[s-cars] Re: [Audi20V_Kruemmer] Re: tubular exhaust manifold and turbo options

[chris frank]

Mike,

This article seems to match Trevor's comments. 

Burns has lots of experiance in turbos and has
fabricated headers for turbo racers with inconel.

here is a link to their request form:
http://burnsstainless.com/Xdesign/Race_Engine_Spec__Form/race_engine_spec__form.htm

They do work exhaust blown, belt blown and N/A motors.

Cheers,

Chris


--- MLP <mlped at qwest.net> wrote:
> Trevor -
> 
> WRG to the "pretty sophisticated" software program
> for header design
> etc., that you mentioned Burns Stainless uses for
> making their
> recommendations on tubular header design, do you
> know what adjustments
> or assumptions, or changes made by the software, or
> the Burns operator,
> to take into account use in a turbocharged
> application?  Do they size
> the runners down at all from what a NA
> recommendation would be, or go
> with the same size?
> 
> I ask in light of the following two points on small
> vs. larger PRE-TURBO
> tube diameters:   
> 
> FIRST, there's the following comments, attributed to
> a Jay Kavanaugh, a
> turbosystems engineer at Garret, responding to a
> thread on
> www.impreza.net on design and exhaust theory that
> have made their way to
> postings in several places:
> 
> “Howdy, This thread was brought to my attention by a
> friend of mine in
> hopes of shedding some light on the issue of exhaust
> size selection for
> turbocharged vehicles. Most of the facts have been
> covered already. FWIW
> I'm an turbocharger development engineer for Garrett
> Engine Boosting
> Systems.
> 
> N/A cars: As most of you know, the design of turbo
> exhaust systems runs
> counter to exhaust design for n/a vehicles. N/A cars
> utilize exhaust
> velocity (not backpressure) in the collector to aid
> in scavenging other
> cylinders during the blowdown process. It just so
> happens that to get
> the appropriate velocity, you have to squeeze down
> the diameter of the
> discharge of the collector (aka the exhaust), which
> also induces
> backpressure. The backpressure is an undesirable
> byproduct of the desire
> to have a certain degree of exhaust velocity. Go too
> big, and you lose
> velocity and its associated beneficial scavenging
> effect. Too small and
> the backpressure skyrockets, more than offsetting
> any gain made by
> scavenging. There is a happy medium here.
> 
> For turbo cars, you throw all that out the window.
> You want the exhaust
> velocity to be high upstream of the turbine (i.e. in
> the header). You'll
> notice that primaries of turbo headers are smaller
> diameter than those
> of an n/a car of two-thirds the horsepower. The idea
> is to get the
> exhaust velocity up quickly, to get the turbo
> spooling as early as
> possible. Here, getting the boost up early is a much
> more effective way
> to torque than playing with tuned primary lengths
> and scavenging. The
> scavenging effects are small compared to what you'd
> get if you just got
> boost sooner instead. You have a turbo; you want
> boost. Just don't go so
> small on the header's primary diameter that you
> choke off the high end.
> ....."  there is more on the theoretical
> optimization of the post turbo
> exhaust system, including FWIW the observation "...
> 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.”
> 
> SECOND, vis-à-vis Audi's 2.7L twin turbo EM design
> and implementation,
> (a) if you have ever looked at the motors two cast &
> cased EM's, while
> the exhaust ports in the heads are "regular" sized,
> the three in each
> manifold squeeze into an extraordinarily small
> common exit/feed into the
> KO3/O4 hot side scroll.  (b) I believe the EM is
> actually enclosed in a
> second, probably insulating clam shell.  Are these
> just a packaging
> design problem for the twin turbo engines or a
> performance design goals
> as well?
> 
> Mike
> 
>   
> 
> 
>