Hi,

I've made the odd appearance on the 200 series forum, but now my 240 is up for sale, and I am the proud owner of a 1995 940S 2.3 LPT. I'm still getting used to the differences between a 240 n/a with a carb and this 'new' fuel injected turbo thing!

My main question is, apart from the pressure output, what is the difference between the LPT unit and regular turbo, are they the same unit? and should I still sit for a minute or so after driving, to let the turbo 'spin down' before switching the engine off?

The other thing I've noticed is that, when accelerating hard to over 4000 rpm, I get a slight surge when I take my foot off the gas to change gear (manual tranny), is this normal?

Apologies for what must be rather common sense questions, but I haven't owned or driven a turbo car before. I like to think that I exercise a fairly high degree of 'mechanical sympathy' when it comes to driving, so any 'turbo tips' anyone can offer and possible signs of trouble that I should look out for, would be very much appreciated.

Cheers,

Jamie B.
- counting the days 'til I have the space for a 242 project car.

Thanks guys for the tips and info, much appreciated. The turbo certainly is fun, even if it is only a low pressure one, whilst allowing the cooling period, I've been admiring the red glow from the exhaust manifold after long runs at speed, it's still quite a novelty ;-)

Cheers,

Jamie B

Both of the other guys are right.

"Spin Down" is a slight misnomer, but the end result is the same. The turbo RPMs actually decrease fairly quickly. The actual reason for letting the engine run for a bit before turning it off is to keep fresh oil and coolant flowing, helping the cooling process along. Particularly on the oil-cooled-only models, it's quite important. Not so important on the water-cooled versions, but still a good idea. I usually let mine run for at least 30 seconds, particularly if I just ran it hard or have been traveling at highway speeds. You can't be too careful. An ounce of prevention, and all that.

Nice car you've got there. Hope you continue to enjoy it.

Go on over to the turbobricks.org and go on their message board and ask the question about the surge when you shift. They will HATE you, because you are lucky enough to have the M90 transmission. I am just kidding, they won't hate you, but they will be very envious. They should be able to help you with a surge problem.

Oh, also, yes, you should let the engine run for a moment, especially after hard driving, and let the turbo spin down. Even if it is watercooled.

Greg

Jamie, I can only offer advice about the LPT vs. Reg. turbos. LPT stands for "light pressure turbo". A light pressure turbo is somwhat smaller than a "regular" turbo, Like a Garret T-3. Turbos are driven by the exhaust that your engine makes, which spins the turbine to provide boost to your engine. This means that your turbo spools up quicker, because it requires less exhaust to get it working. The main benefit is that a LPT has less turbo "lag"(time that is starts working). Your turbo gets working a lot faster. A bigger turbo cannot really start working good until your rpms get up pretty high (exhaust exiting very fast). The main drawback (only if you have a very heavy foot) is that a LPT "tops out" faster in that it gets to its maximum boost threshhold faster than a bigger turbo, so it makes somewhat less boost. There is a lot of really good info at www.turbobricks.org (not sure if that is the right address or not) that goes into a lot more detail than I have. I know that you more than likly know most of this already, so my apologies if I told you what you already knew.

As for letting your engine run, I do not know. I have a '84 245 with a T-3 Turbo and I do have to let mine run about a minute because it is cooled by the oil, which will cook if it is shut off right away. If yours is water cooled (i think it is) then I do not think that you need to let it run.

Just my .02 worth, Robert