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.

How many CFM does your FI setup produce?

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.

Yep, CFM is just much harder to measure. The stock MAF can't measure anything beyond 570cfm.

Everyone has a boost gauge.

well if a fuel injected v8 is running something like 20 psi, u pretty much know it's making lots of power...

so in that sense u want more boost because it more likely means you're making more power.

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

Yes, but if you put a 422 under your blower at 13psi. You would see about the same power just less boost right?

yes, if you use the same pully it would probably the same power but at very low psi

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! :D

What's hard to understand about that?

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?

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.

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. :)

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.

IMO it is useful to hear others boost numbers and also see their list of mods and dyno #. I have seen some with low boost # and still make tons of power it all depends on the setup.

All true. Its more of a resultant than anything else. The real relevance is when comparing very similar setups, but beyond that, its not so important. But its kind of a common language. Those who value it can easily compare "X psi", and everybody else can look at all the other variables along with psi, and also understand.

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.

Mark, you blew it... :devil:

Kinda off topic, but does anyone know how much boost those top fueler's run on their roots blowers?

45 psi, but a TON of cfm ;)

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)