Reducing back pressure is always good, the problem, is a setup that reduces back pressure at flow X3, can increases back pressure at flow X\2.

Unless your racing, you're really wanting to choose based on desired form and level of sound.

With the cats, if you move to a design that reduces the thickness of the material that the catalytic substance is bonded to, and reduce the diameter of the cat to keep the cross section surface area the same. it will be a gain.

Sometimes a cat of lower cell count, can be advertised as "free flowing", when if it used a cruder manufacturing method, it might not outperform the stock setup at all.

 

I've just been informed that the VE in the stock tune is calculated base on the active exhaust valves being open, so pulling the fuse 19 should make no difference to power at all.

 

Thats good to know.. I was about to put the fuse back in...

 

I thought this entry in the exhaust troubleshooting section of the 4.2L workshop manual was interesting.

 

Xk with 100cell cats and xkr rear box

On the dyno there was no significant decrease or increase to hp whether the valve were in open position

In regards to whether the cats made power by themselves I couldn't answer that however as a package that is dyno tune + 100cell cats it made a substantical increase to the tune (excuse the pun) of 25whp or 10% over the pre run, I have also ran an official time of 13.9@101.5 at the WSID making it to my knowledge the fastest n/a 4.2

So whether the cats contributed to the total increase of 25whp or it was all in tune it's hard to say , but being a n/a I doubt all 25whp could actually come from the tune I would suggest the cats would have picked up 8-10whp and rest was the Ecu recalibration.

 

 

A full fancy aftermarket exhaust from Quicksilver, Spires, Supersprint, etc... At least the sound will make it feel faster. Better tires is always money well spent.

 

Found a S-type on dragtimes listed as running 12.9 @107mph

Mods were x-pipe, mina axle back and high flow cats

Considering stock str are running 13.7/13.8 that's a substantial gain

 

Maybe too substantial to be believed........

 

Maybe it a vvt model as they have a 20hp jump from stock ,

I find it hard to belive , mine has more mods than that and seems to run like a clock , but d can't see it cracking late 12's ever without a TS , or meth , or killer chiller .

 

That STR would be 1320racer's car, Jaguar Forums - Jaguar Enthusiasts Forum - View Profile: 1320racer yes it did a 12.9

But... the PCM in a 2005 STR is totally different to the PCM in an X150 XKR.

With the earlier cars running the Denso 32-bit dual-processor PCM (2003-2005 STR, XJR & XKR) the PCM can adapt to mechanical modifications like exhaust, cats, pulley, intake, etc, because it is not a torque-based PCM.

The Denso Pan-Pag PCM in the X150 uses a calculated torque for just about everything, so the tune must be adjusted to suit any mechanical modification you make. If the tune is not adjusted accordingly, you don't get the same sort of gains that you would from the same mods on an earlier car.

 

This is the famous 12.96 run

 

That's a myth (unless you mean the change in SAE ratings that for some cars added a non-existent 20HP). The myth is in several car magazines and the like and just goes on and on being repeated. Even has been on Wikipedia. Still a myth. Jaguar didn't claim the extra 20HP.

The car with the extra 20HP has twin air intakes, twin MAFs, etc. For this one, Jaguar did claim the extra 20HP. (I think it's 30HP. See Curriculum Training etc 2007MY ref 07NP-XKR.)

 

Ok it might not be a jaguar but it's the next best thing a 4.3 aston martin

Based on these test and the 4.3 being part of the aj engine family I'm petty sure we can also apply these sorts of gains to our motors.

To summarise
Stock bhp - 378
200 cell, rs mid pipe (x-pipe), gt4 rear muffler - 399bhp
As above minus the cats - 408bhp