Category: horsepower

The famous Andy Bracket

Next trick after the K&N was installing the Andy Bracket, this advances the timing 5 degrees for better fuel economy and power. How is this possible? Let Andy explain:

Any XJR6 will benefit, in terms of performance, from having extra
ignition advance, provided it is running on 95RON (90pump octane
fuel) or higher. When I mapped the ignition timing, when I was at
Jaguar working on this car, the procedure was to map it 3degrees
back from detonation on the most knock limited cylinder on a mid-
limit compression ratio engine. All mapping was conducted under
steady state conditions on an engine dyno. Consequently the
combustion chamber and piston temps are much higher than they would be during normal road use when wide open throttle can only be
sustianed for a few seconds at a time. This means the transient on-
road margin from detonation is much more than 3degrees. The knock
limit on an engine can vary by up to about 3 degrees from one
cylinder to another, so the least knock limited cylinder will
benefit from even more advance. If a particluar engine is less than
mid limit compression ratio, this will increae its knock limit
further still. Then if you use a fuel with a higher octane than
95RON (90 pump octane) the ignition can be advanced even more. All
these factors mean that the engine can safely run with much more
advance than is mapped in the ECU. The knock control system is very
effective – I know because I personally spent several years
developing it for all AJ16 engines. The knock control system will
ensure that in the unlikely event that the 5 degree bracket
provided too much advance for any individual cylinder, that the
ignition timing on that cylinder was reduced to the optimum level.
In practice I don’t expect the knock system will actually need to
do anything, but it is there just in case. The knock sensing system can only ever retard the ignition from the mapped value, not advance beyond.

I tried to fit the bracket, working in the driveway in summer sun. Couldn’t see a bloody thing, cocked it up so the car wouldn’t start. Six hours later I scraped enough grease off the sensor so it would work. Car now has noticeably more power and excellent economy!