Mr Helmholz - simple model

[Todd....!!]

The way I was taught to roughly but effectively 'tune' my exhaust system
on my 4 stroke v-8's engine's is to bolt about a 2 or 3 foot pipe to the
header collector paint it black with some spray paint (preferably BEFORE
installing the pipe) then do a run down the strip...

After runnin the car at WOT for a 1/4, there will be a point on the
'tuning' pipe where the paint has been burned off, and a point further
up towards the header where the paint isn't burnt at all!

At the point where the paint begins being burnt is where ya cut the
pipe.. Whalaa instantly tuned exhaust...

I've never heard a technical explanation of why this works or even if it
helps or hurts or is just a guess at the correct length of exhaust
pipe...

But after readin all this about a 2-stroke Mr. Helmholz resonance model
and how it's applicable to at least a two stroker... I had to post my
'tuning' rules as passed down to me by a pretty smart engine
builder/tuner...

Any additional info on the 'tuning' technique I've described above?

Thanks for anything!

Will most likely be runnin the 97 Stratus with a 4 banger, 4 vlvs/ cyl
2.0 liter automatic to the strip this evenin....  Wanna see what she
does before I decide to either keep er or give her back to ol
Chrysler...

It DEFINITELY beats the HECK outa my 70 Bee as far as gas mileage, but
the torque department is lackin a bit.... what's it got like 130 lb ft
vs 500+ from the Bee's 440...  We'll see...

$160+ per month for gas for the Bee vs. MAX $60/month for gas for the
Stratus...

If she breaks into the 16's this evenin, I'll be pretty happy!

Will keep ya'll posted...

ALSO, the Stratus' engine cuts off at like 85 mph, would any of ya'll
know how to bypass this?  It's a speedometer thing, I believe cuz the
rpm's aren't much over like 3,000 or so at this speed, the red line is
6,000... so it's not an rpm limiter(Maybe a combination?)

Any clues would help tremendously!

Thanks!

Todd....!!
http://www.c-com.net/~atc347/toddlnk.htm

Stuart Baly wrote:
> 
> >If this opens a whole new box of problems, just ignore.  But, I've noticed
> >what a huge change expansion chambers have had of VE in 2 strokes, and
> after
> >seeing the Mercedes Benz GT (Sedan, whatever they call em) with the v-6,
> and
> >3 into 1 exhausts, and running 2 expansion chambers (one per side), I just
> >wonder, how they came up with that...
> >   Is it the shape of the cones or volume that makes a "E.C." work, or
> >both?.
> >Grumpy
> 
> For a blue-smoke, it's the shape more than the volume. Things happen in
> this order:
> 1. the piston uncovers the exhaust port, sending a pressure pulse along the
> exhaust at the speed of sound. The exhaust gas begins travelling along the
> pipe somewhat slower than this.
> 2. the pressure pulse reaches the expanding part of the exhaust (i.e.
> increasing diameter). The change in diameter produces a reflected wave of
> lower pressure - this low pressure wave travels back towards the engine.
> 3. The piston, still travelling downwards, uncovers the transfer port. F
> uel-air mixture starts to displace exhaust gas from the cylinder.
> 4. The original pressure pulse reaches the reducing part of the exhaust
> (i.e. reducing diameter). This produces a reflected wave of higher
> pressure, travelling back towards the engine.
> 5. The reflected wave from pt. 2 reaches the engine - this draws the
> exhaust mixture from the cylinder, and in extreme cases, even draws some
> fuel-air into the exhaust.
> 6. The reflected wave from pt4. reaches the engine - this pushes the
> fuel-air back into the cylinder just in time for the rising piston to close
> the exhaust port off.
> 
>         I'm sure that the real world operation of a two-stroke exhaust system has
> many many more factors affecting it, and that this is a greatly sanitised
> version of reality, but it's a start.
> 
> Stuart Baly.
> 
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