ALi-B

iTrader: (1)

Theres not much I don't know but one thing that perplexes me is this:

Why does the Turbo produce very little boost when revving the engine netrual?

I know it spins up, but the gauge reads very little over 0 Bar even when WOT to the redline (I don't make a habit of it )

Just wondered why. Is because it doesn't have chance to spool up before I have to back off, or is there some ECU control afoot. Silly thing is the wategate solonoid clicks aways as usual dumping the pressure applied to the wategate, so in theory the wategate should be shut or nearly shut at the least (although I never actually checked it).

Any thoughts?

JIM THEO

The more mixture the more exhaust gases thus the turbo spins faster (and produces boost)!
If you slightly press the throttle to the red line there are leaner mixture than on full throttle (thus the worse fuel economy) not to mention that wastegate stays open with part throttle.
This is how I understand thinks, may be I am wrong though!
JIM

GBruce

It's because there is no load on the engine

ALi-B

iTrader: (1)

I did mean WOT (full throttle) to the red line...surely there is load in the 1.5 second it takes to get there?

Full throttle...maximum airflow Throttle Pot will give the ECU a WOT signal, MAF should register increase in airflow, and fuel it to suit?

I would have thought I'd get some boost, when all it gets is about 0.1 bar max....and if that's the boost, how on earth can the wastegate open if the opening pressure is roughly 0.5Bar (7psi) with the purge solonoid disconnected? With it connected it clicks away like a good'n, so that would raise the opening pressure further.

Another pause for thought...does the ECU know that the car is stationary (no signal from the VSS)? Or does it it know it's not in gear or the clutch is disengaged and therefore take according action (i.e super strict Lambda = 1 for low idling exhaust emissions)? Although I don't think a classic scooby's ECU is that clever

Still, I think perhaps most likely cause is the 1.5 seconds for the engine to hit the red line is too quick for the turbo to spool and produce any significant boost to cope with feeding the engine that is rapidly accelarating towards 7500+rpm.

Jolly Green Monster

iTrader: (4)

There is no load on the engine as said and the ecu has fuel and igition values in tables indexed by boost.. no load, no boost, no high fuel values, to ECU does know due to the low boost etc..

JGM

Jolly Green Monster

iTrader: (4)

PS: You are risking engine damage doing this btw.

ALi-B

iTrader: (1)

The engine does have load placed upon it. It has to accelarate it's own inertial mass and the flywheel. If it had no load it would hit the redline instantly and not take 1.5 seconds. Blip a race spec 911 and it'll hit 8000rpm in half the time a standard scoob takes to hit 7000rpm

Anyway...I've answered my own question....IT WAS THE TURBO!! ...

Some muppet had messed with my wategate pipework. Put it back as it should be and hey presto - 0.8 - to 1 BAR boost on full throttle before I hit the redline. Also answers to why its been driving like crap recently, Although it seemed to boost ok, probably the purge soloniod working over time or something to get the required boost

So I think it prooves me right in that there is Load when revving in neutral

And exactly what damage would you do? Big ends and rods are under nowhere near as much strain as held under 1.2 BAR of boost or excessive laboured by some idiot doing 30mph in 5th. As for valve gear, it's within the maximum rev range so no problems with float. Maybe an issue with the crank not liking the torsional stress of being accelarated at that rate...But your more likely to cause damage by doing full bore standing starts than revving aimlessly!

Sorry to be pedantic...that's just the way I am

asagi

[QUOTE=ALi-B]The engine does have load placed upon it. It has to accelarate it's own inertial mass and the flywheel. If it had no load it would hit the redline instantly and not take 1.5 seconds. Blip a race spec 911 and it'll hit 8000rpm in half the time a standard scoob takes to hit 7000rpm


8000 rpm i. 1.5 sec for a race prepped Porshe is not too shabby, but consider this a Formula One engine would hit a theoretical 100,000rpm is less than a second if floored while in neutral.

Been waiting for years to say that and this thread has been my first opportunity!!

ALi-B

iTrader: (1)

GBruce

And I always thought the boost was load related.........

RR power runs done in high gears
A slipping clutch will result in low boost
When someone quotes a rough spool up time for thier turbo it is usually 1 bar by ??? rpm in 4th/5th gear (More load on engine)
You get higher boost peaks in the higher gears

I agree with what JGM said


George

Jolly Green Monster

iTrader: (4)

Thank you Gbruce,

I have had a couple of disagreements with Ali in the past on here I do believe..

I don't feel there as any point me trying to reason with you again Ali, if you really think it fine revving your engine to the redline at a stand still, then that says it all really.

JGM

ALi-B

iTrader: (1)

What on earth was the last disagreement? Very rare in fact for me to have a banter in the technical forums. IIRC the last one I had was on oil viscosities, I'm not sure if you were in it or not (search not working and I can't VIP you anymore...doh! )

I revved engines all the time to the redline. Mainly when I'm trying to scrabble my landy up a muddy hill - Almost stationary - little load due to spinning the wheels. With an old ORIGINAL 1972 rover V8 and NO REV LIMITER. Ok, I know that Rover V8's can rev way past their rated 5500rpm due to their extremely short stroke. And it's naturally limited breathing through 2 SU's, add to that a worn camshaft, rockers and pushrods. And that I do not have anti-pump lifters so I get valve float (I will admit the engine is now almost dead, but that is more due to old age, sludge from the tired headgaskets weeping and it not having enough oil changes before I owned it...plus splitting an oil filter did not help one bit ).

Perhaps referring to a completely different engine makes this completely irrelevant, but surely if a knackered old Rover V8 can do it....can a Subaru? Are these engines so brittle that they will dissolve in to a pile of magnesium alloy dust when abused?

Have you seen a modern well maintained engine be damaged by simply revving it whilst standstill (NOT including damage from overheating)?

I ask this simply as you seem to know it does damage. Well you seem to think (know?) so.

So please, educate me, tell me what exactly I will damage by doing this?

Regards

AL

ALi-B

iTrader: (1)

LOL

Just remembered......

I forgot...you don't READ my posts properly do you!!

Without digging up the oil argument, I think my issue with that thread was the fact people were saying

"it's cuz your usin' the wrong oil m8"

And totally ignoring the more likely causes of failure due to a sensor fault (MAF) or component failure (pressure relief valve), Even though it was mentioned, the thread went on to blaming incorrect oil for the cause, and sadly you got tied up in the middle over a petty argument of recommended lubricants My real case on that issue was to try and balance the "scaremongering" that was becoming evident by questioning the validity of the opinions given.

That is all

I tend not listen to people who do not give valid reasoning behind their advice, Judgments or knowledge. And on occasions, give a voice of reason to the balance what seems to be a one sided judgement, which in my eyes is either slightly incorrect or a very narrow minded view on the situation at present.

Like I said; I'm just a pedantic old bugger!!