So the standard XFR center section post cats i have consists of a single silencer of straight through design perforated tubes and glass pack silencer wool.......as its just a single box a small....v small amount of cross bank scavenging may occur from this.......we also believe, but pics to show pending that this is where the X pipe is fitted on the RS. On from this and still in the center section you have another silencer of resonator design.....this is the one i cut open. No exhaust bank mixing occurs in this silencer.........looks like the RS also has one.

then moving down stream in the exhaust system we have the rear silencers.......or mufflers.

Hope this helps

 

Thought I'd chime in here guys, although I'm a 5.0 XKR owner. The factory X-Pipe on the R-S models is in the position of the rear resonator (the box closest to the back box on the stock system). This seems to go against common logic of placing a crossover closest to the engine, but it might be why the XKR-S etc. retain the muscle car burble, which can sometimes be lost when placing an x-pipe closer to the engine.

Also regarding upping supercharger boost via the ECU map; this can indeed be done on some cars; take the 3.0 supercharged Audi motors, they gain close to around 100hp from a map alone as boost is being bled heavily by the bypass valve from the factory. The 5.0 superchargers have a boost bypass valve, however, I'm not sure if this is electronically controlled via the ECU, although I'd guess it might be.

My car was mapped by Evolve (stock pulley) and is putting out around 575bhp. These guys are well known/respected in the UK, particularly with BMW's; they write all their own software etc. In my initial discussions with them they stated more boost could be obtained through the map (as they had found on their project 5.0 F-Type).
Post map my torque curve is flat from about 2500rpm to the redline with no drop off in the high revs - this didn't happen with their development F-Type (which had a more traditional hump in the middle), and indicates torque is being limited elsewhere i.e. the TCU. The 8-speed in the F-Type is stronger than the ZF6, hence the TCU torque limits may be higher from the factory.

 

I'm looking at evolve to tune mine having seen their F-type developments. What other mods do you have to get 575bhp? I've got a cat back exhaust only but considering BMC air filters, an intake and potentially 200 cell cats before the tune.

Back on topic though, I'm not sure how the tcu could limit torque without communicating with the Ecu and controlling it there.. Does an Ecu remap not manipulate/suppress that communication?

 

The transmission has no way of measuring input torque, there are no sensors for that purpose, and the existing sensors in the transmission can't be used to determine torque. So the TCM program is not where a torque limitation is programmed.

There are torque limiters built in to the engine ECU program, but these are based on things like MAF rate @ rpm/speed, in certain gears. As it's known that a certain amount of air equals a certain torque/power if the engine sees "too much" air then it backs off.

The earlier 5.0L engines had a vacuum operated bypass valve, the newer ones have an electronically controlled one. This change in bypass valve design did not change the power output, the 5.0L XKR-S for example had both versions. The bypass was not used to bleed off boost, only the throttle position.

Have also seen the flat-line torque "curve" on other cars (the earlier 4.2L for example) and this was only done by the ECU pulling back the throttle electronically. Same thing on the 5.0L which is how the power output is limited to the marketing specs.

More throttle equals more boost too which is why there was some noticeable differences in boost between the factory tunes, 7psi, 9psi, 11psi, for example.

Other examples of the torque limitation; "throttle limitation at low vehicle speed", "torque reduction during gear shifts" "torque reduction for traction control" and so on.

It's all in the ECU... which is where the R-S cars have it over the regular R's.

 

Absolutely nothing at the time. I've since replaced my exhaust centre section though, removing the 2 silencers/resonators (I actually thought one of these was a secondary cat) and replacing them with straight pipes with a H-Pipe crossover where the factory crossover would be. So I'd maybe expect a bit more power now, nothing major though.

 

Interesting. Not an expert by all means but I would have thought there was still the ability for the TCU to have torque limiters built in (which are activated by data from the ecu possibly?). As far as I know the TCU's in VW DSG's, Mercedes etc. All have the ability to do this?

 

Hey matey......so the H pipe u have put in....is it at the rear most part of the center section or near the headers........can u post some pics and a sound clip???? Any more pops and crackles like the RS?? This is exactly what i am looking at doing!! Thanks

 

Interesting!

So the throttle position and boost is controlled by the MAF sensors. In which case, could we use some kind of MAF tuning device (basically a cheap resistor) to fool the Ecu?

Flame suit on!!

 

No it's not that simple

 

The XFR to begin with is underrated, an ecu tune, filter, exhaust and if you want a new pulley will get you in the 600 horsepower range.