Weight Distribution
Regarding The Slippery Stakes - Wet Road Tyre Grip. There is much debate
over loss of control accidents with various opinions from experts and the
public. What the average person and some experts are not aware of is that there
can be as high as 950 pounds or more weight on the front axle of their vehicle
than the back. A 3000lb car with a weight ratio of 65% front weight and 35% rear
weight will weigh 1950lb on the front and 1050 on the rear. After you use 10
gallon of fuel one of the front wheels has as much traction as both rear
combined. So a car that feels like a limousine on the front holds like a golf
cart on the back. If you analyze single vehicle accidents you will find most of
them had better tires on the front than the back or a very large weight
difference. In fact the worst balanced cars have 4 times as many fatalities as
cars designed with better balance. How are you going to tell how fast is too
fast under these conditions when it is possible for a balanced car to handle
fine on a slippery surface at 50 mph and an unbalanced car to loose control at
20 mph and both to feel the same to the drivers.
Harvey McFadden
Canada
Pressure Drops with Altitude
In Using a Vacuum Gauge for Engine Diagnostics in issue 312, your author
states that pressure drops i inch of ercury for every 2000 feet of altitude. It
actually drops approx 1 inch of Hg for every 1000 feet. I think he meant to say
1 PSI for every 2000 ft which would be 1 inch of Hg per 1000 feet. (2 inches
Hg/PSI approx)
Edward A. Nauman
United States
Thanks - fixed
Intake Manifold Insulating Spacers
In June 2008 you reprised an article originally
published in 2000, written by Sean Morgan of Outlaw Engineering on the topic of
phenolic insulating spacers for intake manifolds. Upon first reading the
article, I got pretty excited about it, and began investigating the possibility
of coordinating a group buy for the Porsche 924 community via my membership at
924board.org. There is a pretty lengthy thread there on the topic, but to cut a
long story short, after lengthy debate and discussion, I am now beginning to
question the objectivity of the article. The following list summarizes the
points of contention brought up in the aforementioned discussion:
* The intake temp claims are somewhat deceptive
because the article discusses the temperature of the intake manifold itself, NOT
the intake air temperature.
* The objectivity of the author is in question
because he works for a company that manufactures these spacers
* The dyno numbers provided are simulated by
software, not actual dyno numbers, and are therefore not very persuasive or
conclusive
* The before-and-after speed results are
questionable because they were not measured on the same day under the same set
of circumstances...the test was not conducted very scientifically, and by the
author's own admission, separated by several months
* The author makes a somewhat dubious claim by
saying "During its residence in the intake manifold casting, the air charge
picks up unwanted heat from the manifold". After debating at length on this and
consulting with other performance experts here in Detroit, I am beginning to
doubt this claim. The laws of fluid dynamics, boundary layers, and heat exchange
from metal to air (which I am admittedly NOT an expert) seem to defy the notion
that the intake manifold casting, designed to optimize air flow, would actually
have MINIMAL ability to transfer heat to the charge air, especially on a forced
induction application with an intercooler. That being the case, it would seem
that phenolic spacers would actually have very little impact at all on intake
air temp
* Another point brought out by a Detroit area
performance expert was that even WITH a phenolic insulator, on long runs, such
as extended highway driving, or even long race events, the intake manifold would
eventually equalize to about the same temperature as without an insulator
because it would absorb heat being cast off into the hot engine bay.
What is sorely needed is a follow series of tests
that are carefully planned and executed. Two primary factors need to be
documented:
1. The actual change in intake air temperature
(i.e. NOT the intake manifold itself)
2. Before-and-after dyno runs in a more
scientifically controlled environment
If it's of any interest, the thread referenced
above is available here: http://www.924board.org/viewtopic.php?t=26775
It would be GREAT to see a follow up article that
would examine these points in more detail. Thanks in advance for your
consideration.
Dan Beckett
United States
As with any modification, if you don’t believe
it will be effective, don’t do it! As you have noted, the article was clearly
sourced externally to AutoSpeed; we haven’t ever done it to any of our cars and
can’t see ourselves doing so in the future. That said, the article is still a
very interesting one and we believe the fundamental principle to be
sound.
Sheds
2c more about sheds!
- If you're considering installing a vehicle
hoist, make sure the slab is rated for it (currently remedying this the hard
way!)
- Consider having computers, test equipment on a
separate circuit to welding gear etc. to protect from voltage spikes / noise
- Flame cabinets or similiar are nice to store
fuel, thinners, paint.. and fire extinguishers!!
Ben Guymer
Australia
Wheel Centre Rings
Re: Custom Wheel Centre Rings Thanks for educating
people about this. I've often seen people selling (for instance) VE Commodore
rim, saying that they'll fit onto older models. Unfortunately for the
unsuspecting buyers, they'll get vibration problems because the rims will need
centre rings to suit their older car. However, more to the point... If they
don't get the correct rings fitted, they'll eventually break wheel studs,
because they're not made to take the weight of the car... That's what the wheel
centre rings are supposed to do! Thanks again for the article.
