Turbo tech discussion...
 

Alright, Ive been searching and searching forever, found some info, but want to come to a conclusion on this.

Ive had people tell me, that a small turbo at 5 psi will create less power than a larger turbo at less boost. Is this true? I dont think so.

Wouldnt boost be boost? no matter how small or big the turbo is? Granted, a smaller turbo will have to spin faster, and might not be able to hold boost at high RPM, but it still will make the same power, given its actually creating the desired boost. Boost is just the pressure created by the turbo. heck, it could be created by me blowing into the charge pipe, and if i can create 5 psi i will still get the same result.

However, there is one issue to consider. Your car will make less power with a smaller turbo, if it loses efficiency before your engine's peak power range. Thats obvious.

My conclusion: 5 psi on a T4 will give you the same power as 5 psi on an RHB5.

How does everyone else feel about this? Agree, disagree?

Re:Turbo tech discussion...
 

Please give me substantial arguments if you disagree, not just no youre wrong.

Re:Turbo tech discussion...
 

A smaller turbo will give you more restriction in the ehxaust, so thats one reason why A larger turbo will give you more powa! But the main reason why a larger turbo gives out more powa! is the CFM, 5 Psi on a little IHI is not the same as 5 psi on a T4

Re:Turbo tech discussion...
 

a bigger turbo conatins more Oxygen per lb of boost

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its all about CFM...the T4 will be able to push more air into the engine AT 5psi than a IHI......---- this is hard to explain...how about this: a sqirt gun sprays out a stream of water = 5psi (for example) not much water is it even at 5psi? now try a garden hose at 5psi....you understand now? :-*

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No, CFM is completely irrelevant here. It's all about lbs/min of air! Hot air at the same CFM means less lbs/min airflow, hence less power!

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Sounds like someone needs to take a mechanical systems design course, or consult the MEEB (thats Mechanical+ Electrical Engineering for Buildings)

It IS about moving Cubic feet per minute.

Picture this you place a little fan (18" in Dia.) turning at about 500 rpms. Preasure behind the fan will be @ XX atmospheres This would generate an ACH (air change per hour) of ohhh say .25

Now lets say you put a fan that is 8' in Diameter in the window and it turns @ 100 rpms. The Air speed would be 5x less giving it about 5x less preasure behind the fan.

However the big fan would generate an ACH of say 1.75

Got it ?

Re:Turbo tech discussion...
 

Well, I seem to be getting the same arguments I have always heard, with very little to back it up.

The exhaust restriction argument seems to be the most relevant. I didn't think about that before.

What some people dont understand is, yes a larger can flow more CFMs, but if you have a big turbo at 5 psi, it can only flow enough cfms to create 5 psi. The smaller turbo creates the exact same number, but it just has to spin faster.

Doesnt that make any sense to anyone?

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Someone give me a trustworthy source for your argument!

Don't just tell me its all about the cfm's!

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What seems a little wrong about this, is that you dont consider the fact that the air from both fans, to be comparable to a turbo, would have to be channeled into a pipe of the same diameter for both fans. Thus, from the big fan, youre gonna get more air speed, and either as much or more boost as the small fan.

Re:Turbo tech discussion...
 

anyone thats got a copy of maximum boost like to share?

I would like a clear explanation as well.

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I had that book but I ran out of toilet paper so I used that wortless book instead.

Which flows more air; a 5 inch diameter piece of pipe or a 1 inch diameter piece of pipe? And thats not even considering compressor efficiency

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;D

the new issue of MODIFIED MAG has an article in it talking ot the prez of PTE (Precision Turbo & Engine, the ones with the bad ass turbos)....maybe you should all give it a read...

Re:Turbo tech discussion...
 

see, again. a 1 inch pipe can flow just as much air, the air just has to be moving faster. A smaller turbo, given, will have to be spinning faster to flow enough air to create a given boost, but its the same thing.

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compressor efficiency says its not the same thing

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s1ngle, bottom line a bigger turbo flows more cfm. cfm makes power not psi. if its the same thing why doesnt jeff run a ihi rhb5 on his built ls/vtec? should be the same right as a t3/t4.....wrong. rhb5 flows 190cfms a t3/t4 flows like 780 cfm. both at 5psi of pressure who flows more denser air.... 190 at 5 or 780 at 5 ...you make the call

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thats like you saying if you blew through a coffee stirer you could move as much air if you blew through a mcdonalds straw. not going to happen and youd need to blow harder thru the stirer which means less efficiency, and more heat, which equals even less power.....ugh you get the picture now?

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he is abously not getting it...we have said the same think several times now.... ::)

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he just wants a source, I believe the CFM story, but I don't understand it, thus it's no use to me, someone needs to explain completely, I'm stupid.

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LB/min makes power!!! Not raw CFM!
1000cfm of 150°C air will get you way less power than 1000cfm of 0°C air. 50lb/min of air is the same amount at 0 degrees or a 150 degrees, it just occupies smaller space, effectively LESS CFM at 0 degrees!
Why are compressor maps given in lb/min and never CFM? Because CFM doesn't take the air density into account!

