s1ngle

My hat is off to you, thats the best explanation ive had yet, and things are starting to come together for me. I appreciate all the input, useful and not useful. I figure we're generating some converstaion that will explain things and further all of our understanding, right?

however, I have one last thing that doesnt make sense in my mind. Pertaining to bettonracing's examples, theoretically couldnt a garden hose flow just as much as a firehouse, as long as the water is moving appropriately faster through the hose? like if the water is just dribbling out of the firehouse, and the water is blasted out of the garden hose? then how does size matter?

Spenser

Because the Garden hoses enviromental limit is less then the firehoses, not to mention it's easier to push more water threw the fire hose

s1ngle

i agree with both of your statements, however if youre running low psi, then it wouldnt matter would it?

projekteg

that's where effeciency comes into play some force on the other end would have be working a million times harder to get the water through the garden hose, where as the force pushing the dribbling water out of the fire hose is barely doing any work, thus causing extra heat and hotter charge temps from all the extra work for the garden hose.

s1ngle

that does make sense, it goes along with what i said before with the restrictive exhaust housing. I think i get it now, just gonna read that saturn article here....

sean88accord

Lets assume here for a minute that both turbos have the same efficency at 5 psi of CFM and lb/min for a given boost pressure of 5psi.

lets look at the facts

it takes on a 1.6L engine with a VE of 85% a flow of rouhgly 240cfm n/a to fill the cylinders. so to reach 5 psi ( assuming this is sealevel) itll take around 340 cfm. ( not none of these numbers are accurate period. they are simply examples)

so that means each turbo must flow 340 cfm to fill the cylinder 120% to create a positive manifold pressure of 5 psi.

lets look at the simplest form of whats going on

lets assume both turbos are 70% efficent at 5 psi ( they are in fact just so ) then all of this BS abut building blah blah blha is just more hot air.

The fact is that at 5psi with identical charge temps 2 fans of the differing size will produce the same amont of power.

it will always take the same volume of air to produce 5 psi. this is however assuming that the engine RPM and VE arent changed. from turbo to turbo

As for which turbo will make more power always go with the largest exhuast side possiable for your compressor. also dont buy 10x more turbo then you actualy need. its wasteful.

anyways thats al i have to say on the subject. peace out

bettonracing

Couple flaws to your logic sean88accord:
I see your point about "this is the size container we have. Here's how much air we need to fill it, and here's the amount of air that brings it to 5psi" but this assumption would 'only' be true for a static engine (I use the term "only" loosely due to other irrelevant info I could add). Given your info and your constants, I completely agree w/ u. However, release some of your constants (namely VE) and u'll find a vast difference. It is reasonable to hold the boost constant (wastegate) and the compressor efficiency for analytical (say independent compressor) reasons but the constant VE I don't quite grab the usefulness of. I may be sleepy (it's 2am now) so if possible, please elaborate.

Also the "hot air" I was "BS-ing about buildings" was stated as a in this scenario but was used to conceptualize different CFM's in the same "port". Please read carefully before posting.

One last point counterproductive to the static engine theory:
Is a 106mm turbo running at 70% efficiency and 5psi is flowing the same amount of air as a IHI RHB3 (go kart turbo) at 70% and 5psi?..... (let's assume the same exhaust housing and wheel)... Even if the firehose is trickling in this case...


I can see we end up w/ the same result (i.e. go bigger to the point of diminishing returns) but thru different methods. I'd like to fully understand yours.

Please respond. Let me know if/where I'm wrong.

(I can see the replies now: "U are WRONG!!!!" ! !...)
lol

sean88accord

[qoute]
Couple flaws to your logic sean88accord:
I see your point about "this is the size container we have. Here's how much air we need to fill it, and here's the amount of air that brings it to 5psi" but this assumption would 'only' be true for a static engine (I use the term "only" loosely due to other irrelevant info I could add). Given your info and your constants, I completely agree w/ u. However, release some of your constants (namely VE) and u'll find a vast difference. It is reasonable to hold the boost constant (wastegate) and the compressor efficiency for analytical (say independent compressor) reasons but the constant VE I don't quite grab the usefulness of. I may be sleepy (it's 2am now) so if possible, please elaborate. [/qoute]

Well lets go ahead and impose a few constants to help lower the level of banter. let use the same tuebinr wheel and housing for 2 differnet compresor housings and wheels. keeping them in rouhgly the smae class of turbo say a t3 in this instance.

Youll have to assume VE ( whihc is a mechanical function dictaed by rpm,camshaft timing,port design,valve size,port flow,TB size, etc etc etc) with or without the tubro that number will always pretty much be the same at a given baro pressure etc.

What you overlooking is that fact that 2 different turbos say a 42 tirm compressor and a s60 wheel might both be in the same range of abieatic efficency at a given rate of flow. we will say here roughly 20 l/min. given that 20lb/min on our test engine a d15 is gonna euqal a hypthetical 15 psi of boost. no it wont matter which fan blows in becuase power production will be the same for lb/min for each turbo. unless you roll a compressor out of its effiecneyc range there is no power gian with a larger turbo.
It looks good on papaer but in reality there gains might be imeasruabel. having tested numerous compressor wheel and housing combos i can tell you however a 42 trim wheel and a s60 trim wheel will have different behavior and efficencys with different compressor housing a/r's

thats all ive really gotta say