Danny
Australia
Catching Blow-By 1
DIY: An Oil/Air Separator
"All cars vent the blow-by gases through into the intake system. Huh, what's
that mean? When combustion occurs, there is some leakage past the rings and so
down into the sump. This pressurises the sump a bit, with these gases making
their way up to the top of the engine. The oil/air mist is drawn off from the
rocker cover and directed into the intake, where it's sucked the engine and
burnt."
Isn't the leakage past the rings fuel and air,
with gases making their way up to the top, where does the oil come from?
Nitsuj
Australia
The blow-by gases carry with them the mist of
oil that is present inside the running engine above the sump oil level.
Catching Blow-By 2
Been a fan of your site for a long time now, even
have a supercharger kit for my car (whom my mech made with inspiration from your
previous writeup) and bought the air-fuel mixture board from you :D
In your "DIY: An Oil/Air Separator", I'd just like
to share that me and my buddies use a cheap fuel filter (it's maybe AUD$1.50
each?) to collect the blowby; and when it gets sufficiently dirty, we just
replace the unit :D
Here's a link to the pic:- http://i220.photobucket.com/albums/dd289/kohyiaw/My%20Car/OCT/DSC00260.jpgp.s.:
here's another link to the progress of the supercharger, in case you're
interested :) http://myvi.com.my/forum/index.php?topic=2733.0
Adrian Lo
Malaysia
Stopping Distances
I have just read the story by Greg Brindley about
putting Konis and Kings springs in a 318 BMW and testing it at Calder for
braking and cornering – see No Float. Something didn't
seem right to me so I checked the braking figures shown in the article.
Greg has a table of before and after times
and distances to stop from 60 & 80 km/hr.
His figures
|
Before |
After |
|
60 km/h |
1.75 sec |
7.13 m |
1.41 sec |
6.71 m |
|
80 km/h |
2.47 sec |
16.6 m |
2.25 sec |
15.4 m |
The stopping distances seem way out. Digging
out kinematic equations last used at High School!!! and using the times as
a basis for calculation, the "before" stops generate .971g and .917g from
60/80. This would give a stopping distance average of 14.5m and 27.4m,
clearly not the 7.13m and 16.6m shown.
Using the stopping distance as being
correct, this would mean a time to stop of .85 sec and 1.49 sec,
clearly not 1.75 sec and 2.47 sec as shown. Using the distances as being
correct would generate a g force of 1.98g and 1.51 g ...obviously not correct
for a simple road car.
This means that the times shown
are probably correct, but the stopping distances clearly are not
correct. A g force of around 0.97 is very good and about
right for a BMW, hence the "before"timesare correct but the
distances should be 14.5m and 27.4 m.
Same with the "after" values shown ...the
times are probably correct, being 1.41 secs and 2.25 secs (generating 1.2 g
& 1.0g) and this gives distances of 11.75 m and 25 m ..... not the 6.71m and
15.4 m as shown.
Correct values assuming time was
correct:
Before: 60 kph, T=1.75sec, D= 14.58m
gforce 0.97
After 60 kph, T= 1.41sec,
D=11.75 gforce 1.2
Before 80 kph, T 2.47 sec, D =
27.4m gforce 0.917
After 80 kph, T = 2.25 sec, D =
25m gforce 1.0
It seems strange to me because stopping is
usually done by measuring distances rather than time ...too much error in time
measurements unless a beam is used. Distance measurement is far easier to
get accurate provided the "start" point is accurate. Regardless of
the figures, and only a picky prick like me would bother to work it out .... the
improvement is terrific. Gee, if I had a car that stopped in 7m from 60
kph at close to 2g, my eyes would probably pop out!
Ron Sutherland
Australia
No Float
RE:
No Float
After reading this article I was shocked to see
the rating was only 3.71! I rated this article 5! Okay, as a BMW E30 owner &
fan I might be a little biased, but apart from the little red 318i, this article
was as close to perfection as it gets.
- It was written about an interesting and relevant
topic.
- It described a number of tests.
- It provided before and after results. (both in
opinion and ACTUAL data)
- And to top it all off it even told how much it
would cost!
5 out of 5 in my book. Keep up the great work! I
don't agree with all of your opinions, but I do feel that you write what you
believe...
Rick Miles
Australia
Prius Tech
You might want to look again at your article:
The Toyota Prius - Part 2
The last sentence in the paragraph that begins "The MG2 motor's primary role
..." states that "At maximum torque, the motor draws 351 amperes." That would be
one big chunk of copper! We talking heavy duty arc welder. Also, the last
sentence of the paragraph that beings "When absolute maximum power is called
upon ..." seems to add both the engine and MG2 power. We know that about 18 kW
is needed by MG1 to supply counter torque for the engine. The Toyota table at
this page reports "74 kW": http://www.toyota.co.jp/en/tech/environment/ths2/speci.html
I will confess that modeling Prius energy flows is
not trivial.
Bob Wilson
United States
We’ve changed the total power output figure. We
haven’t changed the maximum current flow, which was listed as such by
contemporary Toyota documentation. We assume that it is a very short term
maximum.
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