[T3] MPGs??

Dave Hall dave at hallvw.clara.co.uk
Fri Jul 25 16:06:09 PDT 2014


I did a CO test with my 1972 FI Fastback and it was about 0.5%.  I usually
tuned the twin carb Variant for around 3% CO.  You could smell the exhaust a
bit, but many classic cars are more like 6% or more, and smell of pollution.


When an AA mechanic (AAA in USA?) adjusted my son's Polo 'by ear', he left
it with about 7% CO, which failed the next emissions test, but I adjusted it
in the garage 'by ear' for fastest tickover and a fraction richer, and it
passed fine at around 2% when the tester checked again.

Dave UK VW Type 3&4 Club
========================

-----Original Message-----
From: type3-vwtype3.org [mailto:type3-vwtype3.org-bounces at lists.vwtype3.org]
On Behalf Of Jim Adney
Sent: 25 July 2014 23:21
To: type3 at vwtype3.org
Subject: Re: [T3] MPGs??

On 25 Jul 2014 at 7:47, Dennis Stiefel wrote:

> I usually just drive the car around town so on a typical day she 
> hardly gets over 55.  Sounds like I need to check the MPGs under these 
> conditions.  I average 70 on those trips because on certain stretches 
> of the interstate I was on if you don't drive at least that fast you 
> could get run over.  When my father drove it to work back in the 70s 
> with the stock set up he said he got about 28 but that was 2 lane high 
> way where the speed limit was no higher than 55.  I talked to some 
> people who had a 70 notch this pasted weekend.  It had an automatic 
> with some kind of duel carb set up and claimed
> 31 MPGs but they did say they averaged 65 to 60 on their speed.  Still 31
> sounded a little high to me but I guess not imposable.      

The mileage you get with any given car is strongly dependent on speed.
You'll get your best mileage in your top gear at a speed that's just high
enough to make the engine "comfortable." In our cars, that's something
around 45 or so.

As your speed increases, the wind drag increases roughly with the SQUARE of
your velocity, so your gas mileage will drop stunningly quickly as your
speed goes up.

We get in trouble when we start to compare older Type 3s with later ones,
since there's an unfortunate tradeoff between NOX emissions and gas mileage.
The FI cars were designed to meet the emission requirements that started in
'67 and got tighter every year after that. So under the same driving
conditions, a '66 will always pollute more and get better gas mileage than a
'72.

I did some test drives a few years ago, with my FI '71 and got ~26 mi/gal at
65 mi/hr and ~29 mi/gal at 60 mi/hr. Those are the best numbers you should
ever expect to see in your '72, unless you've got a tail wind. The earlier
cars, with OE carbs, get significantly better mi/gal, but pollute
significantly more.

-- 
*******************************
Jim Adney, jadney at vwtype3.org
Madison, Wisconsin, USA
*******************************

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