[DeTomaso] Speaking of exhaust systems...

gow2 at rc-tech.net gow2 at rc-tech.net
Sun Feb 26 20:38:45 EST 2012


Each side has a 2 into one with 2 tubes going over the suspension. The 2
tubes were then collected again into one. You can see it some here:

http://www.rc-tech.net/cars2/ts/eh/ex1.jpg

At the time I made a computer program to read and data log parameters on
an engine test stand. This is not a dyno nor was it intended. It has
already be dynoed. It was built more as a torquer low rpm engine with max
rpm of 5500. I did so because I wanted to keep Valve problems to a
minimum.

The engine is a Ford 400 stroked 434. It obtained just short of 500hp at
5500 rpm (495) with 534lbs tq. We were shooting for 500hp and I think it's
pretty much there. Lift and cam is modest but I think it will make a
bullet proof engine.

We did however turn 450lbs of tq at 2000 rpm with a nearly flat tq band
all the way up. The headers on the dyno were pretty small so there may be 
a little left.

With the program and circuit I wrote the first thing I got going was EGT.
With a steady run at 2k rpm look at the difference in EGT:

http://www.rc-tech.net/cars2/ts/egtrun1.jpg

http://www.rc-tech.net/cars2/ts/eh/12082008.jpg

http://www.rc-tech.net/cars2/ts/d2.jpg

I also had backfiring out of both the intake and the exhaust but I didn't
spend too much time sorting out the timing when I saw what my problem was.

At first I thought I had done something wrong with the EGT's so I swapped
them and they were correct. The temp stayed with the corresponding cyl.

Then I analyzed the firing order; something I should have taken more
seriously when building the headers (especially before I had them ceramic
coated).

With 2 cyl collected, one was separated by 2 firings and the other by 6.
All were the same. The first in the collector to fire had no back pressure
and was hot. The second one in the collector still had back pressure and
was 1/2 the temp.

Keep in mind the difference in temp was not the difference in the temp but
the difference in the EGT which was just outside of the cl in the header.

The cyl with no back pressure exited the chamber still burning. The cyl
with back pressure completed the burn inside the chamber and burned clean.
Look at the difference in the exhaust ports you can tell which is which
(and yes the first headers were poorly port matched, the second are far
better).

http://www.rc-tech.net/cars2/ts/eh/ex6.jpg

http://www.rc-tech.net/cars2/ts/eh/ex2.jpg

You can see the exhaust leak in the second photo.

This lead me to wanting to experiment with back pressure.

John Kaase who is known for is Ford 400 builds in the Engine Masters
showed up at a competition with the wrong headers. The headers he grabbed
were too small. He knew this would cost him the competition but he had no
choice to run them. It turned out to surprise even him as he made 15+ more
HP then the engine ever had and actually one the masters with it.

I see so many engine builds where some one changes one part, gets an extra
5hp then says well part "a" is better then part "b". This is especially
true of exhaust. Well the scavage is better, long tubes is better, etc.

Engines are a lot like the front suspension. Like some one mentioned (you
know who you are) if you change caster or camber it changes everything
else. Same is true for engines and there is a much bigger story to hanging
parts some times.

My goal with the tunable back pressure is to find how much back pressure
works best for a cam. The cam is not the only thing that determines the
back pressure need but I would say is by far the biggest thing. This might
even be somehting which could be changed on the fly to make a car more
friendly on the street or more friendly at say low rpm.

G













> 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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