Jaguar Voltage Reduction system for XK8/R 1997 - 2006 Roof Operation

As you know this application has drawn a great deal of interest.  I will do all I can to be impartial and provide the facts as they are.

The equipment used on both cars 2000 XKR & 1999 XK8 to perform the test was the same.  All instrumentation  used to perform this test was the same.

This test was operated on my car a 1999 XK8.  To give us a benchmark and to check for accuracy we connected the data logger to the car by isolating the pressure relief valve and installed the data recorder and connected it to the computer.  I ran the roof down and up and compared the results (normal operation no valve & no resister) of my car to Walts car 2000 XKR and you can see the chart below.   At that time we knew that the unit was recording properly and comparing the two only confirmed it was working properly the day of this test.  I then installed 2- 0.10Ώ 50W resisters in series as instructed in the instructions ( to the white lead of the power source to the pump and opened and closed the roof.  I then removed and reinstalled the resister to the black lead and did the open and close of the roof again and the results were the same. 

Equipment used;

All the data was taken with a Data Instruments Model SA, 0-3000PSIS transducer. 

The logger is a Dataq DI-148U.

The log interval was 100 samples per second.

There two cycles taken for each measurement and the cycles were compared and found to be consistent.

Stock – Was tested on my car 1999 XK8 to verify that the system is operating and recording properly.  The results were compared another test that was taken on a 2000 XKR  .  This test was a complete open and close cycle.  See the chart below for the 2000 XKR results. 

Resistor – Was tested on my car 1999 XK8 this test was a complete open and close cycle resulting in a close latch pressure of 1576psi.

Relief Valve – Was not performed in my car but was performed in a 2000 XKR.  The reason was to show comparison between the different applications.

Please take note that both stock cars 2000 XKR & 1999 XK8 that the data was taken from was at different times hence supporting the validity of the test when compared with each other.

The chart below was taken in 2009 on a 2000 XKR

This is the resister setup I used to do my test.  In that test I placed them in line with the White lead, opened & closed the roof.  I then moved them to the black lead and performed another open and close operation. 

The resister was put together using the procedure outlined in the instructions;
“- a single 0.20 ohm resistor, 100 watt rating w/o heat sink or 50-watt rating mounted on a heat sink."

I used this procedure;

"- two 0.10 ohm resistors in series with each other, 50-watt rating w/o heat sink or 25-watt with heat sink.”

This test was performed by Steve

This is Steve's test with the resister installed with the engine on.

(Chart shows first trial, other two trials were 1632 and 1632 peak pressure)

(Chart shows first trial, other two trials were 1632 and 1617 peak pressure)

As you know this post has been a long time coming.  I had other information from two other testers but hesitated posting it because one of the testers reevaluated and elected to make another test that I now feel was the right thing.  We did not want to post anything that was not accurate.  We had three people including myself & Walt that performed the test.  I should mention that my & Walt test was done with the engine running only with digital equipment, Steve with the engine off and running with digital equipment and Sam was with engine off and running with an analog tester.  Because of the speed of the system Sam's analog gauge was modified by draining the glycerin to improve response time of the meter and it was recorded on video and the video was used to capture the peak readings.  I have no problem with the analog test just that it is not as accurate as the digital.  You may ask why I did not test with the engine off, it was raining and I simply saw no reason.  For that reason I will only be comparing the engine on operation pressures.   As for myself, I put the top up and down at traffic lights and in parking lots with the engine running.  I am not about to turn it off, drop the top and restart.

I will list all three results with the engine running;
  Sam Steve Gus/Walt
Top Down
Top Up
Full Cycle Average

Now the average between the three tests = 1592psi

As you can see we have a difference in the test.  We found that battery voltage plays a big part in the testing.  Sam's test was analog  and Steve's & Gus/Walt were digital  I should also note that both digital tests were done independently and using two different sets of equipment.

We all agree that the operating pressure for all 3 tests was 1650psi with that being said:

Sam’s test is a 80psi reduction, Steve’s test is a 18psi reduction, Gus/Walt’s test is a 74psi reduction.

This is Steve's test with the resister installed with the engine off. 

(Chart shows first trial 1555psi, other two trials were 1540psi and 1540psi peak pressure) Average 1545psi

(Chart shows first trial 1470psi, other two trials were 1479psi and 1449psi peak pressure) Average 1464psi

So my calculations on the resister application with the engine off gives you an average reduction of 150psi benefit from the normal operating pressures.

This test has proven that the Voltage Resister application has fallen short of providing the psi reduction as suggested by the originators.   The reduction was hardly worth talking about when you consider that the replacement hose is around $290.00, 6 hrs if you do it and $1500.00 to $2000.00 if you pay to have it done. 

Now this brings me to my comment stating that my roof stalled a few times while testing.  When the resister application was first presented I decided to test it myself on my car in my driveway.  I made the resister application and purchased a volt/amp meter to install on the load side of the resister.  What I purchased was DOC Wattson Meter.  This meter proved to be extremely helpful.  I also did a video of the operation because the non believers would comment on my findings.  The problem is that my video is packed up in storage from when I sold my house.  When I get my hands on it in February I will post it.

I also have a few charts and photos of the application that, if I get time, I will add them to this post.

If you have the resister system installed in your car then you need to become informed and figure out what to do. It is your car and your investment.

In conclusion Walt and I did all we could to get this information out to you the end user long before this. It is a real shame that this situation deteriorated to this point. What you should get out of this is that this information came to you by the persistence and dedication to providing you the right information.

Thank you Walt for your dedication and friendship, and Steve for your assistance in resolving this issue. It is by your expertise that all of this was possible.



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