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Old 04-21-2013, 06:23 AM
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Turbo engine exhaust system diameter

On a NA engine excessively large exhaust pipe diameter can have a negative effect on exhaust velocity. What about a turbo charged engine? I've read elsewhere that one really can't go too big on system diameter on a forced induction motor. Is this true?

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Old 04-21-2013, 07:00 AM
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You can go too large but it's usually hard to for packaging reasons. You size your pipes based on power output and 400+hp apications would need 3" or larger, with a turbo 400hp is easy to get out of two liters or less. Packaging pipes larger than 3" diameter in most cars gets to be problematic.
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Old 04-21-2013, 08:21 AM
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exhaust diameter

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Originally Posted by Saito View Post
On a NA engine excessively large exhaust pipe diameter can have a negative effect on exhaust velocity. What about a turbo charged engine? I've read elsewhere that one really can't go too big on system diameter on a forced induction motor. Is this true?
can you actually name a situation where an exhaust system and muffler makes more power than tuned headers that are open?
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Old 04-21-2013, 08:40 AM
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can you actually name a situation where an exhaust system and muffler makes more power than tuned headers that are open?
No one is taking about tuned open headers. For most street driven cara that's no even a consideration.
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Old 04-21-2013, 09:22 AM
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turbo exhaust

some turbo systems limit turbo speed with restricted muffler and or exh. size. tho early heavey equ turboed diesel eng had no muffler and a short stack,therapid cooling of spent exhaust helped with turbo spoolup.The ford eco boost turboes are limited byexhaust size,i am told by dealer that change in ex size and muffler would void turbo warranty,not worth the risk. but on a street rod the biger the better would be my choise,tho limited by room
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Old 04-21-2013, 09:35 AM
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The engine in question is a 1.4L Chevy Ecotec Turbo 4. Factory size appears slightly less than 2". Some aftermarket systems are 2.25" while others are 2.5". I was wondering if 2.5" was too big in a turbo application for such a tiny motor. In an NA application a "too big" pipe slows exhaust velocity and hurts low range torque.
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Old 04-21-2013, 09:47 AM
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none sense

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Originally Posted by Saito View Post
The engine in question is a 1.4L Chevy Ecotec Turbo 4. Factory size appears slightly less than 2". Some aftermarket systems are 2.25" while others are 2.5". I was wondering if 2.5" was too big in a turbo application for such a tiny motor. In an NA application a "too big" pipe slows exhaust velocity and hurts low range torque.
exhaust after the turbo is only getting quieter from the system.The less restrictive after the turbo,the quicker the turbo might react,within the limits of the turbo.
go blow on a pin wheel
then do it again with both hands behind the pinwheel blocking as much air as possible after pinwheel
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Old 04-21-2013, 10:11 AM
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Quote:
Originally Posted by Saito View Post
The engine in question is a 1.4L Chevy Ecotec Turbo 4. Factory size appears slightly less than 2". Some aftermarket systems are 2.25" while others are 2.5". I was wondering if 2.5" was too big in a turbo application for such a tiny motor. In an NA application a "too big" pipe slows exhaust velocity and hurts low range torque.
What power level are you looking at? Displacement becomes irrelevant with a turbo, a 2l can make more than a 5l. 2.5" is likely okay unless you're running a really small amount of boost.

You need to be more concerned with bends and mufflers. They're where restriction usually occurs. Also smooth connections and transitions.
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Old 04-21-2013, 11:01 AM
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Its only rated at 138hp and something like 148 lb/ft torque (if memory recalls). Not hoping to pick up alot of power. I mainly just don't want to hurt any power that's already there.
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Old 04-21-2013, 11:51 AM
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At that low of output your 2" is probably adequate, just make sure you have a good cat and muffler. No kinky bends.
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Old 04-22-2013, 05:01 AM
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I have found that restricted turbos (lots of low rpm boost, full boost under 3000 rpm) tend to do better with "oversized" exhaust relative to the amount of hp produced.

For turbos that have less restrictive turbines (higher rpm boost, full boost over 3500 rpm) then the typical exhaust sizes for hp produced will apply.

A single 2.5" pipe is typical good for 250hp. However, I have a turbo engine making around 275 at the wheels with only 2.5" (mandrel bent). I plan to upgrade to 3" one of these days but its not on the short list.
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