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 exhaust systems.
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 to life!
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 catalysts.
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.
Prices:-
| 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. | |