Danger in PSI or HP??

[Race94]

I see most of the time "you can safely run 15 psi" or something like that, lets say i have a 16g and my engine can handle 15psi without any troubles, how about if i put in a bolt on t3/t04b, can is till run 15psi the same way as before? WIth fuel mods and stuff, i mean internals handling the bigger turbo at the same PSI.

thanks

 

[cuttheduck]

No,,

PSI doesnt tell much of the story because you dont know the actual flow (usually measured in CFM).

Its the same reason 12 psi on a 16 g feels much stronger then 15 psi on a t-25. The PSI is only telling half the story.

 

[FireyIce01]

No,,

PSI doesnt tell much of the story because you dont know the actual flow (usually measured in CFM).

Its the same reason 12 psi on a 16 g feels much stronger then 15 psi on a t-25. The PSI is only telling half the story.

This isn't completely accurate, but there's a nice long thread on this... lemme see about finding a link really quick.... oh damn, 20 mins searching to no avail, anyway, there's a thread out there, something like is 15 psi = 15 psi or some such thing... and the reason that 12psi on a 16g feels stronger than 15 on a t-25 has more to do with compressor efficiency and air temps, and many other variables than pressure... but 15 psi, is still 15 psi on any vehicle at the same atmospheric pressure...

There's also this, which has a lot of useful info on how airflow works under boost Converting CFM lbs/min

 

[vteg]

CFM, efficiency and pressure are all involved in creating power. A turbo with more cfm at the same pressure should make more power. Another turbo with the same pressure, and cfm but better efficiency should make more power than the previous.

I say should since depending on state of tune and many other engine factors you may not get the power you thought you should.

 

[FireyIce01]

CFM, efficiency and pressure are all involved in creating power. A turbo with more cfm at the same pressure should make more power. Another turbo with the same pressure, and cfm but better efficiency should make more power than the previous.

I say should since depending on state of tune and many other engine factors you may not get the power you thought you should.

That's sorta what I was getting at... there's a long ass thread on it that was done fairly recently.... but I can't seem to find it... prolly just not searching the right words... *shrugs*

 

[yoshimitsuspeed]

I don't know a lot about turbos and I am putting this together in my head so straighten me out if I am wrong. Doesn't the PSI and RPM determine the CFM? I would think heat and efficiancy would play a big role but shouldnt and engine consume the same CFM at 15 psi on a t25 as a 16g? The only difference I can see is the fact that the 16 g could deliver more PSI at higher RPMs when the T25 started to crap out. That and the fact that it would be blowing cooler air.
Never mind that's pretty much what Fireicy was saying

 

[FireyIce01]

I don't know a lot about turbos and I am putting this together in my head so straighten me out if I am wrong. Doesn't the PSI and RPM determine the CFM? I would think heat and efficiancy would play a big role but shouldnt and engine consume the same CFM at 15 psi on a t25 as a 16g? The only difference I can see is the fact that the 16 g could deliver more PSI at higher RPMs when the T25 started to crap out. That and the fact that it would be blowing cooler air.
Never mind that's pretty much what Fireicy was saying

Follow the link I posted... CFM is determined by your engines VE, displacement, and RPM, and psi... sorta... psi is just the amount of pressure you're putting your intake under. lbs/min is a comulation of all of the above... sorta... there's threads out there that really explain this better than I ever could... just do a search for lbs/min and you'll get a lot of threads on it.

 

[Gigaah]

What they are getting at is lbs/min of air.
12psi on a smaller turbo is less power than 12psi on a larger(more efficient) turbo because the smaller(less efficient) one heats the air more and at the same PSI putting out fewer lbs/mins of air. When air is hotter it is less dense..so fewer air molecules fit in a given space at a given pressure. This makes it weigh less so your lbs/min rating drops.

PSI RPM and CFM are directly related and don't change thier correlation with each other. Air density due to elevation and temperature are the key variables in the explanation of why 12psi on a better turbo is more power.

I'm pretty sure I didn't mess that up and put it all down right...too early to reread any more.

 

[leet]

Pressure is absolute.

Air flow capability (lbs./min), on the other hand, varies from one model turbo to another.

The more pressure you run, the more air you will force into the engine.

Up to a certain theoretical point where either the engine will not be able to handle the power, or you simply cannot cram more air and fuel into it.

Air density can and will affect performance, but at higher altitudes all cars will be at a handicap.

 

[exzercist]

Pressure is absolute.

Air flow capability (lbs./min), on the other hand, varies from one model turbo to another.

The more pressure you run, the more air you will force into the engine.

Up to a certain theoretical point where either the engine will not be able to handle the power, or you simply cannot cram more air and fuel into it.

Air density can and will affect performance, but at higher altitudes all cars will be at a handicap.

hence compressor surge!

 

[Gigaah]

Air density also decreases as temperature increases as I mentioned.

 

[50trimtsi]

i believe only a logger will tell you for sure how much psi you can run, but maybe im wrong. logging knock should at least give a heads up though

 

[leet]

i believe only a logger will tell you for sure how much psi you can run, but maybe im wrong. logging knock should at least give a heads up though

You are correct.

Making logs on your vehicle is essential for for successful, not to mention safe, tuning.

 

[50trimtsi]

good to hear, i would hate to post bad suggestions/info

 

[O_16581_72452_5]

Upgrade the turbo and back off the PSI, with the larger turbo, you should be able to make the same power with less PSI. This is argueably safer on the engine. The more air is compressed, the hotter it becomes, as everyone knows, this means a higher risk of detonation.

 

[FireyIce01]

found the thread I was talking about while looking for another thread... http://www.dsmtuners.com/forums/showthread.php?t=22470&highlight=intake+exhaust+cfm+turbo

 

[yoshimitsuspeed]

found the thread I was talking about while looking for another thread... http://www.dsmtuners.com/forums/showthread.php?t=22470&highlight=intake+exhaust+cfm+turbo

Thanks. That is a good thread even though my head hurts from reading it all. That's pretty much what I wanted to say but said much better. I still don't understand why all the psycics are needed and there are still people who don't get it after reading all that.
It really seems like a simple system IMO