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



On Fri, 21 Nov 1997 Mp23cc@aol.com wrote:

> We have sold 100's of our 3'' downpipes for the Merkur XR4TI. They have
> worked out great, most people have found more power gains with this pipe
> added then the gains with the Borla system alone. One list member found with
>  G-Tech that he gain upto 11hp after he installed the pipe. Most if not all
> systems have been used with the stock 2 1/4'' cat. As for the full round
> mandrel bending of the downpipe, our pipe is mandrel bent but not full round
> and the gains have been great. The exhaust gas will stay to the outside of
> the bend not the inside of the bend. Some people get a hangup about not
> haveing  full round bent pipe. It is not needed unless you are useing a pipe
> size that is to small.

But why?  So you mean you have those bends like you buy at pep boys witht
he smooth(but usuallu flat outer edge) and the krinkled inside radius?
At any rate, why have anything less than a full mandrel bend? If you are
saying "some people have a hangup" about that bend, that kinda implies to
me you have sold some to people and they were kinda pissed.  With that,
why have that bend?  Look, I dont know how much you sell the pipes for,
but if it is the same as what I have seen people post for the Corral pipe
at 130, you are makin a grip of cash on each one.  I KNOW that to make one
with 100 percent mandrel bends couldnt cost you more than 20 to 25 dollars
if you own your own welder. Your saying that 100 dollars isnot enuff
profit for a peice of pipe that takes about half hour to an hour to make? 
You need to cut the 15 dollars for the cost of the full mandrel down to
the 5 dollar krinkle pipe?  I got an idea.  You could start makin them out
of that flex pipe stuff they sell at the parts store and make a killing
with a one size fits all.    

  The bigger downpipe acts like a big expansion
> chamber. It will let more exhaust exit the turbo in less time the the stock
> pipe. The turbo will spool up faster the higher before the backpressure
> builds up from the rest of the exhaust system. If you have a 2.3 turbo it
> will work much better the stock downpipe. You will more power with a single
> 3'' system then a smaller dual system.
>  
Would you agree that absolutly no pipe would flow better than a 3"?
If so(how could you disagree), how bout this....next time I go tot the
track, I will run the car witha stock downpipe, then pull off the downpipe
and run straight turbo and thats it.  that will say jus how bad the
stocker hurts performance wouldnt you say?
You saying that the turbo will spool faster with your expansion chamber
becasue it will take longer for the pressure to rise? well lets see.   
I am going to assume alot of conditions here, but beleive me, they will
help your expansion chamber theory.  Take a 140 cubic inch motor, at 3500
rpm, 100% volumetric efficiency, no boost pressure.  that is 141 cfm of
air entering the engine..now lets say there is no expansion of the gasses
during combusiton, in which there is.  So we have 141 cfm of air leaving
the engine.  I roughly guesstimate the lenght of the downpipe at 36".  A
3" downpipe will have a volume of 254 cu in, and a 2.25 inch pipe would
have a volume of 143 cu in, meaning a 111 cu in difference in volume. 
That 111 cubic inch is equal to .0644 cubic feet.
now lets reveiw your theory before continueing.  your saying that you get
less lag becuase the pressure rise is slower in the 3" due to the fact
there is more volume.  Well, if we have a volume rate of 5 cubic feet per
second, and a 20 cubic foot box, with no pressure rise it would take 20/4
or 5 seconds to fill the box.  The pipe is the same.  Volume divided by
the flow will tell how long it will take to get the same pressure as the
smaller pipe.
So, we have a volume of .0644 cubic feet.  flow rate of 141 cfm, or 2.363
cubic feet per second.  Do the math, and it would take .0272 seconds
longer to reach the same pressure in the bigger pipe. We have hi flow
rates and small volumes here, it doesnt take long.

If that way confused you, look at it this way.  divide the volume of the
2.25 inch pipe by the flow rate, and it will take .0350 seconds to fill a
2.25 inch pipe to a certain pressure. to fill a 3" pipe to the sme
pressure will take .0623 seconds.  subtract those two numbers will give
you  the difference.  which is .0272 seconds.


> When doing testing you need to keep things even or the test do not mean much.
> The car that may come in at 2,600 lbs does not show much to anyone who is
> driving a modern car that comes in around 3,000. This is why the owerns of
> lite cars can get away with borderline thinking and steups and still survive,
> they do not have the same amout of load to deal with. 
> 

Exactly. that is why I propose to drop my pipe off my car and run it.  A
lite car will still slow down if a heavy car would.


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Scott
-71 Pinto, stock 2.3 turbo, 13.67@98, radials
	8.1@85 1/th mile on slicks
	Big intercooler ON!
	T4 Compressor soon to be on!

-85 Merkur, let the modding begin! 
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