Response

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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