PCA SDR

Hi,
Where do you guys mount your AMB transponders in your 944 NA's?

I'm trying to figure out the best place to mount a rechargable AMB transponder i just got in my 944. I had mounted a direct wire transpoinder in another 944 just underneath the airbox, but in hindsight i don't think that is the best location. I know it has to be pretty close to the ground and unobstructed and also not subjected to temps above 122 degrees.

Thanks,
Lawrence

I have mine mounted on the back of the car next to the license plate.

one thing i forgot the mention is, this is for wheel to wheel 24 hours of lemons/chumpcar racing and there is sometimes a lot of bumping of bumpers and fenders sometimes pretty had bumps so i need to make sure it's somewhat protected.

Mine is above the rear bumper about 6" to 9" and bolted to the flat panel between the tail lights and license plate.

For racing, best to check with your sanctioning body - sometimes they have restrictions (like not mounted on a 16 foot long 2x4 extending out the front).
A good location would be on the inside panel of the left front wheel well, just forward of the spring (and inboard, of course). That way, it is reasonably
protected yet the wheel won't rub on it, it's pointing down with a fairly clear window to the track, and it is far enough forward to possibly give a slight
advantage over a rear-mounted transponder (assuming you don't slide backwards across the finish line). While a hard-wired transponder works best
in this sort of installation, you could mount the bracket for the rechargable one where I described, and turn the wheel hard left for access.

Assuming continuous lapping, unless you are concerned with crossing the lines wheel-to-wheel and want to know who crossed first, the fore/aft location should be immaterial. The sensor is measuring the time from successive passes of the transponder over the sensor loop, which should be the same whether the transponder were on the front, back, middle, or being dragged along 10 feet behind the car.

If you ever have a standing start, the furthest aft position would be best. Why? Because your car will be at its maximum possible speed when the transponder crosses the sensor line. If the transponder is mounted on the nose, then you would lose a car-length's worth of additional acceleration over a mounting on the rear bumper. This is why I advise my AX students to hold back from the start line as far as the starter will allow - every additional foot is additional acceleration time before you cross the start line.

This should not normally apply in DE and TT events, unless the first lap from a standing start or from pit road is being counted.

For racing, there are very specific and narrow parameters on where to place the transponder in order to determine who is the first to cross the line. Sometimes those locations are specific to the inch from the front bumper of the car. Check with the LeMons organizers because it's not the bumper that cross the line first, it's the transponder that crosses first.

Kim Crosser wrote: This is why I advise my AX students to hold back from the start line as far as the starter will allow - every additional foot is additional acceleration time before you cross the start line.

***takes notes***

Lawrence,
Many of the 944 Spec cars have theirs mounted on the drivers side fender liner, low and on the inside of the engine compartment. There is a spot with a clear and unobstructed view of the track, including a little ahead of the transponder. It is also close to the ground and within spec of the AMB recommended distance.

In your case, or any racing case, you want it as far forward as possible. This location is fairly close to the front, while being fully protected. Again, check with the organization you will be racing with to get their constraints.

As we will probably be meeting within a day or two anyway, why don't you take a look at both of mine to get an idea.

All 924S cars will be starting 1/8 inch from the line.

That's funny, Kim is talking acceleration advantage in the same breath as a 944

You have to remember, the difference between crossing the start at 1 MPH (front of 944) and 2 MPH (rear of 944) is 100%.

Kim, for AX, if the location did not change, there would be no time difference. For a race, it is whoever crosses the line first, so the farther forward the transponder, there is a slight advantage as the transpponder signal is used, not the nose of the car, as it used to be.

Hi Chuck,
I qualified my original post - "...unless you are concerned with crossing the lines wheel-to-wheel and want to know who crossed first."
For DE and TT, where you are measuring elapsed lap times - not whose nose crossed first - the transponder mounting position makes no difference at all.
For AX - if you were using transponders, the farthest aft position would be best - even in a flat out 944.