Boost Pressure (Yep, another thread)

[Sariandan]

So... I know this has been beat to death, but I didn't find exactly what I was looking for when searching.

Someone asked me the other day, "How much boost are you running?" We obviously don't have a boost gauge, but I have my SCT BDX and it stops measuring boost at 22.47 psi. Why? No idea. Since I hit that at wide open throttle, I would imagine it could be a bit more than that. I know it's different depending on many things determined by the PCM, but we were speaking of WOT. I had to tell him that I don't really know. He said that, at the very least, for engine reliability, that's probably not a good thing to not know.

So, I did some digging around and found something that said take your TIP PRS Boost kpa, subtract atmosphere, and then convert to psi. So, using today as an example, at WOT, I hit a TIP PRS Boost kpa of 305.25 kpa. Atmosphere, at the time was 30.1 inHg or 101.93 kpa. That leaves 203.32 kpa, or 29.49 psi.

Is my 5 Star tune really pushing 29.5 psi of boost? That seems excessive to me, but maybe not? I know that my friend runs 25 psi in his CTS.

Yes, I will just simply ask 5 Star, if the answer is straightforward, which it may not be. I'm not a tuner, so I don't know all the variables. But it's a holiday weekend, so I won't be able to ask them right now. I figured somebody here might be bored and either tell me what I'm missing or confirm that this is how to figure this out, without a boost gauge.

In the grand scheme of things, I don't care. As long as my truck runs, I'm good. And, I haven't had any issues. Of course, neither did that other guy... until he did.

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[MountainGoat]

That does seem high. I had a SR20-swapped 240sx that ran 8psi stock, at 15psi tapped out the OEM turbo and blew the intercooler pipes off. Mitsu Evos were known as high boost back then and I think they were around 20psi. Granted that was decades ago.

 

[Sariandan]

That does seem high. I had a SR20-swapped 240sx that ran 8psi stock, at 15psi tapped out the OEM turbo and blew the intercooler pipes off. Mitsu Evos were known as high boost back then and I think they were around 20psi. Granted that was decades ago.

That’s what I was thinking. The last time I seriously thought about boost pressure was so long ago.

And, I was also under the impression that our turbos were smaller (that’s what she said, while pointing and laughing).

 

[Wytchdctr]

The size of the turbo has a lot to do with the amount of air moving at a given psi. Not sure what ours runs stock but most stock turbos tend to be on the small side to avoid lag and with that higher pressures. The bad part is air likes to heat up when compressed so there is an advantage to running a bigger snail at a lower psi for the same amount of air, trade off being lag.

If that was already obvious to others who made a post, sorry about that. I know a few people that can't seem to grasp that concept and think that 8 psi is the same air regardless of other factors. They probably have a hard time grasping volts an amps as well.



All that said. What boost do these things run stock?

 

[Msfitoy]

Sound about right...mine's stock and I've seen 21-22psi...

 

[Sariandan]

The size of the turbo has a lot to do with the amount of air moving at a given psi. Not sure what ours runs stock but most stock turbos tend to be on the small side to avoid lag and with that higher pressures. The bad part is air likes to heat up when compressed so there is an advantage to running a bigger snail at a lower psi for the same amount of air, trade off being lag.

If that was already obvious to others who made a post, sorry about that. I know a few people that can't seem to grasp that concept and think that 8 psi is the same air regardless of other factors. They probably have a hard time grasping volts an amps as well.



All that said. What boost do these things run stock?

That was not obvious to me, so thank you. I do get amps and volts, though.

I have no idea what we run stock. My 89 Daytona was 7 psi stock. I’ve seen guesses that we are around 15 stock, but that was with the caveats that there is no “real” stock measurement because of variables that the PCM is compensating for. So, I don’t know. I’d think that, despite any variables and compensations, there would be some sort of maximum that the PCM originally says “Okay, no more boost for you.”

 

[deleriumtremor]

I would have to think about it a little, but maybe your starting point on atmospheric pressure might be off as well. I think baro is reported locally corrected for sea level.

