XJR - running without SC belt

[Output Flange]

Was chatting with someone who suggested that if the weather turns bad, it would be sensible to remove the SC belt to lower the amount of power and torque and therefore help with traction in snow/ice.

Can you run without the SC belt connected for extended periods without it becoming an issue? Doesn't the ECU expect a load of compressed air, and adjust the fuelling to match?

[avos]

You can, but what really helps are winter tires and an LSD, that gets me through the winter with 600bhp on tap (for the spots where there is grip ;-)).

[Output Flange]

Thanks. I was less interested in whether it would help driving in winter, and more whether it was safe to run the car without the belt fitted, I guess.

[a8hex]

My X300 3.2 sport is hopeless in the snow wearing P6000s.
Reducing the torque from the XJR engine might help a little, perhaps from very totally undrivable to just totally undrivable.


I'd vote for Avos suggestion too.

The Mrs' MB barge was equally bad, bought her a set of winter snow tyres last year and just couldn't believe the difference. As long as you don't go silly then you seemed to just be able to drive.

[NormanD]

Yes the car will work but power will be even LESS than a N/A engine as the compression ratio is less and the breathing will be through the bypass valve

As Avos said a LSD will help as well as Winter Tyres

You can get LSDiffs fron TLJaguar 0118-976-2899 as you know

I have a LSD in my XKR helps get the power to the road in all condition,
in-fact it's so good I have the Traction Controll OFF most of the time

[Output Flange]

Cheers Norman.

As said, this was really about whether it's ok to run the engine without the S/C belt attached, rather than how to drive in snow

[varsas]

I think the supercharger is de-clutched at low revs, isn't it?

I find it hard to believe the ECU won't go mental, the fueling map will be all wrong as well...

[Output Flange]

varsas said:

I think the supercharger is de-clutched at low revs, isn't it?

I find it hard to believe the ECU won't go mental, the fueling map will be all wrong as well...

It is de-clutched, yes. Not sure to what point, though.

The fuelling map was my concern, too. Surely it would be expecting a load of compressed air, and add fuel accordingly? Or will the reading from the lambda sensor lean it out?

[varsas]

Output Flange said:

varsas said:

I think the supercharger is de-clutched at low revs, isn't it?

I find it hard to believe the ECU won't go mental, the fueling map will be all wrong as well...

It is de-clutched, yes. Not sure to what point, though.

The fuelling map was my concern, too. Surely it would be expecting a load of compressed air, and add fuel accordingly? Or will the reading from the lambda sensor lean it out?

Yeah, I've never been sure..I mean, in theory if you have a lambda sensor you don't need a fuel map...just adjust it on the fly. I assume the lambda sensor either isn't that accurate or isn't fast enough to 'see' changes in the air/fuel mixture to be the main way to car knows how much fuel to put in...it's just there to trim the car by small amounts.

I dare say 'boost pressure' is an input to the map, and even if not the car will know how much air is going in via the air mass sensor so I reckon so you might be OK...assuming you don't run out of map, i.e. go so far outside the values the car expects (e.g. no boost, full throttle, 5,000rpm) that you go outside the parameters the map can handle? Do that and the ECU will get very upset very quickly and probably stop ignition.

Actually, I think I have changed my mind. I reckon that the lack of boost will throw up an error, and the ECU will shut the engine down however by itself I think the car will be able to cope with a lack of boost and that the ECU should be able to compensate. Maybe.

[Output Flange]

I didn't think there was a boost pressure sensor - could well be wrong, though.

The MAF sees the volume of air pre-supercharger, so won't know what happens after that.

This forced induction malarkey is far too complicated for me

[LoudV8]

My X300 XJR once threw the s/c belt and I managed to drive home about 20 miles with no problem. It was a bit (OK very) lethargic but not a single warning light.