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Discussion Starter #1
Ok, let me start by saying that I am not 100% sure about the turbos on my car, other than that the housings are stock Garretts, internals unknown.

Driven by mad curiousity and foolhardy bravery, I've been exploring my turbos and what they can push. My Power FC boost control has two completed maps, one at 1.15bar and one at 1.4bar. The latter is faster, although not dramtically so (but noticably), and uses a lot more gas :p

As an experiment, I set the boost to 2 bar and the duty cycle to maximum (keeping the wastegates closed as much as the PFC will allow). The car boosted without a shred of lag, slammed me into my seat and hit 1.95bar at 5200rpm before the stock recirc valves gave way and started leaking, at which point I let off.

I'm guessing my turbo wheels are steel - if they were ceramic, surely I would have blown them to bits by now (I've been driving the past week on the 1.4bar setting, with quite a heavy foot, because it's so damn fun). My block is uprated with bits to support 600hp or more (all Tomei gaskets, conrod bolts, etc) so I'm really just wondering about the turbos.

The immediacy of the turbos was astonishing. Seems to me that turbo lag wouldn't exist if the turbo started with wastegates closed, then opened up as the rpms climb to maintain target boost. Why don't boost controllers do this?

And (BOVs notwithstanding), why exactly can't I run my turbos at 2 bar? What will I destroy (I know it's something, but I'd like to know exactly what's happening with forced induction systems at that kind of overboost). My map was fine, didn't knock more than 16 btw.
 

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Cant answer what you will blow exactly but i will say one thing...... brave man! :bowdown1:
The most I have ran on my T78 is 1.9 (and im cautious when i do that).
 

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Discussion Starter #3 (Edited)
dammit, I forgot to check what the injector duty was (Denso 700cc running at around 4bar). Dare I repeat the 2 Bar Pull of Death? My AFMs were certainly maxed, they max at 5115mv even with the 1.4bar setting.

What is interesting, and what I didn't know, is that it *appears* that turbos can boost to whatever pressure you fancy. We speak of limits for efficiency, not to blow parts, and what other factors? For example, when we say an N1 or GT-SS turbo's limit is 1.5-ish bar, then what exactly is the rationale behind that "limit"?
 

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If your not sure on your turbo's being steel or not and they turn out to be ceramic and you run at those boost levels with a heavy foot ,I guess you will get your answer soon .As Totalburnout said ,brave man .On the other side of the coin though I did hear from someone ,cant remember who that had a GTS-T with a tired engine that was going to scrapped or rebuilt and they decided to up the boost to insane levels just to finish the turbo off as well .It never went bang though in that period ,all comes down to sods law though:eek:
 

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Why not 2bar? Only REAL reasons not to is if the fueling cant take it, or the engine cant. Mainly due to not high enough octane fuel and/or too high compression ratio, both causing det. Could maybe knock back the timing so there no det, but often its so far retarded its pointless.

High boost my preffered style, making the most out of the smallest turbos you can for the power you want, giving the lowest boost threshold and biggest torque possible for the power.

Need to spec the rest of the engine accordingly though.

I specced my GTR is engine to run 2-2.5bar held on pump fuel, as thats how i like it. Last car ran 2bar held, one before that ran oiver 1.5bar, etc etc.

I got a turbo, may as well make the most of its advantages...
 

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the question is do you want to risk your nice solid engine?

the common thing people do when the turbo exhaust wheel explodes is to back off the throttle and the resultant vacuum in the cylinders sucks all the bits back in damaging the pistons/valves etc..

as said previously you are a brave man :)

report in with your findings.

/Steve
 

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Discussion Starter #7
the common thing people do when the turbo exhaust wheel explodes is to back off the throttle and the resultant vacuum in the cylinders sucks all the bits back in damaging the pistons/valves etc..

not bloody likely the way I drive :p

I've got to see where my injectors were at, but I've got a lot of headroom, and I'm pretty confident in my bottom end and dead sure about my gaskets. I just wonder what the downside to my AFMs being maxed out are in terms of the Power FC not being able to read how much air is coming in.
 

