The "TT" Extractor System
by AJ6 Engineering
For many years we have puzzled over the question of how to create an
efficient extractor exhaust within the limited space around the Jaguar V12
engine. There just is not enough room to accommodate the length of pipes
needed for conventional multibranch headers to work properly. Dispensing
with the first silencers or replacing the standard system with one of
larger bore gives a useful performance gain by virtue of having less
restriction to flow. On the other hand a properly designed extractor system
augments the induction process and lifts the potential power gain to a
different level altogether.
We reasoned that because there are equally spaced discharges with
negligible overlap into each of the four cast exhaust manifolds, each
serving three cylinders, a long pipe from each manifold should generate
quite strong impulses so that each cylinder would aid the next. Calculation
showed, and testing proved, that the ideal pipe size, whilst certainly
long, would provide best mid-range performance by having a surprisingly
small diameter. This increases the gas velocity and the resultant inertia
effect but also generates beneficial resonant pressure waves which have a
synergetic effect on the induction process - as exploited in all racing
Large bore exhaust systems seem to work reasonably well without any fueling
changes, but when we first tried our extractor system it seemed
disappointing - until we started to optimise the fuel mapping. Then it came
That created a problem because we could not just sell an exhaust system, we
had to provide fueling changes to make it work - adding to the cost.
The final arrangement has a pair of long pipes passing along each side of
the engine until they merge behind the transmission. The acronym "TT", for
"twin tube", seems appropriate. To follow them with the usual restrictive
first silencers would spoil the effect so our familiar Silencer Substitute
Pipes provide the connection to the standard rear system going over the
axle through the rear "straight-through" silencers. Because the system is
intended to operate with high gas speeds there is no penalty (other than
right at the top of the speed range) from retaining the standard size rear
section. The usual problem for previous high performance exhaust systems of
threading large pipes around the drive shafts is therefore completely
avoided. There is also an obvious cost benefit.
We aimed for optimum extractor effect in the 3000 - 4000 r.p.m. range.
Maximum torque on a 5.3 litre V12 is then increased by approximately 33
lbs. ft. yet the arrangement outperforms the standard system throughout the
speed range. Even a conventional big bore system only shows to advantage
above 5500 r.p.m. For those who do require extra performance above that
speed the TT exhaust can be supplied with a larger bore stainless rear
section but there is then a slight loss in the lower mid-range.
The TT exhaust is also available with fittings for heated Lambda sensors
(supplied separately) for those cars where it is possible to dispense with
The sound produced by the TT exhaust is different to most other Jaguar
systems. It is not particularly noisy at all but there is a definite
crispness to the note - perhaps like a mellowed Ferrari.
Either a revised EFI chip or an electronic module is included to provide
the fueling changes that are essential to get the best from the TT exhaust.
|TT Y Pipes + Silencer Substitute Pipes + EFI mod ||£450|
|TT Y Pipes + S Pipes + EFI mod + standard size rear section||£700.|
|All items in high quality stainless steel. Vat & delivery extra.|