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Old 09-17-2006, 03:11 PM   #1
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Default PSI vs HP: Which actually kills?

I know alot of misinformation goes around on different forums and that this forum is not necessarily immune to that. I was always taught that it is horsepower that kills an engine not PSI as everyone so freely spouts. Different turbos will flow different amounts of air at different PSI ranges. Therefore turbo A might make X hp at a certain PSI and turbo B will make Y hp at that same PSI. My interest comes from the fact that I am using a GT2554R in my initial turbo build and I want to know if I turn up to boost on it to say 18PSI on a mbc will my engine fail in any short order. The only thing that I would even think that might would be the headgasket. I have read posts on this forum and miata dot net about people running upwards of 300hp on a properly tuned stock engine but they generally run a little bit larger turbos at around maybe 12PSI.

I have built high compression NA engines before and from my experience they have internal cylinder compressions that are much higher than a turbo car and I have successfully used stock headgaskets and parts without failure.

I'm not looking for comments on "You should get a bigger turbo", etc... I just want real world advice from a member with experience of running high PSI to the limits of a smaller turbos efficiency range. I don't track my car yet and wouldn't be able to afford the proper suspension components for years to come, so a small turbo is perfect for me as a daily driven car. If I can get the most out of my gt25r to increase my powerband in the higher rpm range I would prefer that option.

To reiterate, my current understanding is that with a proper tune and cooling, HP kills engines before high PSI.

Brian
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Old 09-17-2006, 03:54 PM   #2
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Actually, I'd say RPMs and clyinder pressure/torque kill engines, not horsepower, per se...but it's all part of the equation.
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Old 09-17-2006, 04:11 PM   #3
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mutiple things can cause engine failure, engine temps , boost spikes,oil line failure, ingnition failure, bad timing, various and numerous causes are key to engine death, indeed high pressures due to boost levels being set at levels beyond what it can handle can cause severe if not total destruction on the engine its self, resulting in more expense!
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Old 09-17-2006, 04:18 PM   #4
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all factors play a role, not just one!
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Old 09-17-2006, 04:52 PM   #5
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PSI is misleading. What you are looking at is flow. A T3/T4 (any wheel and compressor) should flow more air at a lower PSI for example. So you cant say x amout of PSI will blow a motor. Many many factors to take into account
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Old 09-17-2006, 05:08 PM   #6
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Quote:
Originally Posted by RicanmiataRacer View Post
mutiple things can cause engine failure, engine temps , boost spikes,oil line failure, ingnition failure, bad timing, various and numerous causes are key to engine death, indeed high pressures due to boost levels being set at levels beyond what it can handle can cause severe if not total destruction on the engine its self, resulting in more expense!
you're looking at things that im not talking about. I know those things can kill an engine, but I'm refering specifically about air pressures. I could pee in the gas tank and that might kill the engine, but it would have nothing to do with the topic.

Quote:
Originally Posted by Pitlab77 View Post
PSI is misleading. What you are looking at is flow. A T3/T4 (any wheel and compressor) should flow more air at a lower PSI for example. So you cant say x amout of PSI will blow a motor. Many many factors to take into account
I understand that there is a flow difference. That is why I mentioned the turbo a/b thing in my first post. I'm interested in if I can run the max efficient psi on my gt25 without blowing my motor. I have a firend with a 92 galant vr4 and he is able to run his evo 16g at upwards of 18psi on the stock engine. Given the motor is turbo stock, but that is still far more than the engine was originally intended to run.

Assume that I have a perfect tune and that there are not any misc leaks or overlooked lines. Can the stock engine handle that. If there are "many factors" this is the place to discuss them then.
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Old 09-17-2006, 09:55 PM   #7
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As far as i have seen the motors are very stout i have haerd ring waer and everything else is accelerated at 15+ psi from fm but other than that they seem to be very stout. So long as you have the fuel and cooling to handle the flow of the turbo there is no reason a high psi setup cant last awhile on the stokc motor but as i said before the normal wear life of the engine seems to accelerate at this level of boost, pherhaps it is all a function of the heat in the system and some silent knock but i see no reason you couldnt run that much boost but the 2554 at its best only produces about 27 lbmin of air flow and it does this at 14.7 psi roughly so over boosting would mean less flow. you would be lucky to go past 250 chp with that turbo.
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Old 09-17-2006, 10:12 PM   #8
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Thank you, that was the input I was looking for.
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Old 09-17-2006, 10:41 PM   #9
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Quote:
Originally Posted by Pitlab77 View Post
PSI is misleading. What you are looking at is flow. A T3/T4 (any wheel and compressor) should flow more air at a lower PSI for example. So you cant say x amout of PSI will blow a motor. Many many factors to take into account
werd.

CFM, timing, intake temps, fuel all enter into the eq.
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