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  #1  
Old 10-05-2006, 09:59 PM
Diesel newbie ;-)
 
Join Date: Aug 2006
Posts: 412
Turbo bypass

Talking with one of my co-workers today and he had what sounded like a splendid idea:
Tap in to the air intake pre turbo and connect that to the intake manifold. It would be as close to an unrestricted straight pipe as possible, but would have a flapper valve in it, such that when the turbo spooled up the valve would close via backpressure.

I figure it would introduce a bit of lag in the turbo spooling up and kicking in, in exchange for much better pre-turbo performance as the intake air doesn't have to make all those turns through the turbo and over the vanes.

Thoughts? Been there done that's?

-nB

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'83 300D Turbo
Current: ???K mi - 19.2mpg -> 17.4mpg -> 22.9mpg ---> ODO Died
bought at: 233.8K mi - 10MPG For $1.00
3.5 cylinders work: 320 320 100 340 280
Got insurance? FarmersReallySucks.Com
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  #2  
Old 10-05-2006, 10:05 PM
Craig
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I'm not sure it would give you much performance increase. Do you have any reason to believe the intake manifold pressure is too low at low rpm? Try putting a vacuum gage on the intake any see if you get any vacuum before the boost "kicks in."
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  #3  
Old 10-05-2006, 10:12 PM
TheDon's Avatar
Ghost of Diesels Past
 
Join Date: Oct 2005
Posts: 13,282
anyone up for some VNT turboness
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  #4  
Old 10-05-2006, 10:15 PM
Diesel newbie ;-)
 
Join Date: Aug 2006
Posts: 412
Quote:
Originally Posted by TheDon View Post
anyone up for some VNT turboness
I don't get it... need to study more
-nB
__________________
'83 300D Turbo
Current: ???K mi - 19.2mpg -> 17.4mpg -> 22.9mpg ---> ODO Died
bought at: 233.8K mi - 10MPG For $1.00
3.5 cylinders work: 320 320 100 340 280
Got insurance? FarmersReallySucks.Com
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  #5  
Old 10-05-2006, 10:18 PM
Craig
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Quote:
Originally Posted by networkboy View Post
I don't get it... need to study more
-nB
http://www.honeywell.com/sites/ts/tt/PassengerCars_LightTruks3_CP3HXNOKPJPUTB8SLO99Q5SFMZIHC4MW90812155218387_HBFRTGMKQK64U00ACROYP858GKI H564VY0812155701757.htm
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  #6  
Old 10-05-2006, 10:24 PM
Diesel newbie ;-)
 
Join Date: Aug 2006
Posts: 412
Hey, those look cool... expensive, but cool.
I was thinking cheap
wouldn't the bypass, at least to some extent, provide a similar performance improvement?
-nB
__________________
'83 300D Turbo
Current: ???K mi - 19.2mpg -> 17.4mpg -> 22.9mpg ---> ODO Died
bought at: 233.8K mi - 10MPG For $1.00
3.5 cylinders work: 320 320 100 340 280
Got insurance? FarmersReallySucks.Com
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  #7  
Old 10-05-2006, 10:27 PM
ForcedInduction
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Not really. If anything, it would *hurt* performance.
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  #8  
Old 10-05-2006, 10:43 PM
Diesel newbie ;-)
 
Join Date: Aug 2006
Posts: 412
Quote:
Originally Posted by ForcedInduction View Post
Not really. If anything, it would *hurt* performance.
Pray tell why?
Intuitively it seems as if it would help. There is a mess of bends and turbo vanes to get the air through before the turbo spins up, anything to lessen the drag on the intake air should be a good thing no?

I'm really curious, as said co-worker did a similar mod on a gasser and got way better low RPM performance and economy.

I realise not everything maps between gassers and diesel, but since diesels almost always benifit from lots of air...
-nB
__________________
'83 300D Turbo
Current: ???K mi - 19.2mpg -> 17.4mpg -> 22.9mpg ---> ODO Died
bought at: 233.8K mi - 10MPG For $1.00
3.5 cylinders work: 320 320 100 340 280
Got insurance? FarmersReallySucks.Com
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  #9  
Old 10-05-2006, 10:48 PM
Craig
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The main difference is that diesels have significant excess air at low rpm so increasing the air flow will not provide an advantage at low rpm.
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  #10  
Old 10-05-2006, 10:52 PM
ForcedInduction
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At idle, while there is no positive boost pressure, the turbo is still moving alot of air. Every millisecond that valve is open when you take off, that's time the turbo could be pressurizing the air.

Gassers have an instant quick rush of air when the throttle is floored. The air is moving to fill the manifold where there once was a void (vacuum) and the turbo *can* become a restriction for that split second. Since diesels don't have that throttle or vacuum, that mod would just add needless complexity and slower boost response.

Tweaking the ALDA to a higher setting would have a more noticeable positive effect.
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  #11  
Old 10-05-2006, 10:57 PM
Diesel newbie ;-)
 
Join Date: Aug 2006
Posts: 412
Sweet I learned something
__________________
'83 300D Turbo
Current: ???K mi - 19.2mpg -> 17.4mpg -> 22.9mpg ---> ODO Died
bought at: 233.8K mi - 10MPG For $1.00
3.5 cylinders work: 320 320 100 340 280
Got insurance? FarmersReallySucks.Com
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  #12  
Old 10-06-2006, 12:26 AM
sixto's Avatar
smoke gets in your eyes
 
Join Date: Jun 2000
Location: Eastern TN
Posts: 20,832
What you need is the afterburner mechanism in rallye Mitsu Evolutions. There's a fuel injector that fires into the turbine to keep the turbo spooled between shifts. Would require a little more work in a Diesel application.

Sixto
93 300SD
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  #13  
Old 10-06-2006, 12:32 AM
Diesel newbie ;-)
 
Join Date: Aug 2006
Posts: 412
Heh, rice up the benz? Shall we start another thread

Really it sounded like a reasonable idea, but as I've said before, all my experience is gas, though I've only had the diesel for ~2 months and I'm so deeply in love with it that my gassers are, well you can't see out the windshield without a bucket of water and a towel they've sat so long.
-nB

__________________
'83 300D Turbo
Current: ???K mi - 19.2mpg -> 17.4mpg -> 22.9mpg ---> ODO Died
bought at: 233.8K mi - 10MPG For $1.00
3.5 cylinders work: 320 320 100 340 280
Got insurance? FarmersReallySucks.Com
Reply With Quote
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