[DeTomaso] Speaking of exhaust systems...

Guido deTomaso guido_detomaso at prodigy.net
Sun Feb 26 17:19:55 EST 2012


Can't tell exactly from the photos here which cylinders are paired:

http://www.rc-tech.net/cars2/ts/eh/hp.jpg

But here it looks like the driver side forms kind of a "W" * while the passenger 
side is two wyes:

http://www.bacomatic.org/gallery2/v/hidden/dan/dan-cars/album28/white_pantera_engine_403C/high_port_ss_tri_y_03.JPG.html


On the internets, there seems to be a variety of pairings out there.  But is it 
not true with the d-side "W" and the p-side two "wye's", this is a true 270 
degree header system?  Where each cylinder of every pair fires 270 degrees apart 
from its mate?

Thanks,

GD

* W = make a peace sign with both hands, then make an X with your pointing 
fingers...



________________________________
From: Daniel C Jones <daniel.c.jones2 at gmail.com>
To: Pantera REALBIG forum <detomaso at realbig.com>
Sent: Sun, February 26, 2012 10:14:52 AM
Subject: Re: [DeTomaso] Speaking of exhaust systems...

> Um, not be be a doubting Thomas,,,,, but from the very little I understand
> about exhaust would lead me to believe you are going to have fits with the
> primary lengths robbing you of horse power and torque above 4000rpm or
> lower. Most header primary lengths are between 28-36 inches for optimum
> performance. They do look crazy though.

That's misleading.  The length and diameter sets the harmonic but the
pipes resonate at multiple harmonics.  If the ideal length of primary
for a given engine is 30 inches it will also tune in at 15 inches and
60 inches, just on a different harmonic.  However, each subsequent
harmonic is weaker and you need to consider the induction tuning as
well.

> I have a radically different exhaust system I hope to try this spring.
> Instead of going through the suspension it is routed over the suspension.
> It is collected late in a home built muffler (not pretty) with a butterfly
> to change back pressure.

Interesting.  What are the primary lengths and diameter?  So it appears
no direct collector effect.

> I am not 100% on board with the benefits of equal length headers unless it
> is a 180 degree system. You will always have one cyl off unless you cross
> over. My goal was to delay the joining all 4 as long as possible.

Poor exhaust tuning can hinder performance two ways.  First, any residual
exhaust gases left in the cylinder robs the space available for incoming
fresh mixture.  Second, higher cylinder pressures cause by incomplete exhaust
blowdown will cause reversion flow where a portion of the residal gas is
forced back up the intake tract during the intake valve opening event.
This dilutes the induction flow which is pulled back into the cylinder during
the intake stroke.

For 4-into-1 bank separated headers on a 90 degree non-flat plane crank
engine, equal length isn't as big a deal as the timing of the finite amplitude
waves.  There are waves that travel the length of the exhaust (and intake)
tract.  The frequency of these waves are a function of the primary length
and cross-sectional area.  Note that these waves move within the exhaust
(and intake) flow. Depending upon their direction, they can either aid or
hinder flow motion. One characteristic of an finite amplitude wave is that
when it hits an abrupt area change (such as a runner opening into the plenum
in an intake manifold or a primary pipe ending in a header collector), it
will change direction. As a compression wave moves down the header primary,
a portion of it will change direction when it comes to the end of the primary
in the collector and be reflected back as an expansion wave.  The continuing
positive pressure wave will enter the collector and reflect back another
expansion wave when it reaches the end of the collector.  If the collector
length is right, the expanision wave will arrive at the cylinder just slightly
later than the expansion wave from the header pipe end.  This wides the
scavenging wave, increasing the time of negative depression removing residual
spent gases and aiding induction flow by reducing the cylinder pressure below
the inlet pressure during overlap.  That's why collector length is so critical.
The larger the cam overlap, the more important this becomes.

> I also believe changes in back pressure, an equalization of the system
> some times give scavenge more credit then is due. I doubt few will agree
>  with me but that's fine; that's why I like to play.

Looking forward to hearing your results.  I'm in the back pressure is bad camp
but it's the dynamic pressure that is important.

> They were 2 into one but you cannot properly match 2 into one with out a
> cross over. The effects were devastatingly bad; which is good for learning
> some times.

I just so happen to have something similar here:

http://www.bacomatic.org/gallery2/v/hidden/dan/dan-cars/album28/white_pantera_engine_403C/high_port_ss_tri_y_02.JPG.html

http://www.bacomatic.org/gallery2/v/hidden/dan/dan-cars/album28/white_pantera_engine_403C/high_port_ss_tri_y_03.JPG.html

http://www.bacomatic.org/gallery2/v/hidden/dan/dan-cars/album28/white_pantera_engine_403C/high_port_ss_tri_y_03.JPG.html


They fit C302B high port heads and are built like tri-y's but instead of having
a second merge into a collector they went into dual mufflers per side.  Without
the second merge, I didn't think they'd work well so I'm thinking
about modifying
them with dual pipes that route through the suspension into a second merge
making them full length tri-y's.  In previous testing, the Euro GTS Pantera
shorty headers did pretty decently at higher RPM but gave up some low and mid
range to long tube 4-into-1 headers.  With the tri-y approach, I may be able to
get a full length header that fits the chassis.  Nothing has been mocked up yet
but I hope to test them on the 403C we have currently on the dyno. The first
steps are 1 3/4" and the second is 2" with a 2 1/2" second merge outlet leading
to 2 1/2" single inlet/dual outlet Magnaflows.  If the initial testing
is promising,
I have some header design software now that will help me optimize the design.

I'll make another post on the initial dyno results but we're currently running
Pantera shorty high port headers from Precision Proformance:

http://www.bacomatic.org/gallery2/v/hidden/dan/dan-cars/album28/white_pantera_engine_403C/402C_aluminum_bits_misc_parts.JPG.html

http://www.bacomatic.org/gallery2/v/hidden/dan/dan-cars/album28/white_pantera_engine_403C/A3_heads_A331_intake_QFT_carb_PPC_headers.JPG.html


With unported Ford Motorsport A3 heads and A331 Torker (modified for
better low RPM)
through Byars Pantera shorties and 2 1/2" single inlet/dual outlet
Magnaflow mufflers
it made 560 HP @ 6300 RPM and 512 lbs-ft @ 4900 RPM (factoring in
Dave's dyno is 4%
to 5% low compared to the same engine on the calibrated Engine Masters dynos).
Open headers picked up 10 ft-lbs and 5 HP so the 2 1/2" mufflers are a
bit restrictive
but not too bad and nothing like the 50 HP drops we've seen with Euro
GTS mufflers.
Engine is a hydraulic roller cammed 10:1 compression street motor and
there are better
cylinder heads on deck for testing.

Dan Jones
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