Date: Wed Mar 25 17:36:01 1992   
Subject: ansa exhaust systems

>On a recent trip to my dealer, the parts manager and I were discussing
>sport exhaust systems for the 240Z.  He said that ansa (maybe not the
>correct spelling) was the best for an early Z.  

My experience has been that if you retain the stock cast iron manifold
(not bad in its own right), any 2.5" exhaust with a turbo-corvair-style
muffler will work fine.  I started fabricating my own years ago because
I could do it cheaper and I could make it a one piece all-welded affair.
These performed as well as any store-bought system I ever tested.

>I have also been told not to buy headers from a catalog because
>you cannot see how thick the metal is where it attaches to the gasket.
>Is this important?  What can you expect from changing exhaust systems?

Depends.  I have a set of headers on my main Z now that use very thin
flange metal.  I have had no leakage problems, however, because I 
installed the rest of the system properly so that there is no stress on
the headers themselves.  The key is to install a flex joint between the
header and exhaust pipe so that there can be motion between the headers
and exhaust when the engine rotates on its mounts or when the frame
twists.  I have traditionally used a stainless steel bellows made for
aircraft exhaust (check your local FBO) but lately many OEMs have
been including stainless steel braided flex hose in their exhausts.
These should now be available from your car parts store or a muffler 
shop.

The second key is to support the forward end of the exhaust tube so 
it is rigidly mounted.  On rubber, of course, unless you like lots of 
exhaust noise in the cabin.  I generally mount to the rear transmission
stay.  

Lastly, (and none of the commercial exhausts do this that I'm aware of)
a small resonator as close as possible to the header/manifold exit
as possible is necessary to break up the resonance of the long pipe that
will cause a giant flat spot around 4000 RPM.  I usually just prowl the 
local muffler emporium until I find a suitable OEM part.  Typically from
an older Caddy, it should be a glass-pack and have an inner diameter
at least as large as the inlet.  I have used a cherry-bomb-style 
muffler but they flow really badly.  This resonator will completely kill
the boominess headers on Zs are noted for.

John

Date: Mon Jun 15 14:42:18 1992   
Subject: Headers

>Roger, I can't recommend a particular brand over any other but
>one thing I found when running both my 240 and 280 with headers:
>
>If you drive mostly on the street (don't most of us?  :-)   ),
>you might want to consider using slightly smaller diameter pipes
>than what some of the header folks are selling. (2.5" is typical...)
>I used 2.5" pipes all the back from the header collector to a single 
>turbo muffler (the old hot rod standard) with 2.5" inlet and outlets.
>
>The results were less than desired. It was noisy and there was a
>highly noticeable loss of low end power. When I reached 4,000 rpms,
>it was great, but since most of my driving was limited to street, 
>a few autocrosses and regular Sunday morning "banzai" runs, I came
>to regret running such a large pipe. 
>
>When I was in the process of restoring my '76 280 (returning to
>"stock" condition) I opted for essentially the same setup except 
>that I used 2.25" i.d. pipes and a comparable muffler. This setup was 
>much more pleasing for my use but alas, I didn't get a chance to fully 
>enjoy it as the car was destroyed in an accident (taxicab vs. Z; my 
>Z, unfortunately, lost with irrepairable damage to frame) but the 
>couple of months I ran it were great (comparatively speaking of course.)

Ohhh.  too bad about the taxi.  Always hate to hear about a Z meeting
its maker.

On the pipe issue, your solution is one that most likely works but
for the wrong reason.  I've experienced and solved the same problem 
but with a radically different method.  The problem is the long pipe
from the header to the muffler sets up a series of RPM resonances,
audible to you as "boominess" or ringing.  These resonances return
reflected exhaust pulses at all the wrong times and make the engine
feel real flat.  At higher speed, the pipe length is so long and 
back pressure is rising so that these effects are largely gone.
I've investigated this phenomena using a piezo pressure transducer and
scope and am comfortable that my explaination fits the observed data.

The smaller pipe is probably doing is changing the resonant frequency and
raising the static pressure enough to mitigate the effects.

My solution, developed after testing with open headers with a variety
of collector lengths, is to terminate the header with a small resonator
about 9" out from the tubing junction.  This standard glasspack-type
resonator acoustically terminates the collector so that it appears to be 
working against conditions similar to being open.  A second benefit of
doing this is all booming and ringing are gone.  The car sounds 
almost stock until you wind it up.  Then all I hear is the bit of
residual header ring - very nice.  I actually use a 3.5" diameter tube
for the exhaust, mainly because that's what I use on my turbo motors
and am set up for it.

