Is there any way to delete or pass the 3K limiter when tranny in P or N ? Anybody done this already?

 

This begs the question...why would you want to?
That rev limit is electronically controlled to protect the gearbox and torque converter....it is a design feature not to be tampered with. ]

 

I think you know why this should be deleted

 

OK, I'm a dummy too. Why would you want to delete it?

 

Maybe I should record the exhaust sounds when hit the pedal down at 1st gear. Unfortunately that creates so much smoke and two 150ft long stripes, so I still prefer hearing the same thing at P - but seems to be difficult.

 

I think, like removing the speed limiter, it would be a major exercise and might indeed cause some damage.
I'm not an exhaust note cognoscenti but imagine that it would sound quite different when the engine was actually under load.

 

The exhaust note while under load is always different than while in neutral. Revving the crap out of an engine while at a stand still is a habit I grew out of at an early age. I've moved onto different juvenile stuff now.

 

Are you never too old to hear something like this ? PS. I am 40+ : )

 

Honest answer- I cringed and felt sorry for the car for the first 15 seconds or so.

 

Well, the N/A car will rev to 7000 in P or N. However, your
XJR has hydraulic engine mounts, and the lower limit is likely to
reduce damage to engine mounts. Also, the clearance of some
components is tighter, and the twist of the block from the torque
could cause two things to touch.

 

Thanks. Your answer was first reasonable post.

 

Virtually no torque is transmitted to the car while revving in neutral, so the engine mount explanation is not correct.

 

I don't have a copy in front of me so I can't confirm, but doesn't JTIS specifically mention that the 3000rpm limiter exists to protect the Mercedes transmission from a neutral-drop?

 

Mikey, if you've ever revved (in an XJ engine compartment)
over 3000rpm (which is the standard safety limit on any AJ27, including
for restricted performance failsafe) you will see quite a lot of
body/engine twist. There is a significant amount of parts
thrown on top of the engine in supercharged spec, so I'm
sure it was down to engine mounts/ clearance. revving any
engine with no load is ill-advised though.

In my XJ Sport, I got comments on how much body twist
there is from revs. It twists like a sports car when revved,
but it is a big saloon car!

 

ever heard of inertia?

 

I agree wholeheartedly not to rev our engines in neutral.

The Lambo looked like warm-up, a happy V12 with a puff of oil on overrun.

I've stood and watched near boiling oil go into an F1 engine prior to start-up, then dry sump pumps running the oil through the system, the tolerances inside the engine took into account of the block swelling, if started too early things broke due to friction! - it's very different for race engines, or highly tuned units like any supercar. Revving these engines to warm-up temp is advised by the makers. Service on these is £1,000 per cylinder...

 

What you are seeing is an opposing motion of the engine as the rotating mass accelerates - Newtons third law, action = reaction. The torque required to rev an engine in neutral ie overcome the interia and it's equivalent reaction to the engine mounts, is tiny compared to the car being in gear and attempting to accelerate. If there was an interference issue in neutral, it would be worse while in gear.

Here's a good example:

videos :: RedneckFarmTruckDragsterVideoKillSomeTime_WMVV9.mp 4 video by valrico64 - Photobucket

 

Look, the torque application under
load is applied to upper and lower rear
sub-frame connectors. The load on
the engine mounts with no load
may be proportionally dissimlar,
but it is only a transmission input shaft turning.

Perhaps then, they would have limited the revs
to 3000 in "D" too, because of how badly
cars twist under torque when they are in gear?

Except for that they don't because the gearbox
can handle 796 lb-ft. Yes, that much. 1079 Nm
is not anywhere like what an XJR can produce,
in neutral. It can't be a transmission thing other
than the inability to cool in P or N.

 

figured this out when I thought I was in D, floored it, car was in N, moved it into D while it was pegging the limiter, car then revved to the redline and stayed in a "neutral" of sorts while the gear shifter was in drive. no damage done to the car that I could detect, it went into D for real and I started moving once the RPMS dropped back below 3000.

so you can "trick" it into letting you rev all you want, but I'm not sure if it could be an actual problem, I might have just gotten lucky

 

Ian- don't want to argue with you. Just pointing out basic physics.