is to NOT get into an accident (wink,wink)...and I haven't had an accident in over 50 years!

...'Defensive Driving' courses teach you pay close attention to what others are doing stupidly, and to steer clear of them at all costs.

...drive as if _"...everybody is out to kill you..."_ which is probably true on just about all California highways (ha,ha).


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## 70AARCUDA (Nov 14, 2010)

...back to OP for a moment?

...anybody know what the _inside_ diameter (id") is of the exhaust pipe behind the catalytic converter?

...the ideal exhaust gas "mass" velocity is around 260-300 fps inside headers.

...using the _lower_ of those two numbers (ie: 260 fps), one can calculate if the exhaust pipe diameter is too large or too smaller to maintain that flow rate back into the muffler.

...beyond the muffler, the number is lower, around 150 fps, due to cooling of the exhaust gase making it denser and slower.


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## shawn672 (Oct 31, 2010)

Couple things to add:

ZZP added a cutout at some point in the exhaust, I assume right after the Cat and found it to increase hp

Turbo motors generally do not need very much pressure in the exhaust, most any turbo car is ideal with a 3" (ours is SLIGHTLY different because of the smaller turbo/motor, a 2.5" would probably be ideal but I havent done the math)

I think the stock diameter is 1.5" per ZZP's measurements but don't quote me on that


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## 70AARCUDA (Nov 14, 2010)

...using the flow equation, we can estimate the pipe-to-catalytic converter size needed for RPM @ Vg = 260 fps:

*RPM = (d/B)^2 * (Vg*360º)/S*

...where:

RPM = engine speed (6,500 redline)
360º = constant
Vg = exhaust gas mass velocity (260fps)
d = inside pipe diameter, inches (1.5")
B = piston bore, inches (2.85")
S = pistorn stroke, inches (3.25")

RPM = (1.5"/2.85")^2 * (260fps*360º)/3.25" = 7,977.8 ~ 8,000 rpm

...thus, 1.5" id pipe is sufficient for 1.4LT up to 8K rpm, and the pipe _beyond_ the catalytic converter could actually be_ less_ than 1.5" id.

note: at 6,500 rpm, the turbo is _no longer_ boosting to full capacity.


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## shawn672 (Oct 31, 2010)

that's assuming 260fps though


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## 70AARCUDA (Nov 14, 2010)

...300 fps is optimum for a hemispherical piston chamber (which 1.4LT isn't)

...260-280 fps is typical for wedge chambers.

...and, those are "at-the-exhaust" valve maximum velocity values, not down-stream average values.

...of course, if the turbo *is* still pumping (how much?) at that RPM, then those numbers become invalid!

...backing into the volumetric efficiency (VE) equation, we can get an idea of how much the maximum boost is, ie:

*VE = (HP*792000)/(AP*CR*CID*RPM)*

...where:

VE = volumetric efficiency, dimensionless
HP = engine horsepower at RPM (138hp @ 4,900rpm)
AP = atmospheric pressure, in psi (14.6psi)
CR = engine compression ratio (9.5:1)
CID = engine cubic inch displacement (82.932cid)
RPM = engine speed at max HP (4,900rpm @ 138hp)

VE = (138*792000)/(14.6*9.5*82.932*4900) = 1.939 ~ *1.94:1*

...and, thus: 1.94*14.6psi = *28.3 psi* maximum boost, roughly (because temperature effects not included).

• Here's what the people at *Garrett* say about pipe sizes _after_ the turbo:

_"As for 2.5" vs. 3.0", the 'best" turboback exhaust depends on the amount of flow, or horsepower. At 250 hp, 2.5" is fine. Going to 3" at this power level won't get you much, if anything, other than a louder exhaust note. 300 hp and you're definitely suboptimal with 2.5". For 400-450 hp, even 3" is on the small side."_

...so, roughly (red is extrapolated):

3.5" = 400-450 hp
3.0" = 300-350 hp
2.5" = 250-300 hp
2.0" = 150-200 hp
1.5" = 100-150 hp <-- this is where our *138 hp* 1.4LT fits

...of course, they also state: _"...less pressure downstream of the turbine is goodness."_


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## ZincGT (Dec 1, 2010)

Its 2.25 I re did my cat back about a month ago


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## shawn672 (Oct 31, 2010)

ZincGT said:


> Its 2.25 I re did my cat back about a month ago


 pics?


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## LARRY01Z28 (Dec 4, 2010)

ZincGT said:


> Its 2.25 I re did my cat back about a month ago


 
pics and sound bytes?


