At 06:57 AM 7/30/98 -0400, you wrote:
[...]
>For those entertaining modifying their exhaust, I suggest going to the
>attached hyperlink and reading the in depth study done by Thrasher before
>spending the bucks for a minimal gain in performance, assuming performance is
>the required end result. Briefly, automotive engineers assume for each 1" Hg
>reduction of backpressure (bp) there is a gain of 1 hp, e.g, the the C5 vette
>has a backpressure of 10-12" Hg ( which is probably the best that can be done)
>whereas a 97-98 GTP Grandprix ( my wife has one) has approx. 25" Hg bp,
>therefore, assume one were to decrease the bp to 17 -20" bp, the hp gain would
>be around 5-8 hp, less than a tenth at the track. The cost for the exhaust
>mods, hi flow cat, muffler/s, duals?, headers, all could run between $200 to
>$500, or more. The resulting cost per hp would be between $40 to $100, or
>more. Remember, some vehicles respond better than others to mods. Just food
>for thought.
> double click here: <A HREF="http://www.thrasher-ep.com/exhaust.htm">Exhaust
>Backpressure Study</A>
Steve,
Thanks for the info; interesting reading!
I agree that it is definitely best to fully research all of the options
before making a purchase. After reading the article though, I feel that
it doesn't nescessarily apply to the Dakota. They used a 3.8 liter
supercharged engine as their testbed; definitely a different animal
than a naturally aspirated 5.2 or 5.9 liter. Their conclusions were that
a cat-back system would gain them 5-7hp. I can't really comment on that
since I don't know anything about the engine or car in question, but
their horspower estimates were based on the assumption that 1 Hg of
backpressure would equal 1 HP lost. That's interesting to consider,
but without putting the car on a dyno or at least running it down the
strip, there's no way to know exactly what kind of power difference
we're talking about. (IMHO, there was too much theory and not enough
data.)
Gibson claims that the cat-back system on my truck gains about 30hp.
I haven't dyno'd the truck before and after, but based on strip testing
alone (calculating the horsepower from ET's and trap speeds), that
figure seems accurate.
Another factor to consider is that a cat-back or free flowing system is
not the be all and end all when modifying a vehicle. Its about
increasing the breathing throughout the system. The full benefit of
a free flowing exhaust won't be realized until opening up some things
in front of it. (Like porting the TB, using an open element air filter,
adding ram-air, a new intake manifold, heads, headers, etc.)
Just my $.02 :-)
-Jon-
.--- stei0302@cs.fredonia.edu ------------------------------------.
| Affiliations: DoD, EAA, MP Race Team, NMA, SPA, USUA. RP-SEL |
| '96 Dodge Dakota v8 SLT CC (14.85@90.72), '96 Kolb FireFly 447 |
`----------------------- http://www.cs.fredonia.edu/~stei0302/ ---'
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