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Discussion Starter #1
I don't really care now, since my car is no longer bpu... but I was just curious, how dangerous is it to run say 25-27 psi with the stock turbo system w/stock computer and no fuel management? Because that's what I used to run all the time in the high gears and never had any problems at all. Several people I know like to run crazy boost like that too on stock turbos and they haven't had any problems either. I'm just curious... because everyone makes it seem so incredibly risky to run more than 18 psi and more than 15-18 degrees of timing with a single turbo setup... yet there are people running 27 psi with small inefficient turbos at potentially up to 22.5 degrees of timing! Why is it that they are not blowing their motors to pieces? I assume part of the reason is because bpu cars run quite rich, but I know one of the cars is fairly tuned, at least in the 11-11.5:1 range.

-Paul
 

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I've read too many threads like this by you. It's not just about boost pressure, timing and AFR. Octane is a huge factor on what boost and timing are safe for the engine.

27 psi on stcok twins is obviously bad for the turbos. On pump, it's also bad for the engine.

Folks who don't blow up their engines at high boost are usually the ones running high enough octane.

Try reading this stuff:
http://www.sdsefi.com/tech.html

I'd start with;
http://www.sdsefi.com/techcomb.htm
and
http://www.sdsefi.com/meltdown.htm

Some of the best info on octane vs boost with the stock ECU was posted by AZMONGOOSE in
http://www.supraforums.com/forum/sh...threadid=138717

Mike
 
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Discussion Starter #3
I'm talking about on pump gas, sorry. I guess I forgot to mention that. Octane, of course, is the most important thing I agree. It just seems to me like ~27 psi on stock twins on pump gas would be even more dangerous than 27 psi with a single, due to the higher heat, no? Or is there something I'm forgetting about?
 

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I would doubt anyone has run 27psi on pump gas without getting timing retared like CRAZY or blowing their engine. Hell even with lots of timing retard that is still asking to blow the engine. Who has done that?

Also, running that kind of boost on the stock turbos is pointless. I once made two back to back runs while I was on racegas. The first run was a done at 19psi and I ran a [email protected] with 2.0 60'. My next run yielded the exact same ET, MPH and 60' yet I was running 24psi. With all that extra heat and timing retard, you are not making any more power but you are hurting your turbos.
 
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Discussion Starter #5
I used to run 25-27 psi in the high gears all the time on 93 octane gas. Nothing bad ever happened, at least nothing obvious. I know that's a bit of reckless and pointless, like you mentioned, but that's what I did, and other people I know run that high as well, and no problems ever! I think my car was making max power at 20-21 psi and ever that nothing but excess heat. At the time I didn't care b/c I was planning on going single right away heh...

From what I've read, the stock ECU retards timing very very slowly. I used to reset my ECU all the time right before I ran super high boost, so the timing should have gone back to 22.5 or whatever. How come I never heard any audible knocking??
 

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From my experience and others I've read. the stock ECU retards timing VERY quickly. Sometimes it restores it fairly quickly on higher octane or lower boost but sometimes it takes a while. I know someone who seemed to require the ECU reset even after a stretch on race gas to get the timing back. Made almost a 100 rwhp difference on the dyno.

Very few people seem to hear audible knock before their engines blow due to detonation or elevated EGTs from the timing pulled while the stock ECU is avoiding detonation. They just think their cars are puling really well.

From your posts about the EGTs you've seen and the boost you've run on pump, I'm frankly amazed you've never lost an engine. I always put it down to the factory ECU but haven't you switched to an AEM now? Toyota did a fxxxing amazing job on our engines.

For me, 16 psi on 93 pump...if I ever run it again, 1.7 kg/cm2 on 99 MON unleaded race and very tempted to run leaded so I can try 2 bar but worried about my factory and WB O2 sensors...and 11.2 max AFRs and I only hit that on a longer pull (VPC temp sensor in the manifold???). I'm very conservative but I don't race the car and don't think there is a lot of power to be had between where I run and where the danger level increases dramatically.

I ramble...the original question was...
Q: "how dangerous is it to run say 25-27 psi with the stock turbo system w/stock computer and no fuel management?"
and
"yet there are people running 27 psi with small inefficient turbos at potentially up to 22.5 degrees of timing!"

and you mentioned you meant on pump gas.

A: Very and they're not running pump gas. Please reread the thread and the links for more detail.

Mike
 

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The Forbidden Supra said:
I'm talking about on pump gas, sorry. I guess I forgot to mention that. Octane, of course, is the most important thing I agree. It just seems to me like ~27 psi on stock twins on pump gas would be even more dangerous than 27 psi with a single, due to the higher heat, no? Or is there something I'm forgetting about?
I think it has to due with the amount of fuel and air vs combustion products that are in the cylinder when the spark goes off. Consider a better flowing engine. It has more air flow but the intake pressure and therefore??? the cylinder pressure should be about the same. But clearly the T88 w cams is flowing more than the stock twins. So more air and fuel is there to burn and provide power or detonate and cause damage. I've seen info that said EGR could be used to supress detonation by introducing combustion products. The stock twins would seem to have more of that and certainly have less air/fuel than the T88/cams.