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## shawn672 (Oct 31, 2010)

So with the tune and going forward with other mods in mind, you should be looking at 2-2.5"


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## LARRY01Z28 (Dec 4, 2010)

ZZP recommended 2.25 to 2.5


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## 70AARCUDA (Nov 14, 2010)

...*if* 2.25" is stock, there's really no reason (except noise/sound) to go bigger unless _other_ goodies are added that enable _more_ HP to be made.

...I'm thinking it's a lot of money just to "sound" better, without some accompanying "go better" performance.


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## ZincGT (Dec 1, 2010)

The tip looks just like stock, I'll get a vid soon. I might do a diff setup because I think its to ''loud'' for an economy car. Its buy no means loud compared to all of the other cars I drive tho


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## ZincGT (Dec 1, 2010)

Took two vids on my phone. Will post them when I get home at 630 am


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## ZincGT (Dec 1, 2010)

First video
YouTube - Broadcast Yourself.


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## montgom626 (Jan 16, 2011)

ZincGT said:


> First video
> YouTube - Broadcast Yourself.


Link takes me to some videos, but not sure if it takes me to yours?


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## ZincGT (Dec 1, 2010)

It should 00zincgt is username
YouTube - Broadcast Yourself.


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## ZincGT (Dec 1, 2010)

new links*******


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## ZincGT (Dec 1, 2010)

you kinda have to turn up the volume to get a good sense of what it sounds like. I will take some with my video camera soon, possibly later today.


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## LARRY01Z28 (Dec 4, 2010)

sounds pretty good. what muffler did you use. and did you start from down pipe and put all new exhuast tubing in?


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## 70AARCUDA (Nov 14, 2010)

...did you use 2.5" diameter _all_ the way from catalytic converter, to muffler, to tail pipe?


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## ZincGT (Dec 1, 2010)

70AARCUDA said:


> ...did you use 2.5" diameter _all_ the way from catalytic converter, to muffler, to tail pipe?


its 2.25 cat back. idk what muffler it is to honest we just had it laying around, im going to change it eventually. its just a short straight thru.


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## Oh5V (Jan 4, 2011)

Just to point out, the OP didnt ask about adding a catback or what pipe size would be best...

he asked a specific question about a certain part of the factory exhaust that he is trying to identify, yet seems everyone took off on a tangent about catbacks...


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## LARRY01Z28 (Dec 4, 2010)

i guess we did get off point a little


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## montgom626 (Jan 16, 2011)

LARRY01Z28 said:


> i guess we did get off point a little


Any did we expect anything else?  This is a conversation. Let the good times roll!


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## 70AARCUDA (Nov 14, 2010)

...hey, *SpaceMe*, getting back to your question, I'd venture a guess that it's the FIRST catalytic converter (there are TWO). Look at this picture and point out exactly what you're asking about -- item #1 in left picture, or one of the things right after the flange in the right picture #4 (between #7 and #6)?


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## Spaceme (Jan 20, 2011)

Great picture 70AARCUDA. Yes, what I am talking about is the canister in the inset picture on the left. So that is a cat? I wonder if performance could be improved by removing it? Or removing it's internals?


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## 70AARCUDA (Nov 14, 2010)

Spaceme said:


> Great picture 70AARCUDA. Yes, what I am talking about is the canister in the inset picture on the left. So that is a *cat*? I wonder if performance could be improved by removing it? Or removing it's internals?


...yes, it's the "front" catalytic converter, just behind the turbo, it's purpose is to "light-off" quickly and control emissions. The "back" catalytic converter is the "normal" emissions controller and the only one used on the 1.8L engine.

...the Turbo "grabs" a lot of heat so a special, quick-light-off converter is needed to ensure emissions at initial startup don't exceed EPA limits.


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## LARRY01Z28 (Dec 4, 2010)

ZZP is making a o2 housing and i think they claim 9 or 10 HP.


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## hemank (Jan 31, 2011)

70AARCUDA said:


> ...the "trick" is to NOT get into an accident (wink,wink)...and I haven't had an accident in over 50 years!
> 
> ...'Defensive Driving' courses teach you pay close attention to what others are doing stupidly, and to steer clear of them at all costs.
> 
> ...drive as if _"...everybody is out to kill you..."_ which is probably true on just about all California highways (ha,ha).


I appreciate, but I think California highways are a 100 times better than what I drive through daily. (India) I studied in Germany so I know what good quality driving is, and comparatively I would say, We : either have no rules, or nobody knows them, people are too lazy to follow them. 25% people wear a seat belt (front seats). 1% people wear seatbelts - Rear seats. and 20% people wear helmets - bikes. lane discipline does not exist. You all are lucky to live in a disciplined place. cheers. no offence


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