dyno stuff

[Mark S. Riley]

    When I got the Dynojet, I wasn't as concerned with a "big number" as I
was with repeatability run after run. When I'm tuning a car, I want the
changes in numbers to be created by the vehicle and not from a reliability
issue with the dyno. The dyno is a "tool" and a means to an end. Hopefully a
better tuned car quicker and more safely than you could do in the street. As
for any dynomometer giving up "perfectly accurate" numbers, does it really
matter.
    Case in point: Back in the late 60's Formula Vee took off in SCCA and
there was a business in Charlotte, NC and another in Columbia, SC who both
had Studska VW engine dynos. Fellows in Charlotte made some impressive
numbers but customers were consistently outrun by engines from the guys in
Columbia. One of my friends, who will remain nameless, took an engine to
Columbia, dynoed it. loaded it in the trunk and hauled a** for Charlotte.
Got it on the dyno in Charlotte before it had cooled off from the session in
Columbia. With no changes to the engine it made 6 more hp in Charlotte than
it did in Columbia 1 1/2 hours earlier. On an engine making 48 hp this is a
significant gain.
    Taught me that we were racing engines not dynos. Repeatability and
reliability are worth more in a dyno than the big number. Most of the
Winston Cup teams use Superflow engine dynos and Dynojet chassis dynos for
this reason, not for a big number. If it's repeatable and does the same
thing every time, You can use it to get better results. Besides, road
testing "It's got a little skip about 135. See if you can find out what it
is?" gets real old, real quick. Mark Riley

----- Original Message -----
From: "Eric Bryant" <BRYANTE at ghsp.com>
To: <gmecm at diy-efi.org>
Sent: Thursday, May 03, 2001 8:23 AM
Subject: RE: dyno stuff


> > Here's one--I had a SB Dodge car at 6200 RPM, peak torque was
> > 1774 with a
> > manual trans. I had the
> > torque calculated at 389 ft/lbs at the flywheel--then doing
> > the math it was
> > 459 HP--yet the actual dyno HP was substantially less. That's
> > why I'm still
> > questioning this thing...SnapOn's formula is really
> > strange--as soon as I
> > can find it again, I'll post it.
>
> If you're getting HP numbers that are way off, it could just be
> characteristic of the dyno.
>
> On the car side of the issue, I've noted that people obtain much different
> numbers on Dynojet dynos than they do on Mustang dynos.  I'm not familar
> with the Mustang dyno at all, so I really can't comment on the issue.
>
> With motorcycle dynos, there's two big names - Dynojet and Factory.  The
DJ
> motorcycle dyno is just like a downsized DJ car dyno - it uses the inertia
> of the roller to provide resistance.  The Factory dyno is an eddy current
> dyno.  The Factory dyno will read 15% lower than the DJ dyno, and so no
one
> likes to use the Factory equipment - it doesn't make for impressive
numbers.
>
> What's my point?  I don't really know.  Different dynos will produce some
> strange numbers.  I'd just like to know why it's so difficult to get a
> "real" reading - I understand minor differences between dynos of different
> brands, but it's almost like some manufacturers are using some very
> "special" math.
>
> Eric Bryant
> mailto:bryante at ghsp.com
> http://www.novagate.com/~bryante
> --------------------------------------------------------------------------
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