What's normal turbo boost when revving?

I recently bought a 2001 996 turbo with 97,000 miles, despite having no driving license. I hope to get my license back soon but naturally, in the meantime I'm reading the paperwork and revving the car on the drive. Going through the paperwork, I discovered a receipt for "Investigate non boost problem". It was NOT followed by more paperwork saying "fixing non boost problem". The car only revs to 3,000 rpm in park after which a limiter cuts in, but even holding at or near 3,000 rpm, the boost (as displayed on the dash computer) remains at precisely zero 0.0 at all times. Is this normal behaviour? I'd expect it to get off zero but maybe not? On a related note, I may be mistaken but there could be a hint of a "blowing exhaust" type sound on the right hand side only. I presume this is unrelated.?

The only time I've revved a turbo to that level whilst in neutral was for a noise test prior to a track day. It's not something I'd recommend doing too often. I can't recall looking at the boost gauge whilst doing it but I suspect it staying at zero is normal if the car isn't under load. iirc on my 996T boost didn't really come in under load until 3,000rpm+. It was the biggest difference I noticed when I got my 997T. The VTGs spool up much earlier. Good luck with getting it sorted out and be aware these cars are excellent at helping you to lose your licence again quite quickly. :grin:

That's reassuring, if true. If 3,000rpm is needed under load to get the turbos going, 3,000 with no load definitely wouldn't - as there will be significantly less exhaust gases with no load. fingers crossed it's all working as normal then.

You should not be getting boost revving with no load. 0.0 is fine. You should also avoid revving the engine with no load. It doesn't like that. Standard turbo boost reads typically 0.6-0.7 bar on the dash, the exact boost level will vary, depending on air temperature, engine temperature etc. From memory the 996 ecu tries to hit a set target for 'cylinder filling' as a percentage and will vary the boost level automatically to achieve this. If it's an X50/Turbo S then it will read 0.8-0.9 as standard, again this is under load while driving.

Thanks. We were able to take the car out and it boosts fine. :thumb: Do you have any argument as to why revving a warmed up engine to 3,000 under zero load might be worse than say, slowly decellerating in gear at 3,000 rpm with minimal throttle such that there is zero load on the engine?

Why do you need to rev a turbo like that for any length of time? It's not as though it's to hear a nice noise. :dont know:

Porsche never teach their mechanics things like this so my own opinions .. rev limiter when stationary .. if there wasn't one then reving a car flat out at any temperature point and the rev limiter would not be able to catch it in time and you could get some serious over revs . Doing this on a cold engine is very bad . When driving the car has a warning .. it can see the revs rising so it knows when to apply it .. idle and it's far to fast for the over rev limiter to cut ignitions / injectors before it goes into over rev areas . Over heating .. sometimes in winter when we have 5 degrees in the workshop i can't get a car hot enough to measure the oil level after a service .. i will indeed rev the car at or close to 3K rpm to get the oil hot enough ... any model . When refilling coolant after a loss and this is exactly what we and every one of us does .. rev the car at 3K and add coolant to the max lvl then refit the cap asap . On a road test but leaving a car in lower gears it will heat the oil very quick , far quicker than revving in the workshop .. .. things like cayennes / macans we have to do this as they just don't get hot enough in the workshop when idling . Ever car has a 2 stage cooling process .. slow speed and high speed fans .. unless in the height of summer i've never managed to get a high speed fan working .. even then i have to rev them .. 3K is what most of us mechanics consider the limit for revving at idle regardless of a rev limiter .. some models have higher settings . Stationary and the car will cool itself via the 2 stage fans so i personally don't consider reving a car at idle to be an issue . Tip or Pdk over revs .. down hill at rev limit and it can over rev .. going airborne and it certainly will .. no load is the cause . merely IMHO . The car boosts though so the question has been answered

What's important to is that a) if it really was harmful I would want to avoid doing it and b) I have a general disposition to attain a particularly deep understanding of stuff. The purpose of revving on this occasion was I sought to confirm the car had boost because there was a receipt in the book showing "diagnose absence of boost" and I didn't see on the test drive whether or not it had boost.