Question

[Sammie]

i been searching around forums and you all know im new here and new to skylines and turbos,could anyone explain or direct me to a thread that explains both what boost is how it works, and psi i read in a number of threads ppl changing psi etc really wanna know what it is and how boost gauges work sorry if i sound like a newbie but id really like to know thnx

[Josh]

howstuffworks.com has a great model of how turbochargers work, will find a link for ya

[Sammie]

cheers josh u been very helpfull

[Josh]

http://auto.howstuffworks.com/turbo.htm

[mitchy_]

'boost' is what a turbo creates.

a 'normal' engine, ie one without a turbo works by sucking air in, mixing it with fuel, igniting it and using the explosion to turn the crank, thus creating power.

so say you had a 5.7L V8, it would at any time have 5.7L of air/fuel in it to be ignited, and obviously more air/fuel will cause a bigger explosion, and thus create more power.

now, a turbo engine works by the turbo 'forcing' air into the engine, mixing it with fuel, igniting it and using the explosion to turn the crank, again creating power.

this is why you see alot of the turbo engines are alot smaller, ie the 2.0, 2.5, and 2.6L of the skyline, yet they can still pump out the same power as a big V6, or even a V8. say you have a RB25DET, 2.5L turbo. now whilst the turbo hasnt kicked in(ie low revs) the engine will have approx. 2.5L of air/fuel in it to ignite, and create power with, *but* once that turbo kicks in, say you are running 1 bar(14.7psi of boost, ill explain this in a bit) you are effectively pushing twice the amount of air into the engine, so that 2.5L engine is taking in as much as a say a 5L engine.

now onto 'psi', the word stands for pounds per square inch.

a normal, un-turboed engine runs at negative psi, meaning that the engine is *sucking* in air.

however a turbo engine runs *positive* psi, meaning that air is being forced into the engine, and the higher the psi, the more pressure, or 'boost' your turbo is creating.

say you had again 2 RB25DET's this time... engine A running 7.5psi of boost, and engine B running 15psi of boost.

now engine A will have approx. 3.75L of air/fuel in it at any time, whereas engine B will have approx 5L of of air/fuel in it at any time.. so the more psi your turbo makes, the more boost created, making your engine effectively larger, and creating more power.

now i better get an A for this essay...

[mitchy_]

....bastard josh, i was going to link him to that site, but i forgot what it was called!

its too early.

[Sammie]

thnx alot mitchy that was very helpfull i should be getting m ycar in around 2 weeks how do u know wat psi your turbo is on or wateva sorry if im saying it wrong

[mitchy_]

if its got an aftermarket boost gauge, it should show you what psi/kpa it hits (1000kpa == 14.7psi) or if it has just the stock boost gauge in the dash, work off this... the +7 at the top is about 14.7psi, and yours will probably hit around the middle mark, so ~7-10psi

[Kaido_RR]

thnx alot mitchy that was very helpfull i should be getting m ycar in around 2 weeks how do u know wat psi your turbo is on or wateva sorry if im saying it wrong

<{POST_SNAPBACK}>

hey Sammie,

i through i add my 2cents and see if i can help you

The stock turbo has something on it called an Actuator, this controlls boost on your turbo. When your car is stock the turbo should run around 5-6psi. But if you start to mod your skyline like putting an airfilter or exhuast the boost will slowly go up by abit, so you may be running 9-10psi.

Thats why its always good to get an aftermarket boost gauge when you you start modding you car, as its good to know where your boost levels are at.

also another tip more boost doesnt always mean more power, if you boost your turbo out of its Effectiveness range (for example the stock turbo max lvl of boost is around 12psi) you will not make anymore power.

and good luck with the new car

-Michael

[paulr33]

some very important facts about turbocharging also to note:

more psi or more boost means more heat

more psi or more boost doesnt always mean more power

compressing the air intake (or making boost) heats up the air, thus a need for an intercooler

an intercooler takes the heat charge off the air intake after it is compress, most people think it cools the engine down.

a boost controller can be a wastegate (external) or internal wastegate flat controlled by an actuator

boost is a resistance to air, if you add more boost you generally make more power upto a certain limit which will be the limit of compressor wheel, once you reach this limit any more psi over it generally just adds stacks more heat and it makes no more power

a bigger a/r turbocharger will come on later in the rpm range but make more power top end.

a smaller a/r turbocharger will come on earilier in the rpm range but make less power in top end.

a/r is a measurement for area / radius. a stock r33 turbocharger (gtst model) is around 0.50a/r

cars that run a twin turbo setup generally use two smaller a/r turbochargers and a single turbo car generally runs a larger single unit

pressure and volume are two different things

if one car runs 12psi and another runs 9psi this means absolutely nothing other than the amount of pressure they run

the less boost you run the better, the less friction, the less heat, the less lag and stress. make the required power at the least amount of boost possible

[Staunch]

heyas, since we're on the topic....I've recently bought a 33 GTS-T, everything stock. I'm surprised to find that when the needle sits half way between +7 and 0 it means around 7-10 psi....I originally thought that it would mean 3-4 psi. If this is true, then I rekon my skyline ain't that quick

[race_snooze]

if its stock then its only putting out about 150rwkw so that aint much, but they are reasonable quick compared to anything else of that year range.

[paulr33]

150rwkw is pretty high for complete stock. 130rwkw is more reasonable i would imagine

[shif_tea]

heyas, since we're on the topic....I've recently bought a 33 GTS-T, everything stock. I'm surprised to find that when the needle sits half way between +7 and 0 it means around 7-10 psi....I originally thought that it would mean 3-4 psi. If this is true, then I rekon my skyline ain't that quick

<{POST_SNAPBACK}>

EDIT: I'm a dumbass. Sorry brain fry

No halfway should mean 7psi. 7mmHg is about 1bar (14.7psi).

Stock should be about 5psi till 4500rpm then go up to 7psi.

Edited December 15, 2005 by shif_tea