divil

This is my first turbocharged car. Everyone knows not to push an engine hard when it's cold, especially on older cars like ours. But if I have to choose between revs and turbo boost...which is worse for a cold engine? 2 of the 3 directions I can drive from my apartment are uphil. If I use a high enough gear to keep the revs low then the boost gauge climbs up. I can keep the boost down by dropping a gear and going with higher revs....that feels safer to me. Thoughts?

ramius665

Well, your owners manual states that you shouldn't rev above 3k rpm until the engine is warm. The rule of thumb is that oil takes twice as long as coolant to reach normal operating temperature. Also, the owners manual states that you shouldn't leave the car idling to warm the motor. It only takes a few minutes (5-8 minutes) for my car to reach operating temperature. If your car is already at normal operating temperature by the time you're reaching the hilly portion of your commute, I'd drop down a gear or two for power. If your car is still too cold, just keep the revs below 3k.

Paulyy

you've lost me here.
how do you boost if you keep the revs down and have a soft foot?

ramius665

You don't!!

Ronin-951

Give him a break, ... coming to grips with having to do the speed limit is enough pain at one time.

Paulyy

the stock boost gauge has probably confused him. because it's impossible to idle a turbo car on 0.4 bar of boost.

TO The OP. when your gauge says 1bar you're on 0 psi of boost. the stock gauge is measuring atmospheric pressure not actual pressure. so if you don't pass 1 bar your fine.

divil

Hmm...ok. But the gauge moves a lot depending on the load on the engine... I don't pay attention to what it says in bars, I just go by where the needle is. If I'm driving on a flat stretch of road at, say 30mph in 4th gear, then I start to go uphill, the needle on the boost gauge suddenly goes from to the left up to about half way. If the road levels off, the needle goes back down again. I took that to mean the turbo is spinning up, which I thought would be bad when it's cold. Is that not what's happening?

Paulyy

the turbo will always be spinning when the car is on. with more load the turbo will spin more but not necessarily build boost.

when the gauge is in the middle it's on 1 bar which means 0 boost. when you pass 1bar or the middle the turbo will spin fast enough to create pressure in the intake and then you've got boost.

The load on your engine is what you should be worrying about, the turbo is constantly being lubricated by oil. a cold engine shouldn't really see to much load. when it's warm, rev it and boost it as much as you want.

ramius665

So back to my original point. The owners manual says to let the car reach proper operating temp before going over 3k. You're not going to get much positive manifold pressure under 3k, especially if you're not flooring it.

divil

OK that's what I was getting at, I shouldn't have used the word "boost". My question was more about whether it's bad to let the turbo spin faster like that. But actually it brings me to another question...why does the turbo spin faster in that situation (like my example above). Whereas if I change down to 3rd and let the engine rev a little higher, the turbo slows back down again. I don't really understand why that happens.

pettybird

the boost gauge measures engine vacuum (until the 12 o clock position) and then positive manifold pressure (after 12 o clock position.) it does not measure rotational speed of the turbo. when the boost gauge is straight up, it means the engine is breathing in air with little to no restriction. when it's to the right, it means the engine is under light enough load that it COULD be ingesting more in relation to the RPM it's turning, and when it's to the right it means the turbo is spinning quickly enough to produce pressure above ambient.

if you're staying in the 9:30-12:00 zone, you're not working the engine very hard at all. until the gauge reads past noon, the turbo is simply along for the ride like a pinwheel in the breeze.

short version: you're doing fine.

divil

This confused me a little, but I think I get it now. When I go uphill in a high gear, the engine slows down and can't consume air fast enough to maintain the vacuum...so the manifold pressure approaches atmospheric pressure, and the gauge goes up. I drop a gear, the engine sucks more air and restores the vacuum, so the needle goes down.

reno808

LOL

JohnKoaWood

IIRC I can make your car hit 1 bar boost by 2800 RPM...


Blah Blah Blah.... owner manual.... blah blah blah

Aaron..
Aaron...
Aaron....
AARON!....

Danger Zone....

TurboTommy

Bingo, you got it.

And further to that:
You could be zippin' along in third gear at 5,000 RPM, your stock boost gauge shows fairly decent vacuum (.5 bar; like ten o'clock position); yet your turbo is spinning a hell of alot faster in this case as opposed to your slow uphill scenario (12 o'clock position, 1 bar absolute)