Silly q .. revving in a tunnel and engine/tranny damage!?

[AlanD]

Ok, yeah, I know it's rather uncouth, but .. it's good to be fore-armed (that sounds wrong!). When one has a V8 on a nice sunny day (remember them?) and an empty, narrow, echoey (is that a word?) tunnel, it is a little tempting to stop, wind down the windows, and give it some!

Now while spin out starts are all very good fun, they are also 1) expensive on tyres, and 2) create tyre noise over the engine soundtrack, and 3) .. wind!

Sooo .. in the interest of not destroying my transmission, how does one safely rev an automatic!? Some Googling around (mostly American posts) comes across horror stories of inappropriate torque and all sorts of nasties. I can't separate fact from fiction or whether it just applies to un-sophisticated US autos! Therefore, three questions:

1) Does revving in P risk damage to the transmission?
2) Does revving in N risk damage to the transmission?
3) Does revving in either P or N with the brake pressed risk damage to the transmission?

Finally .. having done it a couple of times anyway, I notice the box limits the revs quite low and the speed of the revs dropping back is very slow. Why is this?

 

[rorf]

It is the worst thing to do, reving an engine which is not under load - all the bearings and pistons start to rattle and you reduce the longevity of the engine quite substantially.

But Mercs are clever - they do not allow you to rev much over 4000 rpm when in neutral or park:bannana:

 

[AlanD]

But is that specific to an automatic, and if so, why?

Re Mercs, yes, that appears to be the case! What's actually stopping the revs?

 

[Stratman]

But is that specific to an automatic, and if so, why?

Re Mercs, yes, that appears to be the case! What's actually stopping the revs?

The engine control unit (ECU). The boffins at MB have programmed it specifically to prevent children destroying their father's car when he lets them drive it

Incidentally, the same ECU will let the engine rev to the red line when in kickdown.

 

[Howard]

Why would you stop in a tunnel to rev your V8 ?

Just put the window down ( while still moving ) and bury the loud pedal in the carpet ....

Double the fun.

Mine sounds better when under load anyway ....

 

[golferson]

where is this tunnel? i could stand there and hear it for free!, kidding aside lucky XXXXXXX

 

[Dieselman]

I have heard that getting very revved up in a dark tunnel causes Tranny damage...

 

[st4]

I have heard that getting very revved up in a dark tunnel causes Tranny damage...

Depends how deep into the tunnel you can go

 

[golferson]

check the oil and alls well!

 

[AlanD]

As an ex-biker, I can assure you that a wide open launch in a small tunnel (it gets better all the time!!) is a visceral and aurally pleasurable experience

The problem in a C55 is that foot to the carpet in 1st creates so much wind noise so quickly with that pesky body wrapped around the driver, that's it hard to fully appreciate! Also, you need a long tunnel .. like the Alps. A wee little railway tunnel in Greater London is not that!

It's not like it's something you'd do on a regular basis, I just figured it was best to know whether it was damaging to do full stop. And yeah, I know not to dump it in D from a highly-revved neutral

 

[Dieselman]

And yeah, I know not to dump it in D from a highly-revved neutral

Doesn't matter if you do, it won't engage gear over 1200rpm.

 

[AlanD]

The engine control unit (ECU). The boffins at MB have programmed it specifically to prevent children destroying their father's car when he lets them drive it

Incidentally, the same ECU will let the engine rev to the red line when in kickdown.

So it's an electronic limiter rather than anything to do with the torque converter stall speeds or similar (can't find the link now, but some American was going on about how it would hold the revs and create lots of undesirable heat)? Again, pinch of salt since many US autos are prehistoric technology wise and not everyone on teh ol' Intraweb knows what they heck they're banging on about!

 

[AlanD]

Doesn't matter if you do, it won't engage gear over 1200rpm.

Yeah, I noticed something along those lines a few months back when I "missed" D from reverse and made some silly noise in neutral with cars waiting before doing pretty much nothing in D until the revs died back down! Just as well really.

 

[Stratman]

So it's an electronic limiter rather than anything to do with the torque converter stall speeds or similar (can't find the link now, but some American was going on about how it would hold the revs and create lots of undesirable heat)? Again, pinch of salt since many US autos are prehistoric technology wise and not everyone on teh ol' Intraweb knows what they heck they're banging on about!

If you try to rev it in P or N the ECU limits it to 4000 RPM. If you rev it in gear against the brakes then what you have described above happens. It's a quick way of destroying the ATF.

 

[LTD]

Why would you stop in a tunnel to rev your V8 ?

Just put the window down ( while still moving ) and bury the loud pedal in the carpet ....

Double the fun.

Mine sounds better when under load anyway ....

Sounds even better if you watch somebody else horse it away ....

 

[AlanD]

Sounds even better if you watch somebody else horse it away ....

Yeah, well funnily enough I've never been driven fast in my own car (no, that's not an invitation!) :bannana:

Did have to do an emergency swap over on the motorway recently due to getting dangerously tired in poor conditions on a long journey and not wanting to risk waiting for the next services ... once she got in, I persuaded her to stuff it in the carpet up to full speed so we didn't get run over by fast approaching lorries! She .. "didn't know it would reach 70mph that quickly" ..