>P.S. I also used a thermal header wrap (was from iPD, the Volvo guys)
>to quiet the "pinging resonance" of the headers that was so annoying.
>Worked great!

yep.  Highly recommended.  In the US, Summit racing also carries it.

John

Date: Mon Jun 15 18:32:01 1992   
Subject: exhaust

>I've got the same problem, but with the stock manifold and a 2.5"
>`turbo' exhaust.  Rumbles real nice at idle and on the highway.  But
>that 2200 RPM resonance gets _real_ old in town.
>
>Except for the header wrap, I dont see that the proposed solution is
>specific to headers;  any reason the resonator wouldn't work with a
>manifold?  Is 9" down from the manifold flange still about the right
>place? [The 2 internal pipes join essential at the flange.]
>
>This (2.5") "standard glasspack-type resonator";  is this something I can
>easily pick up at a local parts place, or did you have something
>specific in mind?


Don't see why it would not work.  You might want to look to make sure
your exhaust is not touching something.  I know it's an obvious thing
but it's fooled me before.  I've built some 3.5" exhausts that 
connect to the stock manifold (works real well) and have never
noticed the booming.  I'd suspect distance would not matter too much
with the stock exhaust manifold.  Might be worth doing some testing.

The resonator is a standard catalog item.  I think it is for an old
60s vintage Caddy.  It looks like a turbo muffler except a bit
shorter and the pipes enter and exit from the center of the ends.
I just prowled around in the Walker catalog 'til I found what I wanted.

I can also tell you what does NOT work.  Cherry bombs.  What a piece of
sh*t!  I got more pressure from a CB with no pipe aft than I did
from the stock system!  The lack of matching to the inlets and the 
heavily louvered core really kills flow.   Never tried any other 
brand.

John

Date: Tue Jun 16 04:27:24 1992   
Subject: Re: Headers

>The smaller pipe is probably doing is changing the resonant frequency and
>raising the static pressure enough to mitigate the effects.
>
>John,  how does the higher back pressure prevent the reflected finite
>amplitude pulses from reaching the engine?  Is the flow rate at high
>revs great enough to mostly disipate the reflections or does it have
>something to do with whether or not weak shock waves are generated?

Good question.  I'd guess it has to do with whether or not shock
waves form.  It might also have to do with the change in 
temperature with RPM changing the speed of sound enough to cause 
the effect.  I know that's an issue in two stroke expansion chambers.
Some racing bike tuners are now insulating the chambers to reduce 
this effect.  I tend to get rushed for time on things like this 
and end up noting the interesting data from the instruments and
postulating a plausable theory but not doing a whole lot of work to
back it up.  yeah, I know, a bit sloppy but my work on creating a 36 hr
day has not been going well of late :-)

Also, what effect does the presence of a turbo have on all this?

In this context a turbo does exactly the opposite of what is desired.
Off-boost, the turbine has practically no effect on the acoustic energy
being passed.  That is, of course, when the issue of boominess arises.
Under boost, the turbo is a quite adequate muffler by itself.  I got
in a pinch in my first turbo conversion waaaaay back in 74 and 
ended up driving the car sans muffler and tailpipe for a couple of
weeks.  I learned to WOT it whenever I saw a cop.  :-)  The car
was actually quieter under boost than at idle.  And ohhh that turbine
whine! :-)

73 John

Newsgroups: wiz.hotrod
Subject: Re: Header paint
Date: Thursday, Sep 10 1992 17:11:45
From: jgd (John De Armond)

> I've tried nearly everything, including sandblasting brand new headers
>and drenching them with VHT header paint.  The Hooker "lifetime"
>aluminized headers lasted a few months before they started rusting, and
>so forth.
>
> I found something called "Barbecue Grill Paint" at the hardware store.
>It lasts a bit longer than the VHT, and it's much cheaper.

Here's something I've used for a long time that works pretty well.  The
last set I did was on my Z engine two years ago.  No rust yet.  Sandblast
them clean and chromate passivate the bare metal.  Then apply a couple of
very heavy coats of aluminum paint.  Allow to dry and heat fairly hot
to cure.  After curing, paint with your favorite color Bar-B-Que paint.

The chromate treatment is a pretty standard body undertreatment available
at the body shop supply store.  The aluminum paint is ordinary aerosol
paint.  I just choose the brand whose label indicates the highest solids
percentage.  I think my last can was American Auto Parts brand.  

