what's with the obsession with psi?
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From: Tampa Bay
what's with the obsession with psi? ok here is my question. everyone likes to talk in terms of psi, but shouldnt you talk in terms of total cfm the blower (turbo or supercharger) can produce? psi is a measure of resistence and i could run a ton of psi on stock 5.3 heads and be disappointed but a set of blower ported c5r heads would look "weak" with low psi yet produce an enormous amount of power. just my thoughts today.
the thing that makes the power is the cylinder pressure.. but people dont have cylinder pressure gauges.. they most commonly have boost gauges, so thats what they talk about.. and while it does definitely not represent cylinder pressure or power output.. it does correlate to a change in cylinder pressure when you change boost level.
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From: Austin, TX
Originally Posted by Pro Stock John
How many CFM does your FI setup produce?
Everyone has a boost gauge.
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From: Downers Grove,IL
gator's 99TA ,well of course your right about this. We all like to see those pressure readings though. 
I run 13psi on my mild 346. 13psi on a 422 with good heads is going to be a hell of a lot more cfm than on mine.
My maf and pcm is modified to read to 67lbs/min.
simple close estimate is lbs-min /.069
I hit 67lbs around 6000rpm and it flatlines from there.
So I am in the neighborhood of pushing 1000cfm.
Steve
I run 13psi on my mild 346. 13psi on a 422 with good heads is going to be a hell of a lot more cfm than on mine.
My maf and pcm is modified to read to 67lbs/min.
simple close estimate is lbs-min /.069
I hit 67lbs around 6000rpm and it flatlines from there.
So I am in the neighborhood of pushing 1000cfm.
Steve
Originally Posted by S_J_H
gator's 99TA ,well of course your right about this. We all like to see those pressure readings though.
I run 13psi on my mild 346. 13psi on a 422 with good heads is going to be a hell of a lot more cfm than on mine.
My maf and pcm is modified to read to 67lbs/min.
simple close estimate is lbs-min /.069
I hit 67lbs around 6000rpm and it flatlines from there.
So I am in the neighborhood of pushing 1000cfm.
Steve
I run 13psi on my mild 346. 13psi on a 422 with good heads is going to be a hell of a lot more cfm than on mine.
My maf and pcm is modified to read to 67lbs/min.
simple close estimate is lbs-min /.069
I hit 67lbs around 6000rpm and it flatlines from there.
So I am in the neighborhood of pushing 1000cfm.
Steve
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From: Raleigh, NC
Very simple.
If you run good at zero PSI and find it to be a rush at 5 PSI, the most mentally challenged car buff can probably deduce 10 or even 15 PSI is going to knock his socks off!
What's hard to understand about that?
If you run good at zero PSI and find it to be a rush at 5 PSI, the most mentally challenged car buff can probably deduce 10 or even 15 PSI is going to knock his socks off!
What's hard to understand about that?
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From: Tampa Bay
my point was comparing boost pressures really isnt a great way to compare setups. to me, saying i want 20 psi on 346" is just too vauge event when comparing other 346" combos. i just wondered if anyone else has thought of this as well. import guys love to talk about boost pressure. it doesnt always make huge power output since they dont flow much total cfm in thier motors. motors which are really just air pumps in thir most simplified forms. our duramax tow rig makes about 30 psi of turbo boost with the mods we have. it just isnt as impressive or comparative with its restrictive heads and intake.
maybe i am completely wrong or maybe others have thought the same thing.
PSJ, why did you ask me this question?
maybe i am completely wrong or maybe others have thought the same thing.
PSJ, why did you ask me this question?
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From: Raleigh, NC
Relatively speaking, boost IS pertinent to one's own vehicle... that's the one I tune and drive. If you notice the Boosted List, we don't just compare boost levels; engine and mods are listed.
Your technical point is valid, but your post title's intent seemed to chastise people for wanting more boost. It is appropriate for me to want more boost, all other things being equal, to achieve more power.
Your technical point is valid, but your post title's intent seemed to chastise people for wanting more boost. It is appropriate for me to want more boost, all other things being equal, to achieve more power.
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From: Raleigh, NC
The question remains, do you know how many CFM your setup produces? Almost everyone knows what their boost level is and can monitor it constantly... it is relavent to visually monitoring boost setup performance as they race or tune.
THAT is more useable information to me as I drive and race. The CFM thing is more helpful as I fine-tune it and try to determine efficiency or capability... maybe.
THAT is more useable information to me as I drive and race. The CFM thing is more helpful as I fine-tune it and try to determine efficiency or capability... maybe.
I know the difference but I'll still ask what kind of boost someone is running. It's just for reference and a general idea of the power levels they should be in the ballpark of.
Launching!
Joined: Dec 2001
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From: Wallingford, CT
Originally Posted by gator's 99TA
my point was comparing boost pressures really isnt a great way to compare setups.
PSJ, why did you ask me this question?
PSJ, why did you ask me this question?
My guess is that PSJ was getting on you for not having FI. Hell, I look in the nitrous section occasionally even though I have no intention of getting it.
And its not really CFM, its massflow. Some of the discharge temps can get pretty high.
Teching In
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Here is the answer Intake psi along with cubic inches is the best way determine the output from a particular engine. For example a 5.7 L running 15psi boost is theoretically flowing twice as much air mass as a N/A 5.7L (atmospheric pressure is ~15psi)
Note that a 2.8L engine will have to run approx 45psi boost to achieve the same mass air flow (which is directly related to fuel flow and power)
From this example you can see that theoretically, every 15psi increase in boost should give a particular engine a 100% gain in power (note that making the boost uses some power and heat reduces air mass)
Note that a 2.8L engine will have to run approx 45psi boost to achieve the same mass air flow (which is directly related to fuel flow and power)
From this example you can see that theoretically, every 15psi increase in boost should give a particular engine a 100% gain in power (note that making the boost uses some power and heat reduces air mass)