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Discussion Starter #1
Ok here is another question for you guys.. maybe the same guy who replied to me earlier knows the answer to this as well..

ever since I got into turbo cars, all the books on turbo theory say "make sure your turbo is properly matched.. if too small you will overspeed it and kill it" makes sense..

BUT.. i do not know ONE SINGLE PERSON who has hurt a turbo by overspeeding it, running too much boost, whatever.. I know guys who run stock turbos way out of their efficiency range just because they can (like.. a front mount and an alky setup).. running something like 26+ psi on a stock 86/87 turbo (about 560cfm turbo.. its small.)

me, I run about 18psi on a 390cfm turbo in street trim.. @ the track im going to run over 20psi..

so how come supra guys kill turbos? thats all ive read the moment i came back to this site and started reading posts again.. guys killing turbos buy spinnin em too fast.. running too much boost.. what is with that? annnd.. does this apply to you guys running bb turbos too?

thanks guys
 

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It all depends on the size of the turbo. You can destroy a turbo's bearings by "over-spinning" the turbo. This can be caused by making the turbo run too much boost. Most turbos can probably handle around 150k rpm's (just guessing the number) before they start to get inefficient. When a turbo is run too hard, it builds up lots of extra heat aside from extra wear on the bearings.

The reason that Supras can blow up their turbos is because they have two very small turbos and a very good stock fuel system. Most cars would probably blow the engine due to a lean situation before the turbos could overspin. But the Supra's stock fuel system can pretty much handle anything that the stock pea shooters can throw at them.
 
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Discussion Starter #3
I guess that answer is good enough for me.. although my car's fuel system is adequate for low 12s anyway..

by any chance would you know the 'max' amount of boost a supra guy should run with stock turbos.. and maybe the flow in cfm of a stock turbo?
 

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I think one big reason the turbos fail in supras is onlypartialy related to overboosting( once you get past the efficny rating in a turbo all you are doing is creating heat not pressure) In any event it is because of the failure of he com;icated sequential system the systme ws designed for 11psi with a gentle prespool and the second turbo carrying 1/2 the load at 3500rpm. Instead in bpu and higher the first turbo goes to 10 the seocnd comes on like a monster aquickly get to 18+ a lazy vsv or acutator and the turbo gets to boost against a closed valve... compressor surge and a twisted shaft results. ( one reason many people choose TTC BTW)I have heard of people getting 20+ psi on our turbos but I havenot seen any dyno evidence that they continue to make HP from them supposedly the compressor map falls off after around 20. I am not an expert but have read many a discussion on the issue here and on the mkiv list.
 
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Discussion Starter #5
BUT.. i do not know ONE SINGLE PERSON who has hurt a turbo by overspeeding it, running too much boost
How do you know that? The turbos don't jump out of the car in mid-boost and saunter away with a banner saying "overspun." Continual overboosting takes it's toll on the shaft and seals. One day without warning, it will death whine, or worst. Could be 10K miles, could be 100K miles.

Supras are not alone in blowing turbos. The sequential setup does not help, but I personally believe Toyota strengthened the turbos in 95+ Supras. You always hear about 93s and 94s going out, but rarely later - this is above and beyond the age correlation.

A typical scenario is this: a Supra is sold stock by it's owner at 60K miles, who totally disregarded the manual and treated the Supra like an NA car. Cold start, fast takeoffs and hot immediate shutdowns. Due to the car's popularity, it's put to BPU by it's new owner, doubling the stress on the turbos who are already tired of years of neglect. The car likely has a different brand of oil with a different viscosity. It's little wonder they go out. I would bet, however, if you weighed the Supra turbo longevity stock-to-stock against any other factory turbocharged vehicle, it would be well above average.

Running over 18 psi is also a game of fast diminishing returns. Little power is gained above that, though the torque spike feels nice. These turbos were designed to handle around 11 psi. The Supra spins to 6800 rpms stock, making it much easier for the turbos to run out of breath compared to the lower redline GNs. As far as CFM, I find lbs/min a more helpful statistic, as it measures mass and not volume. The amount of oxygen per unit volume can vary greatly, but not mass. The stock Supra turbos probably flow around 50 lbs/min together.

Hope this clears somethings up.
 
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Discussion Starter #6
alright now were getting somewhere..

with the overspeeding comment.. no one I know has ever attributed failure to overspeeding. id also assume that if they killed one turbo in a month after normal use, they would kill another turbo the next month... alot these guys really dont ever turn the boost down to a normal level... then again thats an assumption...

I see what you mean about the failure due to neglect.. of course thats gonna happen with any car.. hopefully in the future, for the cars' sake.. manufs will put some kind of built in turbo timer, or maybe keep the wastegate wide open until the oil reaches a set temp or somethin ya know? I have a friend with a DSM who showed off for about 5 min with me in the car then got out and turned it off, i screamed at him to turn it back on immediately and let it idle for a few minutes.. owner neglect will kill a turbo faster than anything...

thanks for the response man.. i like to hear new sides to turbo theory and stuff like that..

just to inform... my car's redline is 6000rpm. although the turbo and intake prohibit any real gain above 5000rpm.. they are stock of course.. different intake turbo and cam.. along with replaced valvesprings and you can hit 6500+.. though most wouldnt want to..
 
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Discussion Starter #7
Yeah, sounds like good ole American low rpm grunt. My 5.0 friends only would spin their cars to 5000 when stock, and not much higher with bolt-ons. It's quite a different world. I go to 50 mph and 8000 rpms in first gear, and my friend with 3.73s in his stang can't get through the intersection without being well into 2nd. I wish I could match gearing to my modified engine - make up for the shifted power band.
 
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