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the reasons boost limits are advised is that once the turbo goes past the rated pressure they start to become inefficient (spelling) due to the heat generated by a smaller turbo. charge air becomes hotter than is effecient and so detrimental to performance. Most turbo's will run far more than they are rated but it is pointless most of the time as it will be running past its effeciency limit and so can cause problems etc etc.

If you do have ceramic wheels and they do blow...dont lift off straight away as they will be sucked back into the engine and shaft your engine good and proper...finger crossed with the throttle floored they will just go down the exhaust.
 

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Discussion Starter #9
What turbos SteveN? My knock was at 16 so nothing bad going on in the det department.
 

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not bloody likely the way I drive :p

I've got to see where my injectors were at, but I've got a lot of headroom, and I'm pretty confident in my bottom end and dead sure about my gaskets. I just wonder what the downside to my AFMs being maxed out are in terms of the Power FC not being able to read how much air is coming in.
You will run lean if they are maxed out as they will only supply fuel for what they can read coming through the afm's
 

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What turbos SteveN? My knock was at 16 so nothing bad going on in the det department.
On which car? The GTR is running a turbo nobody hear wouldve really heard of, so bit pointless giving it as an example.

The thing about "no point after a certain level cause of heat" thing is a questionable IMO in most cars, IF you have a suitable way of cooling the inlet charge temp.
If a turbo is miles too small the engine would consume more air than the turbo would provide and the boost wouldnt hold at the top end anyhow.

Might not be as efficient as a bigger turbo overall, but doesnt affect the powerband so often enough a better bet IF the engine is specced correctly for it, peak power isnt everything.

Im not really into this idea of big boost on pump fuel with high compression (well, 8.5+ anyhow) so dont think im encouraging that, esp if we talking high speeds/loads for long periods.
 

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The reason why turbo's die in your case is that they are oparating in a verry unefficient flow area and / or extreme high turbine speed (rpm), that will put a lot load to bearings, especialy the trust bearing, and eventualy as it wears the turbo strarts smoking and get a lot of shaft play, till the wheels touch the housing and break or wear. I don't exacly know how ballbearing turbo's respond to this, but I assume thay will wear too, since they have more metal contact than normal bearings.

I had the same on my 200sx, super boost, lot of fun!! but my thrust bearing gave up a while after..., and it started smoking severly cause the turbine shaft had so much play that the oil seal on the turbine side could leak oil into the exhaust..
 

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Discussion Starter #14
so it's really down to rpm's and bearing wear then, although I'd like to hear about the effects of extreme heat on turbos as well.

How much boost then can journal bearings take? Technically, in operation, doesn't the shaft not contact the bearing (i.e. floating on oil)? Stock turbos are journal bearing, but then again, so were the Nismo LM turbos.
 

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I just wonder what the downside to my AFMs being maxed out are in terms of the Power FC not being able to read how much air is coming in.
All that will happen is that the map will advance on one less parameter, and so become slightly less accurate - the car will not necessarily run lean as the fuelling will still be increased by the engine RPM input that is also fed into the ECU.
 

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surely the car had to be mapped to 2 bar or the fuelling ignition airflow will be out? surely the turbos have to be big enough to flow 2 bar! so capable of over 700bhp?
 

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Discussion Starter #18
stock turbo size, that's what gets me. Not 2530s, not T04Z, stock sized housings and 1.95bar at 5000rpm! Maybe more if the BOVs didn't start leaking and I didn't let off. This wasn't even at WOT mind you.
 

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the common thing people do when the turbo exhaust wheel explodes is to back off the throttle and the resultant vacuum in the cylinders sucks all the bits back in damaging the pistons/valves etc..
How do you get vacuum exhaust-side?

Phil
 

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How do you get vacuum exhaust-side?

Phil
Ive never understood this either.

All this "turbos blowing and wrecking engine too" thing id never heard of until the skyline world.

Compressor bits getting into the engine would be very unlucky (as they get caught up in the intercooler 99% of the time) but this exhaust wheel into engine thing seems bizzare to me.

Im not saying its wrong, but id like to understand how you get a vacumn on the exhaust side :confused: :confused: :confused:
 
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