 

[Sariandan]

I would have to think about it a little, but maybe your starting point on atmospheric pressure might be off as well. I think baro is reported locally corrected for sea level.

Correct. I was using local readings. Are you thinking that I should just be using the standard 14.7 psi, or 101.35 kpa? That would make my final number a bit higher.

I’m just inland from the east coast, at about 20 ft above sea level.

 

[deleriumtremor]

Correct. I was using local readings. Are you thinking that I should just be using the standard 14.7 psi, or 101.35 kpa? That would make my final number a bit higher.

I’m just inland from the east coast, at about 20 ft above sea level.

If you are at sea level, then the reported local baro would reflect actual baro, I think even corrected for temp (it has been so long since I thought about this stuff, I think I will have to go and lay down now.. ).

 

[Dereku]

These Ecoboost run stock diesel boost figures from the 90s and early 2000s. Back then pushing a few PSI on a gas engine was good. 10 psi was exotic. I had an 02 power stroke pushing 65psi. It's nice when the turbo is all you can hear.

However I would think anything under 30 is ok for these as long as the tune is good. You could blow a stock motor at stock boost levels with a bad tune. So many more factors into long term reliability than a peak boost number. Plus we have a blow off valve so that takes a lot of strain off the motor at throttle lift.

 

[Zetterbeard]

I have a mechanical boost gauge installed and it hits 23-24psi at WOT. Mods in signature.

 

[Frenchy]

So... I know this has been beat to death, but I didn't find exactly what I was looking for when searching.

Someone asked me the other day, "How much boost are you running?" We obviously don't have a boost gauge, but I have my SCT BDX and it stops measuring boost at 22.47 psi. Why? No idea. Since I hit that at wide open throttle, I would imagine it could be a bit more than that. I know it's different depending on many things determined by the PCM, but we were speaking of WOT. I had to tell him that I don't really know. He said that, at the very least, for engine reliability, that's probably not a good thing to not know.

So, I did some digging around and found something that said take your TIP PRS Boost kpa, subtract atmosphere, and then convert to psi. So, using today as an example, at WOT, I hit a TIP PRS Boost kpa of 305.25 kpa. Atmosphere, at the time was 30.1 inHg or 101.93 kpa. That leaves 203.32 kpa, or 29.49 psi.

Is my 5 Star tune really pushing 29.5 psi of boost? That seems excessive to me, but maybe not? I know that my friend runs 25 psi in his CTS.

Yes, I will just simply ask 5 Star, if the answer is straightforward, which it may not be. I'm not a tuner, so I don't know all the variables. But it's a holiday weekend, so I won't be able to ask them right now. I figured somebody here might be bored and either tell me what I'm missing or confirm that this is how to figure this out, without a boost gauge.

In the grand scheme of things, I don't care. As long as my truck runs, I'm good. And, I haven't had any issues. Of course, neither did that other guy... until he did.

I cant speak for how much without a tune but I have noticed with the Livernois Tow Tune running 91 the boost has been between 22-24 PSI at max depending on load conditions.

As long as you are being smart in general you will be fine.

Or you could just send it until it sounds expensive!!! ??

 

[Dgc333]

The stock boost pressure is about 18.psi with an over boost for a few seconds to 20 psi. The typical stage 1 tune will give you 22 to 23 psi.
Over 25 psi the turbo is in such an inefficient region you won't see any more power and may lose some.

 

[Wytchdctr]

The stock boost pressure is about 18.psi with an over boost for a few seconds to 20 psi. The typical stage 1 tune will give you 22 to 23 psi.
Over 25 psi the turbo is in such an inefficient region you won't see any more power and may lose some.

Do you happen to have the map for the stock turbo? At one point I could read/plot them but it has been a few years since I cared to do that.

 

[Dgc333]

Do you happen to have the map for the stock turbo? At one point I could read/plot them but it has been a few years since I cared to do that.

I have seen the map but don't have a copy.

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