[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: DYNO RESULTS -- STOCK vs AFTERMARKET WHEELS
Hey Ben,
Yep, he's still healthy. :)
As you know, the run 2 years ago was in Manassas, VA. So, the
runs this time were obviously on a different dyno. They should, of course,
be accurate to within 1-2hp. Then, the first run I did was at 55'F (nearly
perfect conditions for my engine), and this one was at 88'F. Despite using
the calculated values to SAE, you can expect a few hp either way-- and
especially after I found out that DynoJet is constantly updating their
conversion programs.
The result last time (corrected to SAE) was 105.5hp, and the
results this time (I don't have the graphs with me) were something like
103.5 and 102.9. Since they're so close, and because of the differences in
the dynos themselves and the atmospheric conditions, the difference is
probably not statistically significant. I went in there _expecting_ a huge
difference (like 92hp or something), but the values are so close.
The other thing that was interesting is that the curves are
exactly the same up until about 5000... perfectly evenly spaced with about
2hp difference. After that, the torque curve dropped off a little bit more
than it did before, but retained that power a little longer. The only
changes I made to the engine since the last test were new wires, Jamex
intake, and a new muffler... so I can probably attribute them to those
small changes.
But again, since the differences were so small, I'd say it's
running just fine.
Jason
At 07:29 PM 4/19/2000 , Benjamin Harder wrote:
>Jay,
> This is some good info...thanks for the homework!
>
>I just have to know...what were the actual results?
>Is your 16v still *healthy* or did you see a decline in results
>since your last dyno runs?
>
>Ben H.
>
>
>--- 16v Jason <jason@scirocco.org> wrote:
> > (2nd attempt at posting this message)
> >
> >
> > Hey all,
> > There was a local dyno day sponsored by the RX-7 club in my
> area.. $65
> > for
> > 4 runs-- so I talked to the organizers and asked if I could do 2 runs
> > instead, but swap my 15" TSW Hockenheims for the 14" stock teardrops
> > while
> > I was on the dyno. I figured it would finally put an end to the mystery
> > of
> > how much power the wheels robbed.
> >
> > I haven't weighed either of the wheel & tire combos, but the
> consensus
> > among guys there was that the Hocks are slightly heavier than the
> > teardrops. In addition, because of the larger wheel size, the weight is
> >
> > distributed further from the axle, and therefore, the hypothesis was
> > that
> > running larger wheels would (significantly) reduce effective power
> > output
> > of my engine.
> >
> > From a physics point of view, the effect of greater wheel weight
> would
> > be
> > present the faster the wheel was accelerating. Obviously, in 4th gear
> > (the
> > gear of choice for dyno runs because of traction), acceleration is not
> > as
> > brisk as it would be in, say, 1st gear. Therefore, I was expecting the
> > power loss to be less than what it might be in lower gears. I expected
> > there to be little difference at, say, 1200rpm, when the wheels are
> > barely
> > being accelerated, and more of a difference at the torque peak, when the
> >
> > wheels are being accelerated the most quickly.
> >
> > I had the dyno operator start the test at 1000rpm in 4th gear
> (usually
> > they start between 2000 and 2500), and continue until the rev limiter
> > kicked in, no matter what the tach said. So, the results for both runs
> > are
> > from 1000rpm to 7300rpm. I haven't yet scanned the results (my
> > scanner's
> > dead), but I will do so as soon as possible.
> >
> > THE RESULTS:
> > There was *no* appreciable power loss anywhere in the rev range using
> > the
> > heavier wheels. At lower rpms (and therefore, speeds), the two curves
> > were
> > almost exactly the same. As the revs increased, I expected the 15s to
> > effectively lose power when compared to the 14s, but that wasn't the
> > case. The 15s actually put *more* power to the ground. Why?
> >
> > Well, the dyno results show a vibration in the wheels caused by an
> > unbalance in the tires. Of course, those vibrations are
> > speed-dependent,
> > and lasted from 3000-4000rpm and then again from 5000-6000rpm. Betwen
> > 4000
> > and 5000rpm, when the curve was smooth, the 14s put less power to the
> > ground than did the 15s. Why? Again, most likely because of
> > inbalance. The difference, however, (between 1 and 2hp) is
> > statistically
> > insignificant, as back-to-back dyno runs can show differences of 2-3hp.
> >
> > Therefore, the conclusion is that for my tire & wheel combination,
> > there
> > should be no appreciable difference in power to the ground using either
> > the
> > 14s or the 15s. The biggest factor in this test was probably the
> > balancing
> > of wheels. So, rather than worrying about losing power by using larger
> > wheels, you'll gain more by having your wheels balanced.
> >
> > Therefore, the handling benefits of using larger wheels is not
> > compromised
> > by their weight (at least at the 15" level). Of course, common sense
> > dictates that 17" wheels would be even heavier than 15s, and may show a
> > significant power loss...
> >
> > Now, if I could find my Physics books and get the formula for the
> force
> >
> > required to turn different weights, we could do a theoretical
> > analysis...
> > but for the time being, I'm satisfied in knowing that I'm not losing any
> >
> > power by running 15" wheels.
> >
> > Jason
> >
> >
> >
> > ----------
> > 1987 Scirocco 16v
> > 1989 Mercedes 190E Sport Euro
> >
> >
> > http://members.aol.com/rocco16v
> >
> > --
> > Email problems to: scirocco-l-probs@scirocco.org To unsubscibe send
> > "unsubscribe scirocco-l" in the message to majordomo@scirocco.org
> >
> >
>
>__________________________________________________
>Do You Yahoo!?
>Send online invitations with Yahoo! Invites.
>http://invites.yahoo.com
----------
1987 Scirocco 16v
1989 Mercedes 190E Sport Euro
http://members.aol.com/rocco16v
--
Email problems to: scirocco-l-probs@scirocco.org To unsubscibe send
"unsubscribe scirocco-l" in the message to majordomo@scirocco.org