Mike
 
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Discussion Starter #8
Oh it does retard timing quickly? That would explain why they hold up then. I had heard otherwise. Who said I haven't lost an engine, by the way? heh... What do you mean "they're not running pump gas". They ARE running pump gas. Several people I know locally, including myself back in the day, like to run 25-27psi just for fun, on pump gas. I know it's stupid, but those are the facts. I guess the amount of oxygen at super high boost levels bpu must just be so low that it's hardly combustable... that along with too much fuel helping to keep it cool. The stock engine, turbo system, and ECU just blow me away. It's unbelievable how reliable the stock setup is. It's almost completely fool proof. Toyota must have done that on purpose knowing people were going to upgrade the car without knowing anything (like me, at the time)

-Paul
 

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Yeah, Toyota really did do a good job. With that said however, how do you know you havn't done damage to the engine Have you performed a compression/leakdown test?
 

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your turbos stood up to 26psi??? very impressive, how long did you have them like that. good thing the ecu retards very very quickly.
 

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I've seen up to 1800F in the #2 runner (before letting off) at 1.2 bar on pump gas due to timing pull. I've seen up to 1700F climbing to 1780F after long (4 minute 80-140) pulls in cool weather on 104. (no timing pull, just hot turbos)

The only people that've blown motors on stock turbos (that I know) have done it running 18psi on pump gas on extended hwy. runs. I would imagine that running 25+psi would heat the turbos even more, and cause even more timing pull.

Not to meantion that much boost will significantly shorten the life of your turbos.
 
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Discussion Starter #12 (Edited)
VeilsideTT-
Well, I have a different block in my car now. Had some technical difficulties in the past heh... not due to running 27 psi bpu though. Blew it up after I went single. I had done several compression/leakdown tests when I was bpu though and my compression was always perfect, 170-175 or so.

LYTLdiablo-
Yep, my turbos held up just fine! I couldn't believe it. I ran very high boost fairly often over 30k miles or so, and when I took the turbos out they seemed just fine. I used to do fairly long pulls at 26-27 psi... not usually more than a minute or two though... by that time I was going several times the speed limit and had to slow down hehe. I sold both turbos to some guy and the last time I checked they were still working great!

Eventhough my turbos held up, I wouldn't recommend boosting more than 20-22 psi. In my opinion, 18 psi is best for daily driving, 20-21 psi is just fine for racing. If you overboost, don't worry about it, but I don't think it's a good idea to do very long pulls at more than 18-20 psi.

-Paul
 

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The Forbidden Supra said:
I used to do fairly long pulls at 26-27 psi... not usually more than a minute or two though... by that time I was going several times the speed limit and had to slow down hehe
-Paul
LOL, I'd guess froma dead stop, I'd be up to at least 150 mph in 30 seconds. A minute or two at WOT??? Sure it didn't just seem that way Paul? What speeds were you hitting?

Mike
 
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Haha true. Yeah, I tested my 0-150 mph once (bpu) and I think it was 29-31 seconds. I never did any continuous pulls for more than 45 seconds or so, but I was largely at WOT for at least a couple minutes. That's what I meant. I hit 180 something when I was bpu. I tested my 0-150 with my sp63 once. I can't remember what I did exactly, but I think it was only about 16-18 seconds! The boost was fairly high.
 

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Turbos will be out of their efficiency range and engine will blow

greg
 
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Discussion Starter #16
The turbos are definitely out of the efficiency range, but the engine will definitely not blow, at least from what I've seen many times. =P
 

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Remind me never to buy a car from you.
For someone who supposedly worked for a company that sold turbo kits, I have seen you ask some of the most inane and ridiculous questions I've ever seen from a Supra owner. Aren't you the same guy who used to have a Supra site up with a bunch of fake ass kill stories?
 
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LOL, this was many years ago when I didn't know better. Forgive me for asking dumb questions; I'm just trying to learn.
 

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VeilsideTT said:


Also, running that kind of boost on the stock turbos is pointless. I once made two back to back runs while I was on racegas. The first run was a done at 19psi and I ran a [email protected] with 2.0 60'. My next run yielded the exact same ET, MPH and 60' yet I was running 24psi. With all that extra heat and timing retard, you are not making any more power but you are hurting your turbos.
Yep, all technical talk aside, this is the reason you don't want to run more than 18-19psi on the stock turbos. Why....because it is inefficient and useless. I've also tested this at the track and it doesn't yield any performance results whatsoever.

More boost is not always better. You have to operate within the turbo's effeciency range.
 
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Come on, Mike, just turn up the boost. Everybody's doing it...

Shifting Impaired? LOL. I just noticed that. Does it say that automatically if your car is an auto or did you put that?

-Paul
 
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