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Top speed
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At 09:52 PM 11/7/2002, L F wrote:
>There is one reason;
>If the motor doesn't make enough power at anything less than 3000rpm to
>propel the car at 70mph.
That is true, mein Herr.
But the VR6 doesn't have that problem.... here's why:
http://www.scirocco16v.org/golf/dyno.jpg
The VR6 has a nice plateau of torque between 120 and 130lb-ft from idle on
to 3000, where it starts to really pick up. That means a few things:
1. Specific fuel economy, which is, in general, directly related to
torque, is just as good at 2500rpm as it is at 3000rpm... so fuel economy
would improve significantly by reducing rpms.
2. The car should probably have more than enough torque to manage 70mph at
2500rpm..
Let's find out:
The total resistance of a Mk3 at 70mph is approx. 580N. With stock gearing
and a stock VR6, the output to the wheels creates 1680N on the car at full
throttle in 5th gear (3000rpm) at 70mph. Thus, 1100N remains to accelerate
the car or maintain speed up hills, etc...
If we reduce the 5th gear to 0.75, that 3000rpm drops to 2500rpm. The
gearing reduces output, and we wind up with 1470N acting on the car. Even
still, the resistance to overcome is only 580N... so the engine would be
able to manage it no problem.
The 890N left over is a 19% reduction in available torque for hills and
acceleration versus the stock gearing -- but I think the tradeoff would be
worth it. After all, what is 4th gear for? :)
(For those who are curious, top speed would drop from 139 to 134mph... The
fuel economy benefit at a constant 70mph would, in my estimation, be around
10%. You're looking at a 16% reduction in revs and an increase in throttle
(reducing losses), but on the other hand a slight decrease in specific fuel
economy).
Jason
PS: 580N on the car at 70mph equals about 25hp at the wheels. So figure
that you could achieve 70mph in your Mk3 with a 30hp engine and the proper
gearing.
>
>Larry
>>----- Original Message -----
>>From: <mailto:Captnbr@aol.com>Captnbr@aol.com
>>To: <mailto:jason@scirocco.org>jason@scirocco.org ;
>><mailto:Scirocco-L@scirocco.org>Scirocco-L@scirocco.org
>>Sent: Thursday, November 07, 2002 6:25 PM
>>Subject: Re: Top speed
>>
>>In a message dated 11/6/2002 11:27:05 PM Eastern Standard Time,
>><mailto:jason@scirocco.org>jason@scirocco.org writes:
>>
>> > There is no reason in hell that motor needs to be
>> > spinning at 3000rpm to cruise at 70mph.
>>
>>Oh yes I agree with you 100% especially that I do 100 miles a day at
>>80mph, 3 times a week.
>>
>>_______________________________________________
>>Scirocco-l mailing list
>><mailto:Scirocco-l@scirocco.org>Scirocco-l@scirocco.org
>>http://neubayern.net/mailman/listinfo/scirocco-l
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At 09:52 PM 11/7/2002, L F wrote:<br>
<blockquote type=cite class=cite cite><font face="arial" size=2>There is
one reason;</font><br>
<font face="arial" size=2>If the motor doesn't make enough power at
anything less than 3000rpm to propel the car at
70mph.</font></blockquote><br><br>
That is true, mein Herr.<br><br>
But the VR6 doesn't have that problem.... here's why:<br>
<a href="http://www.scirocco16v.org/golf/dyno.jpg"; eudora="autourl">http://www.scirocco16v.org/golf/dyno.jpg</a><br><br>
The VR6 has a nice plateau of torque between 120 and 130lb-ft from idle
on to 3000, where it starts to really pick up. That means a few
things:<br><br>
1. Specific fuel economy, which is, in general, directly related to
torque, is just as good at 2500rpm as it is at 3000rpm... so fuel economy
would improve significantly by reducing rpms.<br><br>
2. The car should probably have more than enough torque to manage
70mph at 2500rpm.. <br><br>
Let's find out:<br><br>
The total resistance of a Mk3 at 70mph is approx. 580N. With stock
gearing and a stock VR6, the output to the wheels creates 1680N on the
car at full throttle in 5th gear (3000rpm) at 70mph. Thus, 1100N
remains to accelerate the car or maintain speed up hills,
etc...<br><br>
If we reduce the 5th gear to 0.75, that 3000rpm drops to 2500rpm.
The gearing reduces output, and we wind up with 1470N acting on the
car. Even still, the resistance to overcome is only 580N... so the
engine would be able to manage it no problem.<br><br>
The 890N left over is a 19% reduction in available torque for hills and
acceleration versus the stock gearing -- but I think the tradeoff would
be worth it. After all, what is 4th gear for? :)<br><br>
(For those who are curious, top speed would drop from 139 to 134mph...
The fuel economy benefit at a constant 70mph would, in my estimation, be
around 10%. You're looking at a 16% reduction in revs and an
increase in throttle (reducing losses), but on the other hand a slight
decrease in specific fuel economy).<br><br>
Jason<br><br>
PS: 580N on the car at 70mph equals about 25hp at the wheels.
So figure that you could achieve 70mph in your Mk3 with a 30hp engine and
the proper gearing.<br><br>
<br><br>
<blockquote type=cite class=cite cite> <br>
<font face="arial" size=2>Larry</font><br>
<blockquote type=cite class=cite cite>----- Original Message ----- <br>
<b>From:</b> <a href="mailto:Captnbr@aol.com";>Captnbr@aol.com</a> <br>
<b>To:</b> <a href="mailto:jason@scirocco.org";>jason@scirocco.org</a> ;
<a href="mailto:Scirocco-L@scirocco.org";>Scirocco-L@scirocco.org</a>
<br>
<b>Sent:</b> Thursday, November 07, 2002 6:25 PM<br>
<b>Subject:</b> Re: Top speed<br><br>
In a message dated 11/6/2002 11:27:05 PM Eastern Standard Time, <a href="mailto:jason@scirocco.org";>jason@scirocco.org</a> writes:<br><br>
> There is no reason in hell that motor needs to be <br>
> spinning at 3000rpm to cruise at 70mph.<br><br>
Oh yes I agree with you 100% especially that I do 100 miles a day at 80mph, 3 times a week.<br><br>
_______________________________________________<br>
Scirocco-l mailing list<br>
<a href="mailto:Scirocco-l@scirocco.org";>Scirocco-l@scirocco.org</a><br>
<a href="http://neubayern.net/mailman/listinfo/scirocco-l"; eudora="autourl">http://neubayern.net/mailman/listinfo/scirocco-l</a></blockquote></blockquote></html>
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- References:
- Top speed
- From: Captnbr@aol.com (Captnbr@aol.com)
- Top speed
- From: rocco16v@netzero.net (L F)