Re: [other] auto tranny powerloss and Jay Brunberg

[Jason <jason@scirocco.org>]

At 08:27 PM 11/6/98 , Ryan Schuermann wrote:
>Tell me if I'm drunk, was re-reading the premier issue of MAX Power,
>theur Passat 1.8T project car, they add a chip and dyno and claim 
>170hp, then go on to say, but this was the automatic transmission so 
>you have to add back 15-17%. Did I read this right? They are saying 
>that an automatic tranny looses 15-17% over a standard?

	Yep.


>what is the power loss due to a torque converter?

	It depends on the car... it probably ranges from like 10% to 35%.
Automatics (i.e. slushboxes) are very, very inefficient.  There's no direct
contact between the engine and the wheels-- and all the slippage you feel
(i.e. when you see revs rise and drop as soon as you hit the gas and/or let
off) is just lost power.  


 I mean once the 
>tranny is engaged, is an auto slower than standard? 

	Yes.  Look at any factory specs or the like, and you'll always see the
acceleration figures for the stick vs. the automatic.  The difference
depends on a tremendous number of variables, including the efficiency of
the unit, how many speeds it has, the torque curve of the engine, gearing,
etc.. But if you find a car that does 0-60 in aroun 8 seconds with a stick,
figure about another 0.8 to 1.0 seconds for the automatic.
	The one difference you will find is with turbocharged cars.. Autoboxes
with Turbos tend to be just as fast (if not faster) to 60mph than the
manual cars because (a) you can spool the turbo up before the launch by
brake-torqueing, something you (usually) can't to with a 5-speed, and (b)
you're always under load, so therefore the turbo is always spooled up--
whereas with the manual, you let off of gas (and therefore lose boost)
during shifts...

	The only time an automatic is as efficient as a manual is if it has a
lockup torque converter, which just about every one does nowadays.  The
lockup mechanism generally only activates in the top gear (or top two), and
only under relatively light throttle-- and what it does is locks the
turbines of the torque converter together to create a direct connection
between engine and wheels.  You can usually feel it lock up; it feels
almost like a shift.  With it engaged, the transmission is *almost* as
efficient as a manual.

how much power is 
>lost shifting in an anto tranny compared to standard, even say of 
>shifting in the auto is reduced to 0.2 seconds, is it neglitible or 
>noticable? thanks

	Generally speaking, Automatics shift faster than most humans can... of
course, there are exceptions (JASON BRUNBERG, not to mention names)... but
even if the tranny shifted instantaneously, the stick would still be
faster...  
	Automatics work best (i.e. affect the acceleration figures) least when
used in a large, torquey engine... like a GM V6 or V8..  The 7.7 second
0-60 launch that Road & Track got with the 16v Scirocco in 1986 would
probably turn into 10+ seconds if the 16v was ever offered with an
Automatic, simply because there's no way to launch an automatic at high
revs (well, without Neutral-Dropping it) to bypass the lower-torque region
below 4000 or so.  In a GM 3.8 V6, on the other hand, which has its torque
peak at 2500rpm, it's not necessary, and the cars don't suffer that much of
a loss.

	That's all for now. ;)
			Jason






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