turbos...

pest007

New member
i know how they work i know wat they do but i still have questions.....i wanna know wat the difference is between buying a turbo kit and building a turbo kit form different parts ...and also does hte psi u set depend on how big the turbo is?
 
pest007 said:
i know how they work i know wat they do but i still have questions.....i wanna know wat the difference is between buying a turbo kit and building a turbo kit form different parts ...and also does hte psi u set depend on how big the turbo is?

The difference between a custom kit and a bolt on kit is that a bolt on kit usualy is pre tuned on a dyno and you know it's gona work out of the box..

A custom kit is going to be hard to tune and you have to know what you are doing to find the right parts and settings.

Bolt on kits are verry good imho but i don't have the $$$ for one so i build the kit's my self.


And Psi vs Cfm are 2 diffrent thing.
A high flowing head will require less psi for more power as it will accept greater volume.
a small turbo will put out more psi easely but will loose pressure as the volume requirement increase.
 
soncep said:
And Psi vs Cfm are 2 diffrent thing.
i know what CFM are but psi is a bit obscure
CFM cubic feet per finute can also be called lbs per minute
but PSI ... per square inch, is that a ratio comparing to atmospheric pressure ?
i mean atmospheric pressure at sea is something like 14.3psi i think, so if your turbo spools up 10 psi that means your pushing 24.3psi (without calculating ari filter restriciton and other stuff) ?
 
PSI means Pounds per Square Inch. That is why people say "I got 15 pounds of boost" sometimes. It is an absolute measure, not a comparative one.

However, in the turbo world, boost in PSI is given in relative to atmospheric pressure, just like you said.
 
Big Pat said:
PSI means Pounds per Square Inch. That is why people say "I got 15 pounds of boost" sometimes. It is an absolute measure, not a comparative one.

However, in the turbo world, boost in PSI is given in relative to atmospheric pressure, just like you said.
Your explanation didn't teach me much :(
anyway as long as i know that it's cfm or lbs/min that matters it's ok :D
 
And Psi vs Cfm are 2 diffrent thing.
A high flowing head will require less psi for more power as it will accept greater volume.
a small turbo will put out more psi easely but will loose pressure as the volume requirement increase.

On the other hand, if you could get both turbos to run at the exact same efficiency and boost on the same engine, the power output will also be the same, no matter the size of the turbo.
 
CFM isn't really cubic feet per minute, because then you could have 1 cubic foot per meter of thin air and 1 cubic foot of air of compresed air and have a difference in the number of molecules going in your engin, because there is more air per volume in the compressed one(Pounds per square inch.). So, they kept this simble because it is well known simble, but it's not actually correct. What it really mesures is cubic feet per minute at a constant pressure.

So, lets say that one cubic foot per minute(mesured at a constant pressure) = 5 molecules of air going threw the turbine every minute(not real figures). And then compare it to having 2 cubic feet of air per minute or 2*5=10 molecules of air per minute goin threw the turbine. Since you have multiplied by 2 the amout of air and left the volume the same, you could say that there is twice as much pressure in the intake piping, because the engin will take approx the same % of air.

Another facter that will determine the amout of pressure/ CFM that go into the engin is the size of the engin. If your turbo gets 5molecules of air to your engin and your engin sucks all four, there will be no pressure in the intake piping.

There is also temperature that plays a kee role. If the air is warm, it expands, so there is more room between molecules. This brings up the the pressure without getting more air in the engin, so no more CFM but more pressure.

Don't know if this helped, but thats what I understood. I can try and find my old chemestry books to find. (la loie des gas parfait to get simple formulas for you, if that would help)
 
200sxBoY said:
i know what CFM are but psi is a bit obscure
CFM cubic feet per finute can also be called lbs per minute
but PSI ... per square inch, is that a ratio comparing to atmospheric pressure ?
i mean atmospheric pressure at sea is something like 14.3psi i think, so if your turbo spools up 10 psi that means your pushing 24.3psi (without calculating ari filter restriciton and other stuff) ?

