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Re: SVO: Re: Some Ideas on Preformance Exhaust For The Turbo Coupe

On Thu, 20 Nov 1997, Dave Compton wrote:

> Continued thread...
> Scott said
> > they do??  not saying that none do, but I have never seen one. Only times
> > I see it go down is in a y pipe on a V engine...
> They do.  Look at mom and pop type cars, and read.  I'm not making this up.
Ok,,,joe said your rite that on stock cars alot do step down, but its not
for that reason.....Joe says it makes em quieter.
Do performance cars step down in pipe size?  I think a stock stang is 2.25
all the way out.  Grand Marquis and Colony Parks, yeah, cars built to
perform, no.  

> > And I hav enever seen a pipe size change as drastic as 3" to 2.25". Thats
> > rejected.  how coem the outlet piping is not smaller on intercoolers? the
> > change in temp is high there too.
> When AIR cools is becomes more dense, you don't want to waste that by
> making the piping on anintercooler smaller.  And exhaust gas is not air.
Explain how ehxuast gas, and air(another gas) could somehow have totally
different laws...Are you saying exhaust gas does not become more dense as
it cools? 

> >  make big tubing
> > > (downpipe) at front.  Yes, the rear will help too, but I believe that
> the
> > > improved compopnets contribution to poewr is almost equal.
> > > 
> > 
> > your saying that just having a bigger downpipe for about 40" of the
> system
> > is equal to having a bigger cat back, AND bigger mufflers? I would be
> > willing to bet that if you put a 3" downpipe(especially a crushbent one),
> > on a stock exhaust, you would be hardpressed to gain much of anything.
> Maybe, maybe not.  But I ante'd up the money and bought one, and I'm glad I
> did.  I think it works.
Ahhh, I see....usin that "seat-o-da-pants dyno" huh?  Vendors love that

> > But lets talk disturbances of flow.....
> > lets say you put on a 3" downpipe.  Right at the joint where the pipe
> goes
> > from the outlet of the turbos 2.25 inch to 3", there is a resistance to
> > airflow, that is not there with a stock pipe.  
> A step up in size does not create a disturbance, quite the opposite in
> terms of impeding flow.

Wow, my fluids book, and PhD professor is wrong!  Wrong, it does.  Unless
you have a transition with an angle of aprroxamatley 5 degrees, you will
lose flw at that point.  Thats not to say that the whole system will
suffer nescassarily, but it does hurt.  Thre will become a point when the
advatages of the bigger pipe will outweigh the decrease, but its still
Its in my textbook......Like I said, unless all these PhD researchers are

> >then the exhaust happily
> > flows thru the larger pipe, until we get to the point where it meets up
> > with your stock cat, or stock cat back.  thre is another decrease in flow
> > there, where the pipe has to drop down to 2.25" again.....
> And the exhaust gas has now cooled, and needs less space, or volume.

So if the ehaust was 100 feet long what would ber the final acceptable
size? .75"?  Im tellin ya, your on to soemthing here...Proving decades of
technology wrong....When were stepping up we should really be stepping

> > its a whole lotta reduction on flow.  made up for by the cooling of the
> > pipe? I doubt it.  
> Maybe not completely compensated for by the cooling exhasut gas.

Ok, ok, I'll bite....just how much does it cool?  Whats the density of the
exhaust gast at the turbo and at the outlety of the downpipe? I would
doubt it cools all that much, because the ehaust has to be atleast a
certain temp for the cat to work.  And how long does it take for the
exhaust to go from the turbo to the inlet of the cat at WOT?  A split

> > if the cooling affect helps so much, why do the nascar guys step UP their
> > header size as they go away from the head??  
> Gee this works for them, but you just said that the step up in the headpipe
> causes a "resistance to
> airflow, that is not there with a stock pipe".

Yes, the step up does introduce a restriction, but guess what.  The
reducer that is on the other end of the pipe is twice as big a reduction
of flow.  To put it into perspective, the step down from the 3" to 2.25,
is FIVE TIMES the restriction of a 45 degree mandrel bend......

> It works the same way.

Yep it does....

> > Like i said, I dont know the quantification of the cooling of the exhaust
> > and its affect on pipe size requirements, but it helps more than the
> > addition of a higher flowing, bigger muffler, especially with all the
> > resrtictions that system has...
> > 
> Huh? That sentence lost me..

I was saying I am not going to talk out of my ass like some other may.
Without knowing the temps of the exhaust, and the CFM flow at the outlet
of the turbo, I cant actually say what the improvemant/loss would be.

> I am not saying that this is an all out race system, but I think a lot of
> guys don;t want to pony up big bucks for a complete system.  This *is* the
> cheap way out, but it's a big improvement.
>From the "seat of the pants dyno"?  Haha....
I went from running absolutly no exhaust on the pinto to running a Stock
Merkur downpipe that goes to a 2.5" open side pipe after the flex joint
and LOST NOTHING!  How could a 3" pipe be an improvement?

And I want to get something straight. I am not saying that a 3" pipe would
not improve some cars.  But it will not improve a car where the pipe is
not the restriction.  If you have a 3" cat back, a 3" downpipe would help.
But if you have a 2.25" cat back, a 3" downpipe does nothing.  

PS: If you are in the market for a  3" downpipe, make SURE you ask the
salesman if it is MANDREL BENT!  No matter who is selling it, you would be
suprised the garbage some "gurus" turn out...


-71 Pinto, stock 2.3 turbo, 13.67@98, radials
	Big intercooler ON!
	T4 Compressor soon to be on!
-85.5 Escort, SOLD! 
-85 Merkur, let the modding begin!