Category: SCCA Trans-Am

Mustang Vintage Racer

Mustang Vintage TA Car

Aerodynamics is probably the most important aspect of the modern race car. Those of us who are F1 fans see how those teams spend untold sums of money, expend more man hours in wind tunnels and employ unimaginable computer power to gain just the slightest advantage in down force or drag reduction. Who would have imagined a couple of years ago that the engines exhaust gases could be used to increase downforce? Or that how that was executed would be the difference between a world beater and a mid pack car.

But how, if at all, does aerodynamics effect our world, where the bodywork is made from carbon fiber or fiberglass, and all made from the same molds? The answer isn’t simple, and I will freely admit that I dont know everything that is going on here.

But we do know that in the days when steel roofs were required, things were creative.  A steel roof was required to prevent the cheating up of the windshield. However a stock roof will not fit the molded bodywork. Not only was the metal stretched, but it was sectioned. In other words a pie shaped section cut out so that the stock windshield fits but the greenhouse is as small as possible.

But you say that’s just vintage cars whats that got to do with the cars we run now? True, point well taken. But remember that the laws of physics are the same for an F1 car or a GT1 car. And  its all about managing the flow of air around the vehicle and underneath the car. So I will just point some things in no particular order. And remember, in making these points I am not accusing anybody of doing anything.

First, back in the old days of the Trans-Am series they required that the body not below the line of the chassis. As part of the tech inspection a straight edge be placed across the bottom of the car. The advantage of course being that dropping the body below the frame, (which has a belly pan) you create diffuser tunnels between the door and the frame rail.

Even if the body is even with the frame rails, you can do the same thing with the filler panels between the body and frame. This requires a little creativity so as not to be conspicuous.

Speaking of the area between the door panel and the car itself, I have seen some radiused pieces placed at the front of the filler panel. The purpose was obvious, but how do you get that air out from under the car? Its blocked by the rear wheel tub, so wouldnt it be better to get it out at the front wheel opening?

A few years ago one of the major Ford teams cars cars appeared to be a little different. Just by observation it seemed that the rear undertray had more of a slope than the other Fords. Of course the part had the proper approval stickers.

The mesh on the grill opening can effect the amount of downforce on the front of the car. Of course the finer the mesh the less air can get through. And using one consistent mesh is just a matter of convenience right?

Speaking of Fords, the 93-up Mustang had a huge flat rear deck. That made these cars more responsive to body rake. By getting that deck exposed to more airflow, you increased the downforce. Almost like using a larger spoiler. Other makes may have the same issues.

Dive planes of course are useful in tuning the front end.

And the primary goal is doing anything possible to first prevent air from getting under the car, secondly to exhaust the air that does get under the front of the car. I had a steel bodied Mustang, that used a steel hood, with a scoop, that had all the reinforcement removed. Down the straightaway the rear of the hood would rise up to the full extent of the hood pins. Perhaps 6″ in the center. If we could have prevented that it could have meant some nice gains. Food for thought.

If its allowed by the rules, opening up where the rear license plate was allows a place to exhaust air from the rear. many people  use this as a place to place an oil cooler for the trans or rear.

And of course the wickerbill on the rear end can be used as a tuning tool, as well as the angle of the wing itself will increase rear downforce.

Like anything else when you change one end of the car it effects the other as well. We’ve just thrown a few things out there, and obviously just scratched the surface of what may be going on. But if you look closely there may be things that make you say “hmmm?”

Corvette in South America

Trotnow built Corvette

By now I’m sure most people have seen that the Trans-Am Series has released their 2012 race schedule. Eight races with the possibility of an additional two more.

Most of these tracks are at the traditional Trans-Am venues and are in the Eastern part of the U.S. as well as the annual trek to Mosport.

While I am sure that some people are disappointed that  VIR is not on the schedule, all in all it seems like a good schedule.

According to the press release that accompanied the announcement, reducing travel costs was a major goal. And supposedly this was reduced by about 40%. If so, this can only help the teams that continue to support this series.

So now people can begin to finalize their plans, arrange sponsorship, and of course get the cars ready.

I really think that this will be a turnaround year for the Trans-Am. The new mangement/owners group actually has skin in the game. And they have all been involved in it for years, so they know what works and what doesn’t.

