pressure vs power when setting boost psi
03-08-2009, 08:39 PM
#1
pressure vs power when setting boost psi
The car I recently purchase was set to 15 psi, and the car ran fine. The owner never had any problems, and the car was tracked. I was under the impression that 12 psi was safe limit for stock engine. This is a 1.6. I was told that it is based more on the power the engine is outputting (when setting boost) and the engine is good for about 250 rwhp. I though that it was based more on the internal pressure of the engine. Since setup could dictate different power outputs at a given psi of boost. I've detuned to 12psi, but what is the correct thought process? Thanks
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03-08-2009, 08:48 PM
#3
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It's internal pressure. Boost pressure is just a measurement of the restriction in your intake manifold; cylinder pressure is what you want to stay down from. 12psi used to equate to around 220whp, and at those boost levels you can run a motor pretty much forever. Up it to 14-15 and start getting into the 240-250 range and you'll significantly shorten the lifespan of the motor (mine lasted around 29k miles before upchucking a rod).
Careful, now. The last guy who asked this question was indicted on capital murder charges recently. :teehee:
Careful, now. The last guy who asked this question was indicted on capital murder charges recently. :teehee:
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03-08-2009, 08:53 PM
#4
I agree about "how much power, how much boost"
I agree 100%. I am starting to tune my car, but datalogs won't tell you if your engine is about to go pop. 12psi seems to be an agreed upon "safe" limit. Just want to make sure that people agree on this. While I don't plan on rebuilding my engine anytime soon, I am all for running at a seemingly safe limit. If the engine happens to go belly up at that point, well I did take some precaution.
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03-08-2009, 10:07 PM
#9
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The car I recently purchase was set to 15 psi, and the car ran fine. The owner never had any problems, and the car was tracked. I was under the impression that 12 psi was safe limit for stock engine. This is a 1.6. I was told that it is based more on the power the engine is outputting (when setting boost) and the engine is good for about 250 rwhp. I though that it was based more on the internal pressure of the engine. Since setup could dictate different power outputs at a given psi of boost. I've detuned to 12psi, but what is the correct thought process? Thanks
The relationship between boost pressure, compressor and turbine size and efficiency, volumetric efficiency, peak cylinder pressure, BMEP, PPP, EGT's, overlap, and many other variables that contribute to power output are somewhat misunderstood. No one thing can be changed without having a daisy chain effect on other subsystems down the line. There is no free lunch. It's not just "boost pressure" any more than it is just "internal pressure*"
*someone define this term that's been thrown out there.
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03-09-2009, 12:38 AM
#12
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My engine builder, dyno operator, turbo builder, and I think 15psi is safe in my car. My spark map is conservative with a ****-load of headroom, 11.5:1afr, in the center of the turbo's efficiency range, and lowered static compression motor. I know many with stock or modified STI and Evos with 14.7 (stock) and much more boost over 100k miles who track the cars once per month.
12psi from savinton's turbo is a ****-ton different from 15psi on my turbo
An ugly spark table is an ugly spark table, a happy spark table with a reasonable AFR is happiness.
12psi from savinton's turbo is a ****-ton different from 15psi on my turbo
An ugly spark table is an ugly spark table, a happy spark table with a reasonable AFR is happiness.
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03-09-2009, 01:45 AM
#13
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Basically most people who have a proper understanding of how the various factors of a boosted motor influence each other know that there is no solid answer to what is "safe".
However, most everyone has agreed that 12 psi is about as far as you want to go on a stock motor to maintain a decent amount of reliability and longevity.
Detonation (more accurately, avoiding detonation) is pretty much the #1 factor to the lifespan of a boosted motor though imo. For example, right now I am at 10 or 11-ish psi. I would not go higher than that with my current setup, but if I installed water injection, that along with my big intercooler would probably make 15 psi "safe" i.e. fully resistant to detonation.
On a side note, the rough equivalent of power that is produced at 10 psi is the average breaking point for a 1.6's differential ring gear. The rough equivalent of power that is produced at 15 psi is the average breaking point for a 5 speed. So, while there is no exact psi that is the max "safe" amount for the motor, there is a rough "safe" psi for a given car. We don't all drive around with Torsens and 6 speeds.
-Ryan
-Ryan
However, most everyone has agreed that 12 psi is about as far as you want to go on a stock motor to maintain a decent amount of reliability and longevity.
Detonation (more accurately, avoiding detonation) is pretty much the #1 factor to the lifespan of a boosted motor though imo. For example, right now I am at 10 or 11-ish psi. I would not go higher than that with my current setup, but if I installed water injection, that along with my big intercooler would probably make 15 psi "safe" i.e. fully resistant to detonation.
On a side note, the rough equivalent of power that is produced at 10 psi is the average breaking point for a 1.6's differential ring gear. The rough equivalent of power that is produced at 15 psi is the average breaking point for a 5 speed. So, while there is no exact psi that is the max "safe" amount for the motor, there is a rough "safe" psi for a given car. We don't all drive around with Torsens and 6 speeds.
-Ryan
-Ryan
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03-09-2009, 03:02 AM
#16
Most importantly man u can run 20 psi and only make 100 hp and the only that will breack is your heart as we pull on you. These pressure benchmarks assume everything is humming and you are within a nominal range of normal compared to people of a similiar setup. So the real answer here is find a compressor map and a turbine map for your **** figure out your timing and fueling and then we can tell u wether to be worried or not or even better u read them and figure it out for yourself wether your estimated hp/tq via cfm airflow and overall Air density is enough to breack things.
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