I would think that 10psi of boost is 10psi over ambiant pressure. (just think how a mechanical boost gauge works)
 
mazda2002 said:
I would think that 10psi of boost is 10psi over ambiant pressure. (just think how a mechanical boost gauge works)
i never really stoped to this , i don't really know how it works but it must be quite simple.
anyway your cfm theory is quite good, never tought of cfm's at different temperature. there's also pressure that comes into play but i don't quite remember what maximum boost said.
anyway im at my parents house for christmas time so il have plenty of time to read maximum boost again :D
 
ive read a bit :
Pressure ratio = ( (atmospheric pressure)+(boost Psi's) ) / (atmospheric pressure)
which would mean for a 12 psi boost 1.82
CFM is "not" good, Air/Lbs is way more precise
CFM has to be multiplied by the density of air at the correct altitude which is 1.0 at sea level and 0.947 at 15000feets
the final "intake charge" is calculated by Density ratio, The better the turbo system is, the closer the density ratio will be to the pressure ratio
in other words, pressure ratio is an "optimal" value , when everything is working at 100%. Density ratio is real time :D

gotta love Corky Bell for his wonderfull book :D :D
 
It's not realy for turbo, but read that help me a bit to understand Volumetric efficiency: http:/www.yawpower.com/martech.htlm
 
The boost is the pressure at which the air is compressed.
The CFM is the amount of air going through something (like piping and intake manifold)
A big turbo that spools at 7 psi equals the CFM of a small turbo that spools at 15 psi for example.
For a quick, easy to understand example: Blow in a straw (you might be able to acheive 1 psi) and blow in a towel paper tube (0 psi) but there is alot more air exiting the end in the tube than in the straw.
It's that easy.
Another example, I'm running my K03 sport at 18 psi and i hardly have 210whp and a buddy of mine is runing 20 psi with his gt30R and he got dynoed @ 301whp. Notice the difference!? the actual compression of the air very similar but since he's got about 2 times more air flow (CFM) it ends up producing 100whp more than my set-up. This may sound strange but it's the honnest truth of PHYSICS...

I hope that this helped
:D
 
Faouzi 1.8T said:
The boost is the pressure at which the air is compressed.
The CFM is the amount of air going through something (like piping and intake manifold)
A big turbo that spools at 7 psi equals the CFM of a small turbo that spools at 15 psi for example.
For a quick, easy to understand example: Blow in a straw (you might be able to acheive 1 psi) and blow in a towel paper tube (0 psi) but there is alot more air exiting the end in the tube than in the straw.
It's that easy.
Another example, I'm running my K03 sport at 18 psi and i hardly have 210whp and a buddy of mine is runing 20 psi with his gt30R and he got dynoed @ 301whp. Notice the difference!? the actual compression of the air very similar but since he's got about 2 times more air flow (CFM) it ends up producing 100whp more than my set-up. This may sound strange but it's the honnest truth of PHYSICS...

I hope that this helped
:D
so if i put an intake tube with 300mm of diameter, il push like 30 psi but still get the same cfm's ...
but im probably gonna send the turbo in surge and toast it :rolleyes:
 
let's say you have a t25 turbo (which is pretty small) you'll not even be able to push 10 psi in a 100mm tube but with a gt28R or gt30R you'll be able to push at least 20psi... but the CFM amount will be ridiculously higher with eiher gt28 or gt30 than the t25.
Try to heat your house up with a small heater that heats up to 500 Celcius or try to keep the same temperature with a heater that heats up to 250 Celcius but twice as big with a huge fan... Same result with turbo... The big one takes longer to be effective (more lag) but blow alot more.
It's pretty simple
 
dont forget , the turbo bore and piping cross sectional area also make a difference when it comes to PSI and CFM.

PVA=PVA
P=pressure
V=velocity
A=cross sectional area

if you have 2 piping and you want the air in both the piping to travel at the same velocity, and one is double the cross section of the other, the one taht is double the size will require half the pressure to maintain the same velocity as the one half its size.

This is another thing to look at when choosing a kit or designing your own.
 
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