One thing that I would personally like to see is more participation by the club racers who normally race at the tracks the series attends. While I know that the intimidation factor is there. Think of what great water cooler conversations it would generate.

So now we know. I look forward to seeing many of you at the tracks this year.

Chassis under construction My apologies for the quality of the above photo. But you can see that it is a collage of photos showing the side view of a chassis under construction. No points for what type, but look at the braces between the front of the greenhouse.

Earlier in this blog, I had posted a photo sent me of a car that someone wanted me to help sell. Being several states away, we never went to see the car but did mention it to several people that we knew who dealt in similar things.  As it turned out the gentleman was able to sell it on his own and we  moved on to other things.

This weekend we were contacted by the person who had bought the car and seen the photo which we had posted. It appears that the information we had been given by the seller was not exactly correct. That the car was not in fact what he had indicated but rather a homebuilt attempt at a replica using spares from similar cars.

Now I certainly am not going to accuse that person of anything unseemly. For all I know he had acquired it from someone else in the interim and was merely repeating what was told to him.  In addition the price he was asking was more than reasonable, (read cheap), and about the value of the spares package.

But the moral of the story  is this. Many of these cars and chassis have been around for quite some time.  . Some of them have been owned and/or raced by multiple people over the years. And in a variety of configurations, even different manufacturers bodywork and running gear. So at what point of its history are you going to restore it to?Only some by the larger fabricators even have serial numbers, and the lack of a number may not confirm anything, although it may eliminate some others.

You need to be sure you personally look at the car, and do the research to find out exactly what is being presented to you.

Now btw, the picture at the top? Its not a Roush chassis, but a similar chassis built by a name fabricator which was a Riley type design below the belt, and a late Roush style greenhouse. Food for thought.

Chassis of the "Baja Boats" Capri pictured a couple of columns earlier

"Roush" chassis stripped bare

One of the things that racers love to worry about is the weight of various components. And of course it is exceedingly important. After all we’ve never found a way around the law of inertia and that little thing called momentum. So it does behoove us to plan carefully and to not carry any unnecessary baggage with us on the track.

To the professional racer this is so important that teams go to what seems like ridiculous lengths sometimes. In an article recently it was revealed that last year McLaren wanted to add an additional sponsors logo to the drivers uniforms. This caused a major row within the team’s management because the logo weighed _37 grams_! Admittedly F1 is a totally different world than anything seem here in the states but the point is well taken.

In our world, I.E. club racing as well as the Trans-Am style cars it takes on a different spin. On more than a few occasions, I have had potential customers for bodywork pass on what were attractive deals. Their reason? They didn’t want anything that had any repairs to it. Not because of aesthetics or financial reasons but because they didn’t want the additional weight. While certainly their prerogative and understandable regarding the car, it sometimes make you wonder. Many of these same people, and I am certainly one of them, could more than offset that by putting the driver on a diet.

So I suppose the moral of this is that like so many other things about racing it is the total package. To be truly effective you have to incorporate every facet, sometimes it makes no sense to save .75 of a pound by using aluminum washers or leaving them off entirely if the driver is 30 pounds overweight. Food for thought if you will excuse the pun.

We want to wish everyone a Happy New Year!

Please be safe out there tonight. We want you back , to join us in what promises to be an eventful, and exciting, if challenging 2012.

I think many of us believe that motorsport in general may be at or at least near a crossroads, so lets see what happens.

They say that with great challenges come great opportunities, and I for one am looking forward to it.

Again, Happy New Year!

Russ Edwards

Another Capri

Jim Miller Capri at Firebird

Most of us have heard about sway bars, and can recognize them when we see them. But what do they do? Quite simply they control the transfer of weight from one side of the car to the other. When does this happen? Why when the car goes around a turn. When the car leans over, from the force of inertia, the stiffness of the bar, which is the only component connecting both corners of the car, resists this action. That is why they are commonly called roll bars.

When you look at the tube frame GT1/Trans-Am cars you immediately notice that the sway bars are different from your street car, or a stock car. Not only do they look different but they are in a different location. That is partly by necessity, partly from design even thought they serve the same function. We will look at each of the two separately. For the purpose of this discussion we will only be talking about the front bar.