Bottom line. It's about AIR MASS, not AIR VOLUME!

Re:Turbo tech discussion...
 

Yes, people have been saying the same thing over and over, but none of them really explain it and give good sources. but I will admit the last few posts are a bit better.

I have been doing some reading on the topic, and here's what i have found: the main thing about smaller turbos is the restriction in the exhaust housing. That makes it harder for the engine to get the exhaust out fast, thus more backpressure and wasted power.

However, I can't find any sources that say that a larger compressor makes denser air :-[

Re:Turbo tech discussion...
 

read this and tell me what you guys get from it:

http://turbonation.com/turbo.htm

Re:Turbo tech discussion...
 

just shut up and get a bigger turbo

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yeah, dumbasses like you would do that wouldn't they.

Re:Turbo tech discussion...
 

no, i already have a big enough turbo. you keep egging this thread on by saying "all of you are saying the same thing, but you're not explaining it", well, i just read this post for the first time and saw it explained to you about as many ways as it can be, all the way from an electrical fan down to a ------- coffee straw. buy 'max boost' if you want to educate yourself on cfm's, a/r's etc.

Re:Turbo tech discussion...
 

Ok. Lemme take a shot at this...

I'll split them up into different posts to make it easier to read.

There are a few factors that come into play:

1) Compressor efficiency at a certain airlow/psi.

eg. @ 100% efficiency and 14.7psi, the compressor would double the amount of air injected into the engine. Most compressors run at about 70% efficiency at their peak (note: most & about). This means that they'll give u about 70% of the max [effective] air at that psi (and CFM...) due to heating of air when compressing (laws of physics: it will heat up). (this is my horrible attempt at Layman's terms...) (If u disagree, we can argue it out in another post. PM/email me)

Take a look at a compressor map and u'll see that at a given airflow and psi (u have to calculate airflow using rpms and engine size [mainly] in order to use the map), the efficiency of a small turbocharger compared to a larger one, is usually lower. However, this isn't always true (being that the efficiency line is not linear). It is possible that a smaller turbo has a higher efficiency (at that rpm & psi) than a bigger turbo, and given that the CFMs are close enough for the same psi, the small turbo should out perform the bigger turbo (at that rpm/psi). (comparison criteria: Rpms are equal. psi's are equal. CFMs are close (700 to 195 will not work). small eff is higher than big eff.)

BTW, some compressor maps are given in cfm... they account for the mass by assuming constant weight or something to that effect. Similar effect to lbs/min map.

If everything I just said is jibberish (which it seems like to me after rereading...), refresh your memory on reading compressor maps then read again.

verdict: Bigger usually= better, but not always. However vast diff in size, bigger wins.

(SEE #2 in next post)

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2) CFMs as explained before, does make a difference.

The straw analogy applies but is somewhat incorrect. What if both turbos are breathing through the same 2.5 diam inlet pipes? Well technically, if u somehow could hook a firehose to a straw, it would still flow more than a garden hose thru the same diam straw (both at the same psi). Neglecting factors such as turbulence, etc.

Same thing w/ the fans analogy. If they both blow into the same diam pipe, the bigger one will still flow more at teh same psi.

Here's a bad example that might help put things in perspective:
A building hallway. A small fan blowing air straight thru the hall at 15psi. A gust of wind blowing thru the hall @ 15psi. (bad ex but kinda conceptual).

Verdict: Bigger = better

Re:Turbo tech discussion...
 

this argument has turned into more of which turbo is capable of more hp. Your engine has requirements. so long as those requirements are met, it doesn't matter which turbo you use to get there. Boost is created by stacking air tighter then before. 5psi in a thimble, or 5 psi in a swimming pool is 5psi. you have to remember to compare apples to apples. The turbo that is going to create that 5psi where you want it, most efficiently is going to create more power then the one that over heats the air.

so far as exhaust restriction, that's another ball game too. Just remember apples to apples here. A tighter exhaust housing .42 vs .69, is going to be more of a restriction. But, you have to have this restriction to create boost. The .42 is going to create boost sooner, but it's going to limit rpm more.

These are very simple things to figure out, you just need to know which numbers to put in place. A compressor map is going to tell you what cfm and boost a certain setup is capable of. Find out what you need, and then find the compressor to fit the bill. Then, figure out where you want you power. This is going to be a give and take situation... find out what you want. all on by 2500, and end at 5000, or all on by 3500, and good till 8000rpm. Useable torque, or racing power?

There are no right turbos for the job, but there is one closer than any other, then make sure it has ball bearings.

does any of this matter if you are going to use the first one you find in a junkyard anyway?

Re:Turbo tech discussion...
 

s1ngle is you dont understand now, you may be handicapped.

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2 mins on google and then reading a surprisingly well written article on a Saturn forum should explain it for you s1ngle if it doesn’t then no one here can help you
http://www.turbosaturns.net/articles...sor%20maps.htm

its all about the right size turbo and how to pick it ..
3 pages happy reading

Re:Turbo tech discussion...
 

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?

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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

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

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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.

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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....

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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

Re:Turbo tech discussion...
 

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

Re:Turbo tech discussion...
 

[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