Redlining a diesel

[gldgti]

huh - no wonder you guys with the newer tdi's see so much blowby, having all that torque at such low piston speeds.

Greg - since I got the provent from you, and fitted it to my aaz - i have collected only a few drops of oil in the bottom of the container. Thats in about 6000km.

I guess my big ass turbo and my driving style prevents a lot of leakage past the pistons.

I often rev up to 5000rpm.

FWIW - over-reving at no load (downshifting) is worse than under load because the piston has to do very little work to push the exhaust charge out of the cylinder (because theres very little there) - and this puts more load on the bearings as the piston slows down.

the difference probably isnt that much though.

[kaanage]

FWIW - over-reving at no load (downshifting) is worse than under load because the piston has to do very little work to push the exhaust charge out of the cylinder (because theres very little there) - and this puts more load on the bearings as the piston slows down.

the difference probably isnt that much though.

I would have thought that force required to decelerate the inertia of the piston in this instance would be far less than that imposed by the burning mixture expansion in a full accelerator powered stroke (with this being higher at low rpm than at high rpm). It is a reverse loading so I guess the pistons could be weaker in this direction

[gldgti]

It is a reverse loading so I guess the pistons could be weaker in this direction

bah - i had a nice reply typed up and lost it.

your right - because the loading is in the other direction, all the clearances add up the other way, and this brings the pistons closer to the valves. If the high rpm is causing some valve float, the pistons and valves can meet.

Under load, the charge is very dense and so during the exhaust stroke the piston has significant work to push the exhaust charge out of the cylinder. Also, the valve is almost closed as the piston approaches TDC so this helps slow the piston, rather than complete reliance on the bearings being loaded in the other way.

[Greg Roles]

Was just noticing yesterday that I do all my routine driving from 1800-2600 due to the grunt. Interesting.

[maxrob200]

Agree with Greg, I use 1st to get me up and running then accelereate to around 3 - 3.5 in other gears. Car just about leaps from gear to gear with a good shove in the back. No fast standing starts for the diesel IMO, leave it to the guys with big V8

[kaanage]

I usualy only accelerate up to 1800 unless going up a hill or going for a punt.

[Transporter]

I boot up my T5 at least once a day. It keeps the VNT in shape.

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[Frankenstrat]

Mine gets a daily boot, too, Kwinana Freeway northbound on-ramp in Oakford, got to merge with the fast-moving traffic! She flies when the revs get up there.

I've only hit the limiter once, and that was to get myself out of the way of a very fast moving car getting much too close in my rear view mirror. I was in 1st gear and had to plant my foot to get clear of him. He then overtook me on a blind bend with double white lines.