On the stock car the bar is typically mounted as low as possible, in front of the wheels. Earlier designs were mounted in two blocks on the bottom of the frame rails, like your street car. Newer designs place it inside a tube which connects the frame rails. This allows the car to be run at a slightly lower ride height. The arms are removable and slip onto splined ends on the sway bar itself. These arms connect the bar to the lower control arm. This design, while not adjustable, is simple and effective.  Its placement is made possible by the “kickup” on the front subframe.

The first thing you notice about the swaybar on a tube frame GT car is its placement. Unlike the stock car, it is mounted high, above the upper frame rail, and generally in front of the wheels. (see the picture above) The reason for this location is that these cars use a flat frame rail. Thus there is no room under the car to mount the bar. The bars are generally mounted in one of two ways. The traditional way is for it to be sandwiched in a pair of split blocks bolted to the upper frame rails. Some newer designs have a heim joint threaded through the bar itself, this is simply attached to a bracket on the upper frame rail with a bolt. Regardless, it like the stock car design is connected to the lower control arm. In this case be tubular bars with heim joints in either end for adjustability of length.

The ends on these  bars are a mixture of fixed and rotating ends. (see the picture for an example of a fixed arm) The fixed arm, while it has different mounting locations  for the links, is not adjustable once attached. The rotating end is unique in that it is driver adjustable while the vehicle is in motion. It consists of a flat bar which is bolted to the sway bar. Mounted inside a bearing on the sway bar, it is free to turn.  The other end of course is, like the non adjustable end, attached to the control arm via means of a link. Driver adjustablity is by means of a cable run back to a quadrant mounted inside the cockpit. By moving the lever the cable causes the blade to be rotated from the vertical. This reduces its ability to resist the vertical forces on it, thus reducing the resistance to roll. While this provides the driver with an ability to reduce handling  problems during the race it is not perfect. The change is not linear. There is no constant amount of change per movement of the bar.

This of course is just a simplistic explanation of sway bars, and I welcome your comments.

Example of sway bar mounting on 2011 Trans-Am car.

Chevy Beretta Trans-Am type car

While running around getting ready for Christmas I thought I would throw this picture up.This is a car that was built to be a spare car for the team. Never finished, it was recently sold to someone who hopefully will complete and put it on the track. Very nice piece though.

We haven’t forgotten the post on sway bars, but it may have to wait until after Christmas.

Merry Christmas to all, be safe and spend as much time as you can with family and friends.

Another photo of the Capri

As millions of us get ready to take to the highways, remember safety first!

Left front of Trans-Am car

Left front of Trans-Am Car 2010

For years now one of the trademarks of a first class SCCA Trans-Am, or IMSA GTO car was the centerlok wheels. Just by a glance at the wheels you could tell who was a serious contender, or a pretender. Generally those wheels were made by BBS, although Jongbloed and a couple of others were occasionally seen.

What was the reason that the centerlok, more properly center knockoffs, rather than the almost universal 5 x 5 pattern wheels were used? Basically there were three reasons.
1. Unsprung weight. The suspension components and hubs were lighter than on an equivalent 5 x 5 assembly.

2. Suspension geometry. Most designers are proponents of the “zero scrub” design. This requires getting the wheel mounting flange as far outboard as possible. In other words a typical three piece centerlok front wheel will have a 1″ or 1.5″ outer rim half. Because of its spindle design a 5 x 5″ wheel has to use a wider outer rim half, perhaps 3.5″ or 4″.
3. Pit stops. With the single nut, the time to change tires was less. Admittedly this was the least important of the three factors.

But nothing is without drawbacks, and this is no exception. The price of a centerlok suspension assembly is far more than that of a 5 x 5. How much, did you say? Well it varies but it is hundreds of dollars per corner. Wheels for the 5 x 5 are far more readily available and at a fraction of the cost. And lastly since most races no longer require pit stops the speed of tire changing is pretty much irrelevant.

I should note that there is a hybrid design, used back in the 90’s by Peerless and a few others that adapted a 5 x 5 hub to use centerlok wheels. This was neither fish nor fowl, didn’t solve the geometry issue, and added about one pound of weight per corner.

So which is the right way to go? Depends on your wallet I guess. If money is the most important thing than by all means go with the 5 x 5. But if performance, and looking the part, are critical than the centerlok is still the way to go.


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