From: hotrod@dixie.com (The Hotrod List)
Subject: Re: engine brakes
Date: Mon, 11 Jan 93 07:54:36 GMT
Organization: Dixie Communications Public Access.  The Mouth of the South.
To: hotrod@dixie.com
Reply-To: hotrod@dixie.com
Posted-Date: Monday, Jan 11 02:54:31
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>  >
>  Back in the old days, while this was still the boonies, I experimented
>  with some shop-built engine brakes.  ( At the time, I had a foreign car
>  shop, so the scale may be a *little* off here).  After some abortive
>  attempts at creating a water brake, and some _smelly_ tries with an old
>  Peterbuilt 5-disk clutch assembly,  I cobbed on to a large (to me) fluid
>  pump.  Had a 2" shaft, 3" inlet, and a 1" outlet. Biggest *I'd* ever seen.
>  Anyway, that pump had absolutely no problems handling the 200+ BHP, at 
>  least for the short periods that I used it (2 ea. 55 gal. drums for a
>  reservoir, max press at outlet: 300 PSI, homemade restrictors). 
>  My question: why is this not a more common method (i.e., light oil).
>  
>  als
>  
>      
> [Are you talking about a positive displacement hydraulic pump or  or
> some other kind?  I've built several motorcycle-grade dynos using 
> hydraulic pumps and there used to be a company (Pabco or something like
> that) that made one commercially.  This works really well.  I've not
> extrapolated up to automotive HP levels to see what would be involved.
> I imagine a couple of those huge pumps like used on garbage pumps
> would absorb 500 hp or so.  JGD]
> 
> ----------
> Posted by: emory!hounix.org!als (Alan Squyres)
>  
> 
This was a twin-rotor positive displacement mech.  It was pretty well used
when I got it, so it was not as tight as a new one of the breed.  I never
could get a turbine type big enough to try, but that probably would have 
matched the application a bit better.  I did toy with the idea of matching
up a truck-size torque converter, but in those days, Allison automatics 
were still scarce.  I have aquired (since then) a friend that does 
maintenance on high-pressure (pipeline) pumps.  If this is of any real
interest, I could quiz him on the types that could stand the considerable
back pressure this type of application would require.  Unfortunately, I
now have no place to experiment, nor do I have any real justification for
cobbling up another dyno (other than the fact that it is a subject that
still interests me).  I would, however, be more than happy to share any
previous experiences with anyone serious about re-creating this animal.
Please bear in mind that I have absolutely no formal education in 
hydraulics, and anything I could relate would depend upon a (not-always-
dependable) memory.

P.S. The pipeline rig that brought this to mind had (has) 2-count'em-2
8v71 Detroit stationary engines.  *I* don't know the HP rating, but it
surely adds up to >500 HP. 

als

[Oh absolutely, please post any information you care to type.  We'll
get a clue or two from it.  On the torque converter, I have my doubts.
The Rutgers SAE team built a dyno using an automotive one.  'Bout
the time the engine hit 80 HP or so we smoked everything :-)  
Converter was smoking, the cooling pump melted, the LARGE truck radiator
being used as an oil cooler was smoking, etc.  The other problem 
we ran into was how to load the thing.  The drag vs RPM curve is 
real steep, as should be intuitive, and we never came up with a
good way to vary that curve.  We were short on time so I didn't work
with it a bunch.  One thing that lessened the load was to inject
some air into the oil supply.  Made a nice emulsion whose viscosity
I could vary with the amount of air injected.  Only problem was the
emulsion was very hardy and shed air only slowly.  JGD]
----------
Posted by: emory!hounix.org!als (Alan Squyres)
Newsgroups: alt.hotrod,wiz.hotrod