John

Date: Thu Sep 17 14:49:10 1992   
Subject: Re:  Experiences with V-8 conversion in 240Z - installment #1

>Personally, I would go with 2 1/4" dual exhaust on a small block chevy.  The 
>cam you are using would be best served with a little larger exhaust.  Also,
>if you havent bought it yet, go with a 650 cfm carb.  If you have then the 
>750 should work O.K., but is pushing the limits of a 327.

What I use on my high output Turbo engines, which should flow about the 
same as the V-8 is a 5" pipe from the turbo outlet to below the engine.
Drop to 4" run to a Flowmaster muffler (no, don't remember the part number
right ofhand.)  mounted in the drive shaft tunnel.  From there split out into 
two 2.5" tubes to the rear.  The two tubes are vastly easier to route than 
one 3.5-4" tube.

John

Date: Mon May 2 23:26:51 1994   
Subject: Re: request
From: emory!proteon.com!bhaley (Bruce Haley)

>   >	   If I run stock exhaust to a 2.5 inch exhaust is that
>   >	   doing anything without a HEADER?
>
>   Sure - makes it a whole lot LOUDER.  It may buy you some performance
>   increase, but not without the header.  Even with the header, don't
>   expect eye-popping performance gains without intake mods - exhaust
>   scavenging can only do so much.  In fact, with 2.5", you will probably
>   over-scavenge, negating some of the performance gain.  On my basically

[some BFH setup info deleted]

>   [Now I'm gritting my teeth :-) Overscavenge?  Huh?  As far as power
>   goes, headers are a waste of money on an otherwise unmodified engine.
>   (speaking L series engines here.) The stock exhaust manifold is
>   surprisingly good.

[some good JGD input deleted for brevity]

Yes, overscavenge.  I read somewhere (perhaps in the Zcar FAQ ??) that
headers on a stock engine actually rob some performance due to
the fact that they are pulling some of the intake charge through
before ignition due to the freer exhaust flow.  A modified intake
(which would presumably supply a bigger intake charge) compensates for
this loss, from what I remember.

Any truth in this, JGD ?  I don't normally disagree with the Z-car
deity (and promise to say 5 Hail Marys and 5 Our Fathers if I am
wrong, and I am not even Catholic !), but I read this recently.  I
remember this, because up until I read it, I was under the impression
that you could get an easy performance increase just by freeing up the
exhaust with a header and big pipes.

Bruce (waiting for the good word of the Z-car lord . . .)

  
[Alright, cut it out!! :-)  But if you want to kiss my feet..... :-)

Back to exhaust.  Think about how the 4 stroke engine works for a
moment.  The exhaust valve is opened somewhere before BDC on the power
stroke and stays open until sometime after TDC on the exhaust stroke.
It stays open past TDC because the exhaust gas has inertia and so that
the exhaust system can continue to scavenge after TDC.  Meanwhile the
intake opens a little before TDC on the exhaust stroke and stays open
awhile after BDC on the intake stroke.  The period during which both
valves are open at the same time is called the overlap period.  It opens
early to allow any vacuum created by the exhaust system to start the
intake flow early and it stays open to allow the ram effect of the
intake system to push additional charge in after BDC.  Let's look at
some real numbers.  These numbers are for the cam I use in my turbo
engines:

Intake opens   10 deg BTDC
	   closes  46 deg ABDC
Exhaust opens  45 deg ATDC
       closes  1 deg  ATDC
	   overlap 11 deg

The only time "overscavenging" could occur would be during the 11
degrees of overlap where there is a direct open path between the intake
and exhaust - 11 degrees in this instance.  But overscavenging could
occur only if the headers were operating - returning scavenging pulses
at the proper instant - and that only happens in the speed range the
headers are designed for.  At that speed, the inertia of the gas streams
prevents it.  At any other speeds, overscavenging isn't possible because
the headers are not working.  What DOES happen in engines with high
overlap at low speed is the bacpressure in the exhaust system pushes
exhaust back through the exhaust into the chamber and ultimately back
out the intake.  This dilution effect is one of the things that makes a
high overlap cammed engine idle roughly and load up.  The other is the
aforementioned reverse flow in the intake.

Now consider the ideal situation.  In a perfect world the headers would 
return a perfect vacuum pulse just as the exhaust valve closes.  This
would leave nothing in the cylinder to dilute the incoming intake charge.
Of course, we can't achieve the ideal but properly designed headers can
return a substantial vacuum pulse to the cylinder.  JGD]