pressure vs power when setting boost psi - Miata Turbo Forum - Boost cars, acquire cats.

Welcome to Miataturbo.net   Members
 


General Miata Chat A place to talk about anything Miata

Reply
 
 
 
LinkBack Thread Tools
Old 03-08-2009, 09:39 PM   #1
Elite Member
Thread Starter
iTrader: (11)
 
Join Date: Feb 2009
Posts: 2,982
Total Cats: 10
Default 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
miatauser884 is offline   Reply With Quote
Old 03-08-2009, 09:46 PM   #2
Murderator
iTrader: (76)
 
18psi's Avatar
 
Join Date: Apr 2008
Posts: 36,165
Total Cats: 2,573
Default

I dont think there is a "set" boost level that is the limit for a certain engine. Many run different levels of pressure with completely different results. Not much help at all, I just dont want this to turn into another "how much power with how much boost" thread.
18psi is offline   Reply With Quote
Old 03-08-2009, 09:48 PM   #3
Supporting Vendor
iTrader: (31)
 
Savington's Avatar
 
Join Date: Nov 2006
Location: Sunnyvale, CA
Posts: 14,353
Total Cats: 1,319
Default

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:
Savington is offline   Reply With Quote
Old 03-08-2009, 09:53 PM   #4
Elite Member
Thread Starter
iTrader: (11)
 
Join Date: Feb 2009
Posts: 2,982
Total Cats: 10
Default 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.
miatauser884 is offline   Reply With Quote
Old 03-08-2009, 10:02 PM   #5
Murderator
iTrader: (76)
 
18psi's Avatar
 
Join Date: Apr 2008
Posts: 36,165
Total Cats: 2,573
Default

Quote:
Originally Posted by Savington View Post
Careful, now. The last guy who asked this question was indicted on capital murder charges recently. :teehee:
18psi is offline   Reply With Quote
Old 03-08-2009, 10:40 PM   #6
Senior Member
iTrader: (5)
 
Join Date: Jan 2008
Location: Central, TX / Bay area, CA
Posts: 1,272
Total Cats: 3
Default

If you want the car to go 1 million miles go with less boost if you want to be a man crank it up.
Gotpsi? is offline   Reply With Quote
Old 03-08-2009, 10:42 PM   #7
Murderator
iTrader: (76)
 
18psi's Avatar
 
Join Date: Apr 2008
Posts: 36,165
Total Cats: 2,573
Default

Quote:
Originally Posted by Gotpsi? View Post
If you want the car to go 1 million miles go with less boost if you want to be a man crank it up.
if you want both build the engine and crank it up
18psi is offline   Reply With Quote
Old 03-08-2009, 10:53 PM   #8
Senior Member
iTrader: (5)
 
Join Date: Jan 2008
Location: Central, TX / Bay area, CA
Posts: 1,272
Total Cats: 3
Default

+1 on 18psi. I ran mine until it died and then fully built a motor after that.
Gotpsi? is offline   Reply With Quote
Old 03-08-2009, 11:07 PM   #9
I'm Miserable!
 
Join Date: Mar 2009
Posts: 59
Total Cats: 0
Default

Quote:
Originally Posted by djp0623 View Post
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
You can't have too much boost for starters. You might not have enough rod or piston though.

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.
johnhanson is offline   Reply With Quote
Old 03-09-2009, 12:01 AM   #10
Tour de Franzia
iTrader: (6)
 
hustler's Avatar
 
Join Date: Jun 2006
Location: Republic of Dallas
Posts: 29,114
Total Cats: 351
Default

I'm running at least 20g's.
hustler is offline   Reply With Quote
Old 03-09-2009, 12:06 AM   #11
Supporting Vendor
iTrader: (31)
 
Savington's Avatar
 
Join Date: Nov 2006
Location: Sunnyvale, CA
Posts: 14,353
Total Cats: 1,319
Default

internal pressure = peak cylinder pressure. This is why detonation is so bad: the peak pressures SKYROCKET.
Savington is offline   Reply With Quote
Old 03-09-2009, 01:38 AM   #12
Tour de Franzia
iTrader: (6)
 
hustler's Avatar
 
Join Date: Jun 2006
Location: Republic of Dallas
Posts: 29,114
Total Cats: 351
Default

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.
hustler is offline   Reply With Quote
Old 03-09-2009, 02:45 AM   #13
Supporting Vendor
iTrader: (3)
 
Join Date: Jul 2006
Location: San Diego
Posts: 2,862
Total Cats: 484
Default

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
ThePass is offline   Reply With Quote
Old 03-09-2009, 02:53 AM   #14
Murderator
iTrader: (76)
 
18psi's Avatar
 
Join Date: Apr 2008
Posts: 36,165
Total Cats: 2,573
Default

Quote:
Originally Posted by ThePass View Post
-Ryan

-Ryan
18psi is offline   Reply With Quote
Old 03-09-2009, 03:39 AM   #15
Supporting Vendor
iTrader: (3)
 
Join Date: Jul 2006
Location: San Diego
Posts: 2,862
Total Cats: 484
Default

I like hearing my own name...
ThePass is offline   Reply With Quote
Old 03-09-2009, 04:02 AM   #16
:(
iTrader: (7)
 
Join Date: Jul 2006
Location: nowhere
Posts: 8,281
Total Cats: 2
Default

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.
magnamx-5 is offline   Reply With Quote
Old 03-09-2009, 09:05 AM   #17
Tour de Franzia
iTrader: (6)
 
hustler's Avatar
 
Join Date: Jun 2006
Location: Republic of Dallas
Posts: 29,114
Total Cats: 351
Default

wtf? Why can no one understand that 12psi from a Savington's turbo, is nothing like 12psi from Pat's turbo?
hustler is offline   Reply With Quote
Old 03-09-2009, 10:04 AM   #18
Junior Member
 
Join Date: Sep 2008
Posts: 218
Total Cats: 0
Default

Since the 1.6L has the same rods and stroke but with less bore, shouldn't a higher combustion chamber pressure result in the same pressure upon the rod and bearing?
JimAtFSU is offline   Reply With Quote
Old 03-10-2009, 02:39 AM   #19
:(
iTrader: (7)
 
Join Date: Jul 2006
Location: nowhere
Posts: 8,281
Total Cats: 2
Default

Quote:
Originally Posted by hustler View Post
wtf? Why can no one understand that 12psi from a Savington's turbo, is nothing like 12psi from Pat's turbo?
not everyone can grasp what we are saying man u just have to be patient they either learn or **** up forever.
magnamx-5 is offline   Reply With Quote
Old 03-10-2009, 03:17 AM   #20
Junior Member
 
Join Date: Sep 2008
Posts: 218
Total Cats: 0
Default

Aren't we talking about raising the boost on a turbo rather than comparing one turbo to the other?
JimAtFSU is offline   Reply With Quote
 
 
Reply

Related Topics
Thread Thread Starter Forum Replies Last Post
1.8, C30-74 Rotrex, 9psi, 235WHP/190WTQ (E85) Lincoln Logs Dynos and timesheets 4 09-23-2015 01:26 PM
Mystery Engine Trouble. Halp, mt.net! vehicular General Miata Chat 12 09-14-2015 04:17 PM
Dsm t25 big16g or somethig else? karcher DIY Turbo Discussion 0 09-06-2015 06:02 PM
E-Manage Base Maps faviles5566 ECUs and Tuning 0 09-04-2015 12:50 PM
E-Manage Base Maps faviles5566 ECUs and Tuning 0 09-04-2015 12:50 PM


Thread Tools

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off



All times are GMT -4. The time now is 05:26 AM.